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.
James G. Hay, Qi Liu, and James G. Andrews
Ewald M. Hennig, Gordon A. Valiant, and Qi Liu
Using a 15-point rating scale, subjects rated perception of cushioning during running on a treadmill with three different footwear constructions of varying midsole hardness. During overground running, various biomechanical ground reaction force and pressure variables were collected and compared to the perception of cushioning scores. The perception scores identified the three shoes as very hard, medium soft, and soft. Peak pressures in the heel, the force rate, and the median power frequency of the impact force signal demonstrated increases in values with the perception of less cushioning. In the harder shoes, the subjects altered the loading patterns under their feet, resulting in lower impact forces and increased weight bearing of the forefoot structures.
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.
Bin Chen, Lifen Liu, Lincoln Bin Chen, Xianxin Cao, Peng Han, Chenhao Wang, and Qi Qi
Context: Measuring isometric shoulder rotational strength is clinically important for evaluating motor disability in athletes with shoulder injuries. Recent evidence suggests that handheld dynamometry may provide a low-cost and portable method for the clinical assessment of isometric shoulder strength. Objective: To investigate the concurrent validity and the intrarater and interrater reliability of handheld dynamometry for measuring isometric shoulder rotational strength. Design: Cross-sectional study. Setting: Biomechanics laboratory. Participants: Thirty-nine young, healthy participants. Main Outcome Measures: The peak isometric strength of the internal rotators and external rotators, measured by handheld dynamometry (in newton) and isokinetic dynamometry (in newton meter). Interventions: Maximal isometric shoulder rotational strength was measured as participants lay supine with 90° shoulder abduction, neutral rotation, 90° elbow flexion, and forearm pronation. Measurements were performed independently by 2 different physiotherapists and in 3 different sessions to evaluate interrater and intrarater reliability. The data obtained by handheld dynamometry were compared with those obtained by isokinetic testing to evaluate concurrent validity. Results: The intraclass correlation coefficients for interrater reliability in measuring maximum isometric shoulder external and internal rotation strength were .914 (95% confidence interval [CI], .842–.954) and .842 (95% CI, .720–.914), respectively. The intrarater reliability values of the method for measuring maximal shoulder external and internal rotation strength were 0.865 (95% CI, 0.757–0.927) and 0.901 (95% CI, 0.820–0.947), respectively. The Pearson correlation coefficients between the handheld and isokinetic dynamometer measurements were .792 (95% CI, .575–.905) for external rotation strength and .664 (95% CI, .419–.839) for internal rotation strength. Conclusions: The handheld dynamometer showed good to excellent reliability and moderate to good validity in measuring maximum isometric shoulder rotational strength. Therefore, handheld dynamometry could be acceptable for health and sports professionals in field situations to evaluate maximum isometric shoulder rotational strength.