Effects of bcaa ingestion on exercise

performance

The effect of BCAA ingestion on physical performance was investigated for the first time in a field test by Blomstrand et al.20 One hundred and ninety-three male subjects were studied during a marathon in Stockholm. The subjects were randomly divided into an experimental group receiving BCAA in plain water and a placebo group receiving flavored water. The subjects also had free access to carbohydrate-containing drinks. No difference was observed in the marathon time of the two groups. However, when the original subject group was divided into fast and slower runners, a significant reduction in marathon time was observed in subjects given BCAAs in the slower runners only. This study has since been criticized for its design and statistical analysis. For example, fluid and carbohydrate ingestion were not controlled during the race, subjects receiving BCAAs were not matched to controls in terms of previous performance, and the retrospective division of subjects into groups relating to their performance times in the race has been criticized as statistically invalid.

A study that examined the effect of BCAA ingestion during exercise in the heat (ambient temperature of 34°C) has provided some further evidence in support of these early findings.21 A 14% increase in the capacity to perform relatively low intensity exercise (40% of maximal oxygen uptake, VO2max) was reported following BCAA supplementation, compared with placebo (Figure 13.6). No difference in peripheral markers of fatigue was reported between the BCAA and placebo treatments, and the BCAA supplementation (which began 1 h before the start of exercise) resulted in a two to threefold reduction in the plasma ratio of fTRP to BCAAs. The capacity to perform prolonged exercise is reduced at high ambient temperatures, and this premature fatigue is not adequately explained by peripheral mechanisms. Indeed, there is now some convincing evidence that central fatigue plays an important role in limiting exercise capacity in the heat.22 However, two recent studies that have examined the effects of BCAA supplementation (approximately 20 g of BCAAs consumed before and during exercise) on cycling exercise capacity in the heat at two different exercise intensities (60% VO2max at 35°C and 50% VO2max at 30°C) failed to find any effect on exercise capacity or ratings of perceived exertion.2324

Indeed, the majority of studies, using various exercise and treatment designs and several forms of administration of BCAA (infusion, oral, and with and without carbohydrates), have failed to find a performance-enhancing effect.25-29 Van Hall et al.27 studied time trial performance in trained cyclists consuming carbohydrate (6% sucrose solution) during exercise with and without BCAAs. A high (18 g/l) and a low (6 g/l) dose of BCAAs were given, but no differences were seen in time trial performance (Figure 13.7). One limitation of most of the studies that have investigated possible performance-enhancing effects of ingested BCAAs is that they have lacked sufficient statistical power to identify small but useful enhancements of performance.

If the central fatigue hypothesis is correct and the ingestion of BCAAs reduces the exercise-induced increase of brain fTRP uptake and thereby delays fatigue, the opposite must also be true; that is, ingestion of tryptophan before exercise should reduce the time to exhaustion. A few studies have included supplemental tryptophan

Time to exhaustion at 40% VO2 max in the heat (min)

PLACEBO BCAA

~30g ingested during exercise

FIGURE 13.6 Time to exhaustion during cycling at 40% VO2max in the heat with or without ingestion of ~30 g of BCAA. *, p < 0.05 significantly different from placebo. (Data from Mittleman, K.D. et al., Med. Sci. Sports Exerc., 30, 83-91, 1998.)

FIGURE 13.6 Time to exhaustion during cycling at 40% VO2max in the heat with or without ingestion of ~30 g of BCAA. *, p < 0.05 significantly different from placebo. (Data from Mittleman, K.D. et al., Med. Sci. Sports Exerc., 30, 83-91, 1998.)

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