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The Mechanisms of Muscle Hypertrophy and Their Application to Resistance Training

DOI:10.1519/JSC.0b013e3181e840f3
Authors:
Brad J Schoenfeld at City University of New York City - Lehman College
Brad J Schoenfeld
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Abstract

The quest to increase lean body mass is widely pursued by those who lift weights. Research is lacking, however, as to the best approach for maximizing exercise-induced muscle growth. Bodybuilders generally train with moderate loads and fairly short rest intervals that induce high amounts of metabolic stress. Powerlifters, on the other hand, routinely train with high-intensity loads and lengthy rest periods between sets. Although both groups are known to display impressive muscularity, it is not clear which method is superior for hypertrophic gains. It has been shown that many factors mediate the hypertrophic process and that mechanical tension, muscle damage, and metabolic stress all can play a role in exercise-induced muscle growth. Therefore, the purpose of this paper is twofold: (a) to extensively review the literature as to the mechanisms of muscle hypertrophy and their application to exercise training and (b) to draw conclusions from the research as to the optimal protocol for maximizing muscle growth.
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THE MECHANISMS OF MUSCLE HYPERTROPHY AND THEIR APPLICATION TO RESISTANCE TRAININ
Brad J Schoenfeld
Journal of Strength and Conditioning Research; Oct 2010; 24, 10;
ProQuest Health and Medical Complete
pg. 2857
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Human muscle strength training: The effects of three different regimes and the nature of the resultant changes
Article
  • Nov 1987
1. Increases in strength and size of the quadriceps muscle have been compared during 12 weeks of either isometric or dynamic strength training. 2. Isometric training of one leg resulted in a significant increase in force (35 +/- 19%, mean +/- S.D., n = 6) with no change in the contralateral untrained control leg. 3. Quadriceps cross-sectional area was measured from mid-thigh X-ray computerized tomography (c.t.) scans before and after training. The increase in area (5 +/- 4.6%, mean +/- S.D., n = 6) was smaller than, and not correlated with, the increase in strength. 4. The possibility that the stimulus for gain in strength is the high force developed in the muscle was examined by comparing two training regimes, one where the muscle shortened (concentric) and the other where the muscle was stretched (eccentric) during the training exercise. Forces generated during eccentric training were 45% higher than during concentric training. 5. Similar changes in strength and muscle cross-sectional area were found after the two forms of exercise. Eccentric exercise increased isometric force by 11 +/- 3.6% (mean +/- S.D., n = 6), and concentric training by 15 +/- 8.0% (mean +/- S.D., n = 6). In both cases there was an approximate 5% increase in cross-sectional area. 6. It is concluded that as a result of strength training the main change in the first 12 weeks is an increase in the force generated per unit cross-sectional area of muscle. The stimulus for this is unknown but comparison of the effects of eccentric and concentric training suggest it is unlikely to be solely mechanical stress or metabolic fluxes in the muscle.
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Nonuniform Response of Skeletal Muscle to Heavy Resistance Training
Article
  • Feb 2000
Skeletal muscle is a heterogeneous tissue that exhibits numerous inter-and intramuscular differences (i.e., architecture, fiber composition, and muscle function). An individual muscle cannot be simplistically described as a compilation of muscle fibers that span from origin to insertion. In fact, there are unique differences within a single muscle and within single muscle fibers with respect to fiber size and protein composition. Electromyographic data indicate that there is selective recruitment of different regions of a muscle that can be altered, depending on the type of exercise performed. Longitudinal resistance-training studies also demonstrate that individual muscles as well as groups of synergist muscles adapt in a regional-specific manner. The author speculates that no single exercise can maximize the hypertrophic response of all regions of a particular muscle. Thus, for maximal hypertrophy of an entire muscle, athletes (particularly bodybuilders) are justified in incorporating various exercises that purportedly stimulate growth in a regional-specific manner.
