Actn Ph,yszol Scand 1992, 146, 403-404
Changes in muscle protein synthesis following heavy resistance exercise in humans: a pilot study J. D. M a c D O U G A L L , M. A. TARNOPOLSKY, A. CHESLEY and S. A. A T K I N S O N Departments of Physical Education, Medicine, and Pediatrics, McMaster University, Hamilton, Ontario, Canada L8S 4K1
It is known that relatively few maximum, or nearmaximum, voluntary contractions repeated two or three times per week will result in substantial increases in muscle contractile protein (MacDougall et al. 1980). This study examined the acute changes in muscle protein synthesis (MPS) in response to a single resistance training session as measured by the rate of incorporation of labelled leucine into biceps brachii. For this method we have made the assumption that plasma a-keto isocaproic acid (KIC) labelling reflects the isotopic enrichment of the leucyl-tRNA pool (Smith & Rennie 1990). Data were collected on four healthy young males (23k2.1 years) who regularly engaged in heavy resistance (bodybuilding) training. In accordance with the University's Human Ethics Committee, they were advised of the risks associated with the study and provided written informed consent. Subjects refrained from training for a period of 3 days, during which energy and protein intake were calculated from selfreported food records. They then underwent a typical training session involving the elbow flexors of one arm only (randomly selected). Exercises included four sets of single arm biceps, concentration and preacher curls, performed at 80% of maximum (1RM). Twenty (k0.2) h after exercise a 20 Ga catheter was inserted into a hand vein for blood sampling while a second was positioned in a contralateral forearm vein for isotope infusion. A priming dose of L[ l-'"C]leucine was administered (1 mg kg-I) followed by a constant infusion (1 mg kg-* h-l) for 6 ( i0.4) h by a Harvard Syringe Pump. Arterialized blood samples (hot box at 65 "C) were taken prior to infusion, at 2 h, 4 h and at the end of infusion (6 h) for the determination of plasma a-KIC enrichment. For 2 h prior to and during the infusion period subjects
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Received 21 April 1992, accepted 7 August 1992 Key words; hypertrophy, L-[ l-13C]leucine incorporation, protein synthesis, weight lifting. Correspondence : J. D. MacDougall, Departments of Physical Education and Medicine, McMaster University, Hamilton, Ontario, Canada L8S 4K1
received 50% of their individual mean energy intake as a defined formula diet (Ensure, Ross Laboratories, Montreal, Canada) to ensure a consistent rate of appearance of endogenous energy and protein. Feedings were in equal aliquots every 30 min. Needle biopsies were taken from the biceps brachii of both arms, 2 h following the priming dose and again following the constant infusion. Plasma a-KIC enrichment was determined by capillary gas chromatography/mass spectrometry as previously described (Tarnopolsky et al. 1991). Muscle L-[ l-13C]leucine content was measured using a modification of the techniques described by Smith et al. (1988) and Scrimgeour et al. (1988). MPS was calculated for each sample according to the equation :
FMPS
= (LEM x
lOO)/(K,, x t ) ,
11) where FMPS = the fractional muscle protein synthetic rate (Yoh-'); LEM = the increment in I3C abundance obtained between the two biopsy samples from each arm; K,, = the mean plasma a-KIC enrichment for the 2, 4 and 6 h blood samples (corrected for background enrichment from the preinfusion sample) and t = the incorporation time (in h) between biopsy samples taken from the same arm (Nair et al. 1988). Habitual protein intake for the four subjects was 1.32 (k0.35)g kg-' d-l. The rate of appearance of exogenous unlabelled leucine entering plasma from the liquid meal was estimated to be 583 pmol leucine g-' protein or 45 ( & 13) pmol kg-' h-'. Mean plasma a-KIC enrichment for the three samples taken during the infusion period was 4.96 atoms yo excess, with a coefficient of variation of < S%, thus indicating an isotopic plateau over the period in which MPS was measured. MPS was 129%) in the exercised significantly elevated (by arm compared to the non-exercised arm (Fig. I). Mean synthetic rate was 0.0447 (i0.015) h-' in the non-exercised biceps and 0.1025 (i0.043) yo h-' in the exercised biceps. T o our knowledge this is the first report ofMPS in biceps brachii in humans. A value of 0.045 9; h-' for
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a Fig. 1. Muscle protein synthetic rate in biceps brachii from the control and exercised arm. 24 h after a typical weight training session. \-slues are means ( ) S D ) . T h e open histogram denotes the nonexercised (control) arm and the hatched histogram denotes the exercised arm ( n = 4).
