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 (I2= 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.


CONCLUSIONS
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.
Department of Physical Therapy, Byrdine F. Lewis School of Nursing and Health Professions, Georgia State University, PO Box 4019, Atlanta, GA, 30302, USA. gwarren@gsu.edu.
Gordon L
GL
Warren
Department of Kinesiology, University of Georgia, Athens, GA, USA.|Regenerative Bioscience Center, University of Georgia, Athens, GA, USA.
Jarrod A
JA
Call
Department of Physical Therapy, Byrdine F. Lewis School of Nursing and Health Professions, Georgia State University, PO Box 4019, Atlanta, GA, 30302, USA.
Amy K
AK
Farthing
School of Public Health, Georgia State University, Atlanta, GA, USA.
Bemene
B
Baadom-Piaro
D000818:Animals; D005221:Fatigue; D006801:Humans; D053580:Muscle Strength; D018482:Muscle, Skeletal; D019415:Torque