The purpose of this study is to describe an MRI-based EMG-driven knee model to quantify tibiofemoral compressive and shear forces. Twelve healthy females participated. Subjects underwent 2 phases of data collection: (1) MRI assessment of the lower extremity to quantify muscle volumes and patella tendon orientation and (2) biomechanical evaluation of a drop-jump task. A subject-specific EMG-driven knee model that incorporated lower extremity kinematics, EMG, and muscle volumes and patella tendon orientation estimated from MRI was developed to quantify tibiofemoral shear and compressive forces. A resultant anterior tibial shear force generated from the ground reaction force (GRF) and muscle forces was observed during the first 30% of the stance phase of the drop-jump task. All of the muscle forces and GRF resulted in tibiofemoral compression, with the quadriceps force being the primary contributor. Acquiring subject-specific muscle volumes and patella tendon orientation for use in an EMG-driven knee model may be useful to quantify tibiofemoral forces in persons with altered patella position or muscle atrophy following knee injury or pathology.
Liang-Ching Tsai, Irving S. Scher and Christopher M. Powers
Douglas E. Young, Doris Trachtman, Irving S. Scher and Richard A. Schmidt
The timing of glove movements used by baseball pitchers to catch fast approaching balls (i.e., line drives) was examined in two tests to determine the responses and temporal characteristics of glove movements in high school and college baseball pitchers. Balls were projected toward the head of participants at 34.8 m·s–1 (78 mph) on average in an indoor test and at speeds approaching 58.1 m·s–1 (130 mph) in a field test. Pitchers caught over 80% and 15% of the projected balls in the indoor and field tests, respectively. Analyses of glove responses indicated that all pitchers could track the line drives and produce coordinated glove movements, which were initiated 160 ms (± 47.8), on average, after the ball was launched. College pitchers made initial glove movements sooner than high school pitchers in the field test (p = 0.012). In contrast, average glove velocity for pitchers increased from 1.33 (± 0.61) to 3.45 (± 0.86) m·s–1 across the tests, but did not differ between experience levels. Glove movement initiation and speed were unrelated, and pitchers utilized visual information throughout the ball's flight to catch balls that approached at speeds exceeding the estimated speeds in competitive situations.
Jeffrey R. Campbell, Irving S. Scher, David Carpenter, Bruce L. Jahnke and Randal P. Ching
Alpine touring (AT) equipment is designed for ascending mountains and snow skiing down backcountry terrain. Skiers have been observed using AT boots in alpine (not made for Alpine Touring) ski bindings. We tested the effect on the retention-release characteristics of AT boots used in alpine bindings. Ten AT ski boots and 5 alpine ski boots were tested in 8 models of alpine ski bindings using an ASTM F504-05 (2012) apparatus. Thirty-one percent of the AT boots released appropriately when used in alpine ski bindings. One alpine binding released appropriately for all alpine and AT boots tested; 2 alpine ski bindings did not release appropriately for any AT boots. Altering the visual indicator settings on the bindings (that control the release torque of an alpine system) had little or no effect on the release torque when using AT boots in alpine ski bindings. Many combinations released appropriately in ski shop tests, but did not release appropriately in the more complex loading cases that simulated forward and backward falls; the simple tests performed by ski shops could produce a “false-negative” test result. These results indicate that using AT boots with alpine ski bindings could increase the likelihood of lower leg injuries.