Effects of resistance training and protein supplementation interventions on muscle volume and muscle function: sex differences in humans

Article information

Phys Act Nutr. 2023;27(4):15-25

Publication date (electronic) : 2023 December 31

doi : https://doi.org/10.20463/pan.2023.0033

Institute of Sports Medicine & Nutrition, Kwangwoon University, Seoul, Republic of Korea

^*Corresponding author : Sok Park Institute of Sports Medicine & Nutrition, Kwangwoon University, 20, Gwangun-ro, Nowon-gu, Seoul, Republic of Korea. Tel: +82-2-940-8321 Fax: +82-2-942-0108 E-mail: winner@kw.ac.kr

Received 2023 September 21; Revised 2023 October 31; Accepted 2023 November 24.

Abstract

[Purpose]

This review aimed to identify differences in the effects of co-intervention with resistance training (RT) and protein supplementation according to sex and provide meaningful information for future research on the development of exercise programs to improve muscle volume and muscle function.

[Methods]

PubMed, Science Direct, and Google Scholar were searched to identify clinical and nonclinical studies that assessed the effects of RT in older adults with sarcopenia; these studies were published between 1990 and 2023. Cross-sectional and double-blind studies (randomized controlled trials, RCTs) were examined in this review.

[Results]

The effects of parallel intervention with RT and protein supplementation on muscle volume and physical function were found to differ according to sex. Both males and females had improvements in muscle strength, muscle mass, and physical function after RT and protein supplementation; however, many studies found a greater increase in muscle volume and function in males than in females. Such difference may be due to differences in physiological characteristics between males and females.

[Conclusion]

Based on the findings of this review, the effects of combined intervention with RT and protein supplementation on muscle strength, muscle mass, and physical function to differ according to sex. Owing to these sex differences in the response and physiological characteristics caused by the parallel intervention of RT and protein supplementation, such differences must be considered to maximize the effects of RT and protein supplementation.

Keywords: sex difference; resistance training; protein supplementation; muscular function; muscle volume; physiological characteristics

INTRODUCTION

Aging and lack of physical activity among elderly individuals are major public health problems [1]. Biological aging is associated with a gradual decline in muscle strength and skeletal muscle mass, and these changes have a negative correlation with human health, quality of life, and survival [2,3]. Age-related changes in the skeletal muscles are associated with a decrease in the ability to perform physical activities related to daily life and an increased risk of falls and fractures, which may ultimately increase the risk of death [4]. Only 27–44% of senior citizens in the United States meet the World Health Organization’s (WHO’s) general recommendations for adult physical activity. Those who fail to comply with these recommendations are twice as likely than those who follow them to have limited physical function [1,5]. Based on current estimates, by 2050, 200 million people worldwide will be affected by sarcopenia [6]. Exercise and protein intake are major factors that control muscle mass and they have a profound effect on muscle synthesis. Several lifestyle factors, including protein intake and reduced physical activity, contribute to a loss of muscle mass [7].

Long-term systematic resistance training (RT) increases muscle strength and mass in males and females of various ages. Muscle adaptation to RT is important for managing muscle weakness, such as sarcopenia, aging, and rehabilitation [8]. In addition, RT was found to be superior to other exercise methods at improving upper limb muscle strength, grip strength, depressive symptoms, physical performance, and walking speed [9-11]. However, the increase in muscle mass and strength induced by RT varies widely and is heterogeneous, with dependence on individual characteristics [12]. Understanding muscle adaptation to RT according to individual types allows the application of personalized exercise programs to optimally improve or maintain healthy muscle function [8].

Protein intake is important for maximizing muscle function during resistance exercises. Accordingly, protein supplementation is important for the treatment and prevention of sarcopenia [13], and can have a positive effect on the supply of essential intracellular amino acid, prevention of protein oxidation, recovery from muscle damage during exercise, and increases in muscle strength and mass [14]. Whey protein maximizes the effects of exercise and can have a positive effect on skeletal muscle anabolism [15]. Recently, athletes and the general population have started engaging in RT in parallel with protein supplementation to increase muscle strength and mass. However, to maximize the effectiveness of dietary protein supplements, proteins must be consumed according to individual characteristics [16]. Therefore, several studies have been conducted to determine the effect of protein supplementation on muscle adaptation to RT; however, studies on the differences in effectiveness of such supplementation according to sex are insufficient [17-19].

In general, females’ have less absolute muscle mass and muscle strength than males, but the decreases in muscle mass and muscle strength due to aging in females are approximately half those of males [20]. A decrease in muscle mass depends on proteolytic hormone production, the inflammatory response, fatigue, recovery time after exercise, and sex differences in muscle fiber size and type. In addition, the responses of muscle protein metabolism to exercise and nutrition differ between males and females [21]. Therefore, sex difference in muscle mass and strength according to age is one of the main factors that should be considered when developing exercise routines to minimize muscle loss [22-24]. Recently, protein metabolism has gained remarkable attention, and various measurement methods have been developed. A study examining sex differences in adaptation to resistance exercise and amino acid intake revealed that the synthesis rate of muscle proteins in males was higher than that in females [21]. Despite these developments, much is yet to be proven regarding sex differences in protein metabolism. However, considering the differences in muscle tissue and physiology between males and females, differences in protein metabolism by sex cannot be ruled out.

Many previous studies have examined the changes in muscle mass and muscle function following RT or protein supplementation; however, the effectiveness of the combined intervention has not been evaluated in many studies. In addition, despite evidence that the effects of these combined interventions can vary depending on personal characteristics, such as sex, age, and race, few studies have performed comparisons according to these attributes, especially according to sex. Therefore, the aim of this review was to identify the differences in the effects of RT and protein dietary supplementation on muscle strength, muscle mass, and muscle function according to sex, and provide meaningful information for future research on individuals with sarcopenia or the development of exercise programs to improve and prevent muscle mass and muscle function reduction.

METHODS

PubMed, Science Direct, and Google Scholar were searched to identify clinical and nonclinical studies that determined the effects of RT in older adults with sarcopenia; these studies were published between 1990 and 2023. The keywords for the search were “sex differences and muscle,” “sex differences and RT effects,” “sex differences and protein metabolism,” “sex differences and sarcopenia,” and “RT and Protein supplementation.”

This review comprised cross-sectional and double-blind studies (randomized controlled trials, RCTs). Animal and experimental studies were excluded from this review. In addition, studies with small sample sizes, those that did not adequately specify the selection criteria, or included groups of patients receiving medication for another disease that affected bone or muscle metabolism were excluded.

RESULTS AND DISCUSSION

Effects of RT and Protein Supplementation on Muscle Strength: Sex Differences

Several studies found a strong correlation between muscle strength and sarcopenia. In patients with sarcopenia, muscle mass decreases at a rate of approximately 1% per year while muscle strength decreases at a relatively faster rate [25]. Decreased muscle strength is a strong predictor of physical injury and diseases in humans [26]. RT has a positive impact on improving muscle function, muscle mass, and bone health, and preventing musculoskeletal and metabolic diseases to maintain and improve an individual’s quality of life. RT is a type of exercise that provides various health benefits, especially in elderly people [27,28]. Therefore, maintaining and increasing muscle strength via RT are important for improving muscle function and preventing physical injury and disease [29,30].

