Minimal Evidence for a Secondary Loss of Strength After an Acute Muscle Injury: A Systematic Review and Meta-Analysis.

Background: An immediate loss of strength follows virtually all types of muscle injury but there is debate whether the initial strength loss is maximal or if a secondary loss of strength occurs during the first 3 days post-injury.
Objective: The objective of this analysis was to conduct a systematic review and meta-analysis of the research literature to determine if a secondary loss of strength occurs after an injurious initiating event.
Methods: Literature searches were performed using eight electronic databases (e.g., PubMed, Cochrane Library). Search terms included skeletal muscle AND (injur* OR damage*) AND (strength OR force OR torque). The extracted strength data were converted to a standard format by calculating the standardized mean difference, which is reported as the effect size (ES) along with its 95 % confidence interval (CI). The calculation of ES was designed so that a negative ES that was statistically less than zero would be interpreted as indicating a secondary loss of strength.
Results: A total of 223 studies with over 4000 human and animal subjects yielded data on 262 independent groups and a total of 936 separate ESs. Our overall meta-analysis yielded a small-to-medium, positive overall ES that was statistically greater than zero (overall ES = +0.34, 95 % CI 0.27-0.40; P < 0.00000001). Considerable variation in ES was observed among studies (I ²  = 86 %), which could be partially explained by the research group conducting the study, sex of the subject, day of post-injury strength assessment, whether fatigue was present immediately post-injury, and the muscle group injured. From the subgroup meta-analyses probing these variables, 36 subgroup ESs were calculated and none were statistically less than zero.
Conclusion: Overall, our findings do not support the presence of a secondary loss of strength following an acute muscle injury, and strongly suggest that strength, on average, recovers steadily over the first 3 days post-injury.
Competing Interests: Compliance with Ethical Standards Funding No sources of funding were used to assist in the preparation of this article. Conflicts of interest Gordon Warren, Jarrod Call, Amy Farthing, and Bemene Baadom-Piaro declare that they have no conflicts of interest relevant to the content of this review.