Chay1
Jon Chay
November 1, 2011
Dr. Bert Ely
Biology 303 Section 501
The Efficacy of Eccentric Muscle Movements in the Development ofSkeletal Muscles in Humans
Eating, walking, moving objects, pushing, pulling and various other actions are performed on a daily basis by virtually every healthy human being. At the root of all these actions are skeletal muscles that make these movements possible. Unlike the smooth and cardiac muscles of the human body, skeletal muscles can be voluntarily controlled. This voluntary control is what allows each person to complete the daily tasks necessary required to survive.
With this voluntary control, many people choose to exercise. Muscle development is a common goal in many exercise programs because it not only allows increased functionality in daily activities, but also because it creates a higher muscle mass in one’s body which often equates to better overall health in general due to muscle cells requiring a significantly larger amount of calories to maintain than fat. Having a higher muscle mass increases one’s Basal metabolic rate,the amount of energy that one’s body expends at rest, thereby decreasing chances of obesity. In 1975, Goldberg et al. first proposed that stressing muscles via using them to generate force is the driving event behind initiating muscle growth in mammals. Ever since their conclusion, much time and effort has been expended in finding the “optimal” workout that would let one “Get the most bang for a buck”, ie. a workout that would maximize muscle force production, hypertrophy and strength gains.
High force, eccentric contractions of the skeletal muscles are thought to be an integral part of this “optimal” workout plan because the greatest magnitude of muscle force production occurs when muscles lengthen during an eccentric contraction (Hortobagyi,2003; LaStayoet al., 2003). Bernhard Katz discovered that force steeply rises when skeletal muscle is lengthened at increasing velocities in his study of eccentric and concentric muscle contractions in1939. It was shown that eccentric contractions can produce up to a 5-fold greater force production compared to concentric contractions (Hill, 1938). Eccentric contractions have even been proven to be effective in muscle growth in the elderly (Hortobagyi, 2003).
In a 2003 study, LaStayoet al.tried to determine the efficacy of eccentric exercise in increasing the functionality of elderly individuals afflicted with sarcopenia. In this study, 21 elderly subjects with an average age of 80 years went through an 11 week program of lower extremity resistance training. The experimental group (ECC) with 11 members performed exercises on a high force eccentric ergometer only (Figure 1). The subjects of the control group, labeled TRAD had 10 members and performed “regular” free weight and machine resistance training exercises. To evaluate whether an increase in functionality occurred, muscle size, muscle strength, balance (via the Berg Balance test) and stair descending abilities were measured. Measurements were made pre- and post- intervention.
The results showed that subjects in both groups experienced a significant increase in muscle fiber cross-sectional area of the quadriceps, with ECC subjects having an average increase of 60% and TRAD subjects having an average increase of 41%. However, only subjects in the ECC group experienced significant improvements in strength, balance and stair descent abilities. Also, onlysubjects in the ECC group went from a high to a low fall risk. See Table 1 on the next page.
Table 1
Better results are in the ECC group are indicated by the higher post training strength and muscle fiber area measurements, as well as better balance and stair descent measurements compared to the Traditional group.
Figure 1- How a high force eccentric ergometer works
The ergometer is powered by a three-horsepower motor that drives the pedals in a backwards (towards the participant, largest arrow) direction while the participant attempts to resist this motion by pushing on the pedals as they move closer (smaller arrows). The result is a lengthening of the quadriceps muscles. The resistance applied by the participants is
monitored on a screen facing them, and they try to match a pre-set target levelresistance denoted on the screen. Workout duration, pedal speed, stroke length and ‘target’ force resistance were all controlled for each training session.
It was also duly noted that subjects of the ECC group never rated the eccentric exercises over a “somewhat hard” on the Borg rating of perceived exertion scale. Furthermore, those subjects in the ECC group of the aforementioned study who completed the study did so with a low rate of muscle soreness. This fact has important implications.
Delayed onset musclesoreness, caused by the eccentric motions of a workout which damage skeletal muscles, usually persists for 24-72 hours post workout (Nosaka, 2008).Symptoms such as decreased muscle strength, a reduced range of motion, and most importantly muscle swelling frequently occur concurrently with the soreness (Peake et. al, 2005). This inflammatory response that occurs can be dangerous for certain individuals afflicted with chronic disease.
In 2011, Flann et al. conducted a study to investigate if symptomatic muscle damage was necessary for muscle growth. To do so, they conducted an experiment with 14 healthy college students (8 males and 6 females). They were divided into two experimental groups: a pre-trained group (PT) and a naïve group (NA) with both groups having the statistically equal demographics (body mass, height and quadriceps volume). The PT group went through an 11 week “high force eccentric cycle ergometry program” (Figure 1) with a gradual increase in workout intensity during the first 3 weeks. The NA group however, went through an 8 week ergometry program, starting during week 4 for the PT group. The experiment was designed so that the amount of work done by each group was the same, 3.2X103kJ (Figure 2). To evaluate the effectiveness of the program, quadriceps muscle size, strength gains, levels of creatinekinase ( a key marker of how much muscle damage has occurred) and levels of IGF-1Ea mRNA (“ a muscle specific isoform of insulin like growth factor-1that has is believed tocontribute in muscle regeneration”) were measured before, during, and post intervention.
