Short-term immobilization after eccentric exercise. Part I: contractile properties.
OBJECTIVE
The purpose of this study was to examine the compound muscle action potential (M-wave) and evoked contractile properties of immobilized muscle after high-force eccentric exercise. We believed that changes in these variables would contribute to the enhanced recovery of maximal voluntary force observed after short-term immobilization of damaged muscle. We hypothesized that immobilization after eccentric exercise would result in an enhanced M-wave and a change in contractile properties toward characteristics of faster muscle fibers.


METHODS
Twenty-five college-age males were matched according to force loss after 50 maximal eccentric contractions of the elbow flexors and placed into an immobilization (IMM, N = 12) or control (CON, N = 13) group. IMM had their arm immobilized at 90 degrees and secured in a sling during a 4-d treatment. Maximal isometric torque (MVC) was assessed at baseline and for 8 d after treatment. M-wave and evoked contractile properties of the muscle (twitch torque [TT], maximal rate of torque development [MRTD], time to peak torque [TPT], and one-half relaxation time [HRT]) were assessed at baseline and for the first 5 d after treatment.


RESULTS
Immediately postexercise, MVC was reduced 43% and 42% in IMM and CON, respectively. Recovery of MVC was significantly greater in IMM during recovery (P < 0.05), 95% of baseline MVC compared with 83% in CON. M-wave was reduced 32%, and all contractile properties were altered immediately postexercise. M-wave, MRTD, TPT, and HRT were not significantly different between groups during recovery (P > 0.05). TT demonstrated enhanced recovery in IMM (P < 0.05).


CONCLUSIONS
Short-term immobilization after eccentric exercise resulted in enhanced recovery of maximal voluntary force. However, enhanced force recovery cannot be explained by muscle activation and evoked contractile properties of the muscle.
Human Physiology Laboratory, Department of Health Sciences, Boston University, Sargent College of Health and Rehabilitation Sciences, 635 Commonwealth Avenue, Boston, MA 02215, USA. ssayers@bu.edu
Stephen P
SP
Sayers
Brian T
BT
Peters
Christopher A
CA
Knight
Maria L
ML
Urso
Jascha
J
Parkington
Priscilla M
PM
Clarkson
D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D004576:Electromyography / Q000379:methods*; D019054:Evoked Potentials, Motor; D005080:Exercise Test; D006801:Humans; D007103:Immobilization; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011336:Probability; D011930:Reaction Time; D012016:Reference Values; D012680:Sensitivity and Specificity