Part 1
Whey protein has been widely used in untrained subjects [1] or in power trained athletes to increase muscle mass and to improve strength and physical performance [2-4]. However, there are relatively few studies examining the effects of whey protein supplementation on body composition and performance in well-trained endurance athletes [5, 6] and the results are sometimes conflicting. For example, Huang et al. [5] reported increased distance run in 12-min running test associated with an increase in whole body muscle mass, with no difference in performance in the placebo group; they also found decreases in “liver” enzymes, LDH, and creatine kinase (muscle damage markers) after 5-weeks of 33.5 g/day whey protein supplementation in endurance track runners. However, Roberson et al. [6] found increased lean mass, a tendency of mitochondrial capacity to be improved, but without significant improvement in physical performance after the ingestion of 25 g whey protein (post-exercise and pre-sleep) during 10 weeks in endurance runners. The inconsistent results of the effects of whey protein supplementation on endurance exercise performance and the associated post-exercise recovery parameters are in part related to some methodological differences such as the duration of supplementation, the amount, type, and timing of protein intake, and the training status of the subject.
According to Phillips & van Loon [7], endurance athletes need more protein than the current recommendation of 0.8 g/kg/day for normal subjects, in order to achieve training adaptations and improve performance [7, 8]. The position statement of the International Society of Sports Nutrition (ISSN) stated that protein supplementation may help to offset muscle damage during and following exercise and promote muscle recovery in athletes [9]. The rationale for the increased protein intake for endurance athletes is that their training volume is typically greater than for powerful athletes, i.e. about 6 days per week so as to attain adequate training distance per week. Further, endurance athletes often use a mixed training approach incorporating eccentric exercises, plyometrics and obstacle courses; these training regimens often induce muscle catabolism as well as resulting in muscle damage [10, 11]. Muscle protein catabolism during exercise is not desirable as the amino acids lost in this process are required to support post-exercise and training adaptations. Also, excessive muscle damage with associated inflammation and requirement for muscle repair slows muscle recovery and impairs subsequent performance [12].