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Arthur Alves Dos Santos, James Sorce, Alexandra Schonning, and Grant Bevill

This study evaluated the performance of 6 commercially available hard hat designs—differentiated by shell design, number of suspension points, and suspension tightening system—in regard to their ability to attenuate accelerations during vertical impacts to the head. Tests were conducted with impactor materials of steel, wood, and lead shot (resembling commonly seen materials in a construction site), weighing 1.8 and 3.6 kg and dropped from 1.83 m onto a Hybrid III head/neck assembly. All hard hats appreciably reduced head acceleration to the unprotected condition. However, neither the addition of extra suspension points nor variations in suspension tightening mechanism appreciably influenced performance. Therefore, these results indicate that additional features available in current hard hat designs do not improve protective capacity as related to head acceleration metrics.

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Hannah E. Wyatt, Gillian Weir, Carl Jewell, Richard E.A. van Emmerik, and Joseph Hamill

Coordination variability (CV) is commonly analyzed to understand dynamical qualities of human locomotion. The purpose of this study was to develop guidelines for the number of trials required to inform the calculation of a stable mean lower limb CV during overground locomotion. Three-dimensional lower limb kinematics were captured for 10 recreational runners performing 20 trials each of preferred and fixed speed walking and running. Stance phase CV was calculated for 9 segment and joint couplings using a modified vector coding technique. The number of trials required to achieve a CV mean within 10% of 20 strides average was determined for each coupling and individual. The statistical outputs of mode (walking vs running) and speed (preferred vs fixed) were compared when informed by differing numbers of trials. A minimum of 11 trials were required for stable mean stance phase CV. With fewer than 11 trials, CV was underestimated and led to an oversight of significant differences between mode and speed. Future overground locomotion CV research in healthy populations using a vector coding approach should use 11 trials as a standard minimum. Researchers should be aware of the notable consequences of an insufficient number of trials for overall study findings.

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Kyle B. Kosik, Kathryn Lucas, Matthew C. Hoch, Jacob T. Hartzell, Katherine A. Bain, and Phillip A. Gribble

Studies have demonstrated that individuals with chronic ankle instability (CAI) have diminished dynamic stability. Jerk-based measures have been utilized to examine dynamic balance because of their ability to quantify changes in acceleration and may provide an understanding of the postural corrections that occur during stabilizing following a jumping task. The purpose of this study was to compare acceleration and jerk following a jump stabilization task between individuals with CAI and the uninjured controls. Thirty-nine participants volunteered to participate in this case control study. Participants completed a jump stabilization task requiring them to jump off 2 feet, touch a marker set at 50% of their maximal vertical jump height, land on a single limb, and maintain balance for 3 seconds. Acceleration was calculated as the second derivative, and jerk was calculated as the third derivative of the displacement of the resultant vector position. Participants with CAI had greater acceleration (mean difference = 55.6 cm/s2; 95% confidence interval, 10.3 to 100.90; P = .017) and jerk compared with the uninjured controls (mean difference = 1804.5 cm/s3; 95% confidence interval, 98.7 to 3510.3; P = .039). These results suggest that individuals with CAI made faster and more frequent active postural control corrections to regain balance following a jump compared with the uninjured controls.

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ZáNean McClain, Jill Pawlowski, and Daniel W. Tindall

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Katie L. Kowalski, Ali Boolani, and Anita D. Christie

Compromised attentional resources during perceived fatigue has been suggested to alter motor control. The authors determined if measures of postural control and gait are predicted by state and trait physical and mental fatigue and energy, and how these relationships are modified by sex, sleep quality, and physical activity. Young adults (n = 119) completed the Modified Clinical Test of Sensory Integration, overground walking, and questionnaires to quantify fatigue and energy, sleep quality, and physical activity. Regression models indicated that trait fatigue, trait energy, and sleep quality were predictors of postural control (p ≤ .02, R 2 ≥ .04). State fatigue, state energy, and sex were predictors of gait (p ≤ .05, R 2 ≥ .03). While the variance explained was low (3–13%), the results demonstrate perceptions of fatigue and energy may influence posture and gait.

