Abstract

Elevated intramuscular carnosine content achieved via -alanine supplementation (BA) can improve human exercise performance. This is most likely due to improved intracellular pH regulation and/or enhanced muscle contractile properties as a result of improved calcium (Ca2+) sensitivity. PURPOSE: To examine the effects of BA on in vivo human skeletal muscle contractile properties and voluntary performance. METHODS: Twenty-three participants completed two experimental sessions, before and after 28 d supplementation with 6.4 g·d -1 of -alanine (n=12; 26 ± 7 y) or placebo (PLA; n=11; 25 ± 5 y). Knee extensor force and surface electromyography (EMG) were recorded during a series of voluntary and electrically-evoked (nerve and superficial muscle stimulation) contractions. Data were analysed using repeated measures ANOVA; significance was accepted at P<0.05. RESULTS: BA had no effect on force-frequency relationship (1 s stimulation, 1-100Hz), or peak force during evoked twitches or octets (8 pulses, 300 Hz). No changes in evoked twitch electromechanical delay (EMD) or time-to-peak tension were shown, although resting and potentiated twitch half relaxation time (HRT) decreased by 12% and 7% after BA (Table 1). BA did not alter maximal or explosive force (25 ms intervals up to 150 ms from onset) during voluntary contractions. CONCLUSION: BA had no effect on the force-frequency relationship, supported by lack of change in twitch force data, implying a lack of influence of muscle carnosine elevation on Ca2+ sensitivity. Nevertheless, HRT was reduced after BA, which may be explained by improved cross-bridge detachment rates or reuptake of Ca2+ , potentially providing important implications for the efficiency of muscle contraction.