This study examined concurrent validity of countermovement vertical jump reactive strength index modified and force–time characteristics recorded using a 1-dimensional portable and laboratory force plate system. Twenty-eight men performed bilateral countermovement vertical jumps on 2 portable force plates placed on top of 2 in-ground force plates, both recording vertical ground reaction force at 1000 Hz. Time to takeoff; jump height; reactive strength index modified; and braking and propulsion impulse, mean net force, and duration were calculated from the vertical force from both force plate systems. Results from both systems were highly correlated (r ≥ .99). There were small (d < 0.12) but significant differences between their respective braking impulse, braking mean net force, propulsion impulse, and propulsion mean net force (P < .001). However, limits of agreement yielded a mean value of 1.7% relative to the laboratory force plate system (95% confidence limits, 0.9%–2.5%), indicating very good agreement across all of the dependent variables. The largest limits of agreement were for jump height (2.1%), time to takeoff (3.4%), and reactive strength index modified (3.8%). The portable force plate system provides a valid method of obtaining reactive strength measures, and several underpinning force–time variables, from unloaded countermovement vertical jump. Thus, practitioners can use both force plates interchangeably.
Jason Lake, Peter Mundy, Paul Comfort, John J. McMahon, Timothy J. Suchomel and Patrick Carden
Logan A. Lucas, Benjamin S. England, Travis W. Mason, Christopher R. Lanning, Taylor M. Miller, Alexander M. Morgan and Thomas Gus Almonroeder
Lower-extremity musculoskeletal injuries are common in sports such as basketball and soccer. Athletes competing in sports of this nature must maneuver in response to the actions of their teammates, opponents, etc. This limits their ability to preplan movements. The purpose of this study was to compare impact accelerations during preplanned versus unplanned lateral cutting. A total of 30 subjects (15 males and 15 females) performed preplanned and unplanned cuts while the authors analyzed impact accelerations using an accelerometer secured to their tibia. For the preplanned condition, subjects were aware of the movement to perform before initiating a trial. For the unplanned condition, subjects initiated their movement and then reacted to the illumination of one of 3 visual stimuli which dictated whether they would cut, land, or land-and-jump. A mixed-model analysis of variance with a between factor of sex (male and female) and a within factor of condition (preplanned and unplanned) was used to analyze the magnitude and variability of the impact accelerations for the cutting trials. Both males and females demonstrated higher impact accelerations (P = .01) and a trend toward greater intertrial variability (P = .07) for the unplanned cutting trials (vs preplanned cuts). Unplanned cutting may place greater demands on the musculoskeletal system.
Rafael F. Escamilla, Jonathan S. Slowik, Alek Z. Diffendaffer and Glenn S. Fleisig
The purpose of this study was to assess biomechanical differences among overhand, 3-quarter, and sidearm arm slot professional baseball pitchers. It was hypothesized that kinematic and kinetic differences would be found among the 3 groups, with sidearm pitchers demonstrating greater movement along the transverse plane and overhead pitchers demonstrating greater movement along the sagittal plane. Based upon arm slot angle at ball release, 30 overhand, 156 three-quarter, and 21 sidearm pitchers were tested using a 240-Hz motion analysis system, and 37 kinematic and kinetic parameters were calculated. One-way analyses of variance (α = .01) was employed to assess differences among groups. The comparisons showed the sidearm group had less shoulder anterior force, whereas the overhand group had the least elbow flexion torque. At ball release, trunk contralateral tilt and shoulder abduction were greatest for the overhand group and least for sidearm group. Additionally, the sidearm group demonstrated the lowest peak knee height, most closed foot angle, greatest pelvis angular velocity, and shoulder external rotation. The overhand group had the greatest elbow flexion at foot contact and greatest trunk forward tilt at ball release. The greater elbow flexion torque and shoulder external rotation exhibited by sidearm pitchers may increase their risk of labral injury. Conversely, the lower shoulder anterior force in sidearm pitchers may indicate lower stress on shoulder joint capsule and rotator cuff.
Roland van den Tillaar
The aims of this study were to investigate the effect of four different shooting techniques (slap, sweeper, drag, and wrist shots) in floorball on velocity and accuracy in experienced floorball players, and to investigate whether target height has an influence on these shooting performances. Ten experienced male floorball players (age, 21 ± 4 years; body mass, 81.5 ± 10 kg; body height, 1.85 ± 0.07 m; and years of experience, 6.9 ± 3.1 years) shot as hard as possible and tried to hit the upper and lower targets with four different shooting techniques from a 4-m distance. The main findings were that shooting techniques and target height could influence ball velocity in the expected way from slap to sweeper shots and drag to wrist shots, whereas accuracy did not change, and thereby, did not follow any velocity–accuracy trade-off like Fitts’ law.
