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(1) Background: Among the myriad of injuries affecting football players, hamstring strains have emerged as a persistent and debilitating concern, underscoring the need for novel approaches to reduce strain rates. The current study aims to analyze the impact of improved running technique on reducing hamstring injuries in football players. (2) Methods: Twenty-two male < 19 years old footballers were randomly assigned to an intervention and a control groups (n = 14 vs. 8), the former performing a running technique program of six weeks. Three-dimensional kinematics, using a markerless motion capture system, assessed linear and angular variables during touchdown and toe-off instants to evaluate pre- and post-intervention. Independent and repeated measure t-tests and effect size calculations were employed. (3) Results: A decrease in hip flexion and thorax external rotation during the touchdown (−2.39° and −2.02°, p ≤ 0.05) and a decrease in pelvic external rotation and an increase in stride length (−3.22° and 0.06 m, p ≤ 0.05) during toe-off for the players that engaged in the running technique development was observed. (4) Conclusions: These findings emphasize the significant impact of improved running technique and sprint mechanics, suggesting a potential decrease in the risk of hamstring injuries during high-speed running in football players. [ABSTRACT FROM AUTHOR]

Purpose: Sprint kinematics have been linked to hamstring injury and performance. This study aimed to examine if a specific 6-week multimodal intervention, combining lumbopelvic control and unning technique exercises, induced changes in pelvis and lower-limb kinematics at maximal speed and improved sprint performance. Methods: Healthy amateur athletes were assigned to a control or intervention group (IG). A sprint test with 3-dimensional kinematic measurements was performed before (PRE) and after (POST) 6 weeks of training. The IG program included 3 weekly sessions integrating coaching, strength and conditioning, and physical therapy approaches (eg, manual therapy, mobility, lumbopelvic control, strength and sprint "front-side mechanics"-oriented drills). Results: Analyses of variance showed no between-group differences at PRE. At POST, intragroup analyses showed PRE–POST differences for the pelvic (sagittal and frontal planes) and thigh kinematics and improved sprint performance (split times) for the IG only. Specifically, IG showed (1) a lower anterior pelvic tilt during the late swing phase, (2) greater pelvic obliquity on the free-leg side during the early swing phase, (3) higher vertical position of the front-leg knee, (4) an increase in thigh angular velocity and thigh retraction velocity, (5) lower between-knees distance at initial contact, and (6) a shorter ground contact duration. The intergroup analysis revealed disparate effects (possibly to very likely) in the most relevant variables investigated. Conclusion: The 6-week multimodal training program induced clear pelvic and lower-limb kinematic changes during maximal speed sprinting. These alterations may collectively be associated with reduced risk of muscle strain and were concomitant with significant sprint performance improvement. [ABSTRACT FROM AUTHOR]

This study (a) evaluated the sex-specific kinetic and kinematic outcomes underpinning change of direction (COD) performance, (b) compared these outcomes across 3 different COD tests, and (c) examined the sex-specific and test-specific outcome most strongly related to COD performance in basketball players. Thirty young basketball players (17 males and 13 females) competing at the national level were assessed for the modified 505 test, modified T test, and V-cut test. The Local Positioning System technology (WIMU PRO, Realtrack Systems S.L., Almería, Spain) was used to measure the maximum values of acceleration (ACCmax), deceleration (DECmax), velocity (VELmax), and centripetal force (CentFmax) in each COD test. Male players displayed greater ACCmax, VELmax, DECmax, and CentFmax outputs for each section of the 505 test, T test, and V-cut test (all p < 0.05), resulting in a faster COD performance than females across tests (all ES > -1.42; 95% CI = -3.45 to -0.57). The 505 test demanded significantly greater kinematic outputs than T test and V-cut test for both sexes (p < 0.01). The ACCmax explained ~26-58% of the variability in COD time for males across tests (p < 0.05) and 40% in females' modified 505-test time (p < 0.05). Likewise, in females, DECmax explained 38% of the modified T-test time variability, whereas VELmax explained 53% in the V-cut test time (both p < 0.05). These findings suggest that (a) COD data should not be used interchangeably across sexes, (b) test specificities should be considered for designing COD training, and (c) the kinematic outcomes explaining COD performance might vary across sexes. [ABSTRACT FROM AUTHOR]

