Adaptations to Concurrent Training in Combination with High Protein Availability: A Comparative Trial in Healthy, Recreationally Active Men

Background: We implemented a high-protein diet (2 g·kg ⁻¹·d ⁻¹) throughout 12 weeks of concurrent exercise training to determine whether interferences to adaptation in muscle hypertrophy, strength and power could be attenuated compared to resistance training alone. Methods: Thirty-two recreationally active males (age: 25 ± 5 years, body mass index: 24 ± 3 kg·m ⁻²; mean ± SD) performed 12 weeks of either isolated resistance (RES; n = 10) or endurance (END; n = 10) training (three sessions·w ⁻¹), or concurrent resistance and endurance (CET; n = 12) training (six sessions·w ⁻¹). Maximal strength (1RM), body composition and power were assessed pre- and post-intervention. Results: Leg press 1RM increased ~ 24 ± 13% and ~ 33 ± 16% in CET and RES from PRE-to-POST (P < 0.001), with no difference between groups. Total lean mass increased ~ 4% in both CET and RES from PRE-to-POST (P < 0.001). Ultrasound estimated vastus lateralis volume increased ~ 15% in CET and ~ 11% in RES from PRE-to-POST (P < 0.001), with no difference between groups. Wingate peak power relative to body mass displayed a trend (P = 0.053) to be greater in RES (12.5 ± 1.6 W·kg BM ⁻¹) than both CET (10.8 ± 1.7 W·kg BM ⁻¹) and END (10.9 ± 1.8 W·kg BM ⁻¹) at POST. Absolute VO _2peak increased 6.9% in CET and 12% in END from PRE-to-POST (P < 0.05), with no difference between groups. Conclusion: Despite high protein availability, select measures of anaerobic power-based adaptations, but not muscle strength or hypertrophy, appear susceptible to ‘interference effects’ with CET and should be closely monitored throughout training macro-cycles. Trials Registry: This trial was registered with the Australian-New Zealand Clinical Trials Registry (ACTRN12617001229369).