Hypertrophy Mechanisms [1/3] - Mechanical tension, Training Strategies and Techniques

Three factors are responsible for initiating the hypertrophic response to resistance exercise: mechanical tension, muscle damage, and metabolic stress (1-5). 

What makes muscle grow is known since 1975 (6). It is suggested that increased tension development (either passive or active) is the critical event in initiating compensatory growth (6).

Mechanical Tension

Mechanical tension seems to be the primary drive for the hypertrophic response (6), mechanical tension alone can produce muscle hypertrophy (7). Increased force development is the critical event in initiating compensatory muscular growth (6,8,9,10).

Mechanical forces are converted into chemical signals in a process called mechanotransduction. This causes molecular and cellular responses in myofibers and satellite cells (11), and mechanical stress alone can directly stimulate mTOR (initiation of protein synthesis) (12,13). Mechanical stress plays a critical role in muscle hypertrophy processes. There’s higher and significant increase in muscle activity during eccentric actions with flywheel training (ECC overload) (14).

In one study the increased in muscle activity was associated to an 11% increase in strength and 6% in muscle mass (15), suggesting that mechanical stress plays a critical role in muscle hypertrophy processes.

Strength and adaptations

Mechanical loading is a critical stimulus to increase strength and size of skeletal muscle (16).

Strength gains are specific to the movement that is trained (37). Moreover, strength gains are due to a combination of muscle hypertrophy and neural adaptations (17,38). In turn, neural adaptations are largely specific to the movement and load used in training (38).

However, changes in muscle size are smaller and slower than changes in strength (18). Interestingly, certain resistance training routines employing high degrees of muscle tension have been shown to largely induce neural adaptations without resultant hypertrophy (19,20).

Strength is increased to a greater extent with high intensity training (21,22,39), even when whole muscle hypertrophy is comparable (23,39).

Training strategies

1. Intensity

Intensity (i.e., load) have a significant impact on hypertrophy. This is usually referred to as a percentage of 1RM in relation to the number of repetitions that can be performed with that percentage.

Repetitions can be classified into 3 basic ranges: low (1–5), moderate (6–12), and high (15+). Different energy systems are used in each range. For example, the phosphocreatine system is used for low repetition sets, and anaerobic glycolysis is used in moderate repetition sets (24). Both low reps and moderate reps elicit a hypertrophic response. However a moderate range (6–12 reps) optimizes the hypertrophic response (1,25,26,27).

Evidence suggests that there is a maximum threshold for tension-induced hypertrophy, above which metabolic factors become more important than additional increases in load (1).

2. Rest Interval

It follows that mechanical tension is maximized by long rest periods, however at the expense of metabolic stress (1,28,29), which attenuate the maximal hypertrophic response.

As with repetitions ranges, rest intervals can be classified into 3 categories: short (30 seconds or less), moderate (60–90 seconds), and long (3 minutes or more).

Short rests does not allow for sufficient time to regain muscular strength, and impairs muscular performance in subsequent sets (30,31). Conversely, long rest intervals afford full recovery of strength between sets, promoting full force capacity for subsequent sets (32).

3. Time under tension

Time under tension is another strategy for mechanical stress. However to extent the time under tension within a set the intensity of load has do drop. Increasing and maintaining continuous tension throughout a set may enhance the potential for microtrauma and fatigueability. Slow-twitch fibers benefit by increased time under. Time under tension has been shown to stimulate optimal growth (33).

4. Repetition Speed

Evidence suggests that faster repetitions are more beneficial for hypertrophy. Performing concentric actions at 1-second cadence vs. three seconds has greater impact on both muscle thickness in elderly men (34). Training at very slow velocities (i.e., superslow training) has been shown to be suboptimal for the development of strength and hypertrophy (1,35,36).

Would you like to know more? Subscribe!

