title: Effects of consecutive days of exercise and recovery on muscle mechanical function.
abstract: OBJECTIVE
  To investigate the effects of three consecutive days of prolonged exercise on muscle mechanical function, 12 volunteers (.VO(2peak) = 44.8 +/- 2.0 mL.kg(-1).min(-1), mean +/- SE) cycled at approximately 60% .VO(2peak) until fatigue.
  
  
  METHODS
  Quadriceps muscle function was assessed before and after exercise on day 1 (E1) and day 3 (E3) and during three consecutive days of recovery (R1, R2, R3), using both voluntary and electrically induced contractions at various stimulation frequencies.
  
  
  RESULTS
  Exercise on E1 and E3 resulted in a 40% (120 +/- 12 vs 72 +/- 10 N) and 35% (117 +/- 14 vs 78 +/- 8 N) deficit (P < 0.05) in force at 10 Hz, respectively, which remained depressed (P < 0.05) by 32-34% during R1-R3. At 100 Hz, force, although not altered by exercise at E1 or E3, was decreased (P < 0.05) by 12-16% during recovery. The maximal rate of relaxation (-dF/dtmax) at 10 Hz was reduced (P < 0.05) by 38% on E1, by 32% on E3, and remained depressed by 38% through R3. At 100 Hz, -dF/dtmax was only depressed (P < 0.05) during recovery. Maximal rate of force development (+dF/dtmax) at 10 Hz was reduced (P < 0.05) by exercise, but not in recovery. Maximal voluntary contraction force was depressed (P < 0.05) with exercise at both E1 and E3 and remained depressed (P < 0.05) throughout recovery. The reduction (P < 0.05) in motor unit activation assessed with the interpolated twitch technique, observed during recovery, suggests that part of the incomplete recovery (weakness) is central in origin.
  
  
  CONCLUSIONS
  These results demonstrate that three consecutive days of prolonged exercise result in a weakness that persists for at least 3 d, compromising force during both voluntary and induced contractions.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: Riley D
authors.initials: RD
authors.lastname: Stewart
authors.forename: Todd A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: Sharon
authors.initials: S
authors.lastname: Rich
authors.forename: A Russell
authors.initials: AR
authors.lastname: Tupling
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Green
mesh_terms: D000293:Adolescent; D000328:Adult; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D009864:Ontario; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology*; D013997:Time Factors