Effects of α-lactalbumin on strength, fatigue and psychological parameters: a randomised double-blind cross-over study

Purpose The neurotransmitter serotonin has a strong effect on behaviour and motor control. Regarding motor control, serotonin contributes to the development of fatigue and is also involved in the ability of motor neurones to operate across a large range of forces (gain control). The consumption of tryptophan-rich supplements (such as alpha-lactalbumin) is of interest because this amino acid is the only precursor for brain serotonin synthesis. Therefore, the purpose of this study was to determine the effects of alpha-lactalbumin supplementation on neuromuscular performance. Methods Using a randomised double-blind cross-over design, 16 healthy participants performed plantar flexor and handgrip maximal voluntary contractions, a 30-s submaximal handgrip contraction, and a plantar flexor fatigue protocol before and 90 min after consuming either 40 g of alpha-lactalbumin, an isonitrogenous beverage (Zein) or an isocaloric beverage (corn-starch). Sleepiness, mood, and cognition were assessed to evaluate any psychological effects. Results alpha-Lactalbumin decreased force steadiness by 25% during the sustained submaximal handgrip contraction (p < 0.01) and induced greater fatigue (15% reduction in total torque-time integral, p = 0.01) during the fatigue protocol. These effects were not observed for the other control beverages. No effects were found for maximal or explosive strength, or psychological measurements. Conclusions 40 g of alpha-lactalbumin increased handgrip force variability and reduced performance during fatiguing muscle contractions but did not influence brief maximal contractions or psychological parameters in healthy individuals. These findings support the hypothesis that the consumption of alpha-lactalbumin can increase motor neurone input-output gain and exacerbate central fatigue during sustained maximal exercise.

Automated summary

This study aimed to investigate the effects of alpha-lactalbumin supplementation on neuromuscular performance. The results showed that alpha-lactalbumin intake decreased force steadiness and increased muscle fatigue during sustained contractions, but did not affect maximal strength, explosive strength, or psychological measurements in healthy individuals.