Results showed that the PT group averaged CK levels below 107 Ul-1which is indicative of PT subjects experiencing little to no symptomatic muscle damage. The NA group however had much higher CK levels which correlates to the NA group subjects reporting significant amounts of soreness (Figure 3).Both groups showed similar increases in muscle strength and quadriceps volume. Also, results of the RT PCR of IGF-1Ea mRNA showed that levels increased in both groups with a mean increase of 55% in the PT group and 85% in the NA group, signifying the upregulation of IGF-1Ea during eccentric exercise.
Figure 2
The graph shows that the NA group did more work than the PT group from weeks 4-11. However, the experiment was designed so the amount of work done by the PT group in 11 weeks was the same as the work done by the NA group in 8 weeks. The histogram on the right shows that the total work performed over the eight-week training session also did not vary statistically between the groups (P>0.05).
Figure 3
Plasma creatinekinase (CK) levels were measured in each participant weekly. CK levels increased significantly in the NA group for the weeks 5–8 (*statistical difference between groups; P<0.05). By contrast, the PT group was never above the control CK level (150Ul–1), representing the muscle damage threshold.
The results of this study suggest that muscle rebuilding can be initiated independent of any discernible damage to muscles via a gradual increase in intensity of workouts that involve eccentric contractions. McKay et al. (2008) have shown strong evidence that “an acute eccentric muscle damage event results in upregulation of IGF-1Ea”. However, mRNA levels of IGF-1Ea increased in both groups of this study, supporting the hypothesis that symptomatic muscle damage is not required for hypertrophy to occur. Also, both groups went through eccentric muscle training which resulted in similar gains in strength and muscle volume. However, it seems that a gradual increase in intensity of workouts leads to the same result with less muscle soreness and damage, proving the commonly known statement “no pain, no gain” wrong.
The use of eccentric muscle contractions for exercisesin this experiment implies the superiority of eccentric muscle contractions over concentric contractions. Roig et al. came to a similar conclusion. At the end of their study they concluded that eccentric muscle contractions promote more muscle growth in terms of mass and cross-sectional area compared to concentric contractions.
Eccentric contractions are not only shown to be more effective for muscle development than concentric motions, but also eccentric contractions require a lower energy cost for a higher force production (Lastayo et al., 2003). This observation coupled with the findings of Flann et al. (2011) that muscle growth occurs independent of muscle soreness, has significant implications for therapeutic interventions for the frail, elderly, and those afflicted with chronic diseases. The low energy requirement and high force production of eccentric contractions can be utilized to create exercise regimes that involve a gradual increase in intensity of eccentric resistance training to develop and build the skeletal muscles of individuals like those mentioned earlier who might sensitive to the effects of muscle inflammation. Eccentric contractions are perfectly suited for such exercise intolerant individuals and can be utilized to increase muscle mass and quality of life.
References
Flann, K.L., LaStayo, P.C., McClain, D.A., and Hazel, M. (2011). Muscle Damage and remodeling: no pain, no gain? The Journal of Experimental Biology. 214, 674-679.
Goldberg, A. L., Etlinger, J. D., Goldspink, D. F. and Jablecki, C. (1975). Mechanism
of work-induced hypertrophy of skeletal muscle. Med. Sci. Sports 7, 185-198.
Hill A. V. The heat of shortening and the dynamic constants of muscle. Proc Roy Soc. 1938; 126B: 136-195.
Hortobagyi, 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.
Katz B. The relation between force and speed in muscular contraction. J Physiol. 1939;96:45–64.
LaStayo, P. C., Ewy, G. A., Pierotti, D. D., Johns, R. K. and Lindstedt, S. L. (2003).
The positive effects of negative work: increased muscle strength and decreased fall
risk in a frail elderly population. J. Gerontol. A Biol. Sci. Med. Sci. 58, M419-M424.
Nosaka, Ken. (2008). “Muscle Soreness and Damage and the Repeated-Bout Effect”. In Tiidus, Peter M. Skeletal muscle damage and repair.Human Kinetics.pp.59-76.
McKay, B. R., O’Reilly, C. E., Phillips, S. M., Tarnopolsky, M. A. and Parise, G.
(2008). Co-expression of IGF-1 family members with myogenic regulatory factors
following acute damaging muscle-lengthening contractions in humans. J. Physiol. 586,
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Peake, J. Nosaka, K., Suzuki, K. (2005). Characterization of inflammatory response to eccentric exercise in humans.ExercImmunol. Rev. 2005; 11:64-85.
Roig, M., O’Brien, K., Kirk, G., Murray, R., McKinnon, P. (2008). The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. J Sports Med. 43:556-568.