A nutritional Intervention is an important strategy for improving and maintaining muscle strength, muscle mass, and muscle function [31,32]. According to a previous study, the combination of RT and protein supplementation increased muscle protein synthesis to a greater extent than RT [33]. In older adults, protein supplementation has been demonstrated to increase overall lean body mass and grip strength only when combined with RT [34]. The combination of RT and protein supplementation has been shown to induce increased plasma amino acid levels and stimulate muscle protein synthesis [35]. This combination has also been proven to increase individual muscle strength and lean body mass; however, studies considering personal characteristics, such as sex, age, and race, are limited.

Sex-specific physiological characteristics must be considered when RT and protein supplementation are recommended to improve muscle strength and prevent sarcopenia. Body composition, including muscle mass and body fat, generally varies according to sex. Therefore, the effects of RT and protein supplementation on human muscle strength must be considered according to sex [36]. In general, males have higher muscle masses and lower body fat percentages than females. Moreover, there are differences in the type of muscle and the distribution of muscles in the musculoskeletal system according to sex [37]. Females have relatively less muscle strength as they have a higher distribution of type 1 muscle fibers than males [38]. Despite the differences in physiological characteristics according to sex, studies on sex differences in the effects of RT and protein supplementation on muscle strength are lacking.

In 2019, a study comprising 18 males aged 20–30 years examined the changes in muscle strength in response to co-treatment with RT and protein supplementation. After 12 weeks of intervention, male muscle strength improved significantly (preacher bench biceps curl: +23.14 kg, leg curl: +23.22 kg) [16]. In 2018, another study comprising young males examined the effects of RT and mixed protein intake on muscle strength and found significant improvements in muscle strength (leg press: +36 kg, bench press: +9 kg) [39]. In 2015, 21 males aged 65–75 years were monitored to derive their response to the combined intervention of RT and protein supplementation. In this study, the muscle strength of males significantly improved (lat pulldown: +8.2 kg, bench press: +4.3 kg) [40]. In 2014, another study comprising elderly males examined the effects of RT and whey protein supplementation on muscle strength and found significant muscle strength improvement owing to the treatment (bench press: +28.6 kg, leg press: +141 kg) [41]. Many studies that investigated the effects of RT and protein supplementation on muscle strength in males reported similar results (Table 1, Table 2) [42,43]. In 2019, we examined the effects of RT and protein supplementation on muscle strength in 26 females older than 60 and found some improvements in muscle strength; however, the result was not significant (knee extension: +3.1 kg, chest press: +2 kg, preacher curl: +2.7 kg) [44]. In 2018, another study examined the effects of RT and whey protein supplementation on muscle strength in 75 elderly females and found significant improvements in muscle strength (knee extension: +2.6 kg, rip strength: +1.2 kg) [45]. In 2017, a study comprising 31 females aged 60 or older found improvements in muscle strength after concurrent interventions of RT and protein supplementation (knee extension: +8.5%, chest press: +6.3%, preacher curl: +14%) [46]. Of note, many studies that investigated the effects of RT and protein supplementation on muscle strength in females have reported similar results (Table 1, Table 2) [47,48]. Comparing the results of studies with males and females confirmed a greater improvement in muscle strength in males than females after RT and protein supplementation. In addition, among the studies on females, no significant improvement was found. Nevertheless, some studies with males did not report a significant increase in muscle strength [49]. By comparing these findings, a sex difference can be observed in the muscle strength response to RT and protein supplementation. Nevertheless, proving this sex difference is insufficient as studies have not directly compared the effects of combined interventions of RT and protein supplementation by sex (Table 1, Table 2).

Table 1.

Sex differences in the effects of resistance exercise and protein supplementation in humans on muscle strength, muscle mass, and muscle function.

Table 2.

Details of the resistance training program and protein condition.

Effects of RT and Protein Supplementation on Muscle Volume: Sex Differences

Decreased muscle mass causes insulin resistance, a reduced ability to control blood sugar, and an increased prevalence of cardiovascular and metabolic diseases. This decrease is also directly related to mortality because it affects the occurrence of cardiovascular diseases and cancer [50,51]. Muscle mass is a major evaluation factor for sarcopenia caused by aging, and maintaining or improving individual muscle mass is an important factor in healthy aging. RT has been demonstrated to have a remarkable effect on the maintenance and improvement of muscle mass [52]. Although the effect of RT on the body muscle mass varies according to personal characteristics, such as sex, age, and race, few studies have been conducted on RT prescriptions that consider these individual differences.

Protein supplementation stimulates anabolic hormone components, such as the growth hormone, insulin-like growth factor (IGF-1), and testosterone, to induce protein synthesis, resulting in increased muscle mass [53]. Protein supplementation before and after resistance exercise also increases muscle protein levels during recovery and protein synthesis after exercise [54]. Protein supplementation can further enhance the effects of increased muscle mass on RT in elderly individuals [55,56]. However, studies investigating the combined effects of RT and protein supplementation on muscle mass have yielded conflicting results, thereby leading to a lack of proof of the efficacy of protein supplementation. Several studies have investigated the effects of RT and protein supplementation in older adults; however, only few studies have directly compared the differences according to individual characteristics [56-58].

In 2018, Mathias et al. found that eight weeks of RT and protein supplementation significantly improved muscle mass in males (fat-and-bone-free mass: +2.6 kg) [39]. Another 2018 study comprising 22 young males found an increase in muscle mass after co-therapy (quadricep muscle cross-sectional area, +9%) [5]. According to a 2015 study by Mathieu et al., 12 weeks of RT and protein supplementation significantly increased muscle mass in elderly males (muscle mass: +2.29 kg) 40 . In 2014, 22 elderly males had significant increases in muscle mass owing to a combination of 12-week RT and protein supplementation (lean body mass, +1.8 kg) [41]. Several studies investigating the effects of RT and protein supplementation on muscle strength in males reported similar results [16,49]. According to Hellen et al., 12 weeks of RT and protein intervention in elderly females resulted in a slight improvement in muscle mass; however, this result was not significant (total lean soft tissue: +1.2 kg) [44]. In 2018, a study surveyed 75 elderly females to determine the muscle mass following combined intervention with RT and protein for 24 weeks. Based on the results, a significant improvement in muscle mass (lower limb muscle mass: +0.5 kg) was found [45]. Similar results have been reported in several studies examining the effects of RT and protein supplementation on muscle mass in females [44,47,48]. By comparing the results between males and females, muscle mass increase in males was confirmed to be greater after intervention with RT and protein supplementation than in females. In addition, among studies comprising females, we confirmed that no significant improvement was found. Therefore, a sex difference exists in the muscle mass response to RT and protein supplementation. Nevertheless, further studies are needed to demonstrate these sex differences, as no studies have evaluated the effects of combined RT and protein supplementation interventions on muscle hypertrophy responses by sex (Table 1, Table 2).

