Leucine-enriched protein supplementation does not influence neuromuscular adaptations in response to a 6-month strength training programme in older adults

This study investigated the effect of protein supplementation enriched in leucine on muscle hypertrophy and strength gain in response to a 6-month strength training programme of the plantar flexor muscles in older adults (aged over 60 yr). To this end, changes in neuromuscular parameters were compared between two groups (matched for age, sex and initial maximal strength) that trained twice a week for 24 weeks, with one group receiving a protein supplementation enriched with leucine (supplementation group, n = 12), and another group receiving a placebo (control group, n = 13) that provided subjects with a similar energy intake that the protein supplementation. Muscle thickness and pennation angle of gastrocnemius medialis were used as indices of muscle hypertrophy. Maximal strength and associated electromyographic activity of leg muscles, and voluntary activation (assessed by the interpolated twitch technique) were recorded. Peak torque in response to 3-pulse train delivered to the tibial nerve was also recorded. After training, muscle thickness (+ 8.4%) and pennation angle (+ 13.4%) were increased, regardless of training groups (p < 0.05). Maximal plantar flexion strength (+ 28.2%) and voluntary activation (+ 29.5%) increased to the same extent for both training groups. Peak torque evoked by 3-pulse train increased similarly between training groups (+ 13.4%, p < 0.001). Regardless of protein supplementation, results obtained in twelve subjects indicate that muscle hypertrophy mainly occurred in the last 12 weeks of the programme. Our results suggest that protein supplementation enriched in leucine neither potentiated the neuromuscular adaptations to strength training, nor influenced the time course of these adaptations in older adults.