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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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Mu Qiao

Although the dynamics of center of mass can be accounted for by a spring-mass model during hopping, less is known about how each leg joint (ie, hip, knee, and ankle) contributes to center of mass dynamics. This work investigated the function of individual leg joints when hopping unilaterally and vertically at 4 frequencies (ie, 1.6, 2.0, 2.4, and 2.8 Hz). The hypotheses are (1) all leg joints maintain the function as torsional springs and increase their stiffness when hopping faster and (2) leg joints are controlled to maintain the mechanical load in the joints or vertical peak accelerations at different body locations when hopping at different frequencies. Results showed that all leg joints behaved as torsional springs during low-frequency hopping (ie, 1.6 Hz). As hopping frequency increased, leg joints changed their functions differently; that is, the hip and knee shifted to strut, and the ankle remained as spring. When hopping fast, the body’s total mechanical energy decreased, and the ankle increased the amount of energy storage and return from 50% to 62%. Leg joints did not maintain a constant load at the joints or vertical peak accelerations at different body locations when hopping at different frequencies.

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Nathálya Gardênia de Holanda Marinho Nogueira, Bárbara de Paula Ferreira, Fernanda Veruska Narciso, Juliana Otoni Parma, Sara Edith Souza de Assis Leão, Guilherme Menezes Lage, and Lidiane Aparecida Fernandes

This study investigated the influence of chronotype on motor behavior in a manual dexterity task performed at different times of the day. Sixteen healthy adults of each chronotype (morning, evening, and neither), as measured by the Morningness–Eveningness Questionnaire, practiced both conditions of the Grooved Pegboard Test either in the morning or in the afternoon to early evening. The “neither” chronotype (65.12 ± 7.46) was outperformed (ps ≤ .03) by both the morning (56.09 ± 7.21) and evening (58.94 ± 7.53) chronotypes when the task had higher cognitive and motor demand but was not outperformed in the task with lower demand (morning = 18.46 ± 2.11; evening = 19.34 ± 2.79; neither = 21.47 ± 2.54; p > .05). No difference between the morning and evening chronotypes was found at the different times of the day (ps > .05), suggesting that a manual dexterity task is not sufficiently demanding to be influenced by chronotype.

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Victoria Sanborn, Lauren Todd, Hanna Schmetzer, Nasha Manitkul-Davis, John Updegraff, and John Gunstad

Anxiety and depressive symptoms are prevalent in athletes. The pandemic of novel coronavirus (COVID-19) may increase risk for symptoms due to fear of exposure during competition or uncertainty regarding participation. The current study examined the prevalence of COVID-19 anxiety in 437 National Collegiate Athletic Association Division I student-athletes and its association with psychological symptoms. Only 0.2% of participants endorsed COVID-19 anxiety symptoms above cutoff. COVID-19 anxiety did not change after postponement of fall sports or differ between persons competing in different seasons. However, higher levels of COVID-19 anxiety were significantly associated with depression, anxiety, and stress. Though student-athletes generally reported low levels of psychological symptoms, females endorsed significantly higher levels than males. Low levels of COVID-19 anxiety in student-athletes may reflect protective factors (e.g., health knowledge, emotion regulation) or the tendency for this population to minimize psychological symptoms. Further investigations on the psychological impact of COVID-19 in athletes is needed.

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Hillary H. Holmes, Randall T. Fawcett, and Jaimie A. Roper

Walking is an integral indicator of human health commonly investigated while walking overground and with the use of a treadmill. Unlike fixed-speed treadmills, overground walking is dependent on the preferred walking speed under the individuals’ control. Thus, user-driven treadmills may have the ability to better simulate the characteristics of overground walking. This pilot study is the first investigation to compare a user-driven treadmill, a fixed-speed treadmill, and overground walking to understand differences in variability and mean spatiotemporal measures across walking environments. Participants walked fastest overground compared to both fixed and user-driven treadmill conditions. However, gait cycle speed variability in the fixed-speed treadmill condition was significantly lower than the user-driven and overground conditions, with no significant differences present between overground and user-driven treadmill walking. The lack of differences in variability between the user-driven treadmill and overground walking may indicate that the user-driven treadmill can better simulate the variability of overground walking, potentially leading to more natural adaptation and motor control patterns of walking.

