Resistance training and muscle protein synthesis

Latest research to increase strength and muscle mass

Last time, Gary O’Donovan explained that resistance training guidelines are largely based on poor quality research. Here, in part two of the series, he goes back to the laboratory and explains how the latest research might be used to increase strength and muscle mass.

Translational research

Basic research takes place at the laboratory bench and is aimed at increasing knowledge. Applied research takes place outside the laboratory and is aimed at developing and evaluating new interventions. Translational research is the process of taking the findings from basic research and putting them into practice: from bench to bedside in health research. The discovery of penicillin and the translation of a mould into a medicine is a great example of translational research (1).

The translational research model used in health care is rarely used in sport science (2). Certainly, a continuum of basic and applied research did not lead to the resistance training guidelines that are currently in practice (3). However, the Exercise Metabolism Research Group at McMaster University in Canada has used the translational research model to increase knowledge about muscle protein synthesis(4) and to develop and evaluate new resistance training interventions(5). The aim of this article is to summarise the group’s recent work and to explain how it might be put into practice: from bench to gym.

Acute effect of resistance exercise on muscle protein synthesis

It is likely that muscle protein synthesis must be stimulated for hypertrophy to occur (4). In 2010, the Exercise Metabolism Research Group reported the effect of a single bout of exercise on muscle protein synthesis (6). Fifteen “recreationally active” men aged around 21 years took part in the study. The investigators chose to study men who were familiar with lower body resistance exercise “to minimize neuromuscular-based gains in strength” (6). Participants visited the laboratory and one repetition maximum (1RM) was determined using a standard leg extension machine. Participants returned to the laboratory at least two weeks later and were randomly allocated to two of three resistance exercise conditions: (a) 90% of 1RM to failure; (b) 30% of 1RM with the same amount of work as 90% of 1RM to failure; or (c) 30% of 1RM to failure. For the 90% of 1RM to failure and 30% of 1RM to failure conditions, participants performed the exercise and were given verbal encouragement until concentric failure. Exercise was not performed to failure in condition b. For all conditions, participants performed four sets and were given three minutes’ rest between sets. Verbal cues and a metronome were used to facilitate a cadence of one-second concentric action, zero-second pause, and one second eccentric action.

The investigators tried to minimize the confounding effects of physical activity and diet (6): participants were asked to avoid physical activity for three days before visiting the laboratory; they were asked to record their diet for three days before visiting the laboratory; they were asked to replicate their diet before visiting the laboratory on subsequent occasions; and participants were asked to fast overnight and consume a liquid breakfast before visiting the laboratory (the liquid breakfast provided around 15% of estimated daily energy need, and consisted of 61% carbohydrate, 15% protein and 24% fat). Participants were given an infusion of a stable amino acid isotope and muscle biopsies were taken from the vastus lateralis in order to assess pre- and post-exercise muscle protein synthesis.

Box 1 shows muscle protein synthesis at rest, four hours after exercise, and 24 hours after exercise (6). The results suggest that, when performed to failure, a single bout of resistance exercise at 30% of 1RM is as effective in stimulating muscle protein synthesis four hours after exercise as a single bout of resistance exercise at 90% of 1RM. The results also suggest that, when performed to failure, a single bout of resistance exercise at 30% of 1RM is more effective in stimulating muscle protein synthesis 24 hours after exercise than a single bout of resistance exercise at 90% of 1RM. Exercise volume (the product of load and repetitions) was significantly different with exercise to failure at 30% of 1RM and exercise to failure at 90% of 1 RM (1073±70 kg and 710±30 kg, respectively). The investigators suggested that, when performed to failure, resistance training of relatively low intensity and relatively high volume might lead to hypertrophy (6). Interestingly, the number of sets (4) and repetitions (on average, participants performed five repetitions at 90% of 1RM and 24 repetitions at 30% of 1RM) associated with muscle protein synthesis was different to the number of sets (3-6) and repetitions (6-12) recommended for hypertrophy (3).

Box 1. http://secure.newsletters.co.uk/PPonline/images/MuscleProteinSynthesis_i324.gif

Acute effect of resistance exercise and protein ingestion on muscle protein synthesis

It is well documented that resistance exercise and protein ingestion have a synergistic effect on muscle protein synthesis (7,8). The Exercise Metabolism Research Group has tested the novel hypothesis that, when performed to failure, low- or high-intensity resistance exercise will increase this synergistic effect for at least 24 hours [9]. The participants and the exercise protocols are described above (6). Box 2 shows muscle protein synthesis in the fasted and fed states both at rest and 24 hours after exercise. Feeding increased muscle protein synthesis and exercise-and-feeding increased muscle protein synthesis to a greater extent; but, as hypothesized, this synergistic effect 24 hours after exercise was only present in the 90% of 1RM to failure and 30% of 1RM to failure conditions(9).

Box 2. http://secure.newsletters.co.uk/PPonline/images/MuscleProteinBox2_i324.gif

In 2012, the Exercise Metabolism Research Group published a review of its basic research and other groups’ basic research (10). It was suggested that the synergistic effect of resistance exercise and protein ingestion on muscle protein synthesis is greatest immediately after exercise and wanes over time; but, this ‘window of anabolic potential’ may be present up to 24 hours after exercise. It was tentatively recommended that healthy, young adults ingest after exercise around 20-25 grammes of rapidly absorbed protein (corresponding to around eight to ten grammes of essential amino acids)(10). It was also reported that protein ingestion before bedtime might augment the window by promoting greater muscle protein synthesis over the course of 24 hours (10).

