A2 Milk Enhances Dynamic Muscle Function Following Repeated Sprint Exercise, a Possible Ergogenic Aid for A1-Protein Intolerant Athletes?

Abstract

Hyperaminoacidemia following ingestion of cows-milk may stimulate muscle anabolism and attenuate exercise-induced muscle damage (EIMD). However, as dairy-intolerant athletes do not obtain the reported benefits from milk-based products, A2 milk may offer a suitable alternative as it lacks the A1-protein. This study aimed to determine the effect of A2 milk on recovery from a sports-specific muscle damage model. Twenty-one male team sport players were allocated to three independent groups: A2 milk (n = 7), regular milk (n = 7), and placebo (PLA) (n = 7). Immediately following muscle-damaging exercise, participants consumed either A2 milk, regular milk or PLA (500 mL each). Visual analogue scale (muscle soreness), maximal voluntary isometric contraction (MVIC), countermovement jump (CMJ) and 20-m sprint were measured prior to and 24, 48, and 72 h post EIMD. At 48 h post-EIMD, CMJ and 20-m sprint recovered quicker in A2 (33.4 ± 6.6 and 3.3 ± 0.1, respectively) and regular milk (33.1 ± 7.1 and 3.3 ± 0.3, respectively) vs. PLA (29.2 ± 3.6 and 3.6 ± 0.3, respectively) (p < 0.05). Relative to baseline, decrements in 48 h CMJ and 20-m sprint were minimised in A2 (by 7.2 and 5.1%, respectively) and regular milk (by 6.3 and 5.2%, respectively) vs. PLA. There was a trend for milk treatments to attenuate decrements in MVIC, however statistical significance was not reached (p = 0.069). Milk treatments had no apparent effect on muscle soreness (p = 0.152). Following muscle-damaging exercise, ingestion of 500 mL of A2 or regular milk can limit decrements in dynamic muscle function in male athletes, thus hastening recovery and improving subsequent performance. The findings propose A2 milk as an ergogenic aid following EIMD, and may offer an alternative to athletes intolerant to the A1 protein.

Keywords: A2 milk; exercise recovery; muscle damage; muscle function; team sports.

Figure 1

Structure of beta-casmorphin-7. Adapted from [48] (reproduced with permission).

Figure 2

Experimental design of study protocol.

Figure 3

Change in 20-m sprint performance in response to exercise-induced muscle damage in the A2 milk (n = 7), regular milk (n = 7), and placebo (n = 7) groups. * Represents group–time interaction effect (p < 0.05). # Represents main effect for time (p < 0.05). Values presented as mean ± SD.

Figure 4

Change in countermovement jump (CMJ) height in response to exercise-induced muscle damage in the A2 milk (n = 7), regular milk (n = 7), and placebo (n = 7) groups. * Represents group difference (p < 0.05). # represents main effect for time (p < 0.05). Values presented as mean ± SD.

Figure 5

Change in maximal voluntary isometric contraction (MVIC) in response to exercise-induced muscle damage in the A2 milk (n = 7), regular milk (n = 7), and placebo (n = 7) groups. # Represents main effect for time (p < 0.05). No group or interaction effects were observed (p > 0.05). Values presented as mean ± SD.

Figure 6

Change in perception of muscle soreness in response to exercise-induced muscle damage in the A2 milk (n = 7), regular milk (n = 7), and PLA (n = 7) groups. # Represents main effect for time (p < 0.05). No group or interaction effects present (p > 0.05). Values presented as mean ± SD.