Air assault soldiers demonstrate more dangerous landing biomechanics when visual input is removed.

Soldiers are subjected to increased risk of musculoskeletal injuries in night operations because of limited visual input. The purpose of this study was to determine the effect of vision removal on lower extremity kinematics and vertical ground reaction forces during two-legged drop landings. The researchers tested 139 Air Assault Soldiers performing a landing task with and without vision. Removing visual input resulted in increased hip abduction at initial contact, decreased maximum knee flexion, and increased maximum vertical ground reaction force. Without vision, the timing of maximum ankle dorsiflexion for the left leg was earlier than the right leg. The observed biomechanical changes may be related to the increased risk of injury in night operations. Proper night landing techniques and supplemental training should be integrated into Soldiers' training to induce musculoskeletal and biomechanical adaptations to compensate for limited vision.

Running kinematics and shock absorption do not change after brief exhaustive running.

Because of the nature of running, the forces encountered require a proper coordination of joint action of the lower extremity to dissipate the ground reaction forces and accelerations through the kinetic chain. Running-related muscle fatigue may reduce the shock absorbing capacity of the lower extremity and alter running kinematics. The purpose of this study was to determine if a bout of exhaustive running at a physiologically determined high intensity, changes running kinematics, impact accelerations, and alters shock attenuating capabilities. It was hypothesized that as a result of fatigue induced by an exhaustive run, running kinematics, impact accelerations at the head and shank, acceleration reduction, and shock attenuation would change. A within-subject, repeated-measures design was used for this study. Twelve healthy, competitive male and female distance runners participated. Subjects performed 2 testing sessions consisting of a VO2max treadmill protocol to determine the heart rate at ventilatory threshold and a fatigue-inducing running bout at the identified ventilatory threshold heart rate. Kinematic data included knee flexion, pronation, time to maximum knee flexion, and time to maximum pronation. Acceleration data included shank acceleration, head acceleration, and shock attenuation. No significant differences resulted for the kinematic or acceleration variables. Although the results of this study do not support the original hypotheses, the influence of running fatigue on kinematics and accelerations remains inconclusive. Future research is necessary to examine fatigue-induced changes in running kinematics and accelerations and to determine the threshold at which point the changes may occur.

The relationship between biomechanical variables and driving performance during the golf swing.

Swing kinematic and ground reaction force data from 308 golfers were analysed to identify the variables important to driving ball velocity. Regression models were applied at four selected events in the swing. The models accounted for 44-74% of variance in ball velocity. Based on the regression analyses, upper torso-pelvis separation (the X-Factor), delayed release (i.e. the initiation of movement) of the arms and wrists, trunk forward and lateral tilting, and weight-shifting during the swing were significantly related to ball velocity. Our results also verify several general coaching ideas that were considered important to increased ball velocity. The results of this study may serve as both skill and strength training guidelines for golfers.

Minimal additional weight of combat equipment alters air assault soldiers' landing biomechanics.

The additional weight of combat and protective equipment carried by soldiers on the battlefield and insufficient adaptations to this weight may increase the risk of musculoskeletal injury. The objective of this study was to determine the effects of the additional weight of equipment on knee kinematics and vertical ground reaction forces (VGRF) during two-legged drop landings. We tested kinematics and VGRF of 70 air assault soldiers performing drop landings with and without wearing the equipment. Maximum knee flexion angles, maximum vertical ground reaction forces, and the time from initial contact to these maximum values all increased with the additional weight of equipment. Proper landing technique, additional weight (perhaps in the form of combat and protective equipment), and eccentric strengthening of the hips and knees should be integrated into soldiers' training to induce musculoskeletal and biomechanical adaptations to reduce the risk of musculoskeletal injury during two-legged drop landing maneuvers.

Variability in baseball pitching biomechanics among various levels of competition.

The aim of this study was to compare within-individual variability in baseball pitching among various levels of competition. It was hypothesized that variability decreases as level of competition increases. Five fastballs were analysed for 93 healthy male baseball pitchers (20 youth, 19 high school, 20 college, 20 Minor League, and 14 Major League level pitchers). Eleven kinematic, four temporal, and six kinetic parameters were quantified with a 240-Hz automated digitizing system. Three multiple analyses of variance were used to compare individual standard deviations for kinematic, temporal, and kinetic parameters among the five competition levels. There was a significant overall difference in kinematics and in six of the eleven kinematic parameters analysed: foot placement, knee flexion, pelvis angular velocity, elbow flexion, shoulder external rotation, and trunk forward tilt. Individual standard deviations tended to be greatest for youth pitchers, and decreased for higher levels of competition. Thus pitchers who advanced to higher levels exhibited less variability in their motions. Differences in temporal variation were non-significant; thus variability in pitching coordination was not improved at higher levels. Differences in kinetic variation were non-significant, implying no particular skill level has increased risk of injury due to variation in joint kinetics.

Validation of a video-based motion analysis technique in 3-D dynamic scapular kinematic measurements.

BACKGROUND: Current non-invasive 3-D scapular kinematic measurement techniques such as electromagnetic tracking are subjected to restrictions of wired sensors and limited capture space. Video-based motion analysis provides greater freedom with relatively less movement restriction. However, video-based motion analysis was rarely used in and not validated for scapular kinematics. METHODS: Scapular kinematics of five subjects performing abduction, scaption, and internal/external rotation was captured simultaneously with video-based motion analysis and dynamic stereo X-ray, a gold standard for tracking scapular movements. The data from video-based motion analysis was correlated with the data from dynamic stereo X-ray for validity evaluation. FINDINGS: Strong and significant correlations were identified in scapular protraction/retraction and medial/lateral rotation during abduction and scaption, and scapular medial/lateral rotation and anterior/posterior tilt during internal/external rotation. INTERPRETATION: Video-based motion analysis is valid for evaluating a single subject's scapular movement pattern in protraction/retraction during abduction and scaption, and medial/lateral-rotation during internal/external rotation. Anterior/posterior-tilt during abduction and scaption should be investigated with caution. Video motion analysis is also valid for evaluating group average of scapular kinematics except for protraction/retraction during internal/external rotation. While acknowledging the inherent limitations, video-based motion analysis is an appropriate technique for tracking scapular kinematics.

Biomechanical comparison between elite female and male baseball pitchers.

The purpose of the current study was to identify the biomechanical features of elite female baseball pitching. Kinematics and kinetics of eleven elite female baseball pitchers were reported and compared with eleven elite male pitchers. Results suggested that females share many similarities with males in pitching kinematics, with a few significant differences. Specifically, at the instant of stride foot contact, a female pitcher had a shorter and more open stride and less separation between pelvis orientation and upper torso orientation. From foot contact to ball release, a female pitcher produced lower peak angular velocity for throwing elbow extension and stride knee extension. Ball velocity was lower for the female. Foot contact to ball release took more time for a female pitcher. Maximal proximal forces at the shoulder and elbow joints were less for a female pitcher.