Recovery from fatigue of velocity-dependent power in young and old men Brian H Dalton, Geoffrey A Power, Anthony A Vandervoort (FACSM), and Charles L Rice (FACSM) Canadian Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, ON Abstract Methods Results Maximum Voluntary Isometric Contraction † † Recovery of the neuromuscular system following a bout of fatiguing exercise is important for ongoing mobility function of older adults, but has been seldom measured in previous studies. Furthermore, more attention to velocity-dependent muscle contractions that reflect the capacity to generate muscle power is also needed. PURPOSE: Thus, the effects of fatiguing velocity-dependent shortening contractions on the recovery of knee extensor function in 10 young (~24 years) and 10 old (~75 years) men were compared. METHODS: Recovery of neuromuscular properties was assessed immediately and at 0.5, 2, 5, and 10 min following a bout of 30 velocity-dependent (as fast as possible at 20% maximal voluntary isometric contraction (MVC)) shortening contractions. Electrically evoked and voluntary contractions including: maximal twitches, MVCs, and velocity-dependent contractions were compared with baseline and post-task termination measures. RESULTS: For both age groups, at fatigue, the MVC was reduced to ~70% of baseline and did not recover in 10 min. Peak twitch torque, which was reduced to ~85% of baseline following task termination, recovered in both groups by 5 min. Contraction duration (time to peak twitch + half relaxation time) of the twitch was lengthened to ~120% in the old men and recovered by 10 min, but contraction duration was not different at any time point for the young. Although velocity-dependent power was reduced more in the old group (to ~63%) than the young (to ~80% of baseline), recovery was slower in the old men with power not returning to baseline until 5 min, compared with 0.5 min in the young. Recovery of RPE was similar in both age groups from ~8 at task termination to ~4 by 10 min. CONCLUSION: There is no relative age-related difference in the recovery of isometric strength in response to velocity-dependent fatigue. Conversely, power was reduced to a greater extent in the old men than the young and recovery was blunted for the old. These results indicate how recovery from a fatigued muscle state depends not just upon the task, but also on the contractile property that is measured. Experimental Set-up: 900 Graphic design by Andrew Davidson Neuromuscular Properties: † † † Group MVC (Nm) VA (%) Power (W) Young (10) 311.5 + 65.3 97.2 + 2.9 506.3 + 116.7 Old (9) 208.0 + 34.9* 97.6 + 0.9 279.7 + 53.8* Old were weaker and less powerful than young (*p<0.05) MVC recovered similarly but not fully in old and young (†P<0.05) Recovery of MVC was not influenced by voluntary activation (VA) as VA was similar Twitch Contractile Properties: Subject Characteristics: Group PT (Nm) TPT (ms) HRT (ms) Young (10) 50.3 + 10.5 104.8 + 11.4 83.0 + 21.5 Old (9) 29.6 + 7.3* 116.8 + 10.4* 91.0 + 30.1 Velocity-Dependent Power Group Age (yrs) Height (cm) Mass (kg) Young (10) 24.5 + 2.7 177.1 + 8.3 79.5 + 9.8 Old (9) 73.2 + 3.5 175.6 + 4.1 84.1 + 9.4 † Old were weaker and marginally slower than young (*p<0.05) Introduction and Rationale † All data are means + standard deviations † * Ratings of Perceived Exertion (RPE) * Baseline Measures: Twitch contractile properties of knee extensors MVC torque with interpolated twitch technique Maximum voluntary shortening velocity and power at 20% MVC Recovery of the neuromuscular system from a bout of fatigue is important for performance during repetitive tasks Recovery is rarely measured Velocity-dependent power is characterized by a fixed load and is restricted by the subject’s maximum shortening velocity Because older adults fatigue more than young during velocity-dependent tasks, recovery from such tasks may also be limited in older individuals † † * Power did not recover in the old until 5 min (†P<0.05) Power recovered within 0.5 min in young Power was less in the old (*P<0.05) Fatigue Protocol: 30 maximal velocity-dependent contractions at 20% MVC Recovery measures at Post, 0.5, 2, 5, and 10 min Recovery of Shortening Velocity in an Old and Young Man: Conclusions RPE recovered similarly 1 s 100°.s-1 Old Isometric strength recovered similarly in the old and young men Isometric contractile speed recovered similarly in the old and young men Recovery of dynamic maximal shortening velocity and hence, velocity-dependent power may be delayed with age, despite equivalent recovery in isometric properties Half Relaxation Time † Purpose † † † To assess the effects of fatiguing velocity-dependent shortening contractions on the recovery of knee extensor function in young and old men Young † † † Hypotheses * Recovery of knee extensor power will be delayed in the old Recovery of knee extensor maximum voluntary isometric contraction (MVC) torque will be similar in the old and young Half relaxation time (HRT) recovered by 10 min (†P<0.05) HRT was greater in the old (*P<0.05) Pre Post R 0.5 min R 2 min R 5 min R 10 min Time Point Supported by: