Hamstring strength and morphology progression after return to sport from injury.
OBJECTIVE
Hamstring strain reinjury rates can reach 30% within the initial 2 wk after return to sport (RTS). Incomplete recovery of strength may be a contributing factor. However, relative strength of the injured and unaffected limbs at RTS is currently unknown.The purpose was to characterize hamstring strength and morphology at the time of RTS and 6 months later.


METHODS
Twenty-five athletes who experienced an acute hamstring strain injury participated after completion of a controlled rehabilitation program. Bilateral isokinetic strength testing and magnetic resonance imaging (MRI) were performed at RTS and 6 months later. Strength (knee flexion peak torque, work, and angle of peak torque) and MRI (muscle and tendon volumes) measures were compared between limbs and over time using repeated-measures ANOVA.


RESULTS
The injured limb showed a peak torque deficit of 9.6% compared to the uninjured limb at RTS (60°·s, P < 0.001) but not 6 months after. The knee flexion angle of peak torque decreased over time for both limbs (60°·s, P < 0.001). MRI revealed that 20.4% of the muscle cross-sectional area showed signs of edema at RTS with full resolution by the 6-month follow-up. Tendon volume of the injured limb tended to increase over time (P = 0.108), whereas muscle volume decreased between 4% and 5% in both limbs (P < 0.001).


CONCLUSIONS
Residual edema and deficits in isokinetic knee flexion strength were present at RTS but resolved during the subsequent 6 months. This occurred despite MRI evidence of scar tissue formation (increased tendon volume) and muscle atrophy, suggesting that neuromuscular factors may contribute to the return of strength.
Departments of Biomedical Engineering and Athletics University of Wisconsin-Madison, Madison, WI, USA.
Jennifer L
JL
Sanfilippo
Amy
A
Silder
Marc A
MA
Sherry
Michael J
MJ
Tuite
Bryan C
BC
Heiderscheit
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D004487:Edema / Q000209:etiology; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D053580:Muscle Strength; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012008:Recurrence; D013180:Sprains and Strains / Q000473:pathology / Q000503:physiopathology* / Q000534:rehabilitation; D013710:Tendons / Q000473:pathology; D013848:Thigh; D013997:Time Factors; D019415:Torque; D055815:Young Adult