Also read:


1. Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res24: 2857–2875, 2010.
2. Evans, WJ. Effects of exercise on senescent muscle. Clin Orthopaed Rel Res 403(Suppl.): S211–S220, 2002.
3. Jones, DA and Rutherford, OM. Human muscle strength training: The effects of three different regimens and the nature of the resultant changes. J Physiol 391: 1–11, 1987.
4. Shinohara, M, Kouzaki, M, Yoshihisa T, and Fukunaga T. Efficacy of tourniquet ischemia for strength training with low resistance. Eur J Appl Physiol 77: 189–191, 1998.
5. Vandenburgh, HH. Motion into mass: How does tension stimulate muscle growth? Med Sci Sport Exerc 19(5 Suppl.): S142–S149, 1987.
6. Goldberg AL, Etlinger JD, Goldspink DF, et al. Mechanism of work-induced hypertrophy of skeletal muscle. Med Sci Sports. 1975 Fall;7(3):185–98.
7. Jones, DA and Rutherford, OM. Human muscle strength training: The effects of three different regimens and the nature of the resultant changes. J Physiol 391: 1–11, 1987.
8.  Shinohara, M, Kouzaki, M, Yoshihisa T, and Fukunaga T. Efficacy of tourniquet ischemia for strength training with low resistance. Eur J Appl Physiol 77: 189–191, 1998.
9. Vandenburgh, HH. Motion into mass: How does tension stimulate muscle growth? Med Sci Sport Exerc 19(5 Suppl.): S142–S149, 1987.
10. Hornberger, TA and Chien, S. Mechanical stimuli and nutrients regulate rapamycin-sensitive signaling through distinct mechanisms in skeletal muscle. J Cell Biochem 97: 1207–1216, 2006.
11. Toigo M, Boutellier U. New fundamental resistance exercise determinants of molecular and cellular muscle adaptations. Eur J Appl Physiol. 2006;97(6):643–63.
12. Hornberger TA, Chu WK, Mak YW, et al. The role of phospholipase D and phosphatidic acid in the mechanical activation of mTOR signaling in skeletal muscle. Proc Natl Acad Sci USA. 2006;103(12):4741–6.
13. Zou K, Meador BM, Johnson B, Huntsman HD, Mahmassani Z, Valero MC, Huey KA, and Boppart MD. The αβ-integrin increases muscle hypertrophy following multiple bouts of eccentric exercise. J Appl Physiol 111: 1134–1141, 2011.
14. Norrbrand L, Pozzo M, Tesch PA (2010) Flywheel resistance training calls for greater eccentric muscle activation than weight training. Eur J Appl Physiol 110: 997-1005.
15. Tesch PA, Ekberg A, Lindquist DM, Trieschmann JT (2004) Muscle hypertrophy following 5-week resistance training using a non-gravity-dependent exercise system. Acta Physiol Scand 180: 89-98.
16.  Hortobayi T (2003) The positives of negatives: clinical implications of eccentric resistance exercise in old adults. J Gerontol A Biol Sci Med Sci 58: M417-M418.
17. Kraemer, WJ, Ratamess, NA, and French, DN. Resistance training for health and performance. Curr Sports Med Rep 1: 165–171, 2002.
18. Moritani, T and deVries, HA. Neural factors versus hypertrophy in the time course of muscle strength gains. Am J Phys Med 58: 115– 130, 1979.
19. Cote, C, Simoneau, JA, Lagasse, P, Boulay, M, Thibault, MC, Marcotte, M, and Bouchard, B. Isokinetic strength training protocols: Do they produce skeletal muscle hypertrophy? Arch Phys Med Rehab 69: 282–285, 1988.
20. Vissing, K, Brink, M, Lønbro, S, Sørensen, H, Overgaard, K, Danborg, K, Mortensen, J, Elstrøm, O, Rosenhøj, N, Ringgaard, S,Andersen, JL, and Aagaard, P. Muscle adaptations to plyometric vs. resistance training in untrained young men. J Strength Cond Res 22: 1799–1810, 2008.
21. Campos GER, Luecke TJ, Wendeln HK, Toma K, Hagerman FC, Murray TF, Ragg KE, Ratamess NA, Kraemer WJ, and Staron RS. Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones. Eur J Appl Physiol 88: 50–60, 2002.
