Figure 1.

Overall study schematic (A) and acute MyoPS response protocol (B). (A) Participants were randomly assigned to consume a multi-ingredient supplement (SUPP, n = 8) or control (CON, n = 7) beverage twice per day for 21 weeks. Between weeks 8 and 19, inclusive, participants completed a 12 weeks combined RET (twice per week) + HIIT (once per week) exercise training program. Lean tissue mass (DXA) and strength (1RM) were assessed at baseline (week 0), as well as pre- (week 7; Phase 1: SUPP/CON) and post-training (week 20; Phase 2: SUPP/CON + EX). The integrated MyoPS response to acute resistance exercise was assessed during participants' initial RET session (UT, untrained; week 8) and 10 days following their last RET session (TR, trained; week 21). (B) Following a baseline saliva sample, participants consumed 150 mL 70% deuterated water (D₂O; Day 0). On Days 2–4, we obtained a fasting muscle sample from the vastus lateralis. Immediately after their muscle biopsy on Day 2, participants completed a session of resistance exercise at 65% 1RM. Saliva samples were collected regularly throughout each acute response period to assess deuterium (²H) enrichment of total body water. Eight weeks prior to the untrained acute response (–8 weeks), we obtained an unenriched, fasted muscle sample for the measurement of resting FSR. SUPP, supplement; CON, control; RET, resistance exercise training; HIIT, high-intensity interval training; DXA, dual-energy x-ray absorptiometry; 1RM, one repetition maximum; MyoPS, myofibrillar protein synthesis; ²H, deuterium; D₂O, deuterated water; UT, untrained; TR, trained; FSR, fractional synthesis rate.