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Jessica Murphy, Karen A. Patte, Philip Sullivan, and Scott T. Leatherdale

The mental health benefits of physical activity may relate more to the context of the behavior, rather than the behavior of being active itself. The association between varsity sport (VS) participation, depression, and anxiety symptoms was explored using data from 70,449 high school students from the Cannabis use, Obesity, Mental health, Physical activity, Alcohol use, Smoking, and Sedentary behavior study. The model adjusted for potential covariates; interactions by sex and participation in outside of school sport (OSS) were explored. Overall, 70% and 24% of respondents met or exceeded cutoff values for depression and anxiety, respectively. Students participating in VS had lower symptoms of anxiety and depression compared with nonparticipants. Results were consistent regardless of OSS participation; associations were strongest among students who participated in both VS and OSS and males. Participation in VS may prove beneficial for the prevention and/or management of depression or anxiety symptoms, particularly among males. An additive beneficial effect of OSS on depression and anxiety scores may exist.

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Thiago R.T. Santos, Sergio T. Fonseca, Vanessa L. Araújo, Sangjun Lee, Fabricio Saucedo, Stephen Allen, Christopher Siviy, Thales R. Souza, Conor Walsh, and Kenneth G. Holt

The addition of a load during walking requires changes in the movement pattern. The investigation of the dynamic joint stiffness behavior may help to understand the lower limb joints’ contribution to these changes. This study aimed to investigate the dynamic stiffness of lower limb joints in response to the increased load carried while walking. Thirteen participants walked in two conditions: unloaded (an empty backpack) and loaded (the same backpack plus added mass corresponding to 30% of body mass). Dynamic stiffness was calculated as the linear slope of the regression line on the moment–angle curve during the power absorption phases of the ankle, knee, and hip in the sagittal plane. The results showed that ankle (P = .002) and knee (P < .001) increased their dynamic stiffness during loaded walking compared with unloaded, but no difference was observed at the hip (P = .332). The dynamic stiffness changes were different among joints (P < .001): ankle and knee changes were not different (P < .992), but they had a greater change than hip (P < .001). The nonuniform increases in lower limb joint dynamic stiffness suggest that the ankle and knee are critical joints to deal with the extra loading.

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Lazar Tomic, Danica Janicijevic, Aleksandar Nedeljkovic, Bojan Leontijevic, and Amador García-Ramos

Reliability and sensitivity of reaction time (RT) during quasi-realistic soccer situations was explored in 10 professional soccer players (skilled; age = 20.9 ± 3.6 years) and 10 males without soccer experience (nonskilled; age = 23.4 ± 0.5 years). The participants were instructed to react as fast as possible to a stimulus presented via the video-based method while standing on force platforms. RT was computed as the difference between the instant when the rate of force development of any leg reaches 5% of its maximal value and the instant of stimulus presentation. The results revealed acceptable to high reliability of RT (intraclass correlation coefficient median = .90; coefficient of variation ≤ 5.83%), and shorter RT for skilled compared with nonskilled participants in three out of eight comparisons (effect size range = 1.00–1.41). The video-based methods can be confidently used to assess the RT in soccer players.

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Takuya Ibara, Makoto Takahashi, Koichi Shinkoda, Mahito Kawashima, and Masaya Anan

This study aimed to investigate the hip sway and the relationship between the center of pressure (CoP) and kinematic parameters regarding the time series scaling component α in patients with hip osteoarthritis (OA) during a one-leg standing task. The scaling exponent α, SD, hip sway maximal acceleration change, and balance performance, which was measured using CoP parameters, were compared between hip OA and control groups during a one-leg standing task. The relationships between balance performance with CoP parameters and kinematic parameters were investigated with the regression analysis. In the hip OA group, the scaling exponent α was smaller in the medial–lateral direction, and the SD and maximal amount of change in hip sway acceleration were larger in the anterior–posterior direction in the hip OA group. In this group, the CoP parameters were significantly associated with α in the medial–lateral direction (negatively) and in the anterior–posterior direction (positively). In the hip OA group, hip sway adaptability in the medial–lateral direction was limited, while the anterior–posterior direction showed greater movement.