Effects of RT and Protein Supplementation on Muscle Function: Sex Differences

The main issue associated with decreased muscle strength and mass is the decrease in physical ability due to muscle dysfunction. This reduction increases the possibility of falls and various musculoskeletal diseases, and degrades the quality of life of individuals [59,60]. Physical function, muscle strength, and muscle mass are key factors in the diagnosis of sarcopenia [61]. RT has been proven to improve physical functions, such as individual walking speed, stride, flexibility, and balance ability [62-64]. Several previous studies have investigated the effects of RT interventions on physical function in males and females; however, only few studies have directly compared the effects of RT based on sex [65,66].

Among the many factors that lead to decreased muscle mass, inadequate protein intake and decreased physical activity are most important [67,68]. Several strategies are used to prevent muscle loss, including protein supplementation, RT, and hormone replacement therapy [69]. Increasing muscle mass and physical function are major factors in preventing and improving sarcopenia; thus, these need to be treated as important factors [70]. Considering the importance of muscle strength and body function from this point of view, analyzing the effectiveness of RT and protein supplementation in improving sarcopenia symptoms is important [71]. Several studies have identified significant incremental effects of RT and protein supplementation on body functions. However, only few studies have directly compared the effectiveness based on personal characteristics [40,72,73]. As the effects of RT and protein combination may vary depending on physiological characteristics, such as sex, age, and race, various approaches are needed to maximize the effects of RT and protein supplementation considering personal characteristics.

A study published in 2017 found that 12 weeks of RT and protein supplementation intervention improved physical function in elderly males (walking speed: +0.3 m/s, timed up and go: -1.3 s, chair stand: -1.2 s) [40]. In 2021, a study involving 75 males aged 60 or older investigated the effects of 12-week RT and protein supplementation and found significant improvements in physical function (4 m walking test: -1.2 s, timed up and go: -0.82 s, balance test: +4.6 s, stair climbing test: +4.2 rep) [74]. A 2014 study by Matthew et al., which comprised 22 elderly men, found that RT and protein supplementation had a positive effect on improving body function (400 m walk: -16 s) [41]. Conversely, we examined the effects of RT and protein supplementation in 26 females aged 60 or older in 2019 and found some improvement in physical function; however, the result was not significant (10 m walk test: -0.5 s, rising from the sitting position test: -1.4 s) [44]. A 2016 study involving 75 females aged 65 to 80 years investigated the response of physical function to concurrent interventions of RT and protein supplementation and found a slight improvement in physical function; however, this improvement was not significant (gait speed: + 0 s) [45]. Altogether, the results of these studies highlight sex-specific differences in the response of body function to combined interventions of RT and protein supplementation. Studies comprising males have revealed improvements in physical function while studies comprising females have not reported significant increases in physical function. Nonetheless, studies comprising females have found increases in physical function but generalizing the results is difficult to perform as these studies did not directly assess sex differences [75]. Therefore, further studies are needed to demonstrate the sex differences in muscle strength, muscle mass, and body function owing to co-treatment with RT and protein supplementation (Table 1, Table 2).

Sex Differences in Adaptation to RT and Protein Supplementation Based on Physiological Characteristics

The differences in the effects of combined RT and protein supplementation on individuals according to sex remain unclear. However, this potential sex difference may be due to differences in physiological characteristics, such as the the type of muscle, protein metabolism, and hormones [75,76]. An investigation of the structural properties of the skeletal muscle revealed that sex differences may affect responses to RT and protein supplementation. Inborn sex differences cause significant differences in the morphological composition of skeletal muscles. Males have more skeletal muscles than females, which contributes to greater maximum muscle strength in males [76,77]. Females have relatively less muscle mass and muscle strength than males but have more type I muscle fibers that are resistant to fatigue. In contrast, males have relatively more muscle mass and muscle strength, and more type II muscle fibers that are vulnerable to fatigue. These sex-dependent differences in muscle fiber structure can also affect the responses to RT and protein supplementation. In a study involving RT for nine weeks, increased muscle mass was observed in both type I and type II muscle fibers in elderly males [78]. In contrast, a 12-week intervention of RT in older females led to a significant increase in type II muscle fibers but not type I muscle fibers [79]. Differences in muscle type and muscle distribution in the musculoskeletal system may cause sex differences in the effects of combined interventions of RT and protein supplementation [80].

Another physiological trait that can affect the response to combined RT and protein supplementation is the levels of hormones, which affect protein synthesis. Several circulatory expression factors (IGF-1 and testosterone) are presumed to be important for muscle protein balance based on muscle protein synthesis [81]. IGF-1 is upregulated in overloaded muscles and is associated with an increase in myogenic regulators, such as myogenin [82]. When stimulated by a load or myotoxicity, the expected myogenic expression in older muscles is reduced or delayed compared to that in younger muscles [83,84]. Based on this information, sex differences in individual muscle growth due to concurrent interventions of RT and protein supplementation may be associated with muscle IGF-1 levels. Owing to a lack of clear evidence of differences in the response of muscle protein metabolism to RT and protein supplementation, the higher metabolism of protein in males than females may be attributed to hormonal differences. Testosterone treatment in males increased muscle protein synthesis and IGF-1 expression, suggesting that testosterone and IGF-1 are factors regulating muscle metabolism, and are positively correlated with each other. In general, testosterone levels are 10-fold higher in males than in females. Testosterone is an important anabolic hormone, and differences in testosterone concentration can lead to sex differences in protein synthesis during exercise and protein supplementation [85].

Muscle loss is a decreased response of muscle protein synthesis to generally strong anabolic stimuli, such as protein intake and RT [86,87]. A recent study highlighted significant age- and sex-related differences in the regulation of muscle protein synthesis [88]. These data suggest that muscle protein synthesis in males may exhibit a different response to exercise and nutritional supplementation than that in females; however, expanding our conclusions is difficult. As protein degradation and synthetic responses to combined interventions of RT and protein supplementation by sex have not been reported, the problem must be addressed according to sex differences.

According to various studies, rapamycin complex 1 (mTORC1) plays a decisive role in skeletal muscle hypertrophy as it is activated after resistance exercise in humans [89,90]. The ubiquitin-proteasome system is a major proteolytic system. Previous studies reported that RT significantly increased the mRNA expression of muscle RING-FINGER protein-1, which promotes protein ubiquitination [91]. Essential amino acids are known to induce anabolic reactions in muscles, including mTORC1 activation [33,92]. In addition, branched-chain amino acids (BCAAs) have been found to more effectively stimulate mTORC1 when combined with essential amino acids [93]. RT and protein supplementation were previously found to effectively increase the activation of mTORC1 signaling, suggesting that protein supplementation is useful for increasing the effects of RT in males [94].

CONCLUSION

Muscle function decreases with age, resulting in sarcopenia, which is directly related to health and the quality of life. RT has a remarkable effect on the prevention of sarcopenia and improvement of muscle strength and mass. Protein supplementation maximizes the effects of RT and improves muscle mass and hypertrophy. This review suggests the existence of sex differences in the effects of co-treatment with RT and protein supplementation on muscle strength, muscle mass, and physical function. Upon examining the studies covered in this review, the synergistic effects of RT and protein supplementation were identified to be greater in males than in females. In most studies, muscle strength, muscle mass, and physical function in males increased after combined intervention, wih a greater increase found in males than females. In studies comprising females, the muscle strength, muscle mass, and physical function in some females increased; however, this increase was lower than that in males; a study also found no significant increase in these indices. As sex differences exist in the response and physiological characteristics caused by the combined intervention of RT and protein supplementation, these sex differences must be considered to maximize the effects of RT and protein supplementation. However, only few studies directly compared sex. Further, understanding the combined effects of RT and protein supplementation is limited as different results are obtained according to individual characteristics. Therefore, future studies must comprehensively investigate and compare sex differences in the effects of RT and protein supplementation to present effective strategies to improve muscle mass and function.

