These authors contributed equally to this work
Skeletal muscle glycogen is a determinant of endurance capacity for some athletes. Ginger is well known to possess nutritional effects, such as anti-diabetic effects. We hypothesized that ginger extract (GE) ingestion increases skeletal muscle glycogen by enhancing fat oxidation. Thus, we investigated the effect of GE ingestion on exercise capacity, skeletal muscle glycogen, and certain blood metabolites in exercised rats.
First, we evaluated the influence of GE ingestion on body weight and elevation of exercise performance in rats fed with different volumes of GE. Next, we measured the skeletal muscle glycogen content and free fatty acid (FFA) levels in GE-fed rats. Finally, we demonstrated that GE ingestion contributes to endurance capacity during intermittent exercise to exhaustion.
We confirmed that GE ingestion increased exercise performance (p<0.05) and elevated the skeletal muscle glycogen content compared to the non-GE-fed (CE, control exercise) group before exercise (Soleus: p<0.01, Plantaris: p<0.01, Gastrocnemius: p<0.05). Blood FFA levels in the GE group were significantly higher than those in the CE group after exercise (p<0.05). Moreover, we demonstrated that exercise capacity was maintained in the CE group during intermittent exercise (p<0.05).
These findings indicate that GE ingestion increases skeletal muscle glycogen content and exercise performance through the upregulation of fat oxidation.
Skeletal muscle glycogen content changes dynamically due to external stimuli, such as exercise and nutrition. Studies in the 1960s clarified that the restriction of glycogen storage leads to an inability to continue exercise [
Glycogen storage in the skeletal muscle has various metabolic impacts, especially for the mobilization of energy substrates during endurance exercise [
The co-ingestion of CHO-rich foods with other macronutrients or agents (e.g., protein, creatine, and caffeine supplementation) results in a further acceleration of muscle glycogen synthesis [
GE may enhance endurance capacity through energy metabolism, although this effect is not well known. Therefore, in the present study, we examined the influence of GE ingestion on endurance performance and metabolite levels in rats during endurance exercise.
We outlined the following experimental strategy to investigate the effect of GE ingestion on skeletal muscle glycogen content and endurance exercise. First, we confirmed whether the extracts increased the exercise capacity of GE-fed rats. Second, we evaluated the effect of GE on blood metabolites and skeletal muscle glycogen content in rats to estimate the influence of GE on energy metabolism. Third, we tested the efficacy of GE ingestion on exercise capacity across the recovery periods. Male Sprague Dawley (SD) rats were purchased from CLEA Experimental Animals Supply (CLEA Japan, Inc., Tokyo, Japan) and cared for according to the “Guiding Principles for the Care and Use of Animals.” The rats were fed a standard diet CE-2 (CLEA Japan, Inc., Tokyo, Japan). The room temperature was maintained at 25 ± 1 °C, and humidity was maintained under a constant 12:12-hour light/dark cycle (light: 8:00 a.m.–8:00 p.m.). Distilled water was freely available for drinking
Laboratory animals in the control group (without GE) were fed CE-2 (CLEA Japan, Inc. Tokyo, Japan), and for GE-fed rats, CE-2 was mixed ginger extract powder (Ikeda Food Research Co., Ltd, Hiroshima, Japan;
SD rats (n=28, 6 weeks old) were subjected to 25 days of exercise training after a habitation period of 3 days, with
SD rats (n=20, 6 weeks old) were divided into two groups (CE: control exercise group; [n=10] and GE: ginger exercise group; [n=10]) after 3 days of habitation and 7 days of exercise training. These rats were administered GE after exercise training, and they were tested with an all-out test similar to that in Experiment 1. Blood samples were collected before, immediately after (post1), and 1 h after exercise (post2).
This experiment was conducted based on Experiment 2. SD rats (n=20, 6 weeks old) were also divided into two groups (CE: control exercise group; [n=10] and GE: ginger exercise group; [n=10]) after 3 days of habitation and 7 days of exercise training. They were fed GE after exercise training and made to attempt an all-out test. Furthermore, these rats underwent the same all-out test after a 1 hour recovery period to evaluate the influence of GE ingestion on the recovery period.
The rats were exercised on a treadmill (Natsume Seisakusho Co, Ltd, Tokyo, Japan) to habituate them to exercise conditions (10 m/min, 15 min and 25 m/min, 30 min), and they were trained on the same experimental equipment (25 m/min, 30 min) for 25 days. Warming up and cooling down were performed before and after exercise training (15 m/min, 2 min).
This test was carried out 24 h after the final exercise training. The animals were exercised at 30 m/min on a treadmill until they could not maintain this exercise intensity. The animals were exercised for 110 min and the treadmill speed was then accelerated by 2 m/min until all-out. All-out was declared when the rats could not keep up with the exercise speeds, and they could not restore their bodies from the supine position.
