Spinal cord trauma due to head-first collisions is not uncommon in vehicle accidents, shallow water diving, football, or ice hockey. Two approaches to evaluating potential protective devices for ice hockey are described: an evaluative tool based upon an anthropometric test dummy, and a computer simulation of axial head-first collisions. Helmets reduced the peak cervical spine loads during low velocity head-first collisions by up to 8%. It is shown that large thicknesses of appropriate padding are necessary to hold the cervical spine loads to noninjurious levels. A head-first impact of 3.0 m • sec−1 required padding deformations on the order of 94 mm to hold cervical spine loads below 2,000 N.
Richard P. Wells, Patrick J. Bishop, and Malcolm Stephens
Linda Lin, Richard P. Halgin, Arnold D. Well, and Ira Ockene
Alan C. Cudlip, Steven L. Fischer, Richard Wells, and Clark R. Dickerson
This study examined the influence of frequency and direction of force application on psychophysically acceptable forces for simulated work tasks. Fifteen male participants exerted psychophysically acceptable forces on a force transducer at 1, 3, or 5 repetitions per minute by performing both a downward press and a pull toward the body. These exertions were shown previously to be strength and balance limited, respectively. Workers chose acceptable forces at a lower percentage of their maximum voluntary force capacity during downward (strength-limited) exertions than during pulling (balance-limited) exertions at all frequencies (4% to 11%, P = .035). Frequency modulated acceptable hand force only during downward exertions, where forces at five repetitions per minute were 13% less (P = .005) than those at one exertion per minute. This study provides insight into the relationship between biomechanically limiting factors and the selection of acceptable forces for unilateral manual tasks.
Steven L. Fischer, Bryan R. Picco, Richard P. Wells, and Clark R. Dickerson
Exerting manual forces is critical during occupational performance. Therefore, being able to estimate maximum force capacity is particularly useful for determining how these manual exertion demands relate to available capacity. To facilitate this type of prediction requires a complete understanding of how maximum force capacity is governed biomechanically. This research focused on identifying how factors including joint moment strength, balance and shoe-floor friction affected hand force capacity during pulling, pressing downward and pushing medially. To elucidate potential limiting factors, joint moments were calculated and contrasted with reporte joint strength capacities, the balancing point within the shoe-floor interface was calculated and expresess relative to the area defined by the shoe-floor interface, and the net applied horizontal forces were compare with the available friction. Each of these variables were calculated as participants exerted forces in a series o conditions designed to systematically control or restrict certain factors from limiting hand force capacity. The results demonstrated that hand force capacity, in all tested directions, was affected by the experimental conditions (up to 300%). Concurrently, biomechanical measures reached or surpassed reported criterion threshold inferring specific biomechanical limitations. Downward exertions were limited by elbow strength, wherea pulling exertions were often limited by balance along the anterior-posterior axis. No specific limitations wer identified for medial exertions.
Tibor Hortobágyi, Richard G. Israel, Joseph A. Houmard, Kevin F. O'Brien, Robert A. Johns, and Jennifer M. Wells
Four methods of assessing body composition were compared in 55 black and 35 white, Division 1, American football players. Percent body fat (%BF) was estimated with hydrostatic weighing at residual volume, corrected for race; seven-site skinfolds (7 SF), corrected for race; bioelectrical impedance analysis (BIA); and near-infrared spectrophotometry (NIR). Percent body fat with HW in blacks (mean = 14.7%) and whites (19.7%) did not differ (P > .05) from %>BF with 7 SF (blacks, 14.7%; whites, 19.0%). In relation to HW, BIA significantly (P < .05) overpredicted (blacks: 20.1%, SEE = 3.2%; whites; 22.3%, SEE = 4.3%) and NiR underpredicted %BF (blacks; 12.6%, SEE = 3.9%; whites; 17.7%, SEE = 3.6%). The contribution of BIA variables (resistance, phase angle, conductance) and NIR optical density to predict %BF was trivial compared to body mass index. It appears that race may not substantially influence %BF prediction by NIR and BIA. It was concluded that when considering the cost and expertise required with NIR and BIA, SF measurements appear to be a superior alternative for rapid and accurate body composition assessment of athletes, independent of race.