The present study aimed to investigate the relationship between linear deceleration performance and explosive strength capacity of the knee muscles. Fourteen female professional soccer players completed the maximal sprint deceleration tests and knee flexor (KF) and knee extensor (KE) isokinetic concentric (240° and 60°.s⁻¹) and eccentric contractions (30°.s⁻¹). Linear deceleration performance was evaluated from horizontal breaking force (F_H), power (P_H), and impulse (I_H) during a maximal linear deceleration. The peak torque (PT) of KF and KE, PT ratio between KF and KE (conventional and functional H/Q ratio), rate of torque development (RTD) for each muscle group, and RTD between KF and KE (RTD H/Q) were extracted from the isokinetic contractions. Pearson’s correlation coefficients revealed that the eccentric (30°.s⁻¹) and concentric (60°.s⁻¹, 240°.s⁻¹) KE peak torque, and the concentric KF peak torque (240°.s⁻¹) were significantly correlated with F_H, P_H, and I_H (−0.75<r<−0.54). Moreover, a significant correlation was found between KE RTD during eccentric contraction and F_H, P_H, and I_H (−0.63<r<−0.54). Besides, a significant correlation was observed between RTD H/Q at 60°.s⁻¹ and P_H, I_H (−0.61<r<−0.57). No significant relationship was observed between the H/Q ratio, KF RTD and deceleration performance. These main findings indicated the importance of the ability to quickly produce high KE eccentric torque, contributing to braking force production. Meanwhile, RTD H/Q should be assessed for its essential role in knee joint dynamic stability and can be a relevant index to determine deceleration performance.

Self-myofascial release (SMR) is a popular method to potentially increase the compliance and extensibility of the fascia and reduce muscle stiffness. The purpose of this study was to examine the acute effects of posterior muscle chain SMR on flexibility, vertical jump performance and balance ability. Eighteen young participants volunteered to take part in this crossover design study. They performed two self-massage sessions in randomized order separated by at least one week. One session consisted of posterior muscle chain SMR whereas the other one was performed on the upper limbs as a control intervention (CON). Flexibility was measured with the Toe Touch Test (TTT), Weight-Bearing Lunge Test (WBLT), and Straight Leg Raise Test (SLR). Jump performance was evaluated during a squat jump, a counter movement jump and a stiffness jump. Dynamic balance ability was assessed through the Star Excursion Balance Test. All these variables were measured before and after each intervention. A significant increase in flexibility (+3.5 ± 1.8 cm, +1.6 ± 1.0°, and +7.7 ± 4.0° for the TTT, WLBT, and SLR, respectively, p < 0.003) and balance performance (4.8 ± 3.9 cm, p < 0.003) was observed following SMR intervention compared to CON. Conversely, jumping performance was unchanged in both groups. SMR improves joint flexibility and dynamic balance ability.

The objective of this study was to examine the effect of fatigue on maximal and rapid force capacities and muscular activation of the knee extensors and flexors. Seventeen professional soccer players volunteered to participate in this study. Peak torque (T_peak) and rate of torque development (RTD) of knee flexor (90°. s^–1, −30°. s^–1) and extensor (90°. s^–1) muscles were measured before and after fatigue (i.e., 30 maximal knee extension and flexion repetitions at 180°s^–1) performed on an isokinetic dynamometer. Hamstring to quadriceps peak strength and RTD ratios were calculated. Besides, using surface EMG, the mean level of activation (RMS_mean), Rate of EMG Rise (RER), and EMG Frequency-Time maps were measured on quadriceps and hamstring muscles. Following fatigue, T_peak, RTD, RER declined significantly in the two muscle groups (all p < 0.05) without modification of RMS_mean. No decrease in conventional and functional H/Q ratios was observed after fatigue except for a significant increase in the H_ecc30/Q_con180 ratios (1.03 ± 0.19 vs. 1.36 ± 0.33, p < 0.001). Besides, the RTD H/Q ratios decreased significantly after fatigue, and the statistical parametric mapping analysis (SPM) performed on the EMG/angle curves, and EMG Frequency-Time maps showed that fatigue strongly influenced the muscle activation during the first 100 ms of the movement, following the higher EMG frequency component shift toward the lower frequency component. Our results show that the reduction of RTD and RER during the first 100 ms of the contraction after fatigue exercise makes more sense than any H/Q ratio modification in understanding injury risk in soccer players.

