The effect of regional quadriceps anatomical parameters on angle-specific isometric torque expression.

The length-tension relationship affects knee extension performance; however, whether anatomical variations in different quadriceps regions affect this relationship is unknown. Regional (proximal, middle, distal) quadriceps thickness (MT), pennation angle, and fascicle length of 24 males (48 limbs) were assessed via ultrasonography. Participants also performed maximal voluntary isometric torque (MVIT) assessments at 40°, 70°, and 100° of knee flexion. Measures were recorded on 3 separate occasions. Linear regression models predicting angle-specific torque from regional anatomy provided adjusted simple and multiple correlations (√adj) with bootstrapped compatibility limits to assess magnitude. Middle vastus lateralis MT and MVIT at 100° (√adj = 0.64) was the largest single correlation, with distal vastus lateralis MT having the greatest mean correlations regardless of angle (√adj = 0.61 ± 0.05, mean ± SD). Lateral distal MT and architecture had larger (Δ√adj = 0.01 to 0.43) single and multiple correlations with MVIT than the lateral proximal (√adj = 0.15 to 0.69 vs -0.08 to 0.65). Conversely, middle anterior MT had greater (Δ√adj = 0.08 to 0.38) single and multiple correlations than proximal MT (√adj = 0.09 to 0.49 vs -0.21 to 0.14). The length-tension relationship was trivially affected by regional quadriceps architecture. The middle and distal quadriceps were the strongest predictors of MVIT at all joint angles. Therefore, researchers may wish to focus on middle and distal lateral quadriceps anatomy when performing ultrasonographic evaluations. The length-tension relationship is minimally affected by regional quadriceps anatomical parameters. Middle and distal vastus lateralis and lateral vastus intermedius anatomy were consistently the best predictors of torque. Practitioners may focus their assessments on the middle and distal regions of the lateral quadriceps' musculature.