Introduction. A growing body of evidence suggests a strong relationship between age-related declines in muscle mass, strength, and power with impaired cognitive function. To mitigate these effects, current recommendations consist of resistance exercise training (RET) with additional protein intake. The benefits of RET and additional protein intake are purposed to be attributed to increases in muscle protein synthesis (MPS), insulin-like growth factor-1 (IGF-1), and improved sleep. Previous data indicated that immediate post-exercise protein consumption optimizes adaptations to RET, while some long-term data are equivocal. Moreover, nighttime pre-sleep protein intake may be important as overnight MPS can be lower than basal rates, which is problematic in older adults who exhibited blunted MPS to protein intake. However, this has not been well examined in older adults, except for one recent study with a suboptimal protein dose. The main objective of the present study was to evaluate the efficacy of nighttime pre- sleep protein intake on functional and cognitive adaptations during 12 weeks of RET in older adults in comparison to the traditional recommendation of immediate post-exercise protein intake. Our central hypothesis was that nighttime pre-sleep protein intake would significantly improve functional, and cognitive adaptations as much as immediate post-exercise protein group in comparison to the exercise only group. Methods. Healthy, sedentary, older males (N=30) between the ages of 60-75 years were randomly assigned to 1 of 3 groups: 1) Protein immediately post-exercise (Post-ex, n=9), 2) Protein 30 minutes prior to sleep (Pre-sleep, n=11), or 3) No protein supplementation (Ex only, n=10). All 3 groups performed the same 12-week RET program, 2x/wk. The dependent variables consisted of pre to post changes in body composition (e.g., lean mass, fat mass, % body fat), nitrogen balance, free plasma IGF-1, profile of mood states (POMS), sleep evaluation (sleep quantity and quality), and cognitive processing speed (digit symbol substitution task and pattern comparison). Maximum muscular strength (1-RM), muscular power, and quadriceps muscle hypertrophy (via muscle thickness) were assessed at pre-, mid-, and post-intervention. Results. Post-ex exhibited a significant reduction in % body fat (-6%, p = 0.018), but there was no significant change in Pre-sleep (0%, p > 0.999) or Ex only group (–4%, p = 0.077). Post-ex demonstrated accelerated quadriceps muscle hypertrophy from pre to mid (+9%, p = 0.003); however, pre to post increases were similar between groups. Pre to post 1-RM improvements were not different between groups; however, Post-ex (+6%, p = 0.009) and Pre-sleep (+9%, p = 0.003) demonstrated significant increases in chest press 1-RM from mid to post, while Ex only did not (+4%, p = 0.226). Peak power was significantly enhanced in Pre-sleep (+10%, p = 0.040) with a similar increase observed in Post-ex (+13%) but not in Ex only (+2%). All groups were not effective for improving cognitive processing speed. Satiety was significantly higher in Pre- sleep compared to Ex only at post (+89%, p = 0.019). There were no significant changes in POMS or sleep evaluation. Post-ex (+27%, p = 0.022) and Pre-sleep (+40%, p < 0.001) displayed significant increases in free plasma IGF-1, while Ex only (+18%, p = 0.080) did not. Free IGF-1 levels were inversely related to fat mass and % body fat, which demonstrated significant negative (p = 0.002 and 0.046, respectively) moderate (r = -0.667) and low (r = - 0.463) correlations, respectively. Conclusions. Our findings suggest that during a 12-week RET program, 40 g of additional protein intake, but not specifically at post-exercise or pre-sleep time points, augmented the rate of upper body strength adaptations, enhanced peak power, and increased morning satiety levels in older adults to a greater extent than exercise only. Our findings also indicate that post-exercise protein consumption can further enhance resistance exercise-induced improvements in body composition, primarily though fat mass loss, and accelerate muscle hypertrophy in comparison to pre-sleep and exercise only interventions. The reduced fat mass is associated with increased free IGF-1 levels, although the mechanism is not clear.
