The purpose of this study was to compute the 3-dimensional kinetics required to swing 3 youth baseball bats of varying moments of inertia. The 306 swings by 22 male players (age 13–18 y) were analyzed. Inverse dynamics with respect to the batter’s hands were computed given the known kinematics and physical properties of the bats. Peak force increased with larger bat moments of inertia and was strongly correlated with bat tip speed. By contrast, peak moments were weakly correlated with bat moments of inertia and bat tip speed. Throughout the swing, the force applied to the bat was dominated by a component aligned with the long axis of the bat and directed away from the bat knob, whereas the moment applied to the bat was minimal until just prior to ball impact. These results indicate that players act to mostly “pull” the bat during their swing until just prior to ball impact, at which point they rapidly increase the moment on the bat. This kinetic analysis provides novel insight into the forces and moments used to swing baseball bats.
Joseph J. Crisco, Nikolas J. Osvalds and Michael J. Rainbow
Joseph J. Crisco, Michael J. Rainbow and Eileen Wang
In the last decade, dramatic changes in lacrosse stick design are believed to be associated with changes in the play of the game; however, there is a limited understanding of how the lacrosse stick propels the ball. We predicted that the lacrosse stick would perform as a passive extension of the player’s hand and hypothesized that ball shot speed would be equal to the speed at the tip of the stick. Ball and shot kinematics of 16 male and 16 female lacrosse players using four various stick models were tracked at 250 Hz. The speed of the ball was compared with the speed at the tip of the stick, calculated by assuming the stick behaved as a rigid body. Ball shot speeds with men’s sticks were on average 3.5 m/s (7.8 mph) faster than the calculated speed at the stick tip, and ball shot speeds with women’s sticks were on average 0.7 m/s (1.5 mph) faster than stick tip speed. Some lacrosse stick models can shoot the ball significantly faster than predicted when considering the stick as a rigid, passive extension of the player’s hands.
Marcus J. Brown, Laura A. Hutchinson, Michael J. Rainbow, Kevin J. Deluzio and Alan R. De Asha
A typical gait analysis data collection consists of a series of discrete trials, where a participant initiates gait, walks through a motion capture volume, and then terminates gait. This is not a normal ‘everyday’ gait pattern, yet measurements are considered representative of normal walking. However, walking speed, a global descriptor of gait quality that can affect joint kinematics and kinetics, may be different during discrete trials, compared to continuous walking. Therefore, the purpose of this study was to investigate the effect of continuous walking versus discrete trials on walking speed and walking speed variability. Data were collected for 25 healthy young adults performing 2 walking tasks. The first task represented a typical gait data collection session, where subjects completed repeated trials, beginning from a standstill and walking along a 12-m walkway. The second task was continuous walking along a “figure-of-8” circuit, with 1 section containing the same 12-m walkway. Walking speed was significantly higher during the discrete trials compared to the continuous trials (p < .001), but there were no significant differences in walking speed variability between the conditions. The results suggest that choice of gait protocol may affect results where variables are sensitive to walking speed.
Joseph J. Crisco, Michael J. Rainbow, Joel B. Schwartz and Bethany J. Wilcox
The purpose of this study was to examine the batting cage performance of wood and nonwood baseball bats used at the youth level. Three wood and ten nonwood bats were swung by 22 male players (13 to 18 years old) in a batting cage equipped with a 3-dimensional motion capture (300 Hz) system. Batted ball speeds were compared using a one-way ANOVA and bat swing speeds were analyzed as a function of bat moment of inertia by linear regression. Batted ball speeds were significantly faster for three nonwood bat models (P < .001), significantly slower for one nonwood model, and not different for six nonwood bats when compared with wood bats. Bat impact speed significantly (P < .05) decreased with increasing bat moment of inertia for the 13-, 14-, and 15-year-old groups, but not for the other age groups. Ball-bat coefficients of restitution (BBCOR) for all nonwood were greater than for wood, but this factor alone did not correlate with bat performance. Our findings indicate that increases in BBCOR and swing speed were not associated with faster batted ball speeds for the bats studied whose moment of inertia was substantially less than that of a wood bat of similar length.
Christopher M. Saliba, Allison L. Clouthier, Scott C.E. Brandon, Michael J. Rainbow and Kevin J. Deluzio
Abnormal loading of the knee joint contributes to the pathogenesis of knee osteoarthritis. Gait retraining is a noninvasive intervention that aims to reduce knee loads by providing audible, visual, or haptic feedback of gait parameters. The computational expense of joint contact force prediction has limited real-time feedback to surrogate measures of the contact force, such as the knee adduction moment. We developed a method to predict knee joint contact forces using motion analysis and a statistical regression model that can be implemented in near real-time. Gait waveform variables were deconstructed using principal component analysis, and a linear regression was used to predict the principal component scores of the contact force waveforms. Knee joint contact force waveforms were reconstructed using the predicted scores. We tested our method using a heterogenous population of asymptomatic controls and subjects with knee osteoarthritis. The reconstructed contact force waveforms had mean (SD) root mean square differences of 0.17 (0.05) bodyweight compared with the contact forces predicted by a musculoskeletal model. Our method successfully predicted subject-specific shape features of contact force waveforms and is a potentially powerful tool in biofeedback and clinical gait analysis.