Skeletal muscle of the left leg (soleus, plantaris, gastrocnemius muscle) and liver were extracted under anesthesia. The samples were frozen in liquid nitrogen after trimming for storage.
The glycogen concentration of skeletal muscles and liver was measured by the amyloglucosidase method [
Blood samples were collected from the tail vein before and after the all-out test. Blood glucose levels were evaluated using glucose measurements (Onetouch UltravueTM, Johnson & Johnson, Tokyo, Japan). FFA levels were evaluated using a spectrophotometer (V-630BIO, JASCO Corporation, Tokyo, Japan) by measuring the enzymatic reactions (acyl-CoA synthase, acyl-CoA oxidase, and peroxidase) [
All data are expressed as mean ± standard error (SE) and were analyzed using SPSS version 25 (IBM Japan, Tokyo, Japan). One-way analysis of variance was used to test for statistically significant differences among the groups. If a significant difference was detected among groups, the groups were further evaluated using the post-hoc Scheffe test. The significance level for major effects was set at p<0.05.
There were no significant differences in food intake and final body weight among the groups (
The final body weight, body weight gain, and food efficiency significantly decreased in the GE group compared to the CE group (
The skeletal muscle glycogen content in the GE group was significantly higher than that in the CE group before exercise (
The running distance was significantly higher in the GE group than that in the CE group in the all-out test (
Skeletal muscle glycogen content is a determinant of endurance capacity as an energy substrate and intracellular signaling molecule [
A recent study reported that GE ingestion leads to a reduction in body weight and enhancement of fat oxidation in obese mice [
Exercise has a substantial impact on energy metabolism as various substrates need to be mobilized for meeting the energy demand for contractions of the skeletal muscle. In general, skeletal muscle mobilizes energy substrates via the adenosine triphosphate production process, thereby releasing blood glucose through glycolysis to provide CHO substrate for the skeletal muscle [
Skeletal muscle glycogen content is a determinant of endurance capacity in cellular adaptation and exercise performance [
The rapid restoration of muscle glycogen is required between two events or training sessions (e.g., runner’s twice-daily workouts). These results indicate that GE ingestion contributes to the enhancement of skeletal muscle glycogen levels. These effects of GE ingestion might be useful for maintaining endurance capacity in the recovery phase during intermittent exercise, such as during athletic competitions. Therefore, we examined whether exercise performance increased because of GE ingestion during two all-out trials. The running distance and blood glucose levels were significantly different between the two groups (
We focused on the possibility that GE ingestion enhanced endurance capacity due to the upregulation of fat oxidation. However, it is not clear if the upregulation pathway actually activated as a molecular biological approach was not employed in the present study. A previous study reported that GE enhances fatty acid utilization via the PPARδ pathway in an
In conclusion, we demonstrated that GE ingestion decreased body weight and enhanced exercise capacity in experimental animals. The cause of this phenomenon may be related to an increase in fat oxidation and skeletal muscle glycogen content. These findings indicate that GE ingestion is useful for improving exercise performance for athletics.
Food intake (A), change in body weight (B), final body weight (C), and running distance of rats (D). Experimental animals were randomly divided into three groups at the age of 6 weeks (CE: Control exercise group [n=7], LGE: Low ginger exercise group [n=11], HGE: High ginger exercise group [n=10]). *p<0.05 vs CE group. Values are represented as mean ± SE.
Running distance (A) and blood glucose levels (B). Experimental animals were randomly divided into two groups at the age of 6 weeks (CE: Control exercise group [n=10], GE: Ginger exercise group [n=10]). *p<0.05 vs CE group, † p<0.01 vs pre. Values are represented as mean ± SE.
Blood glucose (A), free fatty acid (B), and lactate (C) levels of rats. Experimental animals were randomly divided into two experimental groups at the age of 6 weeks (CE: Control exercise group, [n=10], GE: ginger exercise group [n=10]). Blood samples were collected from the tail vein before and after the all-out test. *p<0.05 vs CE group; ††p<0.01, †††p<0.001 vs pre. Values are represented as mean ± SE.
Glycogen concentration in soleus (A), plantaris (B), gastrocnemius (C), and liver (D) per food intake. Experimental animals were randomly divided into two experimental groups at the age of 6 weeks (CE: Control exercise group [n=10], GE: ginger exercise group [n=10]). Skeletal muscles were collected before and after the all-out test. *p<0.05, **p<0.01 vs CE group. Values are represented as mean ± SE.
Final body weight, body weight gain, food intake, and food efficiency after GE ingestion. Values are represented as mean ± SE.
CE | GE | |
---|---|---|
Final body weight (g) | 312.8±2.6 | 285.6±4.7*** |
Body weight gain (g) | 14.8±2.0 | -7.8±3.7*** |
Food efficiency (g) |
0.5±0.1 | -1.2±0.6 |
Food efficiency was calculated by “body weight gain/food intake.”
p<0.05,
p<0.001 vs GE group.