22. Schuenke MD, Herman JR, Gliders RM, Hagerman FC, Hikida RS, Rana SR, Ragg KE, and Staron RS. Early-phase muscular adaptations in response to slow-speed versus traditional resistance-training regimens. Eur J Appl Physiol 112: 3585–3595, 2012.
23. Mitchell CJ, Churchward-Venne TA, West DWD, Burd NA, Breen L, Baker SK, and Phillips SM. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol 113: 71–77, 2012
24. Robergs, RA, Ghiasvand, F, and Parker, D. Biochemistry of exercise induced metabolic acidosis. Am J Physiol. Reg Int Comp Physiol 287: R502–R516, 2003
25. Kerksick, CM, Wilborn, CD, Campbell, BI, Roberts, MD, Rasmussen, CJ, Greenwood, M, and Kreider, RB. Early-phase adaptations to a split-body, linear periodization resistance training program in college-aged and middle-aged men. J Strength Cond Res 23: 962–971, 2009.
26. Kraemer, WJ, Adams, K, Cafarelli, E, Dudley, GA, Dooly, C, Feigenbaum, MS, Fleck, SJ, Franklin, B, Fry, AC, Hoffman, JR, Newton, RU, Potteiger, J, Stone, MH, Ratamess, NA, Triplett- McBride, T, and American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sport Exerc 34: 364–380, 2002.
27. Zatsiorsky, VM. Science and Practice of Strength Training. Champaign, IL: Human Kinetics, 1995.
28. Kraemer, WJ, Gordon, SE, Fleck, SJ, Marchitelli, LJ, Mello, R, Dziados, JE, Friedl, K, Harman, E, Maresh, C, and Fry, AC. Endogenous anabolic hormonal and growth factor responses to heavy resistance exercise in males and females. Int J Sport Med 12: 228–235, 1991.
29. Kraemer, WJ, Marchitelli, L, Gordon, SE, Harman, E, Dziados, JE, Mello, R, Frykman, P, McCurry, D, and Fleck, SJ. Hormonal and growth factor responses to heavy resistance exercise protocols. J Appl Physiol 69: 1442–1450, 1990
30. Pincivero, DM, Lephart, SM, and Karunakara, RG. Effects of rest interval on isokinetic strength and functional performance after short-term high intensity training. Br J Sport Med 31: 229–234, 1997.
31. Ratamess, NA, Falvo, MJ, Mangine, GT, Hoffman, JR, Faigenbaum, AD, and Kang, J. The effect of rest interval length on metabolic responses to the bench press exercise. Eur J Appl Physiol 100: 1–17, 2007.
32. Miranda, H, Fleck, SJ, Simao, R, Barreto, AC, Dantas, EH, and Novaes, J. Effect of two different rest period lengths on the number of repetitions performed during resistance training. J Strength Cond Res 21: 1032–1036, 2007.
33. Evans, W.J. The metabolic effects of exercise-induced muscle damage. Exerc. Sport Sci. Rev. 19: (-HD-). 99–125. 1991.
34. Nogueira, W, Gentil, P, Mello, SN, Oliveira, RJ, Bezerra, AJ, and Bottaro, M. Effects of power training on muscle thickness of older men. Int J Sport Med 30: 200–204, 2009.
35. Keeler, LK, Finkelstein, LH, Miller, W, and Fernhall, B. Early-phase adaptations of traditional-speed vs. SuperSlow resistance training on strength and aerobic capacity in sedentary individuals. J Strength Cond Res 15: 309–314, 2001.   
36. Neils, CM, Udermann, BE, Brice, GA, Winchester, JB, and McGuigan, MR. Influence of contraction velocity in untrained individuals over the initial early phase of resistance training. J Strength Cond Res 19: 883–887, 2005.
37. Sale D, MacDougall D. Specificity in strength training: a review for the coach and athlete. Can J Appl Sport Sci 6: 87–92, 1981.
38. Sale DG. Neural adaptation to resistance training. Med Sci Sports Exerc 20: S135–145, 1988.
39. Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Tiryaki-Sonmez G, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014 Apr 7.