training and responds readily to training. Use of the human model greatly extends the range of parameters which can be investigated beyond that which could be simulated with an animal model (Timson 1990). In summary, the application of a measurement of muscle protein synthesis (Nair e t al. 1988) to a unilateral exercise model provides a valid method of quantifying the effectiveness of the perturbation in stimulating protein synthesis in humans. It is anticipated that use of this technique will help to advance our knowledge of the nature of the stimulus for h j pertrophy in skeletal muscle. \Ve nish to ackno-ledge the invaluable advice and technical assistance provided by Drs K. Smith and 11.J. Rennie, Department of Physiology, University of Dundee, Dundee, U K . This study was partly supported b j the Natural Sciences and Engineering Research Council of Canada. Dr M. A. Tarnopolsky is the recipient of a National Institute of Nutrition Post Doctoral Fellowship.
REFERENCES the control arm in the fed state is considerabll- lower than the 0.075 O0 h ~ " d u e reported for quadriceps fernoris using similar methods (Smith & Rennie 1990). This difference ma!- reflect relative differences in use of an upper limb muscle compared to a locomotor muscle, 'I'wenty-four h after a bout of heavy resistance training, MPS was approximately 12900 greater in the biceps of the exercised arm than that of the nonexercised arm. T h e exercise was thus a potent stimulator of protein spthesis. Since the measurement reflects only gross synthesis between two single points in time. the net synthesis (the difference between spthesis and degradation) that results from such exercise and the time course for its increase cannot be determined from these data. U'e are presentllexamining the time course by sampling a t several time points following exercise. Application of the measurement of SIPS to a unilateral exercise model controls for individual differences in nutritional background, fibre t! pes, training status and possible residual effects of the preceding training bout, since it is simply the difference in protein synthesis between the exercise and non-exercised tissue w-hich demonstrates the effectiveness of the intervention. Biceps brachii is an ideal muscle for investigation of possible hypertrophlstimuli since it is an easy muscle to isolate during
~IACDOUGALL, J.D., ELDER, G.C.B., SAL.E,D.G., MOROZ,J.R., & SUTTON,J.R. 1980. Effect of strength training and immobilization on human muscle fibres. Europ 3 Appl Physiol 43 25-34. Zair, K.S., Halliday, D. & Griggs, R.C. 1988. Leucine incorporation into mixed skeletal muscle protein in humans. .4m 3 Physiol 254, E208-E213. Scrimgeour, C.M., Smith, K. & Rennie, M.J. 1988. Automated measurement of 13C enrichment in carbon dioxide derived from submicromole quantities of L-( 1-"C)-leucine. Biomed Environ Mass Spec 15, 369-374. Smith, K. & Rennie, M.J. 1990. Protein turnover and amino acid metabolism in human skeletal muscle. I n Bailliire's Clinical Endocrinology and Metabolism 1,461498. Smith, K., Scrimgeour, C.M., Bennet, W.M. & Rennie, X1.J. 1988. Isolation of amino acids by preparative gas chromatography for quantification of carboxyl "C enrichment by isotope ratio mass spectrometry. Biomed Environ Mass Spec 17, 267-273. Tarnopolsky, M.A., Atkinson, S.A., MacDougall, J.D., Senor, B.B., Lemon, P.W.R. & Schwarcz, H. 1991. Whole body leucine metabolism during and after resistance exercise in fed humans. Med Scz Sports Exerc 23, 324-333. Timson, B.F. 1990. Evaluation of animal models for the study of exercise induced muscle enlargement. 3 . 4 p p l PhysioE69, 1935-1945.