EFFECTS OF VEST LOADING ON SPRINT RUNNING BIOMECHANICS

The study investigated the influence of vest loading on relative GRF’s during maximum velocity sprinting, and determined the relationship between flight times and relative vertical GRF’s. As a vertical vector-training stimulus, vest loading decreased flight times and vertical GRFs. Vertical loading does not seem to produce desirable effects on sprinting performance or GRFs

CARRYING A BALL CAN INFLUENCE SIDESTEPPING MECHANICS IN RUGBY

Sidestepping mechanics have been implicated as a risk factor for knee injury in rugby. Carrying a ball is proposed to alter movement patterns. Therefore the purpose of the study was to examine the effects of sidestepping with a ball compared to sidestepping without a ball on lower-extremity biomechanics in male rugby athletes. Three-dimensional kinematics of 18 male rugby athletes were recorded during a maximal effort 45° sidestepping task without and with a ball. Sidestepping with a ball resulted in 15% greater knee adduction angle during weight acceptance and 18% greater hip adduction angle during peak pushoff than without a ball. Future biomechanical evaluations of athletes require the inclusion of the ball specific to the sport to ensure accurate interpretation of movement patterns

MEASUREMENT OF STRIKING IMPACT KLNETKS VIA INERTIAL MODELLING AND ACCELEROMETRY

Striking impact has teen explored repeatedly in combat sports. The majority of methods used in the literature require intricate equipment. This study implemented a novel and simple method of measuring impact kinetics using a common, commercially available striking bag. Impulse and peak force of impacts were determined, with reliability and validity statistics obtained from multiple impacts with a custom ballistic pendulum. Test-retest reliability calculations determined that all measures had acceptable reliability (CVI less than/ equal to 2.4%). Using linear regression modelling, the coefficient of determination scores displayed a good fit for the model (R exponent 2 greater than / equal to 0.96) when plotted with a spectrum of pendulum masses. This novel method represents a reliable and valid approach to measuring striking impact kinetics which is easily adaptable to any type of hanging striking target

The Influence of Head Impact Threshold for Reporting Data in Contact and Collision Sports: Systematic Review and Original Data Analysis

- Background - Head impacts and resulting head accelerations cause concussive injuries. There is no standard for reporting head impact data in sports to enable comparison between studies. - Objective - The aim was to outline methods for reporting head impact acceleration data in sport and the effect of the acceleration thresholds on the number of impacts reported. - Methods - A systematic review of accelerometer systems utilised to report head impact data in sport was conducted. The effect of using different thresholds on a set of impact data from 38 amateur senior rugby players in New Zealand over a competition season was calculated. - Results - Of the 52 studies identified, 42 % reported impacts using a >10-g threshold, where g is the acceleration of gravity. Studies reported descriptive statistics as mean ± standard deviation, median, 25th to 75th interquartile range, and 95th percentile. Application of the varied impact thresholds to the New Zealand data set resulted in 20,687 impacts of >10 g, 11,459 (45 % less) impacts of >15 g, and 4024 (81 % less) impacts of >30 g. Discussion Linear and angular raw data were most frequently reported. Metrics combining raw data may be more useful; however, validity of the metrics has not been adequately addressed for sport. Differing data collection methods and descriptive statistics for reporting head impacts in sports limit inter-study comparisons. Consensus on data analysis methods for sports impact assessment is needed, including thresholds. Based on the available data, the 10-g threshold is the most commonly reported impact threshold and should be reported as the median with 25th and 75th interquartile ranges as the data are non-normally distributed. Validation studies are required to determine the best threshold and metrics for impact acceleration data collection in sport. Conclusion Until in-field validation studies are completed, it is recommended that head impact data should be reported as median and interquartile ranges using the 10-g impact threshold

Lower Limb Mechanical Properties: Significant References Omitted

International audienceWe read with attention the recent narrative literature review by Pearson and McMahon [1]. We were very surprised and quite disappointed by the amount of relevant literature omitted by the authors on lower limb mechanical properties and, specifically, how ‘limb stiffness’ could affect performance and risk of injury. Although this review focuses on muscle-tendon unit (MTU) stiffness, the more global vertical, leg and joint stiffness (i.e. referred to as limb stiffness, collectively) are also reviewed, as the authors assume that limb stiffness is primarily controlled by MTU stiffness

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

Relationship between vertical and horizontal force-velocity-power profiles in various sports and levels of practice

