Little is known about temporal and cumulative effects of repeated bouts of resistance exercise and protein feeding on muscle protein synthesis (MPS), or the protein dose required to maximise post-exercise MPS in women. We aimed to understand: 1) acute (4h, 8h) and extended (24h) effects of two bouts of resistance exercise with protein feeding, in women; and 2) the dietary protein requirement to maximise MPS within this time window.
Method: Following written informed consent and screening, 24 resistance exercise-trained women (26.6 ± 0.7 years) were recruited into the study. A DXA scan was performed and participants consumed 500ml of 70% D2O in 100ml boluses over a 5h period. Twenty-four h later, after an overnight fast, resting state saliva, venous blood and vastus lateralis muscle biopsy samples were obtained, and volunteers performed a whole-body resistance exercise protocol consisting of 3×8 repetitions at 75% 1 rep max. (2 min rest between sets) involving latissimus dorsi pull down, single-leg press and chest press. Immediately after exercise, subjects ingested a whey protein drink containing either 15g, 30g or 60g total protein (n=8/group). After resting for 4h, saliva, venous blood and muscle biopsy samples were collected again, and volunteers then repeated the exercise and protein ingestion regimen. Saliva, venous blood and muscle samples were taken again 4h later (8h) and the following day (24h). Subjects were fed a controlled diet throughout the study and only performed the exercise prescribed. Plasma leucine was quantified using GC-MS. Body water and muscle protein D2O enrichment were measured to quantify the rate of MPS as previously described (1). Statistical analysis was performed using two-way repeated measures ANOVA with Dunnett’s post-hoc test. Values in the text represent mean ± SEM.
Results: Post-exercise ingestion of 15g protein did not alter plasma leucine concentration or MPS over time. Following post-exercise ingestion of both 30g and 60g protein, plasma leucine concentration was increased above baseline (105.5 ± 5.3 µM; 120.2 ± 7.4 µM, respectively) at 4h (151.5 ± 8.2 µM, p<0.01; 224.8 ± 16.0 µM, p<0.001 respectively) and 8h (176.0 ± 7.3 µM, p<0.001; 281.7 ± 21.6 µM, p<0.001, respectively).  Post-exercise ingestion of 30g protein increased MPS above baseline (0.068 ± 0.005 %/h) from 0 to 4h (0.140 ± 0.021 %/h, p<0.05), 0 to 8h (0.121 ± 0.012 %/h, p<0.001) and 0 to 24h (0.099 ± 0.011 %/h, p<0.01). Post-exercise ingestion of 60g protein increased MPS above baseline (0.063 ± 0.003 %/h) from 0 to 4h (0.109 ± 0.011 %/h, p<0.01), 0 to 8h (0.093 ± 0.008 %/h, p<0.01) and 0 to 24h (0.086 ± 0.006 %/h, p<0.01).
Conclusion: Post-exercise ingestion of 30g or 60g protein increased MPS above baseline, acutely, after one bout of exercise (0 to 4h), after two bouts of exercise (0 to 8h) and extended the anabolic window over 24h. The magnitude of the post-exercise increase in MPS was no greater following the ingestion of 60g, suggesting the maximal MPS stimulatory effect was achieved with 30g protein.