The effects of regional quadriceps architecture on angle-specific rapid force expression.

Evaluating anatomical contributions to performance can increase understanding of muscle mechanics and guide physical preparation. While the impact of anatomy on muscular performance is well studied, the effects of regional quadriceps architecture on rapid torque or force expression are less clear. Regional (proximal, middle, and distal) quadriceps (vastus lateralis, rectus femoris, and vastus intermedius) thickness (MT), pennation angle (PA), and fascicle length (FL) of 24 males (48 limbs) were assessed via ultrasonography. Participants performed maximal isometric knee extensions at 40°, 70°, and 100° of knee flexion to evaluate rate of force development from 0 to 200 ms (RFD_0-200). Measurements were repeated on three occasions with the greatest RFD_0-200 and mean muscle architecture measures used for analysis. Linear regression models predicting angle-specific RFD_0-200 from regional anatomy provided adjusted correlations (√adjR²) with bootstrapped compatibility limits. Mid-rectus femoris MT (√adjR² = 0.41-0.51) and proximal vastus lateralis FL (√adjR² = 0.42-0.48) were the best single predictors of RFD_0-200, and the only measures to reach precision with 99% compatibility limits. Small simple correlations were found across all regions and joint angles between RFD_0-200 and vastus lateralis MT (√adjR² = 0.28 ± 0.13; mean ± SD), vastus lateralis FL (√adjR² = 0.33 ± 0.10), rectus femoris MT (√adjR² = 0.38 ± 0.10), and lateral vastus intermedius MT (√adjR² = 0.24 ± 0.10). Between-correlation comparisons are reported within the article. Researchers should measure mid-region rectus femoris MT and vastus lateralis FL to efficiently and robustly evaluate potential anatomical contributions to rapid knee extension force changes, with distal and proximal measurements providing little additional value. However, correlations were generally small to moderate, suggesting that neurological factors may be critical in rapid force expression.