The study investigated the relationship between short sprint performance and mechanical parameters obtained during the acceleration and deceleration tasks with the change of direction (COD) performance in female and male soccer players. The acceleration and deceleration ability were compared in the “High/Fast” versus “Low/Slow” COD performance group based on a median split analysis in each sex group. One hundred three French soccer players were assessed for the sprinting Force-Velocity (F-V) profile (i.e., theoretical maximal force [F0], velocity [V0], power [Pmax]), 10 m performance, linear deceleration test (maximal braking force [HBF_max], braking power [BP_max], deceleration [Dec_max]), and COD performance using 505-test. The 10 m performance was strongly associated with 505-test performance (ES = [0.64 to 0.71]), whereas the sprinting F-V profiles parameters were weakly to moderately correlated with 505- performance (ES = [-0.47 to -0.38]). The BP_max was also moderately associated with 505-test performance (ES: range = [-0.55 to -0.46]). In addition, the High/Fast female COD group presented higher F0, Pmax, HBF_max, and BP_max than the Low/Slow group, whereas the male groups presented very few mechanical differences. Multiple regression analysis shows that the COD performance of male players was determined by 10 m performance and maximum deceleration power. In contrast, no statistically significant model could be found to determine the change of direction performance in female players. In conclusion, the current finding indicated that the only variable strongly associated with COD performance was the linear 10 m sprint time. In the same way, the mechanical parameters obtained from acceleration and deceleration seemed to play a non-neglectable role in this population.

The Volodalen® field method permits to classify runners into aerial or terrestrial, based on vertical oscillation, upper‐body motion, pelvis and foot position at ground contact, and foot strike pattern. The present study aimed to compare the sprint running force‐velocity profiles between aerial and terrestrial runners. Sixty‐Four French National‐Level young soccer players (28 females, 36 males) performed three trials of unloaded maximal 40 m sprints. External horizontal power‐force‐velocity relationships were computed using a validated biomechanical model and based on the velocity‐time curve. Accordingly, the participants were classified into patterns in aerial and terrestrial runners. Terrestrial runners showed a higher maximal horizontal force (F ₀) (6.73 ± 1.03 vs 6.01 ± 0.94 N·kg⁻¹), maximal horizontal power (P _max) (14.04 ± 3.24 vs 12.51 ± 3.31W·kg⁻¹), maximal acceleration (Acc) (6.83 ± 0.85 vs 6.26 ± 0.89 m·s⁻²), and maximal rate of horizontal force (RF _max) (57.41 ± 4.64 vs 52.81 ± 5.69%) compared to aerial runners. In contrast, terrestrial runners displayed a more negative rate of decrease of RF (D _RF) (−11.65 ± 1.71 vs −10.23 ± 1.66%) and slope of the Force‐Velocity relationship (F‐V slope) (−0.83 ± 0.11 vs −0.77 ± 0.10 N·s·m⁻¹·kg⁻¹) than aerial runners. The results indicate that terrestrial runners displayed more efficient force production in the forward direction and displayed more “force‐oriented” F‐V profiles. Nevertheless, aerial runners were more effective in maintaining a net horizontal force production with increasing speed. Our results suggest that terrestrial runners could be more adapted to the specific short distance and high acceleration sprints running.

This study investigated the effect of jump landing direction and leg dominance on the Dynamic Postural Stability Index (DPSI) and the importance of the hamstring-to-quadriceps (H/Q) co-activation ratio. Fifteen female sports players performed unilateral jump landing, for the dominant (DL) and the non-dominant (NDL) legs in anterior (AJL), lateral (LJL), and vertical directions (DJL). The results indicated that the DPSI was higher in DJL compared to LJL and AJL. Besides, the DPSI score during DJL was higher in NDL indicating lower stabilization capacity associated with a lower H/Q co-activation ratio. A significant correlation was found between H/Q co-activation ratio and DPSI in the DL during AJL (r = −0.57). Current results suggest that DJL was more appropriate to evaluate dynamic postural stability since it highlights limb asymmetry. In addition, H/Q co-activation appears to play an essential role in the effectiveness of ground reaction force stabilization during jump landing.