This study aimed (i) to explore the relationship between vertical (jumping) and horizontal (sprinting) force–velocity–power (FVP) mechanical profiles in a large range of sports and levels of practice, and (ii) to provide a large database to serve as a reference of the FVP profile for all sports and levels tested. A total of 553 participants (333 men, 220 women) from 14 sport disciplines and all levels of practice participated in this study. Participants performed squat jumps (SJ) against multiple external loads (vertical) and linear 30–40 m sprints (horizontal). The vertical and horizontal FVP profile (i.e., theoretical maximal values of force (F0), velocity (v0), and power (Pmax)) as well as main performance variables (unloaded SJ height in jumping and 20-m sprint time) were measured. Correlations coefficient between the same mechanical variables obtained from the vertical and horizontal modalities ranged from −0.12 to 0.58 for F0, −0.31 to 0.71 for v0, −0.10 to 0.67 for Pmax, and −0.92 to −0.23 for the performance variables (i.e, SJ height and sprint time). Overall, results showed a decrease in the magnitude of the correlations for higher-level athletes. The low correlations generally observed between jumping and sprinting mechanical outputs suggest that both tasks provide distinctive information regarding the FVP profile of lower-body muscles. Therefore, we recommend the assessment of the FVP profile both in jumping and sprinting to gain a deeper insight into the maximal mechanical capacities of lower-body muscles, especially at high and elite levels

Relationship of Pre-season Training Load With In-Season Biochemical Markers, Injuries and Performance in Professional Soccer Players

IntroductionThere is controversy in the literature in regards of the link between training load and injury rate. Thus, the aims of this non-interventional study were to evaluate relationships between pre-season training load with biochemical markers, injury incidence and performance during the first month of the competitive period in professional soccer players.Materials and MethodsHealthy professional soccer players were enrolled in this study over two pre-season periods. Data sets were available from 26 players during the first season (2014–2015) and 24 players during the second season (2015–2016) who completed two pre-season periods (6 weeks each). External training load was assessed from all athletes during training using Global Positioning System (GPS). Internal training load was monitored after each training session using rate of perceived exertion (RPE). Before and after each pre-season, blood samples were taken to determine plasma lactate dehydrogenase (LDH), creatine kinase (CK) and C-reactive protein (CRP). Injury incidence and overall performance (ranking of the team after the first five official games of the championship) were recorded for both seasons separately.ResultsThere was no statistically significant difference in mean RPE values of the two-preparation periods (2737 ± 452 and 2629 ± 786 AU, p = 0.492). The correlational analysis did not reveal significant associations between internal and external training load (RPE and GPS data) and biological markers. There was a significant positive correlation between RPE and LDH during the 2015/2016 season (r = 0.974, p = 0.001). In addition, a significant negative correlation was found between total distance &gt;20 km/h and CRP during the 2015–2016 season (r = -0.863, p = 0.027). The injury rates for the two seasons were 1.76 and 1.06 per 1000 h exposure for the 2014–2015 and 2015–2016 seasons, respectively (p = 0.127).ConclusionOur study showed that pre-season training load is not associated with overall team performance. This association is most likely multifactorial and other factors (e.g., technical and tactical level of the team, opponents, environment) may play an important role for the collective team performance. Our findings may help coaches to better prepare their athletes during pre-season

