Proceedings of The Physiological Society
King's College London (2009) Proc Physiol Soc 14, C9
Structural and functional adaptations to eccentric versus conventional resistance training in older adults
N. D. Reeves1, C. N. Maganaris1, S. Longo2, M. V. Narici1
1. Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, United Kingdom. 2. Laboratory of Sports Analysis and Human Performance, University of Milan, Milan, Italy.
Resistance training is effective for attenuating age-related muscle weakness and inducing positive morphological adaptations in skeletal muscle (e.g. 1). Conventional resistance training involves lifting and lowering the same load, but because skeletal muscle can develop higher forces when it contracts eccentrically (2), it is likely under-loaded during the eccentric (lowering) contraction phase. We hypothesised that eccentric-only training (using higher loads) would yield greater muscle structural and strength gains than conventional resistance training. Nine older adults (mean±SD age: 74±3 years) were assigned to a conventional (CONV) resistance training group performing both concentric and eccentric contractions and ten (age: 67±2 years) to an eccentric-only (ECC) training group. Both groups trained the knee extensors 3 times per week for 14 weeks at 80% of the 5-repetition maximum, specific to each training mode. Knee extensor torque was assessed with an isokinetic dynamometer during isometric, concentric and eccentric contractions over a range of angular velocities (0-200 deg s-1). Vastus lateralis muscle architecture (fascicle length, pennation angle and muscle thickness) was measured in vivo at rest using ultrasonography. Training loads in the ECC group were 40-110% higher, but the training volumes were equivalent because the CONV group performed more repetitions (P>0.05; independent t-test). Resistance training increased fascicle length in both groups, but this was significantly greater in the ECC (20±14% increase) than the CONV (8±8% increase) group. Conversely, pennation angle significantly increased in the CONV (35±15%), but not the ECC (5±6%) group. Muscle thickness increased to a similar extent in both groups (~12±11%; P<0.05). An increase in fascicular length following resistance training suggests the addition of sarcomeres in-series, consistent with animal models after chronic and intermittent stretch (3,4). An increase in pennation angle is consistent with the addition of sarcomeres in-parallel. These results raise the possibility that the stimulus for adding sarcomeres in-series and in-parallel may be different. In the ECC group, eccentric knee extensor torque increased by 9-17% across velocities (P<0.05; dependent t-test), but concentric torque was unchanged (P>0.05). Conversely, in the CONV group, concentric torque increased by 22-37% across velocities (P<0.05), but eccentric torque was unchanged (P>0.05). Despite much higher loads being used by the ECC group, isometric strength increased similarly between groups (~8%), suggesting that mechanical stress may not be the only stimulus influencing strength gains. Considering the present findings, to match the force-velocity properties of skeletal muscle, an optimal training stimulus should involve using higher loads for the eccentric contraction phase than the concentric phase.
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