The Positives of Negatives: Clinical Implications of Eccentric Resistance Exercise in Old Adults

OCCASIONALLY, it takes time for a great scientific discovery to penetrate clinical practice. Bernhard Katz and Archibald Vivian Hill reported over 60 years ago that force steeply rises when skeletal muscle is lengthened at increasing velocities (eccentric contractions), whereas force sharply declines when skeletal muscle is shortened at increasing velocities (concentric contractions) (1,2), resulting in up to 5-fold greater force production in eccentric compared with concentric contractions. Mechanical loading is a critical stimulus for increasing the strength and the size of skeletal muscle. For years, clinicians and researchers have accepted the obvious hypothesis that the higher mechanical loading afforded by a training program consisting of maximal voluntary eccentric compared with concentric contractions should produce greater hypertrophy and strength gains in frail adults' skeletal muscle. The interest for developing a novel exercise modality was further heightened by another set of classic observations that the metabolic, neural, and cardiovascular demands are lower during eccentric compared with concentric contractions at the same absolute load and velocity (3,4). Thanks to the evolution of isokinetic dynamometers, only very recently has it become also evident that, somewhat surprisingly, age affects less the capacity of skeletal muscle to produce eccentric compared with concentric force (5,6). One interpretation of this observation was that aged skeletal muscle is well suited for eccentric training. Nevertheless, researchers first had to overcome many unexpected difficulties before the recent burst of studies, including the one by LaStayo and colleagues (7) in the current issue, had made it evident that the “high-load-low-cost” approach to exercise can be clinically exploited to combat the epidemic levels of sarcopenia in our aging society (8–14).