Purpose: Ballet dancers are required to achieve performance feats such as exciting and dramatic elevations. Dancers with a greater jump height can perform a wider range of skills during their flight time and implement more specific technical skills related to the aesthetic components of a dance choreography. New findings suggest the relationship between force and velocity mechanical capabilities (F-V profile) as an important variable for jumping performance. A new field method based on several series of loaded vertical jumps provides information on the theoretical maximal force, theoretical maximal velocity, theoretical maximal power, and the imbalance between force and velocity (F-VIMB). The purpose of this study was to observe the effects of 9 wk of individualized F-V profile-based training during countermovement jumps (CMJs) in female ballet dancers. Methods: CMJ and mechanical outputs of 46 dancers (age = 18.9 [1.1] y, body mass = 54.8 [6.1] kg, height = 163.7 [8.4] cm) were estimated in a pre–post intervention. The control group (10 participants) continued with the standardized training regimen (no resistance training), whereas the experimental group (36 participants) performed 2 sessions over 9 wk of a training plan based on their F-V profile. Results: The experimental group presented significant differences with large effect sizes in CMJ height (29.3 [3.2] cm vs 33.5 [3.72] cm), theoretical maximal force (24.1 [2.2] N/kg vs 29.9 [2.8] N/kg), and theoretical maximal velocity (4 [0.6] m/s vs 3.2 [0.5] m/s). Significant differences with a very large effect size were found in F-VIMB (43.8% [15.3%] vs 24.9% [8.7%]). Conclusion: A training program addressing F-VIMB is an effective way to improve CMJ height in female ballet dancers. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze the influence of age and sex on kinematic gait parameters in preschool children, and derive reference values for this population. A total of 383 preschool children (age 3–5 years; 207 girls, 176 boys) participated in this study. We used the OptoGait system to assess the kinematics of gait at a comfortable and self-determined speed. No significant differences between the sexes were found for the main gait parameters. Among the participants, there was a significant increase in double support, reductions in absolute cadence and the coefficient of variation (CV) of cadence, an increase in absolute step length (SL), and an increase in the walk ratio (WR) from 3 to 5 years of age. However, the normalized SL and normalized WR displayed a significant reduction in both sexes. Partial correlation indicated a significant association of age with SL and normalized SL, and WR. Additionally, WR showed a significant correlation with the CV of cadence. To summarize, no relevant differences in gait performance were found according to sex; however, age was found to influence gait maturation. The normative values established for Spanish preschool children can be used to monitor healthy gait development. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the reliability and validity of a simple computation method to evaluate force (F), velocity (v), and power (P) output during a countermovement jump (CMJ) suitable for use in field conditions and to verify the validity of this computation method to compute the CMJ force-velocity (F-v) profile (including unloaded and loaded jumps) in trained athletes. Methods: Sixteen high-level male sprinters and jumpers performed maximal CMJs under 6 different load conditions (0-87 kg). A force plate sampling at 1000 Hz was used to record vertical ground-reaction force and derive vertical-displacement data during CMJ trials. For each condition, mean F, v, and P of the push-off phase were determined from both force-plate data (reference method) and simple computation measures based on body mass, jump height (from flight time), and push-off distance and used to establish the linear F-v relationship for each individual. Results: Mean absolute bias values were 0.9% (± 1.6%), 4.7% (± 6.2%), 3.7% (± 4.8%), and 5% (± 6.8%) for F, v, P, and slope of the F-v relationship (SFv), respectively. Both methods showed high correlations for F-v-profile-related variables (r = .985-.991). Finally, all variables computed from the simple method showed high reliability, with ICC >.980 and CV <1.0%. Conclusions: These results suggest that the simple method presented here is valid and reliable for computing CMJ force, velocity, power, and F-v profiles in athletes and could be used in practice under field conditions when body mass, push-off distance, and jump height are known. [ABSTRACT FROM AUTHOR]

