Preservation of eccentric strength in older adults: Evidence, mechanisms and implications for training and rehabilitation

Abstract

Overall reductions in muscle strength typically accompany the aging process. However, older adults show a relatively preserved capacity of producing eccentric strength. The preservation of eccentric strength in older adults is a well-established phenomenon, occurring indiscriminately across different muscle groups, independent of age-related architectural changes in muscle structure and velocity of movement.The mechanisms for the preservation of eccentric strength appear to be mechanical and cellular in origin and include both passive and active elements regulating muscle stiffness. The age-related accumulation of non-contractile material in the muscle-tendon unit increases passive stiffness, which might offer mechanical advantage during eccentric contractions. In addition, the preserved muscle tension and increased instantaneous stiffness of old muscle fibers during stretch increase active stiffness, which might enhance eccentric strength.The fact that the preservation of eccentric strength is present in people with chronic conditions when compared to age-matched healthy controls indicates that the aging process per se does not exclusively mediate the preservation of eccentric strength. Physical inactivity, which is common in elderly and people with chronic conditions, is a potential factor regulating the preservation of eccentric strength.When compared to concentric strength, the magnitude of the preservation of eccentric strength in older adults ranges from 2% to 48% with a mean value from all studies of 21.6%. This functional reserve of eccentric strength might be clinically relevant, especially to initiate resistance training and rehabilitation programs in individuals with low levels of strength.

Neural control of lengthening contractions

“…In contrast, the force produced during lengthening contractions by the ankle dorsiflexors is substantially greater (∼30-50%) than that during isometric contractions Pasquet et al, 2000;Reeves and Narici, 2003). In older adults, the difference in peak force between shortening and lengthening contractions performed at the same velocity is often greater than in young adults, especially for shortening contractions (see Roig et al, 2010). The absence of substantial changes in voluntary activation for older adults suggests that the differential decline in peak force during shortening and lengthening contractions is mainly attributable to adaptations within the muscle (Klass et al, 2005).…”

Training implications of maximal forces on a computer-controlled and motor-driven leg press by age group, sex, footplate direction, and speed

“…However, older participants trended towards greater IN overloading, primarily due to the reduced IN overloading of younger males, and significance might have been achieved for a greater sample size. As IN overloading of peak forces was found to be inversely correlated with peak OUT force independent of age group or sex, we suspect that the high level of function and conditioning in our older participants masked the established preservation of lengthening strength with age in less fit populations (Raj et al, 2010;Roig et al, 2010) and that these earlier results may reflect an age-related decline in peak force rather than an effect of age alone. We also found significantly greater IN overloading of the areas under the force-time and forceposition curves for faster speeds and trends of greater IN overloading of force in women (Figure 3), but this may also have been due to greater IN overloading in weaker participants.…”

“…Furthermore, lengthening strength tends to be better preserved with age than shortening strength, even in individuals with chronic conditions (Raj et al, 2010;Roig et al, 2010). Because of this potential for greater muscular loading (and concomitant potential for greater strength gains) with less relative effort, training utilizing overloading of lengthening muscle fibers that can also adapt to the specific force-position and force-speed relationships of the exercise and individual is particularly attractive for older adults.…”

Sarcopenia and Exercise “The State of the Art”

“…Great results have also been obtained by using different types of RE, such as flywheel, vascular occlusion, dynamic, isometric, and eccentric [47]. The morphological and functional adaptations to RE include skeletal muscles and nerves, muscle architecture and composition, and myofibrillar proteins accumulation [48]. RE induces a muscle activation and relative signaling events starting from immune/inflammatory responses, hormones and growth factors release, satellite cells proliferation and muscle fiber hypertrophy.…”