title: Decay of force transients following active stretch is slower in older than young men: support for a structural mechanism contributing to residual force enhancement in old age.
abstract: Following active lengthening of muscle, force reaches an isometric steady state above that which would be achieved for a purely isometric contraction at the same muscle length. This fundamental property of muscle, termed "residual force enhancement (RFE)," cannot be predicted by the force-length relationship, and is unexplained by the cross-bridge theory of muscle contraction. Recently, we showed that older adults experience higher RFE than young for the ankle dorsiflexors primarily owing to a greater reliance on passive force enhancement (PFE) and similar RFE for the knee extensors but a greater contribution of PFE to total RFE. Natural adult aging may prove a useful model in exploring mechanisms of RFE which may reside in the dissipation of force transients following stretch. A post-hoc analysis was conducted on previously described RFE experiments in young (~26 years) and old (~77 years) men for the dorsiflexors and knee extensors to fit the force following stretch with a biexponential decay. In both muscle groups the decay half-life of the first exponential was two times slower in the older compared with young men. There were significant associations between PFE and the decay in force, suggesting a greater "non-active" contribution to total RFE across muscles in older compared with young men. The greater "non-active" component of RFE in older adults could be due to structural age-related changes causing increased muscle stiffness during and following stretch.
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada. Electronic address: gapower@ucalgary.ca.
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Power
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Walter
authors.initials: W
authors.lastname: Herzog
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, Canada; Department of Anatomy and Cell Biology, The University of Western Ontario, Canada.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Rice
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology; D008297:Male; D055595:Mechanical Phenomena; D052580:Muscle Stretching Exercises; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology; D012044:Regression Analysis
keywords: Aging; Eccentric; Muscle; Residual force enhancement; Stiffness