References

1. García-Hermoso A, Ramirez-Vélez R, Sáez De Asteasu ML, Martínez-Velilla N, Zambom-Ferraresi F, Valenzuela PL, Lucia A, Izquierdo M. Safety and effectiveness of long-term exercise interventions in older adults: a systematic review and meta-analysis of randomized controlled trials. Sports Med 2020;50:1095–106.

2. Brady AO, Straight CR, Evans EM. Body composition, muscle capacity, and physical function in older adults: an integrated conceptual model. J Aging Phys Act 2014;22:441–52.

3. Clark BC, Manini TM. Functional consequences of sarcopenia and dynapenia in the elderly. Curr Opin Clin Nutr Metab Care 2010;13:271–6.

4. Janssen I, Baumgartner RN, Ross R, Rosenberg IH, Roubenoff R. Skeletal muscle cutpoints associated with elevated physical disability risk in older men and women. Am J Epidemiol 2004;159:413–21.

5. Keadle SK, McKinnon R, Graubard BI, Troiano RP. Prevalence and trends in physical activity among older adults in the United States: a comparison across three national surveys. Prev Med 2016;89:37–43.

6. Volpi E, Campbell WW, Dwyer JT, Johnson MA, Jensen GL, Morley JE, Wolfe RR. Is the optimal level of protein intake for older adults greater than the recommended dietary allowance? J Gerontol A Biol Sci Med Sci 2013;68:677–81.

7. Nair KS. Aging muscle. Am J Clin Nutr 2005;81:953–63.

8. Ahtiainen JP, Walker S, Peltonen H, Holviala J, Sillanpaa E, Karavirta L, Sallinen J, Mikkola J, Valkeinen H, Mero A, Hulmi JJ, Hakkinen K. Heterogeneity in resistance training-induced muscle strength and mass responses in men and women of different ages. Age (Dordr) 2016;38:10.

9. Prevett C, Moncion K, Phillips SM, Richardson J, Tang A. Role of resistance training in mitigating risk for mobility disability in community-dwelling older adults: a systematic review and meta-analysis. Arch Phys Med Rehabil 2022;103:2023–35.

10. Lu L, Mao L, Feng Y, Ainsworth BE, Liu Y, Chen N. Effects of different exercise training modes on muscle strength and physical performance in older people with sarcopenia: a systematic review and meta-analysis. BMC Geriatr 2021;21:708.

11. Carneiro MAS, Franco CMC, Silva AL, Castro-E-Souza P, Kunevaliki G, Izquierdo M, Cyrino ES, Padilha CS. Resistance exercise intervention on muscular strength and power, and functional capacity in acute hospitalized older adults: a systematic review and meta-analysis of 2498 patients in 7 randomized clinical trials. Geroscience 2021;43:2693–705.

12. Timpka S, Petersson IF, Zhou C, Englund M. Muscle strength in adolescent men and risk of cardiovascular disease events and mortality in middle age: a prospective cohort study. BMC Med 2014;12:62.

13. Dent E, Morley JE, Cruz-Jentoft AJ, Arai H, Kritchevsky SB, Guralnik J, Bauer JM, Pahor M, Clark BC, Cesari M, Ruiz J, Sieber CC, Aubertin-Leheudre M, Waters DL, Visvanathan R, Landi F, Villareal DT, Fielding R, Won CW, Theou O, Martin FC, Dong B, Woo J, Flicker L, Ferrucci L, Merchant RA, Cao L, Cederholm T, Ribeiro SML, Rodríguez-Mañas L, Anker SD, Lundy J, Gutiérrez Robledo LM, Bautmans I, Aprahamian I, Schols JMGA, Izquierdo M, Vellas B. International clinical practice guidelines for sarcopenia (ICFSR): screening, diagnosis and management. J Nutr Health Aging 2018;22:1148–61.

14. Kim JY, Lee CH, Park KH, Lee JH. Effect of Protein supplementation on exercise-induced muscle damage. Korean J Sport Sci 2010;21:1298–314.

15. Cereda E, Pisati R, Rondanelli M, Caccialanza R. Whey-protein, leucine- and vitamin-D-enriched oral nutritional supplementation for the treatment of sarcopenia. Nutrients 2022;14:1524.

16. Park Y, Park HY, Kim J, Hwang H, Jung Y, Kreider R, Lim K. Effects of whey protein supplementation prior to, and following, resistance exercise on body composition and training responses: a randomized doubleblind placebo-controlled study. J Exerc Nutrition Biochem 2019;23:34–44.

17. Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 2018;52:376–84.

18. Naclerio F, Larumbe-Zabala E. Effects of whey protein alone or as part of a multi-ingredient formulation on strength, fat-free mass, or lean body mass in resistance-trained individuals: a meta-analysis. Sports Med 2016;46:125–37.

19. Thomas DK, Quinn MA, Saunders DH, Greig CA. Protein supplementation does not significantly augment the effects of resistance exercise training in older adults: a systematic review. J Am Med Dir Assoc 2016;17:959.e1–9.

20. Gallagher D, Visser M, De Meersman RE, Sepulveda D, Pierson RN, Pierson RN, Harris T, Heymsfield SB. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J Appl Physiol (1985) 1997;83:229–39.

21. Tipton KD. Gender differences in protein metabolism. Curr Opin Clin Nutr Metab Care 2001;4:493–8.

22. Kim TN, Choi KM. Sarcopenia: definition, epidemiology, and pathophysiology. J Bone Metab 2013;20:1–10.

23. Hunter SK. Sex differences in fatigability of dynamic contractions. Exp Physiol 2016;101:250–5.

24. Flores DF, Gentil P, Brown LE, Pinto RS, Carregaro RL, Bottaro M. Dissociated time course of recovery between genders after resistance exercise. J Strength Cond Res 2011;25:3039–44.

25. McGregor RA, Cameron-Smith D, Poppitt SD. It is not just muscle mass: a review of muscle quality, composition and metabolism during ageing as determinants of muscle function and mobility in later life. Longev Healthspan 2014;3:9.

26. Doherty TJ. Invited review: aging and sarcopenia. J Appl Physiol 2003;95:1717–27.

27. Nelson ME, Fiatarone MA, Morganti CM, Greenberg RA, Evans WJ. Effects of high-intensity strength training on multiple risk factors for osteoporotic fractures: a randomized controlled trial. JAMA 1994;272:1909–14.

28. Gordon BA, Benson AC, Bird SR, Fraser SF. Resistance training improves metabolic health in type 2 diabetes: a systematic review. Diabetes Res Clin Pract 2009;83:157–75.

29. English KL, Paddon-Jones D. Protecting muscle mass and function in older adults during bed rest. Curr Opin Clin Nutr Metab Care 2010;13:34–9.

