Effect of old age on human skeletal muscle force-velocity and fatigue properties

Callahan DM, Kent-Braun JA. Effect of old age on human skeletal muscle force-velocity and fatigue properties. J Appl Physiol 111: 1345-1352, 2011. First published August 25, 2011; doi:10.1152/japplphysiol.00367.2011.-It is generally accepted that the muscles of aged individuals contract with less force, have slower relaxation rates, and demonstrate a downward shift in their force-velocity relationship. The factors mediating age-related differences in skeletal muscle fatigue are less clear. The present study was designed to test the hypothesis that age-related shifts in the force-velocity relationship impact the fatigue response in a velocity-dependent manner. Three fatigue protocols, consisting of intermittent, maximum voluntary knee extension contractions performed for 4 min, were performed by 11 young (23.5 +/- 0.9 yr, mean +/- SE) and 10 older (68.9 +/- 4.3) women. The older group fatigued less during isometric contractions than the young group (to 71.1 +/- 3.7% initial torque and 59.8 +/- 2.5%, respectively; P = 0.02), while the opposite was true during contractions performed at a relatively high angular velocity of 270 degrees s(-1) (old: 28.0 +/- 3.9% initial power, young: 52.1 +/- 6.9%; P < 0.01). Fatigue was not different (P = 0.74) between groups during contractions at an intermediate velocity, which was selected for each participant based on their force-velocity relationship. There was a significant association between force-velocity properties and fatigue induced by the intermediate-velocity fatigue protocol in the older (r = 0.72; P = 0.02) and young (r = 0.63; P = 0.04) groups. These results indicate that contractile velocity has a profound impact on age-related skeletal muscle fatigue resistance and suggest that changes in the force-velocity relationship partially mediate this effect.