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Two-dimensional analyses of sprint kinetics are commonly undertaken but often ignore the metatarsal-phalangeal (MTP) joint and model the foot as a single segment. The aim of this study was to quantify the role of the MTP joint in the early acceleration phase of a sprint and to investigate the effect of ignoring the MTP joint on the calculated joint kinetics at the other stance leg joints. High-speed video and force platform data were collected from four to five trials for each of three international athletes. Resultant joint moments, powers, and net work at the stance leg joints during the first stance phase after block clearance were calculated using three different foot models. Considerable MTP joint range of motion (>30°) and a peak net MTP plantar flexor moment of magnitude similar to the knee joint were observed, thus highlighting the need to include this joint for a more complete picture of the lower limb energetics during early acceleration. Inclusion of the MTP joint had minimal effect on the calculated joint moments, but some of the calculated joint power and work values were significantly (P < .05) and meaningfully affected, particularly at the ankle. The choice of foot model is therefore an important consideration when investigating specific aspects of sprinting technique.

The authors and publisher regret that incorrect data were reported in JAB Volume 28, No. 2 (May 2012), on pages 222–227, in the article titled “Modeling the Stance Leg in Two-Dimensional Analyses of Sprinting: Inclusion of the MTP Joint Affect Joint Kinetics,” by Neil E. Bezodis, Aki I.T. Salo, and Grant Trewartha. An error in the data-processing script affected some of the calculated joint kinetics. The MTP plantar flexor moments were calculated correctly and are large enough to warrant consideration for a more complete picture of the energetics of sprinting. However, the correct data revealed that choice of foot model has relatively little effect on the calculated kinetics at other joints with the only meaningful differences being present in the ankle joint power and work data. As of November 1, 2012, the online version has been fully corrected and is available at http://journals.humankinetics.com/jab-back-issues/ jab-volume-28-issue-2-may.

To reach the level of elite, most baseball pitchers need to consistently produce high ball velocity but avoid high joint loads at the shoulder and elbow that may lead to injury. This study examined the relationship between fastball velocity and variations in throwing mechanics within 19 baseball pitchers who were analyzed via 3-D high-speed motion analysis. Inclusion in the study required each one to demonstrate a variation in velocity of at least 1.8 m/s (range 1.8–3.5 m/s) during 6 to 10 fastball pitch trials. Three mixed model analyses were performed to assess the independent effects of 7 kinetic, 11 temporal, and 12 kinematic parameters on pitched ball velocity. Results indicated that elbow flexion torque, shoulder proximal force, and elbow proximal force were the only three kinetic parameters significantly associated with increased ball velocity. Two temporal parameters (increased time to max shoulder horizontal adduction and decreased time to max shoulder internal rotation) and three kinematic parameters (decreased shoulder horizontal adduction at foot contact, decreased shoulder abduction during acceleration, and increased trunk tilt forward at release) were significantly related to increased ball velocity. These results point to variations in an individual's throwing mechanics that relate to pitched ball velocity, and also suggest that pitchers should focus on consistent mechanics to produce consistently high fastball velocities. In addition, pitchers should strengthen shoulder and elbow musculature that resist distraction as well as improve trunk strength and flexibility to maximize pitching velocity and help prevent injury.

The forces acting within and upon a limb are derived from three sources: postural (gravitational), inertial, and muscular. A method for decomposition has been established for free limb movements (Hoy & Zernicke, 1986); however, that method does not apply to kinematically constrained tasks whereby the limb exerts force on the environment. Presented here is a method for calculating the muscular and postural components for a quasi-static limb during a kinematically constrained task. It is a modified form of the inverse dynamic method reported by Kautz and Hull (1993) combined with the technique of Gruben and López-Ortiz (2000). This method stabilizes the limb against gravity with moments at each joint of the limb. Data from quasi-static lower limb extension efforts in one individual were analyzed to compare predictions of our method with those of the Kautz and Hull (1993) method. Differences in the postural component of foot force between the two methods increased with knee extension. The novelty of the method presented here was the use of an experimentally derived direction for the muscle component of foot force and the inclusion of a physiologically-based criterion for determining the support of the limb against gravity.

This study aimed to develop and evaluate an image-based method of obtaining anthropometric measurements for accurate subject-specific inertia parameter determination using Yeadon’s (1990) inertia model. Ninety-five anthropometric measurements were obtained directly from five athletic performers and indirectly from digitization of subject-specific whole-body still images. The direct and image-based measurements were used as input into Yeadon’s (1990) inertia model. The overall absolute error in predicted whole-body mass achieved using the image-based approach (2.87%) compared well to that achieved using the direct measurements (2.10%). The inclusion of image-based anthropometric measurements obtained from extremity (hand and feet) images was not found to consistently improve model accuracy achieved using whole-body images only. The presented method provides a successful alternative to direct measurement for obtaining anthropometric measurements required for customized inertia modeling. The noninvasive image-based approach is benefited by the potential for obtaining subject-specific measurements from large samples of subjects and elite athletic performers for whom time-consuming data collections may be undesirable.

Generating consistent maximum ball velocity is an important factor for a baseball pitcher’s success. While previous investigations have focused on the role of the upper and lower extremities, little attention has been given to the trunk. In this study it was hypothesized that variations in pelvis and upper torso kinematics within individual pitchers would be significantly associated with variations in pitched ball velocity. Nineteen elite baseball pitchers were analyzed using 3-D high-speed motion analysis. For inclusion in this study, each pitcher demonstrated a variation in ball velocity of at least 1.8 m/s (range: 1.8–3.5 m/s) during his 10 fastball pitch trials. A mixed-model analysis was used to determine the relationship between 12 pelvis and upper torso kinematic variables and pitched ball velocity. Results indicated that five variables were associated with variations in ball velocity within individual pitchers: pelvis orientation at maximum external rotation of the throwing shoulder (p = .026), pelvis orientation at ball release (p = .044), upper torso orientation at maximum external rotation of the throwing shoulder (p = .007), average pelvis velocity during arm cocking (p = .024), and average upper torso velocity during arm acceleration (p = .035). As ball velocity increased, pitchers showed an increase in pelvis orientation and upper torso orientation at the instant of maximal external rotation of the throwing shoulder. In addition, average pelvis velocity during arm cocking and average upper torso velocity during arm acceleration increased as ball velocity increased. From a practical perspective, the athlete should be coached to strive for proper trunk rotation during arm cocking as well as strength and flexibility in order to generate angular velocity within the trunk for maximum ball velocity.

Investigating balance reactions following continuous, multidirectional, support surface perturbations is essential for improving our understanding of balance control in moving environments. Segmental motions are often incorporated into rapid balance reactions following external perturbations to balance, although the effects of these motions during complex, continuous perturbations have not been assessed. This study aimed to quantify the contributions of body segments (ie, trunk, head, upper extremity, and lower extremity) to the control of center-of-mass (COM) movement during continuous, multidirectional, support surface perturbations. Three-dimensional, whole-body kinematics were captured while 10 participants experienced 5 minutes of perturbations. Anteroposterior, mediolateral, and vertical COM position and velocity were calculated using a full-body model and 7 models with reduced numbers of segments, which were compared with the full-body model. With removal of body segments, errors relative to the full-body model increased, while relationship strength decreased. The inclusion of body segments appeared to affect COM measures, particularly COM velocity. Findings suggest that the body segments may provide a means of improving the control of COM motion, primarily its velocity, during continuous, multidirectional perturbations, and constitute a step toward improving our understanding of how the limbs contribute to balance control in moving environments.