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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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Tetsuo Fukunaga

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Mark L. Latash and Vera L. Talis

The authors have presented an unpublished manuscript by Nikolai Aleksandrovich Bernstein written in the form of a diary in 1949. Bernstein focused on the concept of time as a coordinate in four-dimensional space and discussed a variety of issues, including the definition of time, its measurement, time travel, asymmetry of the past and future, and even linguistics. In particular, he offered a definition of life tightly linked to the concept of time. Overall, this manuscript offers a glimpse into Bernstein’s thinking, his sense of humor, and his sarcasm, intimately coupled with the very serious attitude to scientific discourse.

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John H. Challis

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Alesha Reed, Jacqueline Cummine, Neesha Bhat, Shivraj Jhala, Reyhaneh Bakhtiari, and Carol A. Boliek

Purpose: The authors evaluated changes in intermuscular coherence (IMC) of orofacial and speech breathing muscles across phase of speech production in healthy younger and older adults. Method: Sixty adults (30 younger = M: 26.97 year; 30 older = M: 66.37 year) read aloud a list of 40 words. IMC was evaluated across phase: preparation (300 ms before speech onset), initiation (300 ms after onset), and total execution (entire word). Results: Orofacial IMC was lowest in the initiation, higher in preparation, and highest for the total execution phase. Chest wall IMC was lowest for the preparation and initiation and highest for the total execution phase. Despite age-related differences in accuracy, neuromuscular modulation for phase was similar between groups. Conclusion: These results expand our knowledge of speech motor control by demonstrating that IMC is sensitive to phase of speech planning and production.

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Jack P. Callaghan

Open access

Karin Weman Josefsson

Sweden has adopted a somewhat different approach to handle the corona pandemic, which has been widely debated both on national and international levels. The Swedish model involves more individual responsibility and reliance on voluntary civic liability than law enforcement, while common measures in other countries are based on more controlling strategies, such as restrictive lockdowns, quarantines, closed borders, and mandatory behavior constraints. This commentary aims to give a brief overview of the foundations of the Swedish model as well as a discussion on how and why it has been adopted in the Swedish society based on Swedish legislations, culture, and traditions. Finally, perspectives on how the Swedish model could be connected to the tenets of self-determination theory will be discussed.

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Manuel J. Escalona, Daniel Bourbonnais, Michel Goyette, Damien Le Flem, Cyril Duclos, and Dany H. Gagnon

The effects of walking speeds on lower-extremity muscle synergies (MSs) were investigated among 20 adults who walked 20 m at SLOW (0.6 ± 0.2 m/s), natural (NAT; 1.4 ± 0.1 m/s), and FAST (1.9 ± 0.1 m/s) speeds. Surface electromyography of eight lower-extremity muscles was recorded before extracting MSs using a nonnegative matrix factorization algorithm. Increasing walking speed tended to merge MSs associated with weight acceptance and limb deceleration, whereas reducing walking speed does not change the number and composition of MSs. Varying gait speed, particularly decreasing speed, may represent a gait training strategy needing additional attention given its effects on MSs.

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Daniella M. DiGuglielmo, Mireille E. Kelley, Mark A. Espeland, Zachary A. Gregory, Tanner D. Payne, Derek A. Jones, Tanner M. Filben, Alexander K. Powers, Joel D. Stitzel, and Jillian E. Urban

To reduce head impact exposure (HIE) in youth football, further understanding of the context in which head impacts occur and the associated biomechanics is needed. The objective of this study was to evaluate the effect of contact characteristics on HIE during player versus player contact scenarios in youth football. Head impact data and time-synchronized video were collected from 4 youth football games over 2 seasons in which opposing teams were instrumented with the Head Impact Telemetry (HIT) System. Coded contact characteristics included the player’s role in the contact, player speed and body position, contact height, type, and direction, and head contact surface. Head accelerations were compared among the contact characteristics using mixed-effects models. Among 72 instrumented athletes, 446 contact scenarios (n = 557 impacts) with visible opposing instrumented players were identified. When at least one player had a recorded impact, players who were struck tended to have higher rotational acceleration than players in striking positions. When both players had a recorded impact, lighter players and taller players experienced higher mean head accelerations compared with heavier players and shorter players. Understanding the factors influencing HIE during contact events in football may help inform methods to reduce head injury risk.