Single- Versus Multi-Site Quadriceps Ultrasound Measurements and Their Associations With Physical Performance

Introduction: Skeletal muscle ultrasound of the quadriceps is often performed at the mid-thigh rather than other muscle regions. Moreover, most studies have examined associations between ultrasound-derived measures and a single functional outcome. The first aim was to determine whether averaging ultrasound measurements across the quadriceps femoris provides estimates of muscle size and quality (echo intensity (EI)) comparable with a mid-thigh measurement. The second aim was to evaluate associations of muscle size and EI (multiple vs single site) with different physical performance tests. Methods: In this cross-sectional study, 30 adults (50% women; 24.9 ± 7.9 yr old) underwent ultrasound imaging for analysis of muscle size and EI of the vastus lateralis, rectus femoris, and vastus intermedius at 30%, 50%, and 70% of the femur length. Physical performance was assessed by isometric knee extension torque (laboratory test), stair climb (clinical test), and vertical jump (athletic test). Results: Muscle size averaged across the length of the muscle was smaller compared with single-site measures ( P = 0.03) but showed excellent agreement (intraclass correlation coefficient = 0.985). Muscle EI was similar between multiple versus single-site measurements ( P = 0.17). Multi-site size correlated more strongly with isometric knee extension torque ( r = 0.706, P < 0.001), whereas single-site measures correlated more with stair climb (r = 0.741, P < 0.001). Jump time showed comparable associations for multiple- and single-site measures of quadriceps muscle size ( r = 0.710–0.772) and EI ( r = −0.748 to −0.762; all P < 0.001). Conclusion: Single-site measurements tended to overestimate muscle size/quality relative to multi-site assessments. Muscle size from multiple sites was more strongly associated with isometric knee extension torque, whereas single-site measures better predicted stair-climb performance; jump time was equally associated with both. The imaging approach should be selected according to the functional outcome, as predictive value varies across tests.