RECTUS FEMORIS MECHANICS IN RUGBY KICKING

This study aimed to quantify rectus femoris muscle-tendon unit length and excitation during different types of rugby kick. Seven male rugby players completed a series of kicks during which kinematic and muscle excitation data were collected. Between 0.2 and 0.1 s prior to ball contact in all kick types, the rectus femoris lengthened rapidly whilst muscle excitation also rapidly increased, identifying eccentric action as a possible mechanism for muscle strain injury. Peak rectus femoris muscle excitations occurred later in the kicks with a primary height demand, and differences in the timing of peak muscle excitation existed between different regions of the rectus femoris muscle. This study provides information which can be used to inform the specificity of physical preparation and rehabilitation protocols for rugby kickers

Specificity of jumping, acceleration and quick change of direction motor abilities in soccer players

The purpose of this study was to determine the underlying structure of stretch-shortening cycle (SSC) jumping, acceleration and change-of-direction (COD) abilities in soccer players using principal component factor analysis (PCA). Based on the results of recent studies on male college athletes, we hypothesized that slow SSC jumping, acceleration and COD represent independent motor abilities in soccer players. Forty two soccer players (23.2±2.36 yr) performed three tests for each group of rapid lower-body movements: a) three vertical slow SSC jumping tests - squat jump (SJ), countermovement jump (CMJ) and arm swing countermovement jump (CMJAS), b) three acceleration tests - 5, 10 and 15 meter sprint times (ACC5, ACC10 and ACC15), and c) three COD tests - modified agility test free (MATF), the 505 agility test (505) and 20 yard agility test (Y20). PCA was applied to establish the relationships among the factors (i.e. the motor abilities) underlying the included manifest variables (i.e. the performance tests). This procedure reduced all variables to a smaller number of independent latent dimensions. The results indicated three separate factors that may correspond to slow SSC jumping, acceleration and COD abilities. The magnitude of the correlation coefficients among the three motor abilities extracted was r<.56. Therefore, it is suggested that slow SSC jumping, acceleration and COD abilities represent independent motor abilities and consequently these should be trained and evaluated separately to assess soccer players’ physical profiles

Muscle and intensity based hamstring exercise classification in elite female track and field athletes: implications for exercise selection during rehabilitation

Background: Hamstring injuries are common in many sports, including track and field. Strains occur in different parts of the hamstring muscle but very little is known about whether common hamstring loading exercises specifically load different hamstring components. The purpose of this study was to investigate muscle activation of different components of the hamstring muscle during common hamstring loading exercises. Methods: Twenty elite female track and field athletes were recruited into this study, which had a single-sample, repeated-measures design. Each athlete performed ten hamstring loading exercises, and an electromyogram (EMG) was recorded from the biceps femoris and semitendinosus components of the hamstring. Hamstring EMG during maximal voluntary isometric contraction (MVIC) was used to normalize the mean data across ten repetitions of each exercise. An electrogoniometer synchronized to the EMG was used to determine whether peak EMG activity occurred during muscle-tendon unit lengthening, shortening, or no change in length. Mean EMG values were compared between the two recording sites for each exercise using the Student’s t-test. Results: The lunge, dead lift, and kettle swings were low intensity (<50% MVIC) and all showed higher EMG activity for semitendinosus than for biceps femoris. Bridge was low but approaching medium intensity, and the TRX, hamstring bridge, and hamstring curl were all medium intensity exercises (≥50% or <80% MVIC). The Nordic, fitball, and slide leg exercises were all high intensity exercises. Only the fitball exercise showed higher EMG activity in the biceps femoris compared with the semitendinosus. Only lunge and kettle swings showed peak EMG in the muscle-tendon unit lengthening phase and both these exercises involved faster speed. Conclusion: Some exercises selectively activated the lateral and medial distal hamstrings. Low, medium, and high intensity exercises were demonstrated. This information enables the clinician, strength and conditioning coach and physiotherapist to better understand intensity- and muscle-specific activation during hamstring muscle rehabilitation. Therefore, these results may help in designing progressive strengthening and rehabilitation and prevention programs

Relationships between sprinting, agility, one- and two-leg vertical and horizontal jump in soccer players

The aim of this study was to profile physical characteristics of soccer players measured by acceleration, vertical jump (VJ), horizontal jump (HJ) and change of direction ability (CODA) tests, and to quantify the relationships between these characteristics. Additionally, leg asymmetries between the dominant and nondominant legs during unilateral VJ and HJ were assessed. Thirty-nine male soccer players (22.9±2.8 years, 179.9±6.01 cm, 77.0±8.3 kg), competing in the third division of the Spanish Soccer League, participated in this study. Soccer experience of these players amounted to 15.19±3.15 years. Significant moderate correlations (p<.05) were found between all HJ tests and the modified agility (MAT) or the 505 test, and between all VJ tests and the Y20 or the 505 test. The significant differences between the dominant and non-dominant legs were found for the horizontal drop jump test (p=.001, d=.66) and horizontal three jump test (p=.017, d=.33). No significant differences between the dominant and non-dominant legs were found for VJ tests. The correlation between jumping and CODA varied depending on the characteristics of test types. The significant leg asymmetry in horizontal jumps with bounds found in the present study suggests that soccer players have greater leg asymmetries in the horizontal jump than in the vertical jump

Exploring the Role of Sprint Biomechanics in Hamstring Strain Injuries: A Current Opinion on Existing Concepts and Evidence

