The purpose of this study was to determine the influence of towing force magnitude on the kinematics of supramaximal sprinting. Ten high school and collegiate aged track and field athletes ran 60m maximal sprints under 5 different conditions: non-towed (NT), Tow A (2.0% body weight), Tow B (2.8%BW), Tow C (3.8%BW), and Tow D (4.7%BW). Three-dimensional kinematics of a 4-segment model of the right side of the body were collected starting at the 35m point of the trial. Significant differences were observed in stride length (SL) and horizontal velocity of the center of mass (V H ) during Tow C and Tow D. For Tow D, a significant increase in the distance from the center of mass to the foot at touchdown (D H ) was also observed. Contact time (CT) decreased significantly in all towing conditions, while stride rate (SR) increased slightly (< 2.0%) under towed conditions. There were no significant changes in joint or segment angles at touchdown, with the exception of a significant decrease in the flexion/extension angle at the hip during the Tow D condition. We concluded that towing force magnitude does influence the kinematics of supramaximal running. Furthermore, we suggest that coaches and practitioners adjust towing force magnitude for each individual and avoid using towing forces in excess of 3.8%BW.

ASTM F2333 is a test method for quantifying traction characteristics between an athletic shoe and a sports surface. This standard calls for normal loads of 500-3000 N to be applied between a footform and a playing surface. To assess the effect of varying the normal load on the traction coefficients between cleated athletic shoes and artificial turf surfaces, a new testing device was developed and used to collect traction data. Four different models of cleated athletic shoes were tested on FieldTurfÔ at normal loads ranging from 222 N to 1776 N. Static, dynamic, and peak traction coefficient values were calculated for each condition. There was a significant difference in the slope of the load versus traction coefficient curve for loads below and above 888 N for all three variables measured. No significant differences in traction characteristics were found between shoes for loads below 888 N. Significant differences between the shoes were seen with loads above 888 N. However, buckling and potential permanent damage to the turf surface were seen at loads of 1776 N. The results suggest that traction data obtained on FieldTurf at loads below one body weight are not sensitive to different shoe designs. Therefore, the measurement of traction between cleated shoes and FieldTurf should be conducted at a load of at least 888 N, which is, in part, consistent with the default normal load of 1000 N, in ASTM F2333. However, a normal force of 3000 N defined in the standard for studying stopping may not be feasible without permanently damaging the turf surface.

The purpose of this study was to investigate muscle activation patterns during a landing task in boys and girls through the use of muscle synergies. Electromyographical (EMG) data from six lower extremity muscles were collected from 11 boys and 16 girls while they performed singleleg drop-landings. EMG data from six leg muscles were rectified, smoothed, and normalized to maximum dynamic muscle activity during landing. Data from 100 ms before to 100 ms after touchdown were submitted to factor analyses to extract muscle synergies along with the associated activation and weighing coefficients. Boys and girls both used three muscle synergies.The activation coefficients of these synergies captured muscle activity during the pre-landing, touchdown, and post-landing phases of the single-leg drop-landing. Analysis of the weighing coefficients indicated that within the extracted muscle synergies the girls emphasized activation of the medial hamstring muscle during the pre-landing and touchdown synergy whereas boys emphasized activation of the vastus medialis during the post-landing synergy. Although boys and girls use similar muscle synergies during single-leg drop-landings, they differed in which muscles were emphasized within these synergies. The observed differences in aspects related to the muscle synergies during landing may have implications with respect to knee injury risk.

Background Despite considerable medical advances, arthroscopy remains the only definitive means of Superior Labrum Anterior-Posterior (SLAP) lesion diagnosis. Natural shoulder anatomic variants limit the reliability of radiographic findings and clinical evaluations are not consistent. Accurate clinical diagnostic techniques would be advantageous due to the invasiveness, patient risk, and financial cost associated with arthroscopy. Purpose The purpose was to examine the behavior of the joint stabilizing muscles in provocative tests for SLAP lesions. Electromyography was used to characterize the muscle behavior, with particular interest in the long head biceps brachii (LHBB), as activation of the long head and subsequent tension in the biceps tendon should, based on related research, elicit labral symptoms in SLAP lesion patients. Study Design Controlled Laboratory Study Methods Volunteers (N=21) without a history of shoulder pathology were recruited. The tests analyzed were Active Compression, Speed's, Pronated Load, Biceps I, Biceps II, Resisted Supination External Rotation, and Yergason's. Tests were performed with a dynamometer to improve reproducibility. Muscle activity was recorded for the long and short heads of the biceps brachii, anterior deltoid, pectoralis major, latissimus dorsi, infraspinatus, and supraspinatus. Muscle behavior for each test was characterized by peak activation and proportion of muscle activity. Results Speed's, Active Compression Palm-Up, Bicep I and Bicep II, produced higher long head activations. Resisted Supination External Rotation, Bicep I, Bicep II, and Yergason's, produced a higher LHBB proportion. Conclusion Bicep I, and Bicep II elicited promising long head behavior (high activation and selectivity). Speed's and Active Compression Palm-Up elicited higher activation of the LHBB , and Resisted Supination and Yergason's elicited selective LHBB activity. These top performing tests utilize a unique range of test variables that may prove valuable for optimal SLAP test design and performance. Clinical Relevance This study examines several provocative tests that are frequently used in the clinical setting as a means of evaluating a potential SLAP lesion. [Review Only] What is known about the subject Detecting SLAP lesions in the clinical setting has been frequently examined in the relevant literature. In general, most studies report the accuracy of a SLAP lesion test after a group of patients with suspected SLAP lesions are diagnosed following arthroscopy, and very few of these studies have examined the biomechanical implications of these tests. [Review Only] What this study adds to existing knowledge To the best of the authors' knowledge this is the first study to examine these seven provocative test in parallel and in subjects with no history of shoulder pathology. Again, to the best of the authors' knowledge this study is also the first to examine both activation and selectivity of the long head of the biceps and six other joint stabilizing muscles. In this study...

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