The importance of gender on myokinetic deficits before and after microinjury


Medicine & Science in Sports & Exercise: May 2000 - Volume 32 - Issue 5 - pp 891-896
CLINICAL SCIENCES: Clinically Relevant

BORSA, P. A., and E. L. SAUERS. The importance of gender on myokinetic deficits before and after microinjury. Med. Sci. Sports Exerc., Vol. 32, No. 5, pp. 891–896, 2000.

Purpose: The purpose of this study was to determine the importance of gender on myokinetic deficits before and after muscle microinjury.

Methods: A repeated measures design assessed selected muscle force production characteristics in 20 male and 25 female volunteers. Peak force production (PFP) and the peak rate of force production (PRFP) were assessed before and over a 4-d period after an induced muscle microinjury.

Results: ANOVA revealed statistically significant mean (±SD) differences between men and women for PFP and PRFP (P < 0.0001). Both genders demonstrated significant between-day differences for PFP (P < 0.016), whereas only men demonstrated significant between-day differences for PRFP (P < 0.016).

Conclusions: Our results reveal that muscle force generating capabilities of physically active men exceed that of women both before and after microinjury. Myokinetic deficits were most pronounced acutely, between 24 and 48 h postinjury, followed by a near complete recovery at day 4 (96 h postinjury). Both genders suffered acute and residual deficits for PFP, whereas only men showed significant acute deficits for PRFP. We recommend that athletes, both male and female, refrain from strenuous exercise at least 48 h postinjury, or until force-generating capabilities normalize. More research needs to be conducted to substantiate these findings.

No standard criteria currently exist for safely returning athletes to participation after a musculoskeletal-related injury. Team physicians and certified athletic trainers alike often allow athletes to return to full participation prematurely, thereby creating a possible risk for reinjury or injury (1,27). One criterion that is often used in clinical practice is manual muscle and/or isokinetic testing to evaluate strength recovery (1,32). The production of a maximal voluntary contraction (MVC), either statically or dynamically, has been used as a global indicator of restored muscle function (1). This measure alone is often used as the sole criterion for permitting an athlete to return to full participation following an injury, whereas inadvertently overlooking other relevant muscular characteristics (1). A muscle’s ability to generate force or tension rapidly is reported as an important characteristic involved with sport performance and injury prevention (3,16,25,28). A high magnitude and rate of muscle force production helps to maximize angular joint acceleration, as well as protect a joint during periods of excessive stress (4,17,28,32).

Researchers investigating muscle performance have demonstrated that men generate higher levels of force more rapidly then women (5,9,17,30). To the best of our knowledge, no study has investigated the importance of gender on muscle force production before and after muscle microinjury. Therefore, the purpose of this study was to assess selected muscle force characteristics in physically active men and women before and after muscle microinjury. Our specific aims were to: 1) compare men and women with regard to muscle force production and 2) determine the interaction effects between gender over time. We hypothesize that a muscle microinjury will significantly decrease the rate and magnitude of force production.

Shoulder Kinematics Laboratory, Division of Kinesiology, University of Michigan, Ann Arbor, MI; and Biomechanics Laboratory, Department of Exercise and Sport Science, Oregon State University, Corvallis, OR

Submitted for publication February 1999.

Accepted for publication July 1999.

Address for correspondence: Paul A. Borsa, Ph.D., A.T.C., Director, Sports Medicine Research Laboratory, Oregon State University, 218 Langton Hall, Corvallis, OR 97331-3303; E-mail:

©2000The American College of Sports Medicine