Willems, M., Ponte, J., & Harris, R. (2009). Effect of beta-alanine supplementation on sustained isometric muscle contractions is intensity dependent. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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"The dipeptide carnosine (Beta-alanyl-L-histidine) acts as an intramuscular proton buffer. Beta-alanine supplementation has been shown to increase muscle carnosine content and high intensity cycling performance potentially by postponing muscle fatigue. It is unknown whether the performance enhancing effect of Beta-alanine supplementation is intensity dependent." This study examined the performance of sustained isometric contractions of the quadriceps femoris muscles at two different intensities in the presence of Beta-alanine.

Physically active Ss (M =21; F = 3) participated in a placebo-controlled triple-blind study. Ss upper body was restrained and hip and knee joint angles were kept at 90. The non-dominant leg was connected to a force transducer (sampling frequency 1000Hz). In two sessions, maximal voluntary isometric force (MVIF); time to task failure during 20% MVIF and 70%MVIF, and MVIF 20 seconds after task failure, which were used to calculate a fatigue index, were measured before and after supplementation. Post-supplementation testing of 20% MVIF and 70% MVIF was performed at pre-supplementation MVIF values. Ss were supplemented with 6.4g/day of Beta-alanine (N = 11) or maltodextrin placebo (N = 13) for 38 7 days.

In both groups, there was no change in maximal voluntary isometric force after supplementation. Both groups increased the time to task failure during 20% MVIF by 12-16%. The increase in time to task failure during the 20% MVIF in the placebo group was associated with an increase in the fatigue index (pre: 31.6 10.5%; post: 39.7 14.7%). No change in fatigue index occurred following a 20% MVIF after Beta-alanine supplementation (pre: 42.9 20.3%; post: 47.5 20.3%). For the 70% MVIF, there was a significant 30% increase in time to task failure (pre: 42.4 11.9s, post 55.0 21.0s) with no change in the placebo group (pre: 43.1 9.2s, post 47.3 13.1s). In both groups, there was no change in fatigue index following the 70% MVIF.

Implication. Beta-alanine supplementation in physically active individuals 1) had no effect on the force-producing capability during maximal isometric muscle contractions, 2) had no effect on the calculated muscle fatigue index following sustained isometric muscle contractions at both low and high intensities, 3) enhanced muscle isometric endurance but the effect was intensity-dependent. Beta-alanine supplementation may be beneficial for performance of high-intensity exercise.

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