I recently read an article that stated there is more muscle trauma and fiber recruitment during eccentric work, which I agreed with. It continued to state that isometric work is in second place with concentric work as the least efficient. Can you clear this up, and are there any articles pertaining specifically to this?
Various studies have shown that higher strength values are attained in eccentric contractions than in concentric and isometric contractions. Eccentric contractions are able to generate up to three times more force than a concentric contraction.
Studies have also shown that fewer motor units are recruited for eccentric contractions compared with concentric contractions. Although eccentric exercises may cause more initial damage, they also produce higher strength gains initially.
In regards to isometric and concentric muscle contractions, it is true that by forcing your muscle or muscles to hold a position for a certain length of time, your body will begin to recruit and activate more motor units in order to maintain the contraction. However, you should keep in mind that isometric contractions are only capable of increasing muscle strength at the specific joint angles worked. There is no corresponding increase at other joint angles. Remember that isometric contractions are stabilizing contractions, meaning they are used for strength rather than movement.
Here is some basic physiology on muscle recruitment. Muscles produce force by recruiting motor units (a group of muscle fibers innervated by a motor neuron) along a gradient. During voluntary isometric and concentric contractions, the pattern of recruitment is controlled by the size of the motor unit, a condition known as the size principle. Small motor units, which contain slow-twitch muscle fibers, have the lowest firing threshold and are recruited first. Demands for larger forces are met by the recruitment of increasingly larger motor units. The largest motor units that contain the fast-twitch B fibers have the highest threshold and are recruited last.
No matter what the workout intensity, slow-twitch motor units are recruited first. If the workout intensity is low, these motor units may be the only ones that are recruited. If the workout intensity is high, such as when lifting heavy weights or performing intervals on the track, slow-twitch motor units are recruited first, followed by fast-twitch A and fast-twitch B, if needed.
Delayed onset of muscle soreness (DOMS) is caused by exercise-induced muscle damage. DOMS is delayed for two to three days post-exercise. DOMS does occur to a higher degree during eccentric contraction training. The theory behind why this occurs is because during an eccentric contraction, the muscle is forcibly lengthened, which can potentially damage the muscle sarcomeres. The pain sets in several hours later and peaks at around 48 hours.
- Horstmann, T., Mayer, F., & Maschmann, J. (2001). Metabolic reaction after concentric and eccentric endurance-exercise of the knee and ankle. Medicine and Science in Sports and Exercise, 33, 791-795.
- McHugh, M.P., Tyler, T.F., Greenburg, S.C., & Gleim, G.W. (2002).Differences in activation patterns between eccentric and concentric quadriceps contractions. Journal of Sports Sciences, 20, 83-91.