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Serum Testosterone Response to High-Intensity Resistance Training in Male Veteran Sprint Runners
Article
  • Nov 1997
The purpose of this study was to examine the influence of an 8-wk high-intensity resistance training program on muscular strength and basal serum testosterone in male veteran sprint runners. Twelve healthy veteran sprint runners, ages 45-79, were recruited as subjects and randomly assigned to an experimental (n = 8) or control (n = 4) group. Measured in both groups before and after the resistance training period were body mass, total skinfolds, isoinertial strength (bench press, leg press), peak torque (knee extensors, knee flexors), and basal testosterone levels. ANOVA revealed significant increases (p < 0.05) in both the isoinertial and isokinetic strength of the experimental group following resistance training. However, no significant increase in basal testosterone level was observed in that group after 8 weeks of resistance training. The results suggest significant improvements in muscular strength in veteran male sprint runners following 8 weeks of high-intensity resistance training. Furthermore, the strength gains are not explained by changes in basal serum testosterone and may be due to neurological, physiological, and morphological factors.
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A Brief Review: Testosterone and Resistance Exercise in Men
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Testosterone is a steroid hormone that is secreted in men from the testes in a circadian fashion. Secretion of testosterone from the testes is indirectly controlled by the hypothalamus. In order for secretion to occur from the testes, the hypothalamus must first secrete leutinizing hormone-releasing hormone. Previous research has consistently shown increases in serum testosterone concentration following acute resistance exercise. Testosterone is affected by a combination of factors including the amount of muscle tissue mass stimulated, volume of exercise performed, and intensity of exercise. Testosterone plays important regulatory roles in muscle protein metabolism and influences neuromuscular trainability. There is a circadian rhythm of testosterone, but to date no data exist as to the effects of resistance exercise on the diurnal cycle of testosterone. This area of study should be investigated further in order to gain greater understanding of how resistance exercise affects testosterone responses over the course of a entire day.
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Electromyographical Activity of the Pectoralis Muscle During Incline and Decline Bench Presses
Article
  • Aug 1997
The purpose of this study was to determine the relationship between motor unit recruitment within two areas of the pectoralis major and two forms of bench press exercise. Fifteen young men experienced in weight lifting completed 6 repetitions of the bench press at incline and decline angles of +30 and -15[degrees] from horizontal, respectively. Electrodes were placed over the pectoralis major at the 2nd and 5th intercostal spaces, midclavicular line. Surface electromyography was recorded and integrated during the concentric (Con) and eccentric (Ecc) phases of each repetition. Reliability of IEMG across repetitions was r = 0.87. Dependent means t-tests were used to examine motor unit activation for the lower (incline vs. decline) and upper pectoral muscles. Results showed significantly greater lower pectoral Con activation during decline bench press. The same result was seen during the Ecc phase. No significant differences were seen in upper pectoral activation between incline and decline bench press. It is concluded there are variations in the activation of the lower pectoralis major with regard to the angle of bench press, while the upper pectoral portion is unchanged. (C) 1997 National Strength and Conditioning Association
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Skeletal Muscle Glycogen Loss Evoked by Resistance Exercise
Article
  • May 1998
Biopsies were taken from the left m. vastus lateralis of 9 young men and analyzed for mixed muscle and for single fiber glycogen to infer recruitment, especially among fast-twitch subtypes, during knee extensions with loads of 30, 45, and 60% of 1-repetition maximum. The relative decline in mixed muscle glycogen was related to relative exercise load, as were the percentage of fast-twitch fibers showing glycogen loss and the relative cross-sectional area (CSA) of m. vastus lateralis occupied by type Ha or by fast-twitch fibers that showed glycogen loss (p <= 0.0478, r >= 0.50). The relative decline in mixed m. vastus lateralis glycogen was related to the percentage of both fast-twitch fibers and type Ha fibers, and the relative CSA of m. vastus lateralis occupied by type IIa fibers that showed glycogen loss (p <= 0.0436, r >= 0.51). Type I and IIa fibers were used for all 3 bouts. Type IIab + IIb fibers showed glycogen loss for the heaviest load. The results suggest that mixed muscle glycogen loss is related to load, mainly due to fast fiber usage. It also appears that the general understanding put forth for cycling and running-that fast-twitch fiber type use depends on exercise intensity-holds for resistance exercise. Because type IIab + IIb fibers showed glycogen loss at loads of 60% of maximum, it is suggested that fast-twitch subtypes are used at lower loads than generally appreciated. (C) 1998 National Strength and Conditioning Association
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