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

Risk factors, assessments and prevention of muscle strain injuries

The relationships between mechanical stiffness, eccentric exercise and muscle strain injury are emerging areas of interest to researchers. For example, asymmetries between lower body limbs during athletic movements (i.e. ground reaction forces or mechanical stiffness) are thought to increase the risk of injury and compromise performance. The first two chapters of this PhD reviewed the literature on the topics of mechanical stiffness, and the effects of eccentric exercise on optimum length for force development. Both chapters included implications for muscle strain injuries. The third chapter reviewed the previous literature that has investigated the effects of eccentric exercise on hamstring injury rates. The interventions used were critiqued, and new eccentric exercises and interventions were introduced. The following four chapters included experimental research on: first) the effects of running velocity on running kinetics (e.g. vertical and leg stiffness) (i.e. chapter 5); second) relationships between hamstring injuries and leg asymmetries during running (i.e. chapter 6); third) the relationships between training background and optimum length, and fascicle length (i.e. chapter 7); forth) a case study on an eccentric exercise intervention for a previously injured athlete (i.e. chapter 8); and, finally) the effects of eccentric exercise on the optimum angle (knee flex ors and extensors) and injury occurrence in professional soccer players (i.e. chapter 9). The purpose of chapter 5 was to investigate the effects of running velocity of running kinetics and kinematics in Australian Rules football players. Sixteen semiprofessional Australian football players participated in this study. The subjects performed running bouts at 40%, 60%, 80% and 100% of their maximum velocity on a Woodway non-motorized treadmill. The variables of interest included: vertical force (Fv), relative veriical force (RFv), vertical stiffness, leg stiffness, horizontal force (Fb), relative horizontal force (RFb), contact times, impulse, stride frequency and stride length. As running velocity increased from 40% to 60%, RF v and RF h increased by 14.3% ((Effect Size (ES)= 1.0)) and 34.4% (ES= 4.2) respectively. The changes in RFv and RFh from 60% to 80% were 1.0% (ES= 0.05) and 21.0% (ES= 2.9). And finally, the changes in RFv and RFh from 80% to maximum were 2.0% (ES = 0.1) and 24.3% (ES= 3.4) respectively. The total increase in RFh from the slowest running speed (i.e. 40% max) to maximum was 102.0% (ES= 9.3). Vertical stiffness significantly increased between each increasing running velocity (p \u3c 0.05) while leg stiffness remained constant. Both stride frequency and stride length significantly increased with each increasing velocity (p \u3c 0.05). Conversely contact times, impulse and the vertical displacement of the center of mass significantly decreased with running velocity (p \u3c 0.05). A significant positive correlation was found between Fh and maximum running velocity (r = 0.4 7). For the kinematic variables, only stride length was found to have a significant positive correlation with maximum running velocity (r = 0.66). It would seem that increasing maximal sprint velocity may be more dependent on horizontal force prodnction as apposed to vertical force production. The purpose of chapter 6 was to quantify the magnitnde of leg asymmetry in kinetic and kinematic variables during running in non-injured and previously injured Australian Rules football (ARF) players. The players included a group of non-injured ARF players (n = II) and a group of previously injured ARF players (n = 11; hamstring injuries only). The players in the injured group had at least one acute hamsh·ing injury in the previous two years. The legs of the non-injured players were classified as dominant and non-dominant whereas the legs of the injured players were classified as injured or non-injured. The players ran on a non-motorized force h·eadmill at approximately 80% of their maximum velocity (Vmax). For the noninjured players, there were no significant differences between dominant and nondominant legs for any of the variables. For the injured players, the only variable that was significantly (p\u3c0.001) different between the injured and non-injured leg was horizontal force production (175 ± 30 vs. 324 ± 44 N). Furthermore, the injured leg (injured group) produced significantly less (30.2% and 33.9%) horizontal force than either legs (dominant and non-dominant legs) of the non-injured group, and the noninjured leg produced significantly more (18.2% and 22.5%) horizontal force than either legs of the non-injured group. In the present study, hamstring injures appeared to have an influence on leg asymmetry in horizontal but not vertical force production during running at sub-maximal velocities. The purpose of chapter 7 was to investigate differences in optimum angle of peak torque (knee extensors and flexors) and muscle architecture ( vastus lateralis) between nine cyclists and nine Australian Rules Football (ARF) players. The angles of peak torque of the ARF players were significantly (p\u3c0.05) greater during knee extension 70.8 ± 3.5° vs. 66.6 ± 5.9° and smaller during knee flexion 26.2 ± 2.9° vs. 32.3 ± 3.8° compared with the cyclists. The ARF players had significantly (P\u3c0.05) smaller pennation angles 19.3 ± 2.0° vs. 24.9 ± 2.5° and longer fascicle lengths 7.9 ± 0.7 cm vs. 6.2 ± 0.8 cm in comparison with the cyclists. There were no significant differences between groups in regards to muscle thickness or peak torque ratios between the quadriceps and hamstrings (Q/H ratio). Muscle architectural changes associated with resistance strength training need to be investigated so as the effects of training on architecture and functional perfonnance can be detennined. The purpose of chapter 8 was to present an eccentric exercise intervention, including multi-joint and closed chain exercises, for an Australian Football player with a history of acute hamstring injuries. The athlete was a 24 year old Australian Rules football player with a medical history of three hamstring muscle strain injuries to his right hamstring in the previous four years. After the first three phases of the intervention (i.e. nine weeks), the optimum angle of peak torque during knee flexion decreased from 37.3 to 23.9° in the injured leg, and from 24.3 to 20.3° in the healthy leg. After the first nine weeks, the optimum angles remained constant for another 23 weeks. The optimum angle of peak torque was also shifted in the knee extensors by 3.9° (injured leg) and 3.4° (healthy leg) after nine weeks and remained constant for the remaining 23 weeks. Quadriceps to hamstring peak torque ratio\u27s (Q/H ratios) and peak torque during knee flexion and extension remained constant throughout the intervention. An intervention consisting of multi-joint and closed-chain eccentric exercises can be safe and effective for altering the optimum angle of peak torque (i.e. shifting to longer muscle lengths), after acute hamstring injuries. The purpose of chapter 9 was to investigate the effects of eccentric exercise on injury occurrence (i.e. hamstrings and rectus femoris) and optimum angle of peak torque (i.e. knee flexors and extensors) in professional soccer players. Twenty three members of a Spanish Professional League soccer team (Division II) were randomly assigned to either an eccentric exercise intervention group (EG) or a control group (CG). Both groups performed regular soccer training during the four week study, which was conducted during the clubs pre-season. After the four weeks, the optimum angles of the knee flexors were significantly (p \u3c 0.05) decreased (i.e. increase in optimum length) by 2.0° in the CG and by 4.0° in the EG. The change in the EG was significantly different to the CG. The optimum angles of the knee extensors were significantly increased (i.e. increase in optimum length) in the EG only by 6.7°. Peak torque levels and ratios of quadriceps to hamstring (Q/H ratios) were not significantly altered throughout the study for either group. There were no injuries reported in the EG, but two rectus femoris muscle strain injuries reported in the CG. It appears that eccentric exercise can shift the optimum length of the knee flexors and extensors and these shifts may have a positive influence in reducing the incidence of injury