Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans

Abstract

1. Age-associated loss of skeletal muscle mass and strength can partly be counteracted by resistance training, causing a net synthesis of muscular proteins. Protein synthesis is influenced synergistically by postexercise amino acid supplementation, but the importance of the timing of protein intake remains unresolved. 2. The study investigated the importance of immediate (P0) or delayed (P2) intake of an oral protein supplement upon muscle hypertrophy and strength over a period of resistance training in elderly males. 3. Thirteen men (age, 74 +/- 1 years; body mass index (BMI), 25 +/- 1 kg m(-2) (means +/- S.E.M.)) completed a 12 week resistance training programme (3 times per week) receiving oral protein in liquid form (10 g protein, 7 g carbohydrate, 3 g fat) immediately after (P0) or 2 h after (P2) each training session. Muscle hypertrophy was evaluated by magnetic resonance imaging (MRI) and from muscle biopsies and muscle strength was determined using dynamic and isokinetic strength measurements. Body composition was determined from dual-energy X-ray absorptiometry (DEXA) and food records were obtained over 4 days. The plasma insulin response to protein supplementation was also determined. 4. In response to training, the cross-sectional area of m. quadriceps femoris (54.6 +/- 0.5 to 58.3 +/- 0.5 cm(2)) and mean fibre area (4047 +/- 320 to 5019 +/- 615 microm(2)) increased in the P0 group, whereas no significant increase was observed in P2. For P0 both dynamic and isokinetic strength increased, by 46 and 15 %, respectively (P < 0.05), whereas P2 only improved in dynamic strength, by 36 % (P < 0.05). No differences in glucose or insulin response were observed between protein intake at 0 and 2 h postexercise. 5. We conclude that early intake of an oral protein supplement after resistance training is important for the development of hypertrophy in skeletal muscle of elderly men in response to resistance training.

Figure 1. Strength measurements of knee extension

Absolute values of strength in the group ingesting protein immediately postexercise (P0, n = 7, filled symbols) and in the group ingesting protein 2 h postexercise (P2, n = 6, open symbols). A shows dynamic training strength at 5 RM (▴, P0; ▵, P2). B shows isokinetic strength at 60 deg s⁻¹ (•, P0; ○, P2), and isokinetic strength at 180 deg s⁻¹ (▪, P0; □, P2), pre- (0 weeks), mid- (6 weeks) and post-resistance training (12 weeks) for 3 months. * Significantly different from pre-training (P < 0.05); † significantly different from mid-training (P < 0.05). Data are shown as means ± s.e.m.

Figure 2. Cross-sectional area of m. quadriceps femoris (CSA-q.f.)

Absolute values of CSA-q.f. pre- (▪) and post-resistance training (□) for 12 weeks in the group ingesting protein immediately postexercise (P0, n = 7) and in the group ingesting protein 2 h postexercise (P2, n = 6). * Significantly different from pre-training (P < 0.05); § significantly larger relative increase in P0 than in P2 (P < 0.01). Bars are means ± s.e.m.

Figure 3. Mean fibre area (MFA)

Absolute values of MFA pre- (▪) and post-resistance training (□) for 12 weeks in the group ingesting protein immediately postexercise (P0, n = 7) and in the group ingesting protein 2 h postexercise (P2, n = 6). * Significantly different from pre-training (P < 0.05); § significantly larger relative increase in P0 than in P2 (P < 0.01). Bars are means ± s.e.m.

Figure 4. MHC isoforms

The relative distribution of the MHC isoform MHC-II pre- (▪) and post-resistance training (□) for 12 weeks in the group ingesting protein immediately postexercise (P0, n = 7) and in the group ingesting protein 2 h postexercise (P2, n = 6). * Significantly different from pre-training (P < 0.05). Bars are means ± s.e.m.

Figure 5. Acute response to resistance exercise and intake of protein supplementation

The plasma concentrations of insulin (plasma [Ins]) and glucose (plasma [Glc]) before and during 4 h of recovery from one bout of resistance exercise. •, group ingesting protein immediately postexercise (P0, n = 7); ○, group ingesting protein 2 h postexercise (P2, n = 6). * Significant difference between P0 and P2 at specific time point (P < 0.05); # significantly different from preceding data point in P0; † significantly different from preceding data point in P2.