July 10, 2016
Geoffrey A. Power1, Demetri P. Makrakos2, Daniel E. Stevens2, Charles L. Rice3, and Anthony A. Vandervoort2
1 Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada.
2 Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON N6G 2M3, Canada.
3 Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON N6G 2M3, Canada; Department of Anatomy and Cell Biology, The University of Western Ontario, London, ON N6A 3K7, Canada.
Old Man Strength: Natural adult aging is associated with many alterations to the human neuromuscular system which contribute to impaired function in old age. However, age-related reductions in muscle contractile capacity are disparate when considered in terms of contractile mode, such as those during; shortening (concentric), static (isometric), and lengthening (eccentric) contractions. With adult aging, eccentric strength is better maintained than isometric leading to a higher ratio of voluntary eccentric to isometric maximal force production (ECC:ISO) in older than younger adults.
In our study, “Velocity dependence of eccentric strength in young and old men: the need for speed!” we found, that older adults (~76 years) had similar levels of eccentric strength at faster lengthening velocities (i.e., above 45o/s) as compared with the young (~24 years). Additionally, when eccentric strength was expressed as a relative percentage of isometric strength, older adults had a higher eccentric:isometric ratio across all lengthening velocities as compared with young. This ratio increased with increasing velocity before reaching a plateau. Thus, older men appear to have a velocity-dependence of eccentric strength.
Potential mechanisms of the observed results would be owing to the age-related slowing of cross-bridge cycling. Specifically, the slowed cross-bridge cycling may allow for older adults to develop relatively higher forces during lengthening muscle actions as compared with the young, and with isometric contractions. On average, when the velocity of the stretch is increased, the cross-bridge strain increases which is supported by our result of an increasing peak force with increasing lengthening velocity.
To test the above proposed mechanisms, we followed up with a study (unpublished) in which we lowered muscle temperature of an intrinsic hand muscle in young and older adults thus slowing cross-bridge cycling and biasing the cross-bridge distribution to a weakly bound state (results will be presented at the 2015 CSEP annual meeting in Hamilton). We contest that the maintenance of eccentric strength is not entirely owing to the adult aging process, but that ECC:ISO can be explained, in part, by a strong positive relationship between ECC:ISO and muscle relaxation time. Evidently, the slowing of muscle contractile properties and a greater proportion of weakly bound cross-bridges are likely key contributors to an elevated ECC:ISO, particularly for older adults.
These findings shed new light on the plasticity of the aged neuromuscular system and indicate that fitness interventions could take advantage of the considerable preserved performance seniors have during lengthening (eccentric) contractions.
Geoffrey A. Power, Demetri P. Makrakos, Daniel E. Stevens, Charles L. Rice, and Anthony A. Vandervoort Velocity dependence of eccentric strength in young and old men: the need for speed!. Applied Physiology, Nutrition, and Metabolism. 40: 703–710 (2015) dx.doi.org/10.1139/apnm-2014-0543
This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend citing any information in this article, please consult the original article and cite that source.