Shear wave velocity of biceps femoris and medial gastrocnemius in different positions and intensities: a cross-sectional study in healthy young males

Knee flexor muscles’ (hamstrings and gastrocnemius) mechanical properties are knee angle dependent and can be assessed through shear wave velocity (SWV). Therefore, our study aim to investigate the effect of contraction intensity and knee angle on the SWV of the biceps femoris long head (BFlh) and medial gastrocnemius (MG). Twenty physically active males underwent three assessment sessions. On the first day, demographic data and written consent were collected, followed by an isokinetic dynamometer protocol consisting of three knee flexion maximal voluntary isometric contractions (MVIC), and submaximal contractions. On second and third days, after passive SWV was assessed, participants performed sustained isometric contractions at 10%, 30%, and 50% of MVIC, at 0° and 45° of knee flexion, during which the SWV of the BFlh or MG was assessed. Reliability was evaluated using the intraclass correlation coefficient. A three-way ANOVA was conducted to investigate the effect of muscle, angle and contraction intensity on the SWV. Good-to-excellent reliability was found. A significant interaction (muscle-angle-intensity) was found ( p = 002). Also, a significant effect was found for angle ( p = 0.007) and intensity ( p < 0.001) on the SWV, no significant effect for muscle ( p = 0.066) was found. MG SWV increased across all intensities in both angles. BFlh at 0° increased until 30% of MVIC, while at 45°, BFlh increased from rest to 10%, with no further change. In conclusion, angle and contraction intensity exerted an effect on the SWV of BFlh and MG during submaximal isometric knee flexion