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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.

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.

Movement is essential to the human experience, and efficient biomechanics facilitate effective action across the breadth of tasks one encounters in life. The concept of movement efficiency has been investigated and explored through a variety of means including biomechanical modeling, simulation, and experimental manipulation. Observations of elite performers for a given movement task serve as an additional line of insight into efficiency, as their movements have been driven toward optimization via competitive pressure. The authors first discuss the concept of efficiency in biomechanics from a qualitative perspective and the broad tools with which we explore it. They then highlight biomechanical investigations of elite performers and their contributions to our understanding of efficiency. Examples from various classes of movements illustrate unique insights of the elite performers in informing our understanding of movement efficiency.

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.

In-lab, marker-based gait analyses may not represent real-world gait. Real-world gait analyses may be feasible using inertial measurement units (IMUs) in combination with open-source data processing pipelines (OpenSense). Before using OpenSense to study real-world gait, we must determine whether these methods estimate joint kinematics similarly to traditional marker-based motion capture (MoCap) and differentiate groups with clinically different gait mechanics. Healthy young and older adults and older adults with knee osteoarthritis completed this study. We captured MoCap and IMU data during overground walking at 2 speeds. MoCap and IMU kinematics were computed with OpenSim workflows. We tested whether sagittal kinematics differed between MoCap and IMU, whether tools detected between-group differences similarly, and whether kinematics differed between tools by speed. MoCap showed more anterior pelvic tilt (0%–100% stride) and joint flexion than IMU (hip: 0%–38% and 61%–100% stride; knee: 0%–38%, 58%–89%, and 95%–99% stride; and ankle: 6%–99% stride). There were no significant tool-by-group interactions. We found significant tool-by-speed interactions for all angles. While MoCap- and IMU-derived kinematics differed, the lack of tool-by-group interactions suggests consistent tracking across clinical cohorts. Results of the current study suggest that IMU-derived kinematics with OpenSense may enable reliable evaluation of gait in real-world settings.

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.

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.