Effect Of Age And Range Of Motion On Knee Extensor Muscle Torque-Velocity And Fatigue Characteristics

Abstract

While it is well accepted that muscle fatigue (transient decrease in peak torque) is task-specific, little information exists regarding the influence of joint range of motion (ROM) on fatigue. Further, given the age-related changes in the torque-velocity (T-V) relationship, it is reasonable to expect that ROM may influence fatigue differently in young and older muscle. PURPOSE: To determine the effect of knee joint ROM on knee extensor muscle torque-velocity and fatigue characteristics in young and older adults. METHODS: After providing written informed consent, 7 young (29 ± 5 yr, 5F) and 5 older (70 ± 4, 4F) adults had each leg randomly assigned to a 35 or 75 deg ROM condition. Using dynamometry (Biodex S4, Biodex, Shirley NY), T-V characteristics (peak torque at 60, 120, 150, 180, 240, and 300 deg∙s-1, in random order) were measured in 1 leg and fatigue (% initial peak torque) during 120 maximal contractions (once every 2 s at 120 deg∙s-1) was measured in the other. The protocols were switched at a second visit, such that each leg ultimately completed both protocols at either 35 or 75 deg ROM. All torque data were normalized to thigh lean mass (kg), determined using dual x-ray absorptiometry (Lunar iDXA, General Electric, Chicago IL). Statistics: rmANOVA, mean ± SD. RESULTS:The T-V relationship did not differ by ROM in young (p = 0.10). In contrast, the older adults did not attain 300 deg∙s-1over 35 deg and torques were lower for 35 than 75 between 60 - 240 deg∙s-1 (p = 0.04). Fatigue was greater during 75 deg ROM (young: to 46 ± 14% initial, older: to 28 ± 18%) than 35 deg ROM (young: to 71 ± 13% initial, older: to 66 ± 8%; ROM effect p < 0.001), with no effect of age or age x ROM interaction (p ≥ 0.12). CONCLUSION: Overall, the T-V data showed that young, but not older, adults were able to attain peak torque within 35 deg. Presumably, age-related slowing of contraction velocity contributed to this deficit. Greater fatigue in both groups during contractions at 75 deg ROM, likely due to the greater duty cycle and total work in this task, indicates that ROM is an important factor in the task specificity of fatigue. The apparent lack of an effect of age on the ROM-related difference in fatigue at a moderate velocity suggests that differences in the T-V relationship were not exacerbated by fatigue in the older group. Additional work is needed to confirm this result.