Chronic effect of protein ingestion and resistance training on hypertrophy

The Exercise Metabolism Research Group acknowledged that a training study was necessary to test the suggestion that short-term changes in muscle protein synthesis might lead to hypertrophy(6). To this end, in 2012, the group reported the effect of a 10-week training study on hypertrophy(5). Eighteen men aged around 21 years took part in the study. Participants were recreationally active and had not taken part in resistance training in the last year. Each leg was randomly allocated to one of three leg extension interventions: one set to failure at 80% of 1RM; three sets to failure at 80% of 1RM; or three sets to failure at 30% of 1RM. Each participant trained both legs and was therefore allocated to two of the three interventions. Participants trained three times per week and consumed around 300 millilitres of water and a sports supplement immediately after each training session (PowerBar Protein Plus, which contained 360 kcal, 3.5 grammes of leucine, 30 grammes of protein, 33 grammes of carbohydrate, and 11 grammes of fat). Magnetic resonance imaging was used to assess quadriceps volume before and after the training interventions. The performance of one set to failure at 80% of 1RM three times per week increased quadriceps volume around three per cent; the performance of three sets to failure at 80% of 1RM three times per week increased quadriceps volume around seven per cent; and the performance of three sets to failure at 30% of 1RM three times per week also increased quadriceps volume around seven per cent. The increases in quadriceps volume were not significantly different between the three interventions, but sample size and statistical power may have been too low to detect significant differences. Indeed, the investigators concluded that, when performed to failure, additional sets at 80% of 1RM or 30% of 1RM might result in greater muscle hypertrophy (5).

Chronic effect of resistance training on strength

In the 10-week training study described above(5), increases in 1RM were greater in the 80% of 1RM conditions than the 30% of 1RM condition. The investigators concluded that the results were a reflection of the specificity principle: “practice with a heavy relative load is necessary to maximize gains in 1RM strength” (5). Strength (1RM) and power (maximal instantaneous power) increased in all three conditions and the investigators also concluded that, “hypertrophy is generally beneficial to all strength and power tests that engage the larger muscles” (5). The number of sets and repetitions was probably different to the number of sets (“multiple”) and repetitions (1-6) recommended for strength training (3) (the number of repetitions was not reported, but one would expect an individual to perform around eight repetitions at 80% of 1RM (11)).

Interpretation

The basic research of the Exercise Metabolism Research Group is of the highest quality. The applied research of the group is an important step in putting its basic research into practice, but larger trials are needed (1,12). The available evidence suggests fatigue is an important stimulus of muscle protein synthesis (6) and hypertrophy (5), whether the load is 30% of 1RM, 80% of 1RM or 90% of 1RM. Therefore, to stimulate hypertrophy, one should consider performing three or four sets to failure using a relatively light or relatively heavy load. The available evidence also suggests volume might be an important stimulus of muscle protein synthesis (6) and hypertrophy(5). Therefore, to further stimulate hypertrophy, one should also consider performing additional sets.

The advanced resistance training techniques described in Box 3 may be popular and effective because they induce fatigue and they allow a high volume of work. There are two nutritional strategies that may increase muscle protein synthesis during the ‘window of anabolic potential’ that may be present up to 24 hours after exercise(10). First, one should consider consuming rapidly absorbed, high quality protein immediately after exercise. Second, one should consider consuming high quality protein immediately before bedtime. Resistance training that increases hypertrophy is likely to increase strength(5); however, the specificity principle is such that a relatively high load is necessary to maximize increases in strength.

Box 3. http://secure.newsletters.co.uk/PPonline/images/AdvancedResistance_i324.gif

Dr. Gary O’Donovan and Dr. Liz Gough are the directors of Fitness Doctor Ltd. Email: gary@ fitnessdoctor.org.uk

References
1. Cooksey, D., A review of UK health research funding, 2006, Crown: Norwich.
2. Heneghan, C., J. Howick, B. O’Neill, et al., The evidence underpinning sports performance products: a systematic assessment. BMJ open, 2012. 2(4).
3. ACSM, American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc, 2009. 41(3): p. 687-708.
4. Burd, N.A., C.J. Mitchell, T.A. Churchward-Venne, et al., Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme, 2012. 37(3): p. 551-4.
5. Mitchell, C.J., T.A. Churchward-Venne, D.W. West, et al., Resistance exercise load does not determine trainingmediated hypertrophic gains in young men. Journal of applied physiology, 2012. 113(1): p. 71-7.
6. Burd, N.A., D.W. West, A.W. Staples, et al., Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men. PloS one, 2010. 5(8): p. e12033.
7. Burd, N.A., J.E. Tang, D.R. Moore, et al., Exercise training and protein metabolism: influences of contraction, protein intake, and sex-based differences. Journal of applied physiology, 2009. 106(5): p. 1692-701.
8. Kumar, V., P. Atherton, K. Smith, et al., Human muscle protein synthesis and breakdown during and after exercise. Journal of applied physiology, 2009. 106(6): p. 2026-39.
9. Burd, N.A., D.W. West, D.R. Moore, et al., Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men. The Journal of nutrition, 2011. 141(4): p. 568-73.
10. Churchward-Venne, T.A., N.A. Burd, and S.M. Phillips, Nutritional regulation of muscle protein synthesis with resistance exercise: strategies to enhance anabolism. Nutrition & metabolism, 2012. 9(1): p. 40.
11. Baechle, T.R., R.W. Earle, and D. Wathen, Resistance training, in Essentials of strength training and conditioning, T.R. Baechle and R.W. Earle, Editors. 2000, Human Kinetics: Champaign, IL. p. 395-425.
12. Schulz, K.F., D.G. Altman, and D. Moher, CONSORT 2010 Statement: updated guidelines for reporting parallel group randomised trials. BMC Med, 2010. 8: p. 18.

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