(15) MUSCLE CHARACTERISTICS BETWEEN INDIVIDUALS WITH AND WITHOUT A PREVIOUS ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

Anterior cruciate ligament injuries and reconstruction surgery (ACLR) can have profound effects on the musculoskeletal system, such as between-limb asymmetries in strength, function, and size.

Purpose: This investigation compared maximal voluntary isometric contraction (MVIC) strength, rate of torque development (RTD), and muscle cross-sectional area (mCSA) between healthy individuals and individuals with a previous ACLR.

Methods: Thirty-one (22 female and 9 male; 17 healthy, 14 post-ACLR, mean±SD age: 24.6±7.5 years) individuals volunteered to participate. MVIC strength was assessed for the quadriceps and hamstrings on each leg. Early RTD from 0-50 milliseconds (RTD_0-50­) and maximal RTD (RTD_max) were calculated from the MVIC trial. Panoramic ultrasound assessed mCSA for the three superficial quadriceps (vastus medialis, vastus lateralis, and rectus femoris) and hamstrings (biceps femoris, semimembranosus, and semitendinosus) muscles. Total quadriceps and hamstrings mCSA were summed from the three muscles per muscle group separately to assess total quadriceps and hamstrings mCSA. Both legs were assessed for all variables and were compared for the operative or non-dominant limb (O-ND) and the non-operative or dominant limb (NO-D). Separate mixed-factorial ANOVAs [group (ACLR vs. healthy) x leg (O-ND vs. NO-D)] assessed differences between groups and legs for each variable at p≤0.05. Follow-up tests included independent or paired sample t-tests with Cohen’s d effect sizes.

Results: There were no significant group x leg interactions for any variable (p-range: 0.096-0.853) and there were no group main effects for any variables (p=0.095-0.492). However, there were significant main effects for leg for quadriceps MVIC, quadriceps RTD_0-50, quadriceps RTD_max, hamstrings RTD_max, quadriceps mCSA, and hamstrings mCSA. Follow-up tests indicated that NO-D was greater than O-ND for each variable (mean difference ± SE; p-value, Cohen’s d); quadriceps MVIC (14.1±5.0 N; p=0.009, d=0.506), quadriceps RTD_0-50 (132.2±47.0 N∙s; p=0.009, d=0.508), quadriceps RTD_max (131.4±49.4 N∙s; p=0.013, d=0.479), hamstrings RTD_max (54.8±31.2 N∙s; p=0.025, d=0.427), quadriceps mCSA (2.42±0.85 cm²; p=0.008, d=0.514) and hamstrings mCSA (1.58±0.77 cm²; p=0.048, d=0.372).

Conclusion: Lower-limb quadriceps and hamstrings asymmetries for strength, rate of torque development, and muscle size were observed in healthy and post-ACLR individuals. In this sample, there were no significant differences between groups for any of the outcome variables. However, between-limb asymmetries were evident collapsed across group. PRACTICAL APPLICATION: Resistance training programs should emphasize bilateral and unilateral muscular development to limit inter-limb asymmetries. Practitioners should continually monitor outcomes on both legs separately to determine values that may place individuals at risk for primary or secondary knee joint injuries.

Acknowledgements: None.