30. Reid KF, Pasha E, Doros G, Clark DJ, Patten C, Phillips EM, Frontera WR, Fielding RA. Longitudinal decline of lower extremity muscle power in healthy and mobility-limited older adults: influence of muscle mass, strength, composition, neuromuscular activation and single fiber contractile properties. Eur J Appl Physiol 2014;114:29–39.

31. Devries MC, Phillips SM. Supplemental protein in support of muscle mass and health: advantage whey. J Food Sci 2015;80:A8–15.

32. Miller PE, Alexander DD, Perez V. Effects of whey protein and resistance exercise on body composition: a meta-analysis of randomized controlled trials. J Am Coll Nutr 2014;33:163–75.

33. Churchward-Venne TA, Burd NA, Mitchell CJ, West DW, Philp A, Marcotte GR, Baker SK, Baar K, Phillips SM. Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men. J Physiol 2012;590:2751–65.

34. Kirwan RP, Mazidi M, García CR, Lane KE, Jafari A, Butler T, de Heredia FP, Davies IG. Protein interventions augment the effect of resistance exercise on appendicular lean mass and handgrip strength in older adults: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr 2022;115:897–913.

35. Luiking YC, Deutz NEP, Memelink RG, Verlaan S, Wolfe RR. Postprandial muscle protein synthesis is higher after a high whey protein, leucine-enriched supplement than after a dairy-like product in healthy older people: a randomized controlled trial. Nutr J 2014;13:9.

36. Jones MD, Wewege MA, Hackett DA, Keogh JWL, Hagstrom AD. Sex differences in adaptations in sex differences in adaptations in muscle strength and size following resistance training in older adults: a systematic review and meta-analysis. Sports Med 2021;51:503–17.

37. Janssen I, Heymsfield SB, Wang ZM, Ross R. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr. J Appl Physiol (1985) 2000;89:81–8.

38. Alway SE, Grumbt WH, Gonyea WJ, Stray-Gundersen J. Contrasts in muscle and myofibers of elite male and female bodybuilders. J Appl Physiol (1985) 1989;67:24–31.

39. Vangsoe MT, Joergensen MS, Heckmann LHL, Hansen M. Effects of insect protein supplementation during resistance training on changes in muscle mass and strength in young men. Nutrients 2018;10:335.

40. Maltais ML, Ladouceur JP, Dionne IJ. The effect of resistance training and different sources of post exercise protein supplementation on muscle mass and physical capacity in sarcopenic elderly men. J Strength Cond Res 2016;30:1680–7.

41. Villanueva MG, He J, Schroeder ET. Periodized resistance training with and without supplementation improve body composition and performance in older men. Eur J Appl Physiol 2014;114:891–905.

42. Hulmi JJ, Laakso M, Mero AA, Hakkinen K, Ahtiainen JP, Peltonen H. The effects of whey protein with or without carbohydrates on resistance training adaptations. J Int Soc Sports Nutr 2015;12:48.

43. Reidy PT, Fry CS, Igbinigie S, Deer RR, Jennings K, Cope MB, Mukherjea R, Volpi E, Rasmussen BB. Protein supplementation does not affect myogenic adaptations to resistance training. Med Sci Sports Exerc 2017;49:1197–208.

44. Nabuco HCG, Tomeleri CM, Fernandes RR, Sugihara Junior P, Cavalcante EF, Cunha PM, Antunes M, Nunes JP, Venturini D, Barbosa DS, Burini RC, Silva AM, Sardinha LB, Cyrino ES. Effect of whey protein supplementation combined with resistance training on body composition, muscular strength, functional capacity, and plasma-metabolism biomarkers in older women with sarcopenic obesity: a randomized, double-blind, placebo-controlled trial. Clin Nutr ESPEN 2019;32:88–95.

45. Mori H, Tokuda Y. Effect of whey protein supplementation after resistance exercise on the muscle mass and physical function of healthy older women: a randomized controlled trial. Geriatr Gerontol Int 2018;18:1398–404.

46. Sugihara Junior P, Ribeiro AS, Nabuco HCG, Fernandes RR, Tomeleri CM, Cunha PM, Venturini D, Barbosa DS, Schoenfeld BJ, Cyrino ES. Effects of whey protein supplementation associated with resistance training on muscular strength, hypertrophy, and muscle quality in preconditioned older women. Int J Sport Nutr Exerc Metab 2018;28:528–35.

47. Francis P, Mc Cormack W, Toomey C, Norton C, Saunders J, Kerin E, Lyons M, Jakeman P. Twelve weeks’ progressive resistance training combined with protein supplementation beyond habitual intakes increases upper leg lean tissue mass, muscle strength and extended gait speed in healthy older women. Biogerontology 2017;18:881–91.

48. Nabuco HCG, Tomeleri CM, Sugihara Junior P, Fernandes RR, Cavalcante EF, Antunes M, Ribeiro AS, Teixeira DC, Silva AM, Sardinha LB, Cyrino ES. Effects of whey protein supplementation pre- or post-resistance training on muscle mass, muscular strength, and functional capacity in pre-conditioned older women: a randomized clinical trial. Nutrients 2018;10:563.

49. Kim CB, Park JH, Park HS, Kim HJ, Park JJ. Effects of whey protein supplement on 4-week resistance-exercise-induced improvements in muscle mass and isokinetic muscular function under dietary control. Nutrients 2023;15:1003.

50. Cornier MA, Dabelea D, Hernandez TL, Lindstrom RC, Steig AJ, Stob NR, Van Pelt RE, Wang H, Eckel RH. The metabolic syndrome. Endocr Rev 2008;29:777–822.

51. Lakka HM, Laaksonen DE, Lakka TA, Niskanen LK, Kumpusalo E, Tuomilehto J, Salonen JT. The metabolic syndrome and total and cardiovascular disease mortality in middle-aged men. JAMA 2002;288:2709–16.

52. Larsson L, Degens H, Li M, Salviati L, Lee Y, Thompson W, Kirkland JL, Sandri M. Sarcopenia: aging-related loss of muscle mass and function. Physiol Rev 2019;99:427–511.

53. Kraemer WJ, Volek JS, Bush JA, Putukian M, Sebastianelli WJ. Hormonal responses to consecutive days of heavy-resistance exercise with or without nutritional supplementation. J Appl Physiol (1985) 1998;85:1544–55.

54. Cribb PJ, Hayes A. Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy. Med Sci Sports Exerc 2006;38:1918–25.

55. Tieland M, Dirks ML, van der Zwaluw N, Verdijk LB, van de Rest O, de Groot LC, van Loon LJ. Protein supplementation increases muscle mass gain during prolonged resistance-type exercise training in frail elderly people: a randomized, double-blind, placebo-controlled trial. J Am Med Dir Assoc 2012;13:713–9.

56. Cermak NM, Res PT, de Groot LC, Saris WH, van Loon LJ. Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis. Am J Clin Nutr 2012;96:1454–64.

57. Schoenfeld BJ, Aragon AA, Krieger JW. The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. J Int Soc Sports Nutr 2013;10:53.

58. Naclerio F, Larumbe-Zabala E. Effects of whey protein alone or as part of a multiingredient formulation on strength, fat-free mass, or lean body mass in resistance trained individuals: a meta-analysis. Sports Med 2016;46:125–37.