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Lauren E. Schroeder, Rachel L. Tatarski, and Joshua T. Weinhandl

Decreased dorsiflexion range of motion (DROM) can be modified using static stretching and joint mobilizations and may attenuate known knee anterior cruciate ligament injury risk factors. It is not known how these interventions compare to each other and how they improve knee landing mechanics. This study’s purpose was to determine the immediate effects of static stretching and joint mobilization interventions on DROM measurement changes and right-leg drop jump knee landing mechanics. Eighteen females and 7 males, all recreationally active, completed 2 study sessions. Active and passive DROM, the weight-bearing lunge test, the anterior reach portion of the Star Excursion Balance Test, and a right-leg drop jump landing task were completed before and after the intervention. Change in DROM (ΔDROM) was calculated for DROM assessments between preintervention and postintervention. Pairwise dependent t tests determined no differences in ΔDROM between interventions, and statistical parametric mapping determined increased knee flexion (P = .004) and decreased anterior shear force (P = .015) during landing after both interventions. Increased DROM improves sagittal plane displacement and loading at the knee. Stretching may be a more feasible option in a healthy population for those wanting to maintain range of motion and decrease knee injury risk without physical therapist involvement.

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Ahalee C. Farrow and Ty B. Palmer

This study aimed to examine the effects of age on hip flexion maximal and rapid strength and rectus femoris (RF) muscle size and composition in men. Fifteen young (25 [3] y) and 15 older (73 [4] y) men performed isometric hip flexion contractions to examine peak torque and absolute and normalized rate of torque development (RTD) at time intervals of 0 to 100 and 100 to 200 milliseconds. Ultrasonography was used to examine RF muscle cross-sectional area and echo intensity. Peak torque, absolute RTD at 0 to 100 milliseconds, and absolute and normalized RTD at 100 to 200 milliseconds were significantly lower (P = .004–.045) in the old compared with the young men. The older men exhibited lower cross-sectional area (P = .015) and higher echo intensity (P = .007) than the young men. Moreover, there were positive relationships between cross-sectional area and absolute RTD at 0 to 100 milliseconds (r = .400) and absolute RTD at 100 to 200 milliseconds (r = .450) and negative relationships between echo intensity and absolute RTD at 100 to 200 milliseconds (r = −.457) and normalized RTD at 100 to 200 milliseconds (r = −.373). These findings indicate that hip flexion maximal and rapid strength and RF muscle size and composition decrease in old age. The relationships observed between ultrasound-derived RF parameters and measurements of RTD suggest that these age-related declines in muscle size and composition may be relevant to hip flexion rapid torque production.

Open access

Tetsuo Fukunaga

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Georde Vuillermin, Kelly-Ann Bowles, Ross Iles, and Cylie Williams

Health professionals responsible for return to work plans have little data about allied health movement to guide recommendations following lower back injury. This study aimed to quantify the lumbar movement patterns of allied health professionals within a health care facility throughout a normal workday. An observational case study was undertaken at a public health care facility with 122 allied health professionals. The lumbar movements were recorded with the ViMove together with pain scale measurement. The mean (SD) recording time for allied health was 7.7 (0.7) hours. A mean (SD) 3 (1.4) hours total were spent in standing, 3.8 (1.7) hours in sitting, and 0.8 (0.4) hours in locomotion. Forty-nine flexions were recorded on average per session, most identified as short term (<30 s) within low range (0°–20°). Lumbar movement patterns differed among professions. Thirty-seven (31%) participants reported a history of lower back injury, and 57 (47%) reported low back pain at the end of their workday. This study provides an insight into allied health professionals’ back movement in a hospital or community-based health care setting. These data may inform those who make return to work recommendations or provide rehabilitation services for allied health professionals working with a lower back injury.

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Erika Zemková, Alena Cepková, and José M. Muyor

This study investigates postural responses to unexpected perturbations induced by a load release of different weights. Groups of 26 men (age 22.6 ± 2.4 years, height 178.0 ± 9.1 cm, and body mass 86.9 ± 11.5 kg) and 21 women (age 21.9 ± 2.7 years, height 168.8 ± 6.8 cm, and body mass 65.3 ± 8.7 kg) underwent load-triggered postural perturbations by 1 and 2 kg while standing on a force plate with either eyes open or eyes closed. Postural perturbations induced by a heavier load, representing about 2% and 3% of body weight in men and women, respectively, led to significantly higher peak anterior and peak posterior center of pressure displacements when compared with a lighter load (29.6% and 45.4%, respectively) both with eyes open (36.9%) and closed (42.1%). Their values were significantly lower in men than women only when a higher load was used (∼25%). However, there were no significant differences in time to peak anterior and posterior center of pressure displacements. These findings indicate that heavier load-induced postural perturbations are greater in women than men regardless of visual conditions. This underlines the importance of loading dose in the magnitude of postural responses to externally induced perturbations.