Lydia R. Vollavanh, Kathleen M. O’Day, Elizabeth M. Koehling, James M. May, Katherine M. Breedlove, Evan L. Breedlove, Eric A. Nauman, Debbie A. Bradney, J. Eric Goff and Thomas G. Bowman
Quantifying head impacts is a vital component to understanding and preventing head trauma in sport. Our objective was to establish the frequency and magnitude of head impact mechanisms in men’s lacrosse athletes. Eleven male lacrosse athletes wore xPatch sensors during activity. Video footage of practices and games was analyzed to verify impacts and code them with impact mechanisms. The authors calculated incidence rates (IRs) per 1000 exposures with corresponding 95% confidence intervals (CIs) and used multivariate analysis of variances to compare the linear (g) and rotational (rad/s2) accelerations between mechanisms. A total of 167 head impacts were successfully verified and coded with a mechanism using video footage during 542 total exposures. The highest IR was head to body (IR = 118.08; 95% CI, 89.15–147.01), and the lowest was head to ball (IR = 3.69; 95% CI, 0–8.80) (incidence rate ratio = 32.00; 95% CI, 67.83–130.73). Analysis indicated that impact mechanism failed to significantly alter the combined dependent variables (multivariate F 10,306 = 1.79, P = .06, η 2 = .06, 1−β = 0.83). While head to head, body to head, and stick to head mechanisms are penalty-inducing offenses in men’s lacrosse, head to ground, head to ball, and combination impacts have similar head accelerations. If penalties and rules are created to protect players from traumatic head injury, the authors recommend stricter enforcement.
Melissa Hunfalvay and Nicholas Murray
The purpose of this study was to examine whether prior biped tennis playing experience results in different visual search strategies compared with no prior biped playing experience. A total of 32 wheelchair (WC) tennis players, 17 males and 15 females, ranked between 1 and 16 on the International Tennis Federation rankings participated in this study. Half the players had prior experience playing tennis as a biped player, and half had no prior experience in biped tennis. The athletes viewed 18 different serves from an expert WC player while their gaze was monitored using eye tracking. Results revealed significant differences between the groups in fixation duration and number of fixations. Differences were also found in fixation locations and durations across biomechanical phases of the serve. The WC only players had more fixations for shorter periods than did WC with biped players in the ritual phase. In the preparatory and execution phases, however, the WC only players had fewer fixations for longer duration than the WC with biped players. Results are discussed in terms of long-term memory structures, learning, and considerations when coaching and training WC tennis players.
Glen M. Blenkinsop, Ying Liang, Nicholas J. Gallimore and Michael J. Hiley
The aim of the study was to examine changes in weight transfer, alignment, and shot outcome during golf shots from flat, uphill, and downhill slopes. Twelve elite male golfers hit 30 shots with a 6-iron from a computer-assisted rehabilitation environment used to create 5° slopes while collecting 3-dimensional kinematics and kinetics of the swing. A launch monitor measured performance outcomes. A shift in the center of pressure was found throughout the swing when performed on a slope, with the mean position moving approximately 9% closer to the lower foot. The golfers attempted to remain perpendicular to the slope, resulting in weight transfer toward the lower foot. The golfers adopted a wider stance in the sloped conditions and moved the ball toward the higher foot at address. Ball speed was not significantly affected by the slope, but launch angle and ball spin were. As the coaching literature predicted, golfers were more likely to hit shots to the left from an uphill slope and to the right from a downhill slope. No consistent compensatory adjustments in alignment at address or azimuth were found, with the change in final shot dispersion resulting from the lateral spin of the ball.
Daniel M. Grindle, Lauren Baker, Mike Furr, Tim Puterio, Brian Knarr and Jill Higginson
Prolonged sitting has been associated with negative health effects. Walking workstations have become increasingly popular in the workplace. There is a lack of research on the biomechanical effect of walking workstations. This study analyzed whether walking while working alters normal gait patterns. A total of 9 participants completed 4 walking trials at 2.4 and 4.0 km·h−1: baseline walking condition, walking while performing a math task, a reading task, and a typing task. Biomechanical data were collected using standard motion capture procedures. The first maximum vertical ground reaction force, stride width, stride length, minimum toe clearance, peak swing hip abduction and flexion angles, peak swing and stance ankle dorsiflexion, and knee flexion angles were analyzed. Differences between conditions were evaluated using analysis of variance tests with Bonferroni correction (P ≤ .05). Stride width decreased during the reading task at both speeds. Although other parameters exhibited significant differences when multitasking, these changes were within the normal range of gait variability. It appears that for short periods, walking workstations do not negatively impact gait in healthy young adults.