Sample size was determined with MPS as a primary outcome measure using variance from our previous data ( 18) and the likely chance we could detect a 20% difference between conditions with 80% power and α at 0.05%. Twenty-two healthy older women were recruited from the greater Hamilton area in response to local advertisements to participate in this study. We hypothesized that both acute and longer-term MPS would be greater after consumption of WP than after CP and that RE would enhance the MPS response but more so in WP. As an exploratory, secondary outcome, and given that CP supplementation has been theorized to support greater rates of connective tissue synthesis/renewal ( 17), we determined if CP supplementation would facilitate increases in muscle-derived collagen protein (perimysium) synthesis. Thus, the primary outcome of this study was to compare the acute and longer-term effects of WP or CP supplementation on MPS alone and when combined with RE. Interestingly, a CP supplement improved nitrogen balance in older women ( 16) however, to our knowledge no study has examined the muscle protein synthetic response, and thus whether muscle is the tissue affected by CP supplementation, that may be underpinning the ostensibly favorable CP supplement–induced changes in body composition ( 14, 15) or improved nitrogen balance ( 16). Nonetheless, 2 studies have reported positive effects of supplementation with low quality CP on lean body mass (LBM) gains with resistance training in sarcopenic older men ( 14) (which showed an extraordinary gain in LBM) and premenopausal women ( 15). Our findings highlight the important role that protein quality can play in recovery and retention of muscle mass. Recently, we showed that recovery from inactivity was more effective with consumption of higher quality whey protein (WP), which increased rates of MPS in healthy older men and women ( 13) compared with an isonitrogenous quantity of collagen peptide (CP) placebo. However, to date, few studies have examined the effects of protein supplements of varying quality on the stimulation of MPS in older adults. Further, RE induces marked increases in rates of MPS in both young and older men and women ( 9–11) and serves to sensitize skeletal muscle to the anabolic effects of protein ingestion ( 3, 12). RE improves muscle strength ( 7), increases skeletal muscle mass ( 7), and improves functional outcomes ( 8) in older adults.
Previously, we have shown that older men required ∼40% more isolated high quality (whey) protein per meal to stimulate rates of muscle protein synthesis (MPS) comparable with those of younger men ( 2). This age-related attenuation of MPS has been termed anabolic resistance ( 2, 3). Contributing to sarcopenic muscle decline is a decreased response of muscle protein synthesis (MPS) to normally robust anabolic stimuli such as protein ingestion (and the subsequent hyperaminoacidemia) and resistance exercise (RE). Sarcopenia is the loss of muscle mass and muscle strength with age, progressing at rates of ∼0.8%/y and 1–3%/y, respectively, and these are measurable in the sixth decade of life ( 1).
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