With a validated mathematical model of the head-neck consisting of nine rigid bodies (skull, seven cervical vertebrae, and torso), we simulated head impacts to estimate the injury risk associated with soccer heading. Experimental data from head-linear accelerations during soccer heading were used to validate the nine-body head-neck model for short duration impact loading of the head. In the computer simulations, the mass ratios between head mass and impacting body mass, the velocity of the impacting body, and the impact elasticity were varied. Head-linear and angular accelerations were compared to standard head-injury tolerance levels, and the injury risk specifically related to soccer heading was estimated. Based on our choice of tolerance levels in general, our simulations showed that injury risk from angular head accelerations was greater than from linear head accelerations, and compared to frontal impacts, lateral impacts had greater angular and less linear head accelerations. During soccer heading, our simulations indicated an unacceptable injury risk caused by angular head accelerations for frontal and lateral impacts at relatively low impact velocities for children, and at medium range impact velocities for adults. For linear head accelerations, injury risk existed for frontal and lateral impacts at medium range to relatively larger impact velocities for children, while no injury risk was shown for adults throughout the entire velocity range. For injury prevention, we suggest that head-injury risk can be reduced most substantially by increasing the mass ratio between head and impacting body. In soccer with children, the mass of the impacting body has to be adjusted to the reduced head mass of a child, that is, it must be clearly communicated to parents, coaches, and youngsters to only use smaller soccer balls.
Klaus Schneider and Ronald F. Zernicke
Susan K. Grimston and Ronald F. Zernicke
Physical exercise is touted as being beneficial for enhancing the functional quality of the skeletal system, as well as the cardiovascular and muscular systems. Unwise training practices, however, combined with potential risk factors may dispose an individual to a bone stress reaction (bone responses to repetitive loads within the physiological range) or stress fracture (frank fracture of a bone from clinically significant stress reactions that produce structural failure). Here, we trace the terms that have been used to describe these injuries and recount the etiology of stress reactions and fractures. Epidemiological data have been reported for military and athletic populations, and in many instances recurring risk factors have been identified, both those that can be modified and those that cannot. In this paper, we review epidemiological data and potential risk factors for stress fractures and summarize current thought about the treatment and prevention of these exercise-related injuries.
James L. Croft, Vinzenz von Tscharner and Ronald F. Zernicke
Compliant surfaces are used to challenge postural stability, but assessments are frequently limited to summary measures of center of pressure that do not provide insights into the temporal dynamics of motor coordination. Here, we measured center-of-pressure changes on three surfaces (solid, foam, and air-filled disc) and quantified the relative timing of changes in joint angles and muscle activity with respect to center-of-pressure changes. Nine active male subjects (20–30 years old) performed ten 30-s trials of unipedal stance on each of the three surfaces. Sway range, mean sway, mean sway velocity, path length, and fitted ellipse area increased, monotonically, from solid surface to foam to air-filled disc. The number of significant cross-correlations was greater for the compliant surfaces compared with the solid surface. Muscle activity preceded changes in center-of-pressure displacement, with the type of surface affecting the magnitude of the lead in the mediolateral direction. Center of pressure was more constrained on less stable surfaces and in the mediolateral direction.
David Whiteside, Douglas N. Martini, Ronald F. Zernicke and Grant C. Goulet
With a view to informing in-game decision making as it relates to strategy and pitcher health, this study examined changes in pitching-performance characteristics across 9 innings of Major League Baseball (MLB) games.
129 starting MLB pitchers met the inclusion criteria for this study. Pitch type, speed, ball movement, release location, and strike-zone data—collected using the MLB’s ball-tracking system, PITCHf/x—were obtained for 1,514,304 pitches thrown from 2008 to 2014.
Compared with the 1st inning, the proportion of hard pitches thrown decreased significantly until the 7th inning, while the proportions of breaking and off-speed pitches increased. Significant decreases in pitch speed, increases in vertical movement, and decreases in release height emerged no later than the 5th inning, and the largest differences in all variables were generally recorded between the 1st inning and the late innings (7–9). Pitchers were most effective during the 2nd inning and significantly worse in innings 4 and 6.