59. Janssen I, Shepard DS, Katzmarzyk PT, Roubenoff R. The healthcare costs of sarcopenia in the United States. J Am Geriatr Soc 2004;52:80–5.

60. Nascimento CM, Ingles M, Salvador-Pascual A, Cominetti MR, Gomez-Cabrera MC, Viña J. Sarcopenia, frailty and their prevention by exercise. Free Radic Biol Med 2019;132:42–9.

61. Saeki C, Takano K, Oikawa T, Aoki Y, Kanai T, Takakura K, Nakano M, Torisu Y, Sasaki N, Abo M, Matsuura T, Tsubota A, Saruta M. Comparative assessment of sarcopenia using the JSH, AWGS, and EWGSOP2 criteria and the relationship between sarcopenia, osteoporosis, and osteo sarcopenia in patients with liver cirrhosis. BMC Musculoskelet Disord 2019;20:615.

62. Da Boit M, Sibson R, Meakin JR, Aspden RM, Thies F, Mangoni AA, Gray SR. Sex differences in the response to resistance exercise training in older people. Physiol Rep 2016;4e12834.

63. Gates AT, Mertz KH, Bloch-Ibenfeldt M, Garde E, Baekgaard M, Svensson RB, Kjaer M. Different training responses in elderly men and women following a prolonged muscle resistance training intervention. Transl Sports Med 2021;4:892–9.

64. Vikberg S, Sorlen N, Branden L, Johansson J, Nordstrom A, Hult A, Nordstrom P. Effects of resistance training on functional strength and muscle mass in 70-year-old individuals with pre-sarcopenia: a randomized controlled trial. J Am Med Dir Assoc 2019;20:28–34.

65. Fokkenrood HJP, Bendermacher BLW, Lauret GJ, Willigendael EM, Prins MH, Teijink JAW. Supervised exercise therapy versus non-supervised exercise therapy for intermittent claudication. Cochrane Database Syst Rev 2013;8:CD005263.

66. Häkkinen K, Kallinen M, Izquierdo M, Jokelainen K, Lassila H, Mälkiä E, Kraemer WJ, Newton RU, Alen M. Changes in agonist-antagonist EMG, muscle CSA, and force during strength training in middle-aged and older people. J Appl Physiol (1985) 1998;84:1341–9.

67. Montero-Fernández N, Serra-Rexach JA. Role of exercise on sarcopenia in the elderly. Eur J Phys Rehabil Med 2013;49:131–43.

68. Daly RM, O’Connell SL, Mundell NL, Grimes CA, Dunstan DW, Nowson CA. Protein enriched diet, with the use of lean red meat, combined with progressive resistance training enhances lean tissue mass and muscle strength and reduces circulating IL-6 concentrations in elderly women: a cluster randomized controlled trial. Am J Clin Nutr 2014;99:899–910.

69. Aguiar AF, Januario RS, Junior RP, Gerage AM, Pina FL, do Nascimento MA, Padovani CR, Cyrino ES. Long-term creatine supplementation improves muscular performance during resistance training in older women. Eur J Appl Physiol 2013;113:987–96.

70. Kim H, Suzuki T, Saito K, Yoshida H, Kojima N, Kim M, Kim MJ, Sudo M, Yamashiro Y, Tokimitsu I. Effects of exercise and tea catechins on muscle mass, strength and walking ability in community-dwelling elderly Japanese sarcopenic women: a randomized controlled trial. Geriatr Gerontol Int 2013;13:458–65.

71. Paddon-Jones D, Short KR, Campbell WW, Volpi E, Wolfe RR. Role of dietary protein in the sarcopenia of aging. Am J Clin Nutr 2008;87:1562–6.

72. Hofmann M, Schober-Halper B, Oesen S, Franzke B, Tschan H, Bachl N, Strasser EM, Quittan M, Wagner KH, Wessner B. Effects of elastic band resistance training and nutritional supplementation on muscle quality and circulating muscle growth and degradation factors of institutionalized elderly women: the Vienna active ageing study (VAAS). Eur J Appl Physiol 2016;116:885–97.

73. Bjorkman MP, Suominen MH, Kautiainen H, Jyvakorpi SK, Finne-Soveri HU, Strandberg TE, Pitkala KH, Tilvis RS. Effect of protein supplementation on physical performance in older people with sarcopenia-a randomized controlled trial. J Am Med Dir Assoc 2020;21:226–32.

74. Dulac MC, Pion CH, Lemieux FC, Carvalho LP, Boutros GEH, Bélanger M, Gaudreau P, Chevalier S, Morais JA, Noirez P, Gouspillou G, Aubertin-Leheudre M. Effects of slow- v. fast-digested protein supplementation combined with mixed power training on muscle function and functional capacities in older men. Br J Nutr 2021;125:1017–33.

75. Ansdell P, Thomas K, Hicks KM, Hunter SK, Howatson G, Goodall S. Physiological sex differences affect the integrative response to exercise: acute and chronic implications. Exp Physiol 2020;105:2007–21.

76. Welle S, Tawil R, Thornton CA. Sex-related differences in gene expression in human skeletal muscle. PLoS One 2008;3e1385.

77. Ivey FM, Tracy BL, Lemmer JT, Ness Aiver M, Metter EJ, Fozard JL, Hurley BF. Effects of strength training and detraining on muscle quality: age and gender comparisons. J Gerontol A Biol Sci Med Sci 2000;55:B152–7.

78. Frontera WR, Meredith CN, O’Reilly KP, Knuttgen HG, Evans WJ. Strength conditioning in older men: skeletal muscle hypertrophy and improved function. J Appl Physiol (1985) 1988;64:1038–44.

79. Charette SL, McEvoy L, Pyka G, Snow-Harter C, Guido D, Wiswell RA, Marcus R. Muscle hypertrophy response to resistance training in older women. J Appl Physiol (1985) 1991;70:1912–6.

80. Taaffe DR, Pruitt L, Pyka G, Guido D, Marcus R. Comparative effects of high- and low-intensity resistance training on thigh muscle strength, fiber area, and tissue composition in elderly women. Clin Physiol 1996;16:381–92.

81. Yarasheski KE. Exercise, aging, and muscle protein metabolism. J Gerontol A Biol Sci Med Sci 2003;58:M918–22.

82. Bamman MM, Shipp JR, Jiang J, Gower BA, Goodman A, Goodman A, McLafferty Jr CL, Urban RJ. Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans. Am J Physiol Endocrinol Metab 2001;280:E383–90.

83. Lowe DA, Lund T, Alway SE. Hypertrophy-stimulated myogenic regulatory factor mRNA increases are attenuated in fast muscle of aged quails. Am J Physiol 1998;275:C155–62.

84. Marsh DR, Criswell DS, Carson JA, Booth FW. Myogenic regulatory factors during regeneration of skeletal muscle in young, adult, and old rats. J Appl Physiol (1985) 1997;83:1270–5.

85. Cheng R, Maloney A, Moran J, Newman TH, Gardner EC. Resistance training as treatment for sarcopenia: examining sex-related differences in physiology and response. Clin Ther 2022;44:33–40.

