The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein

Abstract

The currently accepted amount of protein required to achieve maximal stimulation of myofibrillar protein synthesis (MPS) following resistance exercise is 20-25 g. However, the influence of lean body mass (LBM) on the response of MPS to protein ingestion is unclear. Our aim was to assess the influence of LBM, both total and the amount activated during exercise, on the maximal response of MPS to ingestion of 20 or 40 g of whey protein following a bout of whole-body resistance exercise. Resistance-trained males were assigned to a group with lower LBM (≤65 kg; LLBM n = 15) or higher LBM (≥70 kg; HLBM n = 15) and participated in two trials in random order. MPS was measured with the infusion of (13)C6-phenylalanine tracer and collection of muscle biopsies following ingestion of either 20 or 40 g protein during recovery from a single bout of whole-body resistance exercise. A similar response of MPS during exercise recovery was observed between LBM groups following protein ingestion (20 g - LLBM: 0.048 ± 0.018%·h(-1); HLBM: 0.051 ± 0.014%·h(-1); 40 g - LLBM: 0.059 ± 0.021%·h(-1); HLBM: 0.059 ± 0.012%·h(-1)). Overall (groups combined), MPS was stimulated to a greater extent following ingestion of 40 g (0.059 ± 0.020%·h(-1)) compared with 20 g (0.049 ± 0.020%·h(-1); P = 0.005) of protein. Our data indicate that ingestion of 40 g whey protein following whole-body resistance exercise stimulates a greater MPS response than 20 g in young resistance-trained men. However, with the current doses, the total amount of LBM does not seem to influence the response.

Keywords: Fractional synthesis rate; intracellular signaling proteins; lean body mass; protein dose‐response.

Figure 1

Schematic diagram of infusion trial protocol.

Figure 2

Plasma leucine (A), phenylalanine (B) and threonine (C) concentrations following ingestion of either 20 or 40 g of whey protein isolate in both the lower lean body mass (LLBM) and higher lean body mass (HLBM) groups. Data presented as means with 95% confidence intervals. *Significant difference between doses; ^#significant difference between groups; ^$significant difference between doses in LLBM group only (all P < 0.05).

Figure 3

Muscle intracellular (A) and plasma (B) phenylalanine enrichments expressed over time during L‐ [ring‐¹³C₆] phenylalanine infusion in both the lower lean body mass (LLBM) and higher lean body mass (HLBM) groups. Data presented as means with 95% confidence intervals. Data expressed as tracer to tracee ratio (TTR). Ingestion of either 20 or 40 g whey protein isolate occurred at 0 min. *Significant difference between doses (P < 0.05).

Figure 4

Rate of phenylalanine oxidation (A) and plasma urea concentrations (B) following ingestion of either 20 or 40 g of whey protein isolate in both the lower lean body mass (LLBM) and higher lean body mass (HLBM) groups. Data presented as means with 95% confidence intervals. *Significant difference between doses (P < 0.05).

Figure 5

Myofibrillar fractional synthesis rate (FSR) presented for each individual participant following ingestion of either 20 or 40 g whey protein isolate in lower lean body mass (LLBM) and higher lean body mass (HLBM) groups (A). Line represents the mean for each condition. Mean ± SD of myofibrillar FSR following the ingestion of 20 and 40 g whey protein isolate for both groups combined (B). *Significant difference between doses with all participants of each group combined (P = 0.005). FSR was determined over the 0–5 h period following protein ingestion.

Figure 6

P70S6K1 activity following whey protein isolate ingestion (whey protein doses combined) in both the lower lean body mass (LLBM) and higher lean body mass (HLBM) groups. Data presented as means with 95% confidence intervals. *Significant difference from 0 min; ^#main effect of group (P = 0.002) and main effect of time (P = 0.008).