Relationship between vastus lateralis muscle ultrasound echography, knee extensors rate of torque development, and jump height in professional soccer athletes

This study aimed to investigate the relationship between knee extensors maximum voluntary contraction (MVC) torque and rate of torque development (RTD) with jump performance and with echography intensity (EI) from the vastus lateralis muscle (VL). We assessed the MVC torque and RTD from knee extensors by a standard isokinetic device from 16 male professional soccer players (25.5 ± 3.9 years). Counter-movement jump (CMJ) and squat jump (SJ) height were calculated from their flight times. EI was determined from VL ultrasound images’ grayscale histogram acquired in the middle of the tight. Correlation between variables was investigated by the Pearson correlation coefficient. We observed a VL EI of 26.4 ± 7.8 a.u., and the SJ and CMJ heights were 36.0 ± 3.0 and 36.2 ± 4.1 cm, respectively. There was a significant correlation between the MVC torque and absolute late-phase RTD (r = 0.67 and 0.76—RTD200 and RTD250, respectively), between the CMJ height and absolute RTD50 (r = 0.50), and between the normalized early-phase RTD and SJ height (r = 0.53–0.60—RTD50 and RTD150). Additionally, normalized RTD200 (r = − 0.51) and RTD250 (r = − 0.56) were negatively correlated with EI. Such results suggest that athletes with the ability to produce torque explosively in the very beginning (between 50 and 150 ms) of knee extension can jump higher. Also, the muscle quality assessed by the VL IE seems to be more important to maximum strength and later periods of torque rise (> 200 ms).