Effect of short-term heat acclimation on endurance time and skin blood flow in trained athletes.

BACKGROUND: To examine whether short-term, ie, five daily sessions, vigorous dynamic cycling exercise and heat exposure could achieve heat acclimation in trained athletes and the effect of heat acclimation on cutaneous blood flow in the active and nonactive limb. METHODS: Fourteen male badminton and table tennis athletes (age = 19.6 ± 1.2 years) were randomized into a heat acclimation (EXP, n = 7) or nonheat acclimation (CON, n = 7) group. For 5 consecutive days, the EXP group was trained using an upright leg cycle ergometer in a hot environment (38.4°C ± 0.4°C), while the CON group trained in a thermoneutral environment (24.1°C ± 0.3°C). For both groups, the training intensity and duration increased from a work rate of 10% below ventilatory threshold (VT) and 25 minutes per session on day 1, to 10% above VT and 45 minutes per session on day 5. Subjects performed two incremental leg cycle exercise tests to exhaustion at baseline and post-training in both hot and thermoneutral conditions. Study outcome measurements include: maximum oxygen uptake (VO2max); exercise heart rate (HR); O2 pulse; exercise time to exhaustion (tmax); skin blood flow in the upper arm (SkBFa) and quadriceps (SkBFq); and mean skin (Tsk). RESULTS: The significant heat-acclimated outcome measurements obtained during high-intensity leg cycling exercise in the high ambient environment are: (1) 56%-100% reduction in cutaneous blood flow to the active limbs during leg cycling exercise; (2) 28% drop in cutaneous blood flow in nonactive limbs at peak work rate; (3) 5%-10% reduction in heart rate (HR); (4) 10% increase in maximal O2 pulse; and (5) 6.6% increase in tmax. CONCLUSION: Heat acclimation can be achieved with five sessions of high-intensity cycling exercise in the heat in trained athletes, and redistribution of cutaneous blood flow in the skin and exercising muscle, and enhanced cardiovascular adaptations provide the heat-acclimated athletes with the capability to increase their endurance time in the hot environment.

The effect of eight weeks of supplementation with Eleutherococcus senticosus on endurance capacity and metabolism in human.

The aim of this study was to examine the effects of Eleutherococcus senticosus (ES) supplementation on endurance capacity, cardiovascular functions and metabolism of recreationally trained males for 8 weeks. Nine recreationally trained males in college consumed 800 mg/d of ES or starch placebo (P) for 8 weeks according to a double-blind, randomized, placebo controlled and crossover design with a washout period of 4 weeks between the cycling trials. Subjects cycled at 75% VO2 peak until exhaustion. The examined physiological variables included endurance time, maximal heart rate during exhaustion exercise, VO2, rating of perceived exertion and respiratory exchange ratio. The biochemical variables including the plasma free fatty acid (FFA) and glucose were measured at rest, 15 min, 30 min and exhaustion. The major finding of this study was the VO2 peak of the subjects elevated 12% (P < 0.05), endurance time improved 23% (P < 0.05) and the highest heart rate increased 4% (P < 0.05) significantly. The second finding was at 30 min of 75% VO2 peak cycling, the production of plasma FFA was increased and the glucose level was decreased both significantly (P < 0.05) over 8-week ES supplementation. This is the first well-conducted study that shows that 8-week ES supplementation enhances endurance capacity, elevates cardiovascular functions and alters the metabolism for sparing glycogen in recreationally trained males.

Effects of arginine supplementation on post-exercise metabolic responses.

This study investigated the effects of arginine supplementation on acute metabolic responses during recovery after a single bout of endurance exercise in trained athletes. Twelve healthy male judo athletes were randomly divided into two groups and performed a single bout of exercise at a speed estimated to correspond to 75%VO2max for 60 min, and then took either a placebo or arginine at 0.1 g/kg-wt. Blood samples of each athlete were collected before exercise, and 0, 15, 30, 45, 60, 90, 120 min after exercise, respectively. The experiment was repeated two weeks later, but treatments were exchanged for the two groups. The concentrations of glucose, insulin, free fatty acid (FFA), glycerol, lactate, ammonia, creatine kinase, and NOx (NO2(-) + NO3(-)) in blood were examined. No differences in the levels of glycerol, lactate, ammonia, creatine kinase, or NOx between the two groups were observed at any of the time points. However, the concentration of glucose was significantly higher in the arginine group as compared to that in the placebo group at the 15-min recovery point. The insulin concentration was also higher in the arginine group as compared to that in the placebo group at the 30-min recovery point. Furthermore, the free fatty acid levels at the 30, and 45-min recovery points were significantly lower in the arginine group compared to those in the placebo group. The results indicated that arginine supplementation during the exercise recovery period could increase glucose and insulin concentrations, and decrease FFA availability in the blood.