5. Discussion
muscle soreness, muscle damage, skeletal muscle mass
SECONDARY
The aim of this randomized double-blind placebo-controlled trial was to assess the effect of pea protein and whey protein supplementation versus placebo on exercise-induced increases in muscle damage markers within older adults. We found that long-distance walking exercise provoked muscle damage, with peak CK levels around 24 h post-exercise in physically active older men and women. The CK increase is in line with a previous study who measured CK release in vital elderly after comparable bout of walking exercise [The magnitude of exercise-induced CK elevations was similar in active older adults receiving pea protein supplementation compared to placebo. These findings are contradictory to previous studies using other plant-based proteins, such as soy and oat, as an attenuated exercise-induced increase in CK levels was found compared to the placebo group [In contrast to the pea protein group, an attenuated exercise-induced elevation in CK concentrations was observed for the whey protein group. Whey protein supplementation is known to limit exercise-induced muscle damage [The digestibility of whey protein could be another important factor to explain the difference in exercise-induced elevations of CK concentrations compared to pea protein supplementation. Literature about the bio-availability of pea protein is contradictory. In vitro digestibility values are similar between whey and pea protein [Our study did not show effects of protein or placebo supplementation on changes in serum LDH concentrations, muscle strength, muscle soreness and skeletal muscle mass. The pattern of blood LDH showed a different response to the walking exercise compared to the CK response. This finding in our participants is not in line with most other literature where LDH was used as a marker for muscle damage after short periods of intense exercise (30 min–1.5 h) [Several limitations apply to our study. The protocol used for assessment of 1 RM for leg strength made it difficult to determine 1 RM of participants that reached the maximum of 200 kg or the last attempt. This may have hampered the possible effect of protein supplementation on leg muscle strength. Furthermore, this study also had a relatively small population, which could result in less statistical power and the supplementation period could have been too short to have impact on secondary outcomes. At last, this study had a fixed protein supplementation dose (25 g/day) which increased daily protein intake to >1.0 g/kg/day in 93% of our participants. A personalized protein supplementation dose, based on the individual lean body mass, may therefore be recommended to future studies to achieve a maximal effective dose for all study participants.