This study determines whether maximal voluntary ankle plantar flexor torque could be more accurately represented using a torque generator that is a function of both knee and ankle kinematics. Isovelocity and isometric ankle plantar flexor torques were measured on a single participant for knee joint angles of 111° to 169° (approximately full extension) using a Contrex MJ dynamometer. Maximal voluntary torque was represented by a 19-parameter two-joint function of ankle and knee joint angles and angular velocities with the parameters determined by minimizing a weighted root mean square difference between measured torques and the two-joint function. The weighted root mean square difference between the two-joint function and the measured torques was 10 N-m or 3% of maximum torque. The two-joint function was a more accurate representation of maximal voluntary ankle plantar flexor torques than an existing single-joint function where differences of 19% of maximum torque were found. It is concluded that when the knee is flexed by more than 40°, a two-joint representation is necessary. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the relationship between movement velocity and relative load in three lower limbs exercises commonly used to develop strength: leg press, full squat and half squat. The percentage of one repetition maximum (%1RM) has typically been used as the main parameter to control resistance training; however, more recent research has proposed movement velocity as an alternative. Fifteen participants performed a load progression with a range of loads until they reached their 1RM. Maximum instantaneous velocity (Vmax) and mean propulsive velocity (MPV) of the knee extension phase of each exercise were assessed. For all exercises, a strong relationship betweenVmaxand the %1RM was found: leg press (r2adj = 0.96; 95% CI for slope is [−0.0244, −0.0258],P < 0.0001), full squat (r2adj = 0.94; 95% CI for slope is [−0.0144, −0.0139],P < 0.0001) and half squat (r2adj = 0.97; 95% CI for slope is [−0.0135, −0.00143],P < 0.0001); for MPV, leg press (r2adj = 0.96; 95% CI for slope is [−0.0169, −0.0175],P < 0.0001, full squat (r2adj = 0.95; 95% CI for slope is [−0.0136, −0.0128],P < 0.0001) and half squat (r2adj = 0.96; 95% CI for slope is [−0.0116, 0.0124],P < 0.0001). The 1RM was attained with a MPV andVmaxof 0.21 ± 0.06 m s−1and 0.63 ± 0.15 m s−1, 0.29 ± 0.05 m s−1and 0.89 ± 0.17 m s−1, 0.33 ± 0.05 m s−1and 0.95 ± 0.13 m s−1for leg press, full squat and half squat, respectively. Results indicate that it is possible to determine an exercise-specific %1RM by measuring movement velocity for that exercise. [ABSTRACT FROM AUTHOR]

Background: The differences and relationship between joint stiffness and leg stiffness can be used to characterize the lower limb behavior during different walking speeds.Research Question: This study aimed to investigate the differences in whole leg and lower limb joint stiffness at different walking speeds and the interactions between leg and lower limb joint stiffness.Methods: Twenty-seven healthy adults, seventeen males (age: 19.6 ± 2.2 years, height: 176.0 ± 6.0 cm, mass: 69.7 ± 8.9 kg), and ten females (age: 19.1 ± 1.9 years, height: 164.0 ± 3.0 cm, mass: 59.6 ± 3.8 kg), were recruited. Dynamic leg and joint stiffness were calculated during eccentric loading from data recorded using 3D infrared motion analysis and force plates at slow, normal, and fast walking speeds. Differences in dynamic stiffness, joint angles and moments were explored between the walking speeds using Repeated Measures ANOVA with Sidak post-hoc tests. Correlations between leg, joint stiffness, and walking speed were also explored.Results: The results indicated that the leg dynamic stiffness is decreased by walking speed, however, hip and ankle joint stiffness were increased (p < 0.001) and knee stiffness was unaffected. Leg stiffness showed no correlation with hip, knee, or ankle stiffness. A positive significant correlation was seen between hip and ankle stiffness (p < 0.01) and between knee and ankle stiffness (p < 0.001), however, no correlation was seen between hip and knee stiffness.Significance: These results suggest leg stiffness is not associated with lower limb joint stiffness during eccentric loading. This provides new information on the responses of ankle, knee and hip joint stiffness to walking speed. [ABSTRACT FROM AUTHOR]