These data revealed that several aspects of a starting pitcher’s pitching characteristics exhibited changes from baseline as early as the 2nd or 3rd inning of an MLB game, but this pattern did not reflect the changes in his effectiveness. Therefore, these alterations do not appear to provide reasonable justification for relieving a starting pitcher, although future work must address their relevance to injury. From an offensive standpoint, batters in the MLB should anticipate significantly more hard pitches during the early innings but more breaking and off-speed pitches, with decreasing speed, as the game progresses.
Bradley J. Monteleone, Janet L. Ronsky, Willem H. Meeuwisse and Ronald F. Zernicke
Ankle function is frequently measured using static or dynamic tasks in normal and injured patients. The purpose of this study was to develop a novel task to quantify ankle dynamics and muscle activity in normal subjects. Twelve subjects with no prior ankle injuries participated. Video motion analysis cameras, force platforms, and an EMG system were used to collect data during a lateral hop movement task that consisted of multiple lateral-medial hops over an obstacle. Mean (SD) inversion ankle position at contact was 4.4° (4.0) in the medial direction and –3.5° (4.4) in the lateral direction; mean (SD) tibialis anterior normalized muscle activity was 0.11 (0.08) in the medial direction and 0.16 (0.13) in the lateral direction. The lateral hop movement was shown to be an effective task for quantifying ankle kinematics, forces, moments, and muscle activities in normal subjects. Future applications will use the lateral hop movement to assess subjects with previous ankle injuries in laboratory and clinical settings.
Scott E. Gordon, John B. Bartholomew, Richard B. Kreider, Ronald F. Zernicke and Mary E. Rudisill
This is an era in which academic units in higher education are expected to do more with less. State- and institutionally-appropriated funding streams are generally decreasing or stagnant. Federal grant funding is at its lowest level in years, and unlikely to rebound anytime soon. Institutions are restricting tuition increases to allow greater accessibility to students of limited means as well as to heed public demand for more accountability in the “educational product”. Enrollment growth adds pressure to academic units but rarely results in immediate resources directed to the affected units. To compound this problem, kinesiology is one of the fastest growing majors nationwide. With such mounting pressures on academic units and their leaders, creative entrepreneurial resourcefulness is not only rewarded, but required. This paper presents a series of successful and practical resource-generating strategies from the unique perspectives of units at several different institutions.
Karin G.M. Gerritsen, Anton J. van den Bogert, Manuel Hulliger and Ronald F. Zernicke
The purpose of this study was to investigate, theoretically, to what extent muscle properties could contribute to recovery from perturbations during locomotion. Four models with different actuator properties were created: the FLVT model, which encompassed force-length (FL) and force-velocity (FV) characteristics of human muscles as well as muscle stimulation inputs as functions of time (T); the FLT model, which had muscles without force-velocity characteristics; the FVT model, which had muscles without specific force-length characteristics; and the MT model, which had no muscles but was driven by joint moments (M) as a function of time. Each model was exposed to static and dynamic perturbations and its response was examined. FLVT showed good resistance to both static and dynamic perturbations. FLT was resistant to static perturbation but could not counteract dynamic perturbation, whereas the opposite was found for FVT. MT could not counteract either of the perturbations. Based on the results of the simulations, skeletal muscle force-length-velocity properties, although interactively complex, contribute substantially to the dynamic stability of the musculoskeletal system.
Ronald F. Zernicke, Grant C. Goulet, Peter R. Cavanagh, Benno M. Nigg, James A. Ashton-Miller, Heather A. McKay and Ton van den Bogert
As a field, biomechanics comprises research from the molecular and cellular levels, to tissues, to organs, to organisms and their movements. In the past 50 years, the impact of biomechanics research on society has been amplified dramatically. Here, we provide five brief summaries of exemplar biomechanics results that have had substantial impact on health and our society, namely 1) spaceflight and microgravitational effects on musculoskeletal health; 2) impact forces, soft tissue vibrations, and skeletal muscle tuning affecting human locomotion; 3) childbirth mechanics, injuries, and pelvic floor dysfunction; 4) prescriptive physical activity in childhood to enhance skeletal growth and development to prevent osteoporotic fractures in adulthood and aging; and 5) creative innovations in technology that have transformed the visual arts and entertainment.