Comments on "Runners do not push off but fall forward via a gravitational torque" (vol. 6, pp. 434-452)

Comparison of Indirect Calorimetry- and Accelerometry-Based Energy Expenditure During Children's Discrete Skill Performance

Purpose: To compare children's energy expenditure (EE) levels during object projection skill performance (OPSP; e.g., kicking, throwing, striking) as assessed by hip- and wrist-worn accelerometers. Method: Forty-two children (female n = 20, Mage = 8.1 ± 0.8 years) performed three, nine-minute sessions of kicking, over-arm throwing, and striking at performance intervals of 6, 12, and 30 seconds. EE was estimated using indirect calorimetry (COSMED k4b2) and accelerometers (ActiGraph GT3X+) worn on three different locations (hip, dominant-wrist, and non-dominant-wrist) using four commonly used cut-points. Bland-Altman plots were used to analyze the agreement in EE estimations between accelerometry and indirect calorimetry (METS). Chi-square goodness of fit tests were used to examine the agreement between accelerometry and indirect calorimetry. Results: Hip- and wrist-worn accelerometers underestimated EE, compared to indirect calorimetry, during all performance conditions. Skill practice at a rate of two trials per minute resulted in the equivalent of moderate PA and five trials per minute resulted in vigorous PA (as measured by indirect calorimetry), yet was only categorized as light and/or moderate activity by all measured forms of accelerometry. Conclusion: This is one of the first studies to evaluate the ability of hip- and wrist-worn accelerometers to predict PA intensity levels during OPSP in children. These data may significantly impact PA intervention measurement strategies by revealing the lack of validity in accelerometers to accurately predict PA levels during OPSP in children.

Analysis and comparison of lateral head impacts using various golf discs and a Hybrid III head form

The potential for head injuries from discs specifically designed for the sport of disc golf has increased as more disc golf courses are constructed in municipal parks where there is an inherent risk to park users of being struck by a golf disc. This study investigated the potential for head injury of various golf discs used in the sport of disc golf at 18 m/s (40 mph) and 27 m/s (60 mph) using a Hybrid III head form. A matrix of eight modern golf discs were tested to determine if velocity, mass, disc type, or flexibility has a significant effect on the potential for head injury as indicated by peak linear acceleration, peak angular acceleration, Head Injury Criteria (HIC) and Severity Index (SI) values. Regression analyses indicated peak linear acceleration, peak rotational acceleration, HIC, and SI varied by velocity, mass, type, and flexibility. The highest mean linear and rotational acceleration results, 38.5 g and 2512 rad/s² respectively, both associated with a less than 10% likelihood of sustaining a concussion. The findings should be of interest to both researchers and practitioners who seek to balance use and safety of public parks.