The purpose of this study was to investigate relationships between free limb motions and triple jump performance. The subjects were 13 elite male triple jumpers. Three-dimensional videographic data were collected using a direct linear transformation technique with panning cameras. Changes in the velocity of the whole body center of gravity (G), changes in the whole body angular momentum about G, changes in the velocity of G due to free limb motions, and changes in the whole body angular momentum about G due to free limb motions were determined for each of the three support phases. Free limb motions were associated with decreases in the forward horizontal velocity of G and increases in the vertical velocity of G and significantly influenced changes of the corresponding velocity components of G when the changes were large. The free limb motions also created some angular momentum components about G during each support phase but did not significantly influence the changes of the corresponding angular momentum components of the whole body. Neither the changes in the three velocity components of G nor the changes in the three angular momentum components of the whole body about G due to free limb motions were significantly related to the actual distance of the triple jump.
Bing Yu and James G. Andrews
Qi Liu, James G. Hay and James G. Andrews
The purpose of this study was to determine the influence of (a) body roll, and (b) the motion of the arm relative to the trunk, on the medial-lateral component of the path followed by the hand during the pull phase in freestyle swimming. Ten male swimmers swam three trials of freestyle at a long-distance workout pace. Three-dimensional (3D) underwater videography was used to record the body roll angle-time history and the path followed by the hand during the pull phase. A mathematical model was used to characterize the motion of a swimmer's right upper limb in accord with 3D data from the videotape images, and to determine what the path of the hand would have been as a result of body roll alone. The contribution of body roll to the actual handpath was found to be nearly equal to the contribution of medial-lateral motions of the hand relative to the trunk.
James G. Hay, Qi Liu and James G. Andrews
The purpose of this study was to determine the effect that body roll has on the path followed by the hand during the pull phase in freestyle swimming. The trunk and right arm were modeled as two rigid segments joined at the shoulder by a simple hinge joint. The arm segment was assigned an elbow flexion angle, and the hand was made to move in a plane through the shoulder parallel to the sagittal plane of the rotating trunk. Shoulder extension and trunk roll occurred simultaneously at selected rates. Medial deviations of the hand to the midline of the trunk can be obtained with body roll alone and require less roll than is usually observed among competitive swimmers. When body roll exceeds the amount necessary to produce the desired medial deviation of the hand, the swimmer must move the arm away from, rather than toward, the trunk's midline.
John W. Chow, Warren G. Darling, James G. Hay and James G. Andrews
The purpose of this study was to propose and evaluate a method for the in vivo determination of the force-length-velocity relations of individual quadriceps muscles. One female subject performed maximum effort knee extensions on an isokinetic dynamometer. The gravitational and inertial effects were taken into consideration when determining the resultant knee torque. Selected anatomical and geometric parameters of the quadriceps muscles were obtained from radiography and magnetic resonance imaging (MRI). Hill’s (1938) mechanical model was used to represent the force-velocity relation of a muscle at a given length, and the constants in Hill’s model were assumed to vary with muscle length. Experimentally determined knee torque and muscle shortening velocity data were used to determine the unknown parameters in the muscle model. The relation between each muscle parameter and muscle length for each muscle was obtained using regression analysis. On average, the muscle model overestimated the knee torque by 15.5 ± 5.1%. The overestimations may have resulted from the lack of low torque-high velocity data for the determination of muscle model parameters. When a set of fixed Hill constants was used, the knee torque was underestimated by 29.0 ± 10.6%. The results demonstrate the feasibility of the method proposed in this study.
Kevin E. Wilk, Naiquan Zheng, Glenn S. Fleisig, James R. Andrews and William G. Clancy
Closed kinetic chain exercise has become popular in rehabilitation of the ACL patient. While many clinicians agree on the benefits of closed kinetic chain exercise, there is great discrepancy as to which exercises fit this category. This discrepancy stems from the fact that the kinetic chain concept was originally developed using mechanical engineering concepts and not human kinesiology. In this paper, the kinetic chain concept is redefined in a continuum of lower extremity exercises from closed kinetic chain to open kinetic chain. The placement of an exercise in this continuum is based upon joint kinematics, quadriceps and hamstring muscle activity, cruciate ligament stress, and joint weight-bearing load. An understanding of these factors can help the clinician design a comprehensive and effective rehabilitation program for the ACL patient.
Gabrielle G. Gilmer, Jessica K. Washington, Jeffrey R. Dugas, James R. Andrews and Gretchen D. Oliver
Context: Studies have found that a 20% reduction in energy generation from the lumbopelvic-hip complex during overhead throws leads to a 34% increase in load on the shoulder. Objective: The purpose of this study was to assess the effects of lumbopelvic-hip complex stability, via the single leg squat assessment, on throwing mechanics of softball athletes. Design: Prospective cohort study. Setting: Laboratory setting. Participants: A total of 50 softball athletes (164.0 [104.0] cm, 65.6 [11.3] kg, 16.3 [3.8] y, 8.61 [3.62] y of experience) performed 3 overhead throws and a single leg squat on each leg. Intervention: Four stability groups were derived: (1) stable on both legs (bilateral stability), (2) unstable on the throwing side leg (TS instability) and stable on the nonthrowing side leg, (3) unstable on the nonthrowing side leg (NTS instability) and stable on the throwing side leg, and (4) unstable on both legs (bilateral instability). All throws were analyzed across 4 throwing events: foot contact (FC), maximum external shoulder rotation (MER), ball release (BR), and maximum internal shoulder rotation (MIR). Main Outcome Measures: Mann–Whitney U tests revealed significant differences between the bilateral stability and the TS instability groups in trunk flexion at BR; the bilateral stability and the NTS instability groups in trunk flexion at BR, shoulder horizontal abduction at FC, shoulder rotation at FC, and pelvis flexion at MIR; the TS instability and the bilateral instability groups in trunk rotation at FC; and the NTS instability and the bilateral instability groups in trunk flexion at MER and shoulder rotation at FC. Conclusion: These findings demonstrate the different mechanisms in which energy can be lost through lumbopelvic-hip complex instability as evident in throwing mechanics. The findings from this study suggest that the current methods used for classification could act as a tool for coaches, physicians, and athletic trainers when assessing their athletes’ injury susceptibility.
Kevin E. Wilk, James R. Andrews, William G. Clancy Jr., Heber C. Crockett and James W. O'Mara Jr.
Treatment of posterior cruciate ligament (PCL) injuries has changed considerably in recent years. This article discusses current rehabilitation for PCL disruptions in athletes. The treatment of PCL injuries varies somewhat based on the chronicity (acute vs. chronic) of injury and associated pathologies. The authors provide their treatment algorithm for the acute and chronic PCL-injured-knee patient. Nonoperative rehabilitation is discussed with a focus on immediate motion, quadriceps muscle strengthening, and functional rehabilitation. A discussion of the biomechanics of exercise is provided, with a focus on tibiofemoral shear forces and PCL strains. Surgical treatment is also discussed, with the current surgical approach being either the two-tunnel or the one-tunnel patellar tendon autograft procedure. The rehabilitation program after surgery is based on the healing constraints, surgical technique, biomechanics of the PCL during functional activities, and exercise. With the new changes in surgical technique and in the rehabilitation process, the authors believe that the outcome after PCL reconstruction will be enhanced.