Abstract
BackgroundResistance training is a potent stimulus to induce muscle hypertrophy. Supplemental protein intake is known to enhance gains in muscle mass through activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway, which initiates protein translation. While the optimal dose of high quality protein to promote post exercise anabolism in young or older men has been investigated, little is known about the minimum doses of protein required to potentiate the resistance exercise activation of anabolic signalling in middle aged men.MethodsTwenty healthy men (46.3 ± 5.7 years, BMI: 23.9 ± 6.6 kg/m2) completed a single bout of unilateral resistance exercise consisting of 4 sets of leg extension and press at 80% of 1 repetition maximum. Participants were randomised to consume either formulated milk product containing 9 g milk protein (FMP) or an isoenergetic carbohydrate placebo (CHO) immediately post exercise, in a double blind fashion. A single muscle biopsy was collected at pre-exercise baseline and then bilateral biopsies were collected 90 and 240 min after beverage consumption.ResultsP70S6KThr389 phosphorylation was increased with exercise irrespective of group, P70S6KThr421/Ser424 was increased with exercise only in the FMP group at 240 min. Likewise, rpS6 Ser235/236 phosphorylation was increased with exercise irrespective of group, rpS6 Ser240/244 increased to a greater extent following exercise in the FMP group. mRNA expression of the amino acid transporter, LAT1/ SLC7A5 increased with both exercise and beverage consumption irrespective of group. PAT1/ SLC36A1, CAT1/ SLC7A1 and SNAT2/ SLC38A2 mRNA increased only after exercise regardless of group.ConclusionsNine grams of milk protein is sufficient to augment some measures of downstream mTORC1 signalling after resistance exercise but does not potentiate exercise induced increases in amino acid transporter expression. Formulated products containing nine grams of milk protein would be expected stimulate muscle anabolism after resistance exercise.Trial registrationNew Zealand Clinical Trials Registry ACTRN12615001375549. Registered: 17 December, 2015.
Highlights
Resistance training is a potent stimulus to induce muscle hypertrophy
Plasma As expected carbohydrate placebo (CHO) ingestion increased both glucose and insulin concentrations above baseline and were greater than the concentrations observed for Functional milk product (FMP) 30 and 60 min after ingestion of the beverage (P < 0.05) (Fig. 1a&b)
While the present study shows that phosphorylation at the p70S6KThr421/Ser424 site is increased by resistance exercise at 90 min post exercise, this response is only sustained at 240 min following the consumption of FMP. rpS6Ser235/236 phosphorylation was increased by exercise but maintained at a higher magnitude in the FMP compared to the CHO group
Summary
Resistance training is a potent stimulus to induce muscle hypertrophy. Supplemental protein intake is known to enhance gains in muscle mass through activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway, which initiates protein translation. While the optimal dose of high quality protein to promote post exercise anabolism in young or older men has been investigated, little is known about the minimum doses of protein required to potentiate the resistance exercise activation of anabolic signalling in middle aged men. While resistance training can increase muscle mass and strength in both young and older adults [6], the relative magnitude of these gains decrease with age [7,8,9]. Post-exercise protein intake has been shown to augment resistance training induced muscle mass gains [10]. Despite the importance of establishing a maximal effective dose, it is necessary to establish the efficacy of smaller protein doses, including those that are typically incorporated into a range of consumer goods. Many foods consumed after resistance exercise may include a suboptimal protein dose
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