Aims: To compare the effects of 2 and 5 min of passive static stretching (SS) on stiffness and blood flow in the rectus femoris in adolescent athletes using shear wave elastography (SWE) and superb microvascular imaging (SMI).Material and methods: This prospective study included 20 male athletes with median age of 14.5 (12.5–16.5) years. The subjects were divided into two groups based on the SS duration as follows: 2 min (n=10) and 5 min (n=10). At rest and after 2 and 5 min of SS, stiffness and blood flow values were compared in the rectus femoris for each group. Inter-operator reliability was also analysed.Results: There was no significant difference between resting and 2 min of SS in terms of stiffness. The stiffness values decreased significantly from resting to 5 min of SS. The blood flow increased significantly from resting to 2 and 5 min of SS. Inter-operator reliability was moderate to perfect for SWE and SMI measurements (ICC: 0.52–0.83).Conclusions: SWE and SMI can be used to acquire reliable quantitative data about muscle stiffness and blood flow in adolescents. While stiffness parameters significantly decreased from resting after only 5 min, blood flow significantly increased both after 2 and 5 min. For physical rehabilitation protocols, 5 min of SS may be chosen to reduce stiffness. For competitions, 2 min of SS may be sufficient for warm-up exercise because it increases the blood flow optimally. Five min of SS may be preferred for the cool-down exercise to enhance recovery.

Th is study aims to investigate the eff ect of lower extremity (LE) injuries on bilateral hamstring eccentric strength imbalance (HSI) and to determine the relationship between body weight (BW) and HSI in young male soccer players. Eighty-eight young soccer players aged 14-19 in Turkey voluntarily participated in this study. Eccentric hamstring strength measurements were taken using a NordBord® Hamstring Testing Device. To obtain the LE backgrounds of the participants, individual interviews were administered to the players, and the obtained data were verifi ed through a review of previous injury records. While 22 (25%) out of 88 players reported LE injuries in the previous two years (injured players (IP)), the rest of them (75%) did not report any LE injuries (non-injured players (NP)). HSI values as peak forces were computed by extracting the weaker leg values from the stronger leg values. Both the Analysis of Variance (ANOVA) and the Analysis of Covariance (ANCOVA) were performed, controlling the BW eff ect in order to test the eff ects of LE injuries on HSI. Correlation analysis was also conducted, taking into consideration the previous research fi ndings on the relationship between body weight and strength variables. Th ere was signifi cant relationship between BW and HSI ((p<0.05) (0.04> r >0.02)) and non-signifi cant results for HSI (F (1.85) =0.578, p>0.05). However, the eff ect of BW was signifi cant for HSI (F (1.85) =3.91, p<0.05, η2 = 0.068). Th is study supported the hypothesis that hamstring muscle strength imbalance is not aff ected by lower extremity injuries and that body weight is a factor that may aff ect strength imbalance.

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Objective: Self-myofascial release (SMR) and static stretching (SS) are common precompetition applications, aiming at relaxing muscles and surrounding fasciae. However, assessments of their effects on the targeted agonistic muscles and possible effects on antagonistic muscles are lacking. Based on myofascial force transmission, we hypothesized that effects of SMR and SS are (1) different on agonistic (knee flexors) and ( 2) non-trivial on the antagonistic (knee extensors) thigh muscles. Materials and Methods: Twenty-two healthy males (24,05±4,01 years old) were randomly divided into two groups (SS and SMR, n=11 each). The groups were interchanged seven days later (cross-over design). After a stationary bicycle warm-up, isometric strength testing was performed (pre-condition), followed by the SMR or SS procedures consisted of four consequtive applications with 1 minute of durations. After 10 mins, the testing was repeated (post-condition). Results: SS significantly increased torque increase rate (flexors, 18.4%) and average torque (extensors, 4.9 %). SMR caused significant average torque increase (flexors, 6.6%) and time to peak torque (extensors, 16.7%). The change in agonists torque increase rate over time was significantly different between groups (time*group interaction effect [ANOVA], p<0.05). Conclusions: SMR affected force production and SS affected the speed of contraction positively for the knee flexors, and SS affected force production positively for the knee extensors. However, SMR has a negative effect on the speed of contraction of the knee extensors. Widespread effects are ascribed to myofascial force transmission. Although both are utilized for same purpose they can not be regarded as interchangeable methods.