86. Moore DR, Churchward-Venne TA, Witard O, Breen L, Burd NA, Tipton KD, Phillips SM. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. J Gerontol A Biol Sci Med Sci 2015;70:57–62.

87. Yang Y, Breen L, Burd NA, Hector AJ, Churchward-Venne TA, Josse AR, Tarnopolsky MA, Phillips SM. Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men. Br J Nutr 2012;108:1780–8.

88. Smith GI, Reeds DN, Hall AM, Chambers KT, Finck BN, Mittendorfer B. Sexually dimorphic effect of aging on skeletal muscle protein synthesis. Biol Sex Differ 2012;3:11.

89. Witard OC, Tieland M, Beelen M, Tipton KD, van Loon LJ, Koopman R. Resistance exercise increases postprandial muscle protein synthesis in humans. Med Sci Sports Exerc 2009;41144:54.

90. Dreyer HC, Fujita S, Cadenas JG, Chinkes DL, Volpi E, Rasmussen BB. Resistance exercise increases AMPK activity and reduces 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle. J Physiol 2006;576:613–24.

91. Mascher H, Tannerstedt J, Brink-Elfegoun T, Ekblom B, Gustafsson T, Blomstrand E. Repeated resistance exercise training induces different changes in mRNA expression of MAFbx and MuRF-1 in human skeletal muscle. Am J Physiol Endocrinol Metab 2008;294:E43–51.

92. Mitchell WK, Phillips BE, Williams JP, Rankin D, Lund JN, Wilkinson DJ, Smith K, Atherton PJ. The impact of delivery profile of essential amino acids upon skeletal muscle protein synthesis in older men: clinical efficacy of pulse vs. bolus supply. Am J Physiol Endocrinol Metab 2015;309:E450–7.

93. Moberg M, Apró W, Ekblom B, Hall GV, Holmberg HC, Blomstrand E. Activation of mTORC1 by leucine is potentiated by branched-chain amino acids and even more so by essential amino acids following resistance exercise. Am J Physiol Cell Physiol 2016;310:C874–84.

94. Takegaki J, Sase K, Yasuda J, Shindo D, Kato H, Toyoda S, Yamada T, Shinohara Y, Fujita S. The effect of leucine-enriched essential amino acid supplementation on anabolic and catabolic signaling in human skeletal muscle after acute resistance exercise: a randomized, double-blind, placebo-controlled, parallel-group comparison trial. Nutrients 2020;12:2421.

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Factor	Note		Significant difference		Age	Case number	Ref
Factor	Sex	Assessment & Results	Male	Female	Age	Case number	Ref
Muscle strength	M	One repetition maximum (1RM) measurement	+		20 ~ 30	18	[16]
	M	- Experimental group (EG): preacher bench biceps curl 23.14 kg, leg curl 23.22 kg	+		20 ~ 30	18	[16]
	M	1RM test	+		65 ~ 75	21	[40]
	M	PRO+EX (lat pull down: +8.2 kg, bench press: +4.3 kg)	+		65 ~ 75	21	[40]
	M	1RM test	+		68.1	22	[41]
	M	PRO+EX (bench press: +28.6 kg, leg press: +141 kg)	+		68.1	22	[41]
	M	1RM test	+		24.02	18	[39]
	M	PRO+EX (leg press: +36 kg, bench press: +9 kg)	+		24.02	18	[39]
	M	A David 210 horizontal leg press device (David Health Solutions Ltd, Finland)	+		31.4	22	[42]
	M	- PRO+EX (isometric strength Maximal voluntary contraction: +23 kg)	+		31.4	22	[42]
	M	1RM test	NS		20 ~ 30	36	[49]
	M	PRO+EX (leg extensor peak torque: -10.7 N.m, leg flexor peak torque: +4.3 N.m)	NS		20 ~ 30	36	[49]
	M	Isokinetic peak torque	+		20≤	20 ~ 30	[43]
	M	WP+EX (knee extensor: +44.9 N,m)	+		20≤	20 ~ 30	[43]
	F	Maximal voluntary isometric contractions of the knee extensors of the dominant limb were measured using a Con-Trex MJ Dynamometer.		+	60≤	57	[47]
	F	PRO+EX: +10.2 N.m		+	60≤	57	[47]
	F	1 RM test		NS	60≤	26	[44]
	F	- EG: knee extension: +3.1 kg, chest press: +2 kg, preacher curl: +2.7 kg		NS	60≤	26	[44]
	F	1RM test		+	60≤	66	[48]
	F	EG (chest press: 5.6%, knee extension: +9.2%, preacher curl: +11.3%		+	60≤	66	[48]
	F	1RM test		+	60≤	31	[46]
	F	EG (chest press: 6.3%, knee extension: +8.5%, preacher curl: +14%		+	60≤	31	[46]
	F	PRO+EX (knee extension: +2.6 kg, grip strength: +1.2 kg)		+	65 ~ 80	75	[45]
Muscle volume	M	DXA scan	+		24.02	18	[39]
	M	PRO+EX (fat-and bone-free mass: +2.6 kg)	+		24.02	18	[39]
	M	DXA scan	+		65 ~ 75	21	[40]
	M	PRO+EX (muslce mass: +2.29 kg)	+		65 ~ 75	21	[40]
	M	DXA scan	+		68.1	22	[41]
	M	PRO+EX (lean body mass: +1.8 kg)	+		68.1	22	[41]
	M	The use of tape is a convenient tool for measuring circumference due to its pull-out mechanism	+		20 ~ 30	18	[16]
	M	- EG (right mid arm: +2.3 cm, left mid arm: +2.5 cm, right mid thigh: +1.3 cm, left mid thigh: +1.5 cm)	+		20 ~ 30	18	[16]
	M	Magnetic resonance imaging (MRI)	+		31.4	22	[42]
	M	PRO+EX quadriceps muscle cross-sectional area (CSA): +9%	+		31.4	22	[42]
	M	Bioelectrical impedance analyzer (Inbody 620, Inbody, Republic of Korea)	+		20 ~ 30	36	[49]
	M	- PRO+EX (muscle mass: +2.34 kg)	+		20 ~ 30	36	[49]
	M	DXA scan	+		20≤	20 ~ 30	[43]
	M	WP+EX (lean body mass: +4.08%, thigh circumference: + 1.6 cm, total vastus lateralis CSA: +3340 microns2)	+		20≤	20 ~ 30	[43]
	F	Body mass (BM) was measured to the nearest 0.1 kg (MC-180MA; Tanita UK Ltd.)		+	60≤	57	[47]
	F	- PRO+EX: LTM + 3.6%		+	60≤	57	[47]
	F	Whole-body dual-energy X-ray absorptiometry (Lunar Prodigy, model NRL 41990, GE Lunar, Madison, WI)		NS	60≤	26	[44]
	F	- EG: Total lean soft tissue (LST) +1.2 kg		NS	60≤	26	[44]
	F	DXA scan (Lunar Prodigy, model NRL 41990, GE Lunar, Madison, WI)		+	60≤	66	[48]
	F	- EG (upper limb lean soft tissue: +3.4%, lower limb lean soft tissue: +3.2%, skeletal muscle mass: +3.4%)		+	60≤	66	[48]
	F	DXA scan		+	60≤	31	[46]
	F	- EG (upper limb lean soft tissue: +5%, lower limb lean soft tissue: +3.4%, skeletal muscle mass: +4.8%)		+	60≤	31	[46]
	F	Multifrequency bioelectrical impedance (In-Body bioelectrical impedance analyzer; Bio Space, Seoul, Korea)		+	65 ~ 80	75	[49]
	F	- PRO+EX (Lower limb muscle mass: +0.5 kg)		+	65 ~ 80	75	[49]
Physical Function	M	400-m Walk	+		68.1	22	[41]
	M	- PRO+EX: -16 sec	+		68.1	22	[41]
	M	- Walking Speed (6 m)	+		65 ~ 75	21	[40]
		PRO+EX (+0.3 m/sec)
		- Timed Up and Go
		PRO+EX (-1.3 sec)
		- Chair Stand (5 rep)
		PRO+EX (-1.2 sec)
	M	- 4-meter walking test	+		60≤	75	[74]
		PRO+EX: - 0.12 sec (-3.8%)
		- balance test
		PRO+EX: +4.6 sec
		- Timed-Up & Go test
		PRO+EX: -0.82 sec (-7.9%)
		- stair climbing test
		PRO+EX: 4.2 rep (+13.3%)
	F	10-m walk test (10 MW) rising from the sitting position test (RSP)		NS	60≤	26	[44]
	F	- EG (1P MW: -0.5 sec, RSP: -1.4 sec)		NS	60≤	26	[44]
	F	Gait speed was measured in time units (0.01 s), using a stopwatch.		NS	65 ~ 80	75	[45]
	F	- PRO+EX (gait speed: 0 sec)		NS	65 ~ 80	75	[45]
	F	Chair stand test (30 sec)		+	65≤	91	[72]
	F	- PRO+EX: +15%		+	65≤	91	[72]

