ARTICLE Peak power is reduced following lengthening contractions despite a maintenance of shortening velocity Geoffrey A. Power, Brian H. Dalton, Charles L. Rice, and Anthony A. Vandervoort Abstract: Following repetitive lengthening contractions, power (the product of torque and velocity) is impaired during short- ening contractions. However, the relative contribution of each component to power loss and the underlying factors are unclear. We investigated neuromuscular properties of the dorsiflexors in 8 males (27 ± 3 years) and 8 females (26 ± 4 years) for a potential sex-related difference before, during, and after 150 unaccustomed maximal lengthening actions. Velocity-dependent power was determined from shortening contractions at 8 levels (1 N·m to 70% of maximum voluntary isometric contraction (MVC)) before, after, and throughout recovery assessed at 0–30 min, 24 h, and 48 h. Immediately following task termination, both sexes displayed similar impairments of 30%, 4%, and 10% in MVC torque, shortening velocity, and overall peak power , respectively (P < 0.05). Peak rate of isometric torque development (RTD) was reduced by 10% in males, but females exhibited a 35% reduction (P < 0.05). Rate of torque development for the MVC remained depressed in both sexes throughout the 30 min recovery period; however, the RTD returned to normal by 24 h in males but did not recover by 48 h in females. Power was reduced preferentially at higher loads (i.e., 60% MVC), with a greater loss in females (65%) than males (45%). For lower loads (<20% MVC), power was impaired minimally (4%–8%; P < 0.05) and recovered within 30 min in both groups. The reduction in maximal angular velocity persisted until 30 min of recovery, and peak power did not recover until 24 h for both sexes. Unaccustomed lengthening contractions decreased power preferentially at higher loads, whereas peak power was reduced minimally owing to maintenance of maximal shortening velocity. Key words: muscle damage, sex, eccentric, human, dorsiflexors, torque–velocity. Résumé : Une altération de la puissance générée (moment de force × vélocité) est observée pendant des contractions miomé- triques effectuées a ` la suite de contractions pliométriques répétées. Toutefois, la contribution relative de ces facteurs a ` la diminution de puissance n'est pas bien établie. Avant, pendant et après 150 contractions pliométriques maximales inhabituelles, on examine les propriétés neuromusculaires des fléchisseurs dorsaux chez 8 hommes (27 ± 3 ans) et 8 femmes (26 ± 4 ans) pour vérifier la présence possible d'une différence liée au sexe. On évalue la puissance selon la vélocité au cours de contractions miométriques de 8 intensités (de 1 N·m jusqu'a ` 70 % de la tension isométrique maximale (MVC)), et ce, avant, a ` la suite et tout au long de la récupération aux moments suivants : 0–30 min, 24 h, et 48 h. Immédiatement après la fin de la tâche, les deux groupes présentent une diminution similaire, soit 30, 4 et 10 % du moment de force MVC, de la vélocité de raccourcissement et de la puissance de crête globale, respectivement (P < 0,05). Le taux de pointe du développement de la tension isométrique (RTD) diminue de 10 % chez les hommes et de 35 % chez les femmes (P < 0,05). Le RTD pour atteindre la MVC reste bas dans les deux groupes tout au long des 30 min de récupération; le RTD revient a ` la normale en 24 h chez les hommes, mais n'a pas retrouvé sa valeur initiale en 48 h chez les femmes. La puissance diminue surtout aux intensités plus élevées (c.-a ` -d. 60% MVC), la diminution étant plus élevée chez les femmes (65 %) que chez les hommes (45 %); aux intensités plus faibles (<20 % MVC), la puissance diminue légèrement (4–8 %; P < 0,05) et revient dans les deux groupes a ` sa valeur normale en moins de 30 min. La diminution de la vélocité angulaire maximale persiste jusqu'a ` la récupération de 30 min et la puissance de pointe ne revient pas a ` la normale avant 24 h dans les deux groupes. Des contractions pliométriques inhabituelles suscitent une diminution de la puissance surtout aux intensités élevées et la puissance de pointe diminue légèrement a ` cause du maintien de la vélocité maximale de raccourcisse- ment. [Traduit par la Rédaction] Mots-clés : lésion musculaire, sexe, pliométrique, humain, dorsifléchisseurs, moment de force–vélocité. Introduction Optimal power generation is based on the finely tuned relation- ship between torque and angular velocity and is expressed as the torque–velocity (T–V) relationship. As velocity increases, less torque can be generated owing to fewer cross-bridge attachments, and thus an optimal combination of submaximal torques and velocities is required to achieve peak power (Abbott and Wilkie 1953; Lieber and Ward 2010). Following repetitive voluntary lengthening contractions, neuromuscular function can be dimin- ished severely (Barker et al. 2012; Byrne et al. 2004; Power et al. 2010; Prasartwuth et al. 2005; Sargeant and Dolan 1987) due to such impairments as cytoskeletal damage, excitation contraction uncoupling (Allen et al. 2005; Ingalls et al. 1998; Proske and Allen Received 28 February 2013. Accepted 21 May 2013. G.A. Power. Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON N6G 2M3, Canada; Human Performance Laboratory, University of Calgary, Calgary, AB T2N 1N4, Canada. B.H. Dalton. Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON N6G 2M3, Canada; Sensorimotor Physiology Laboratory and Human Neurophysiology Laboratory, The University of British Columbia, Vancouver, BC V6T 1Z1, Canada. C.L. Rice. 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 5C1, Canada. A.A. Vandervoort. Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON N6G 2M3, Canada; School of Physical Therapy, Faculty of Health Sciences, The University of Western Ontario, London, ON N6A 5B9, Canada. Corresponding author: Anthony A. Vandervoort (e-mail: vandervo@uwo.ca). Pagination not final/Pagination non finale 1 Appl. Physiol. Nutr. Metab. 38: 1–10 (2013) dx.doi.org/10.1139/apnm-2013-0092 Published at www.nrcresearchpress.com/apnm on 30 May 2013. Appl. Physiol. Nutr. Metab. Downloaded from www.nrcresearchpress.com by UNIV CALGARY on 10/15/13 For personal use only.