Many of our functional daily and exercise activities include both concentric (shortening) and eccentric (lengthening) muscle contractions (actions). However, eccentric-only or accentuated eccentric contractions are also commonly performed in resistance exercises. It is well known that exercises consisting of high-intensity and/or a large number of eccentric contractions induce delayed-onset muscle soreness and prolonged decreases in muscle function. This is especially true when performed for the first time or infrequently. However, less is known about how preceding eccentric contractions with concentric contractions may affect neuromuscular fatigue and muscle damage. It is possible that muscle damage is exacerbated by the fatigue induced by the preceding concentric contractions.
In our study published in Medicine & Science in Sports & Exercise®, we compared eccentric-only and alternating concentric and eccentric (CON-ECC) exercise protocols of the knee extensors for changes in neuromuscular and neurophysiological parameters. We recruited 12 male and 8 female adults who were assigned to either an eccentric-only exercise group or a CON-ECC exercise group. The eccentric-only exercise consisted of 6 sets of 8 eccentric contractions with the load of 80% of eccentric one-repetition maximum (1-RM). The CON-ECC exercise consisted of 6 sets of 8 alternating concentric and eccentric contractions at 80% of concentric 1-RM and 80% of eccentric 1-RM, respectively. It should be noted that the eccentric 1-RM was 16-53% greater than the concentric 1-RM. Outcome measures included maximal voluntary isometric contraction force, rate of force development, resting twitch force, maximal M-wave, voluntary activation, motor-evoked potentials, corticospinal silent period, short-interval intracortical inhibition and muscle soreness. These measures were taken before, immediately after and 1-3 days post exercise.
We found no significant differences between eccentric-only and CON-ECC protocols for any of the measures. Since both protocols consisted of the same number of eccentric contractions, our findings showed that the addition of concentric contractions had little effect on neuromuscular fatigue and muscle damage. This suggests that eccentric contractions were the main mediators of the fatigue and damage in the CON-ECC exercise.
The findings of the present study are important for practitioners including strength and conditioning coaches, physical therapists and exercise physiologists when prescribing resistance exercise to different groups.
First, high-intensity eccentric contractions have a risk of muscle damage. However, this muscle damage is minimized or prevented by performing light-intensity eccentric contractions at 1-14 days before higher-intensity eccentric exercise, or gradually increasing the intensity and volume. Thus, the risk of muscle damage should not discourage people from performing eccentric exercises.
Second, muscle damage is not affected by including concentric contractions. However, a question remains whether high-intensity concentric contractions should be included in resistance exercise. Due to the low metabolic demand, haemodynamic and cardiorespiratory cost in eccentric exercise, eccentric-only contractions may be more appealing for use in older individuals and clinical populations.
It has been documented that eccentric exercise training produces greater increases in muscle strength and muscle mass, balance and flexibility, and improves insulin sensitivity and blood lipid profile than concentric exercise training. Thus, resistance exercise training focusing on eccentric-only contractions may become more popular. To perform eccentric contractions without a load for concentric contractions requires specific device. So CON-ECC can be used in eccentric resistance training protocols such as lifting a dumbbell with two arms but lowering it with one arm, where performing eccentric-only contractions with load is not possible.
Cassio V. Ruas, PhD, received a doctorate in exercise and sports science from Edith Cowan University in Australia. He is now an adjunct lecturer at Edith Cowan University and a postdoctoral research fellow at the University of Campinas in Brazil. He investigates neurophysiological changes following eccentric exercise interventions; neuromodulation interventions for movement recovery in clinical populations such as stroke and spinal cord injury patients; and resistance training protocols for enhancement of muscle function in children, adults and athletes.
Kazunori Nosaka, PhD, is a professor of exercise and sports science in the School of Medical and Health Sciences at Edith Cowan University in Australia. He has published more than 320 peer-reviewed journal articles, and about 80% of his articles are related to eccentric exercise in relation to muscle damage, neuromuscular fatigue, strength and power training, and exercise as medicine. A longtime advocate of the beneficial effects of eccentric exercise, his goal is to translate his research to practice and make people healthier, fitter and happier. Dr. Nosaka is a member of ACSM.
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