The effects of aging on the muscle length (as inferred by joint angle)-tension relationship was studied in the ankle dorsiflexors of male and female subjects aged 20-40 years (x=25.3; 15d, 159) and 60-80 years (x=68.8; 15d, 159) at 10 joint angles {15°0 through 30°P, in 5° increments). Isometric twitches, voluntary contractions, and 1-sec evoked tetanic contractions {20, 50 & 80 Hz) were measured in the R-tibialis anterior muscle. The resting joint angle for the ankle dorsi flexors was similar between elderly and young adults {13°P ± 3.44). On average, evoked and voluntary torque output increased upon muscle lengthening beyond resting length, and decreased upon shortening. Evoked single twitches of the TA revealed that peak total torque occurred at the extreme of plantarflexion (30°P} in both elderly and young adults. Most importantly, elderly individuals produced similar twitch torque values at all joint angles compared to young adults. Maximal voluntary torque was stronger at the more plantarflexed compared to the dorsiflexed angles, for all subjects, regardless of age, with maximum torque plateauing at 15°P. Elderly subjects demonstrated much reduced MVC torque values compared to young adults at all joint angles (ave.= 18% reduction, p<O.Ol) while maintaining no less than 96% motorunit activation (MUA) . Stimulation of the dorsiflexors at 20, 50, & 80 Hz revealed that the 1-sec peak tetanic torques declined from a maximum at 30°P through to 15°0 for all subjects. Elderly adults produced significantly less tetanic torque at all joint angles compared to young adults (p<0.05). There was no difference between the elderly and young adults in the rate at which the rise in tetanic torque was developed at all joint angles, but elderly adults displayed a significantly greater twitch/tetanus ratio as compared to young adults (p<0.005). In conclusion, these results suggest that there is no age-associated change in the elastic properties of the ankle dorsiflexors, and thus, the length-tension relationship of this muscle group is similar between elderly and young adults. / Thesis / Master of Science (MSc)

Supporters of a nutritional supplement, β-Hydroxy-β-Methylbutyrate (HMB) supplementation, claim that it will increase the muscular strength gains and lean muscle mass gains seen during a resistance training program. It has been suggested that HMB supplementation does this by preventing muscle damage or by regenerating damaged muscle cell membranes. However, no research has evaluated the effect of HMB supplementation on low frequency fatigue. Therefore, the purpose of this study was to determine if three weeks of HMB supplementation could attenuate the effects of low frequency fatigue caused by eccentric muscle contractions of the tibialis anterior muscle. A total of 33 healthy recreationally active subjects (18 males, 15 females; 23.2 ± 4.3 yr) were recruited for this study. All subjects preformed 4 sets of 25 eccentric contractions of the tibialis anterior muscle through a range of motion of 30 degrees. Recovery measures were taken for 20 minutes after the fatigue protocol and at 48 and 96 hours of recovery. The recovery measures included: Maximum voluntary contraction peak torque, 10 Hz peak torque, 50 Hz peak torque, 10/50 Hz peak torque ratio, and EMG measurements. Each subject served as their own control and limbs were randomly assigned to pre-supplement or post-supplement limbs. Following the pre-supplement fatigue protocol and recovery measures each subject completed three weeks of 3g/day HMB supplementation. After the supplementation period the post-supplement fatigue protocol was completed and recovery measures were taken. The 10 Hz peak torque and the 10/50 Hz torque ratio in the pre-supplement limb was still significantly reduced at the 96-hour recovery measurement time, indicating that it was still showing low frequency muscle fatigue at this time. Furthermore, the post-supplement limb, recovered from the fatigue protocol faster, and did not show any signs of low frequency muscle fatigue at the 48-hour recovery measurement time. In addition the pre-supplement limb had significant maximum voluntary contraction torque deficit at the 48-hour recovery measurement time and the post-supplement limb showed no significant deficits. The main findings of this study were that three weeks of HMB supplementation attenuated low frequency fatigue and maximum voluntary contraction torque reduction after an eccentric fatigue protocol.