The Association Of Quadriceps' Muscle Size And Quality With Isometric Peak Torque After ACLR

Isometric testing is used to assess strength after anterior cruciate ligament reconstruction (ACLR); while ultrasound imaging is used to quantify muscle thickness (MT) and echo intensity-derived muscle quality (EI). Since both methods are used to assess individuals post-ACLR, it is important to understand their association with isometric peak torque (PT). PURPOSE: To compare relationships between EI and MT of the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM), and isometric PT for the operated (OP) and non-operated legs (NO) of ACLR patients. METHODS: Forty-six ACLR patients (M/F: 13/33; Age: 28.5 ± 11.9 y; Height: 1.72 ± .09 m; Mass: 77.4 ± 18.2 kg; Time Since Surgery: 29.7 ± 11.7 weeks) completed ultrasound imaging and isometric testing on both limbs at a single time point during rehabilitation. Ultrasound images were taken of the RF, VL, and VM. Images were analyzed to quantify the mean grayscale intensity and thickest point for each muscle. Isometric testing was performed at 90 degrees of knee flexion and the PT was recorded from three repetitions separated by 30 seconds of rest. Prior to analysis, four subjects were detected as outliers using the z-score method and were subsequently removed. Pearson correlations were used to determine the association between isometric PT, EI and MT. Correlations were categorized as negligible (<.30), low (.30 - .50), moderate (.50 - .70), strong (.70-.90), and very strong (>.90). Alpha was set to .05. RESULTS: For correlations of EI to PT of the OP, low to moderate correlations were seen for RF (r = -.424, p = .003, CI95: -.636, -.153), VL (r = -.638, p < .001, CI95: -.783, -.426), and the VM (r = -.464, p = .001, CI95: -.665, -.201); for the NO, in the RF (r = -.354, p = .016, CI95: -.585, -.071), VL (r = -.516, p < .001, CI95: -.702, -.266) and VM (r = -.304, p = .040, CI95: -.546, -.015). For the correlations of MT to PT of the OP, low to moderate correlations were seen for RF (r = .580, p < .001, CI95: .348, .745) and VL only (r = .474, p < .001, CI95: .214, .672); for the NO, in the RF (r = .713, p = < .001, CI95: .534, .831), VL (r = .646, p < .001, CI95: .438, .789) and VM (r = .565, p < .001, CI95: .328, .735). CONCLUSION: The greater associations observed for OP EI suggests that reductions in PT may be due to greater reductions in muscle quality, whereas for the NO leg, MT is a greater indicator of PT performance.