Hamstring strain injuries are one of the most common injuries in sprint-based sports with the mechanism of injury considered the result of an interaction between applied mechanical strain and the capacity of the muscle to tolerate strain. To date, injury prevention and rehabilitation strategies have frequently focused on enhancing the capacity of the hamstrings to tolerate strain, with little consideration of factors directly influencing mechanical strain. Sprint running biomechanics are one factor proposed to influence the mechanical strain applied to the hamstrings that may be modified (towards reduced strain) within rehabilitation and injury prevention programs. This article aims to explore the theoretical mechanistic link between sprint running mechanics and hamstring strain injury, along with the available supporting evidence. In doing so, it hopes to provide practitioners with an understanding of mechanical parameters that may influence hamstring strain injury whilst also identifying areas for further research exploration

Sprint versus isolated eccentric training: Comparative effects on hamstring architecture and performance in soccer players

Aims The purpose of this study was to compare the effects of hamstring eccentric (NHE) strength training versus sprint training programmed as complements to regular soccer practice, on sprint performance and its mechanical underpinnings, as well as biceps femoris long head (BFlh) architecture. Methods In this prospective interventional control study, sprint performance, sprint mechanics and BFlh architecture variables were compared before versus after six weeks of training during the first six preseason weeks, and between three different random match-pair groups of soccer players: “Soccer group” (n = 10), “Nordic group” (n = 12) and “Sprint group” (n = 10). Results For sprint performance and mechanics, small to large pre-post improvements were reported in “Sprint group” (except maximal running velocity), whereas only trivial to small negative changes were reported in “Soccer group” and “Nordic group”. For BFlh architecture variables, “Sprint” group showed moderate increase in fascicle length compared to smaller augment for the “Nordic” group with trivial changes for “Soccer group”. Only “Nordic” group presented small increases at pennation angle. Conclusions The results suggest that sprint training was superior to NHE in order to increase BFlh fascicle length although only the sprint training was able to both provide a preventive stimulus (increase fascicle length) and at the same time improve both sprint performance and mechanics. Further studies with advanced imaging techniques are needed to confirm the validity of the findings.info:eu-repo/semantics/publishedVersio

Can we modify maximal speed running posture? Implications for performance and hamstring injury management

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.</p

Effects of Different Agility Training Programs among First-Grade Elementary School Students

The aim of the study was to determine which agility training program (low, moderate or high contextual interference) was more effective in fi rst-grade primary school students to provide reliable information to physical education teachers for designing more effective agility programs. A total of 57 fi rst-grade elementary school students participated in the present study. They were randomized into three groups to compare the effects of three different agility training programs based on contextual interference: low contextual interference (N=19), moderate contextual interference (N=19), and high contextual interference (N=19). Contextual interference refers to the relative amount of interference created when integrating two or more tasks into a particular aspect of a training session. Signifi cant improvements in agility were found in the low (p<0.01, ES=1.79) and moderate (p<0.05, ES=0.61) contextual interference groups after a 4-week training period. These improvements were higher in the low contextual interference group. The high contextual interference group showed no improvements (p>0.05, ES=0.28) after the intervention program. Our results suggested that the low contextual interference program is still more effective than the moderate contextual interference program in this group of primary school students

Level of hamstrings damage depending on force-generating capacity and creatine kinase activity

The aim of the present study was to categorize the eccentric exercise-induced hamstrings damage by using easy measurable markers such as force-generating capacity and serum creatine kinase activityPeer ReviewedPostprint (published version

Sprint Acceleration Mechanics in Fatigue Conditions: Compensatory Role of Gluteal Muscles in Horizontal Force Production and Potential Protection of Hamstring Muscles

Aim: Hamstring muscle injury is the main injury related to sports requiring sprint acceleration. In addition, hamstring muscles have been reported to play a role in horizontal force production during sprint acceleration performance. The aim of the present study was to analyze (i) the determinants of horizontal force production and (ii) the role of hip extensors, and hamstring muscles in particular, for horizontal force production during repeated sprint-induced fatigue conditions.Method: In this experimental laboratory setting study including 14 sprint-trained male athletes, we analyzed (i) the changes in sprint mechanics, peak torque of the knee and hip extensors and flexors, muscle activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus, and sagittal plane lower limb motion, before and after twelve 6-s sprints separated by 44 s rest on an instrumented motorized treadmill, and (ii) the determinants of horizontal force production (FH) during the sprint acceleration in a fatigue state (after 12 sprints).Results: The repeated-sprint protocol induced a decrease in maximal power output (Pmax) [-17.5 ± 8.9%; effect size (ES): 1.57, large] and in the contact-averaged horizontal force component (FH) (-8.6 ± 8.4%; ES: 0.86, moderate) but not meaningful changes in the contact-averaged resultant (total) force (FTot) (-3.4 ± 2.9%; ES: 0.55, small) and vertical force component (FV) (-3.1 ± 3.2%; ES: 0.49, small). A decrease was found in concentric peak torque of the knee flexors and extensors and in gluteus and vastus lateralis muscle activity during entire swing and end-of-swing phase. An increase was found in contact time and swing time, while step frequency and knee speed before ground contact decreased. Muscular determinants associated with FH and its decrease after the repeated-sprint protocol were concentric peak torque of the hip extensors (p = 0.033) and a decrease in gluteus maximus activity at the end-of-swing (p = 0.007), respectively.Conclusion: Sprint-induced fatigue lead to changes in horizontal force production muscular determinants: hamstring muscle seems not to have the same role than in non-fatigue condition. Horizontal force production seems to be more dependent on the hip extensors and gluteus maximus function. Given the fatigue-induced decrease in hamstring muscle strength, we can hypothesize that muscle compensatory and kinematic strategies reported in a fatigued state could be an adaptation to allow/maintain performance and a protective adaptation to limit hamstring muscles constraints