Ref	Resistance training program	Repetition period	Details of protein condition	Intake timing
[16]	Each exercise consisted of three sets of 10–12 repetitions performed with 80% of 1RM (leg extension, and lying leg curl, bench press, barbell rowing, preacher bench biceps curl, and dumbbell shoulder press)-	12 week 3 days/week	(26.4 g of WP, including 5.8 g of BCAA), 1 g creatine mono-hydrate, 8 g carbohydrate, and 2 g fat.	Before and after each exercise session
[39]	Incline leg press, knee extension and calf raises, bench press, lateral pulldown, seated row, triceps extension, and standing abdominal crunches (80% of 1RM) leg curl, lying cable chest flies, biceps curl (70% OF 1RM)	8 week 4 days/week	0.4 g/kg/bar insect protein	During exercise
[40]	Leg press, bench press, leg extension, and shoulder press, sit-ups, rowing extensions, biceps curls, and leg curls (3X8 repetitions, 80% of 1RM)	12 week 3 days/week	Essential amino acid (EAA) supplements was composed of 379 ml of soy beveragein which was added commercial EAA powder (12 g protein, 7 g EAA [3.5 g from leucine], 39 g carbohydrates, 5.3 g of fat)	After each training
[41]	2~6 sets, 5~6 repetitions (bilateral leg press, flat bench machine chest press, lat pulldown, dumbbell step-ups, bilateral knee extension/flexion, dumbbell Romanian deadlifts)	12 week 3 days/week	liquid whey protein 35 g	After each training
[42]	Hypertrophy-focused strength training contained mainly sets of 8–12 repetitions with 75–85% loads of 1 RM. Maximal strength training in both RT regimens consisted of neural enhancing RT with lower repetitions per set (typically 4–6) and higher intensity (86–95% 1 RM) (bilateral leg press, knee extension, and knee flexion, chest and shoulders, upper back, trunk extensors and flexors, and upper arms)	12 week 2 ~ 3 days/week	37.5 g of whey concentrate (30 g of whey proteins, 5 g of lactose < 1 g of fat)	After each training
[43]	12-week whole-body progressive resistance exercise-training (RET) program	12 week 3 days/week	100% WP isolate 22 g	Every day
[44]	2~3 sets, 8~12 repetitions (chest press, horizontal leg press, seated row, knee extension, preacher curl, leg curl, triceps pushdown, and seated calf raise)	12 week 3 days/week	35 g of hydrolyzed WP	After each training
[45]	- Bodyweight resisted lower body exercises included rising and sitting from a chair, and leg extensions.	24 week 2 days/week	25 g WP (22.3 g of protein, 0.3 g of fat, 0.1 g of carbohydrate, 1225 mg of valine, 2975 mg of leucine and 1175 mg of isoleucine per 25 g of one intake serving)	After each training
[45]	- Resistance elastic band exercises (50–70% of the 1RM)	24 week 2 days/week		After each training
[46]	3 sets, 8~12 repetitions (chest press, seated row, triceps pushdown, preacher curl, horizontal leg press, knee extension, knee curl and seated calf raise)	20 week 3 days/week	35 g of hydrolyzed WP (carbohydrates 5 g; lipids 0.17 g; Protein 27.1 g)	After each training
[47]	4–6 sets, 8–15 repetitions (squats, lunges, hip abduction, shoulder press, latissimus dorsi pull-down or seated row, bicep curls, calf raises, push ups, triceps dips BW and lumbopelvic stabilisation exercises)	12 week 3 days/2eek	WP concentrate hydrolysate (0.165 g/kg)	Protein supplementation was done twice during mealtime of the day. typically breakfast and lunch
[48]	3 sets, Up to 10 repetitions (chest press, horizontal leg press, seated row, knee extension, preacher curl, leg curl, triceps pushdown, and seated calf raise)	8 week 3 days/week	The hydrolyzed WP drink contained 27.1 g of protein, 5.2 g of carbohydrates, and 0.2 g of fat per portion	Pre and post exercise (1 hour)
[49]	60~70% of 1RM chest, back, shoulder, arm, abdomen, and lower-body exercises.	4 week 6 days/week	One pack of WP powder supple-ment contained 20 g of whey protein isolate, 8 g of carbohydrate, and 6.4 g of dietary fiber	Post exercise (RT), morning (rest day)
[72]	The resistance exercise programme was designed to train all major muscle groups based on guidelines provided by the American College of Sports Medicine. 1~2 sets, 15 repetitions (Thera-Band force–elonga from yellow to red and further to black)	24 week 2 days/week	20.7 g protein (3 g leucine, >10 g essential amino acids), 9.3 g carbohydrates, 3 g fat, vitamins (800 IU vitamin D, 2.9 mg vitamin B6, 3 μg vitamin B12) and minerals	Every morning after breakfast and after each training session
[74]	- 3 sets, 12 repetitions, 80% 1RM (high velocity loaded exercises: leg curl, chest press, lateral pull down, and seated leg press)	12 week 1 days/week	30 g (casein or whey proteins containing high leucine concentration)	Every day (10 g of each of the three meals)
[74]	- 3 sets, 10 repetitions, 80% of 1RM (six functional exercises that targeted posture and balance: squats against the wall with a Swiss ball, pelvis rotation on a Swiss ball, shoulder external rotations, stair climbing, biceps curls with dumbbells and bird-dog exercise)	12 week 1 days/week		Every day (10 g of each of the three meals)