It's hypothesized that training with an increased load during the eccentric phase elicits greater strength gains, muscle hypertrophy, and neural adaptation than training with the same load for the concentric and eccentric actions. There has been numerous studies that have constructed these theories built on the premise that increased resistance during the eccentric muscle actions has been shown to produce greater muscle damage.
*(Saxton, J.M., P.M. Clarkson, R. James, M. Miles, M. Westerfer, S. Clark, and A.E. Donnelly. Neuromuscular dysfunction following eccentric exercise. Med. Sci. Sports Exerc. 27:1185–1193. 1995.)
Furthermore, two studies since then have shown the increased ultrastructural damage in muscular tissue in eccentric contractions more than concentric in both untrained men
*(Gibala MJ, MacDougall JD, Tarnopolsky MA, Stauber WT, Elorriaga A. Changes in human skeletal muscle ultrastructure and force production after acute resistance exercise. Journal of Applied Physiology. 78(2): 702-708. 1995)
and men with previous training.
*(Gibala MJ, Interisano SA, Tarnopolsky MA, Roy BD, MacDonald JR, Yarasheski KE, MacDougall JD. Myofibrillar disruption following acute concentric and eccentric resistance exercise in strength-trained men. Canadian Journal of Physiology Pharmacol. 78(8): 656-661. 2000)
This leads to the belief that increased muscle damage resulting from strength training, could be associated with greater strength gains, and increased hypertrophy.
In theory, muscular hypertrophy would seem to accompany an increased eccentric phase through both the increased muscle damage, and the increased motor unit recruitment of fast twitch fibers during this phase.
*(Nardone, A., C. Romano, and M. Schieppetti. Selective recruitment of
high-threshold human motor units during voluntary isotonic lengthening of
active muscles. J. Physiol. (Lond.). 409:451–471. 1989.)
These fast twitch fibers have shown to have greater potential for hypertrophy than slow titch fibers.
*(Lacerte, M., B.J. Delateur, A.D. Alquist, and K.A. Questad. Concentric
versus combined concentric-eccentric isokinetic training programs: Effect
on peak torque of human quadriceps femoris muscle. Arch. Phys. Med.
Rehabil. 73:1059–1062. 1992.)
Increased skeletal muscular hypertrophy has been tested and shown in some studies to be the product of increased resistance performed during the eccentric phase of an exercise program.
*(Tesch, P.A. Skeletal muscle adaptations consequent to long-term heavy
resistance exercise. Med. Sci. Sports Exerc. 20: s132–s134. 1988.)
However, in some studies, eliciting greater muscle hypertrophy was not achieved through the given protocol.
*(Brandenburg J.P., Docherty D. The Effects of Accentuated Eccentric Loading on Strength, Muscle Hypertrophy, and Neural Adaptations in Trained Individuals. Journal of Strength and Conditioning Research: 16(1): 25–32.)
In this particular study, neither protocol (70% concentric max for both concentric and eccentric phases, or, 70% concentric max for concentric phase, 110% for eccentric phase) was effective in producing any skeletal muscular hypertrophy during the 9 week total duration.
These findings seem to be a result of the duration of the study as numerous longer studies with similar protocols have shown to produce muscular hypertrophy.
*(Kawakami, Y., A. Takashi, S. Kuno, and T. Fukunaga. Training induced
changes in muscle architecture and specific tension. Eur. J. Appl.
Physiol. 72:37–43. 1995.)
*(McCall, J.G., W.C. Byrnes, A. Dickinson, P.M. Pattany, and S.J. Fleck.
Muscle fiber hypertrophy, hyperplasia, and capillary density in college
men after resistance training. J. Appl. Physiol. 81:2004–2012. 1996.)
In one particular case, although not differentiating the concentric and eccentric phases, hypertrophy was not present until week 9.
*(Hakkinen, K., M. Alen, and P.V. Komi. Changes in isometric force-
relaxation-time, electromyographic and muscle fibre characteristics of
human skeletal muscle during strength training and detraining. Acta
Physiol. Scand. 125:573–585. 1985.)
Although the 9 week study did not report differences in muscular hypertrophy, the results did suggest that, for some exercises, training with an increased eccentric load may be more effective than standard equal concentric and eccentric training in developing strength within a 9-week training phase. Through the course of the study, the elbow extensors muscle cross sectional area in both groups remained the same, where the eccentric group experienced 9% greater strength gains, and a 24% total increase.
Another study was conducted strictly to show the strength gains correlated with added eccentric resistance in the bench press using 105% concentric max during the eccentric phase of training. Each subject participating increased their concentric max by 5-15lb showing that added eccentric resistance increases maximum concentric strength (p=.008).
*(Doan BK, Newton RU, Marsit JL, Triplett-McBride NT, Koziris LP, Fry AC, Kraemer WJ. Effects of increased eccentric loading on bench press 1RM. Journal of Strength and Conditioning Res. 16(1). 9-13. 2002)
In addition to the increased strength, and possibly hypertrophy, an increased eccentric load has also shown further improvements in neural adaptation
*(Sale, D.G. Neural adaptation to resistance training. Med. Sci. Sports
Exerc. 20: S. 135–S145. 1988.)
The differences between the gains in hypertrophy and neural adaptation have been linked to a relation in number of repetitions performed by the subjects. Where 4-6 repetitions produced more neural adaptations, 8-10 repetitions gave greater gains in hypertrophy.
*(Kraemer, W.J., S.J. Fleck, and W.J. Evans. Strength and power
training: physiological mechanisms of adaptation. Exerc. Sport Sci. Rev.
Also, the study shouldn’t be long enough for the subjects to fall into overtraining, which would hinder their progress, and therefore interrupt the value of the study. Overtraining seems to be an individual matter with many factors as influences, but in any case prolonged periods of intense resistance training to muscular failure has shown to lead the body to overtraining.
*(Tan, B. Manipulating resistance training program variables to optimize
maximal strength in men. J. Strength Cond. Res. 13:289–304. 1999.)
Also, there seems to be differences in physiological adaptation from exercise between males and females which is apparent in many studies. One study showed the gender differences in the adaptive response to ultrastructuaral damage resulting from training with an increased eccentric load.
*(Stupka N, Tarnopolsky MA, Yardley NJ, Phillips SM. Cellular adaptation to repeated eccentric exercise-induced muscle damage. Journal of Applied Physiology. 91(4): 1669-1678. 2001)
So the study I propose is based on the fundamental theory of increased eccentric action causing greater muscle damage, and takes into account the other studies to assume a link of muscular hypertrophy and strength gain correlated with this increased muscle damage. It also takes into account the duration of the overall study, as it’s shown to be a factor in hypertrophy, and gender differences that could play a roll in differentiating results. Although both trained and untrained men were tested with concentric and eccentric contractions in relation to ultrastructural damage, they will both be considered independent variables as an untrained beginner can experience faster initial strength gains due to increased ability to utilize motor units effectively. By separating the two, that no longer could act as a confounding variable in asking the question: Does independently performed eccentric exercise induce muscular hypertrophy, and increase maximal strength capacity (concentric and eccentric measured separately) over a 12 week period of time? Does independently performed concentric exercise induce muscular hypertrophy and increase maximal strength capacity (concentric and eccentric measured separately) over a 12 week period of time?