We tested the hypothesis that exercise training with maximal eccentric (lengthening) muscle actions results in greater gains in muscle strength and size than training with concentric (shortening) actions. Changes in muscle strength, muscle fiber size, and surface electromyographic (EMG) activity of the quadriceps muscle were compared after 36 sessions of isokinetic concentric (n = 8) or eccentric (n = 7) exercise training over 12 wk with use of a one-leg model. Eccentric training increased eccentric strength 3.5 times more (pre/post 46%, P < 0.05) than concentric training increased concentric strength (pre/post 13%). Eccentric training increased concentric strength and concentric training increased eccentric strength by about the same magnitude (5 and 10%, respectively, P > 0.05). Eccentric training increased EMG activity seven times more during eccentric testing (pre/post 86%, P < 0.05) than concentric training increased EMG activity during concentric testing (pre/post 12%). Eccentric training increased the EMG activity measured during concentric tests and concentric training increased the EMG activity measured during eccentric tests by about the same magnitude (8 and 11%, respectively, P > 0.05). Type I muscle fiber percentages did not change significantly, but type IIa fibers increased and type IIb fibers decreased significantly (P < 0.05) in both training groups. Type I fiber areas did not change significantly (P > 0.05), but type II fiber area increased approximately 10 times more (P < 0.05) in the eccentric than in the concentric group. It is concluded that adaptations to training with maximal eccentric contractions are specific to eccentric muscle actions that are associated with greater neural adaptation and muscle hypertrophy than concentric exercise.

The hypothesis was tested that the magnitude of cross education is greater following training with muscle lengthening than shortening. Changes in contralateral concentric, eccentric, and isometric strength and vastus lateralis and biceps femoris surface electromyographic (EMG) activity were analyzed in groups of young men who exercised the ipsilateral quadriceps with either eccentric (N = 7) or concentric (N = 8) contractions for 36 sessions over 12 wk. Control subjects (N = 6) did not train. Concentric training increased concentric strength 30% and isometric strength 22%, and eccentric training increased eccentric strength 77% and isometric strength 39% (all P < 0.05). Eccentric training improved eccentric strength three times more than the concentric training improved concentric strength (P < 0.05), and eccentric compared with concentric training improved isometric strength about 2 times more (P < 0.05). The eccentric group improved significantly from pre- to mid-training in eccentric and isometric strength (P < 0.05). The control group showed no significant changes (P < 0.05). Surface EMG activity of the vastus lateralis increased 2.2 times (pre- to mid-training), 2.8 (mid- to post-training) and 2.6 more (pre- to post-training) (P < 0.05) in the eccentric than concentric group. No significant changes in EMG activity occurred in the control group (P > 0.05). It was concluded that the greater cross education following training with muscle lengthening is most likely being mediated by both afferent and efferent mechanisms that allow previously sedentary subjects to achieve a greater activation of the untrained limb musculature.

It is well established that aging seriously reduces isometric and concentric muscle strength due to atrophy, deterioration of mechanical properties, and motor unit loss. However, there is limited information on the impact of aging on eccentric strength despite the fact that such forces play an equally important role during daily activities. The purpose of this study was to examine the influence of aging on three expressions of muscle strength (isometric, concentric, and eccentric) in relation to muscle fiber characteristics, with special emphasis on eccentric force. Sedentary but healthy men (age range 18-80 years, n = 60) and women (20-74 years, n = 30) were tested for maximal effort isometric, concentric, and eccentric (1.05, 2.09, 3.14 rads.s-1) quadriceps strength, body composition, and muscle fiber characteristics of the vastus lateralis (men only). There was a significant (p < .05) approximately 30 N per decade decline in isometric and concentric forces, but only 9 N per decade reduction in eccentric strength. There was a significant reduction in Type II muscle fiber area with aging (p < .05). Isometric, eccentric, and concentric force correlated r = .33, r = .32 (p < .05), and r = .12 (p > .05) with Type II muscle fiber area, respectively. The correlation between age and fat-free mass/force ratio ranged from r = .39 to .43 in men and r = .27 to .50 in women. The data suggest a relative preservation of eccentric strength with aging in men and women that seems to be independent of muscle mass or muscle fiber type or size.

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