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Susan J. Hall, Jane A. Kent and Vern R. Dickinson

Prolonged trapezing during sailing often results in low back pain among elite sailors. Modifications of the trapeze harness have been proposed as one approach to ameliorating this problem. To evaluate six harnesses incorporating novel features that had tested well during pilot work, myoelectric activity was monitored at C5, T6, and L5 levels of sacrospinalis and at an abdominal site while five elite sailors wore the harnesses. Integrated EMG (IEMG) values were stored by a microcomputer at periodic intervals during each 10-min trial, as each subject maintained a static horizontal trapezing position in the laboratory. Factorial repeated-measures ANOVA indicated no change in IEMG values over time, but significant (p<0.001) differences among harnesses at all four electrode sites. Features of trapeze harness design that appear to minimize muscular tension include heavy, rigid padding throughout the harness, full-length shoulder-to-buttocks support of the trunk, and adjustable leg strap supports as opposed to a crotch strap.

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Jocelyn F. Hafer, Mark S. Miller, Jane A. Kent and Katherine A. Boyer

Older females experience higher rates of disability than males, potentially due to sex-specific differences in gait and muscle function. The authors evaluated the effects of age and physical activity (PA) on gait mechanics and knee extensor muscle function in males and females. Three groups of 20 individuals (each 10 females) participated: young (21–35 y) and highly and less active older (55–70 y) adults. Knee extensor strength and joint mechanics during preferred speed gait were collected before and after 30 minutes of walking. Age by sex and PA by sex interactions indicated older and less active older females had lower concentric knee extensor muscle power and larger hip extension moments than males. After 30 minutes of walking, older less active adults had larger decreases in knee extensor power than their highly active older counterparts, and older adults of both sexes had decreases in ankle dorsiflexion moments while young adults did not. These results suggest that older, particularly less active, adults are susceptible to knee extensor muscle fatigue from moderate activity. For older adults, high levels of PA may be necessary to preserve gait mechanics in response to a bout of exercise. This new information may be important for targeting interventions in at-risk older adults.

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Jebb G. Remelius, Joseph Hamill, Jane Kent-Braun and Richard E.A. Van Emmerik

Individuals with multiple sclerosis (MS) often have poor balance control that is especially apparent during dynamic tasks such as gait initiation (GI). The purpose of this study was to investigate how balance symptoms due to MS alter spatiotemporal variables, coordination, and temporal margins within the stability boundary during gait initiation. Twelve women with MS (Expanded Disability Status Scale [EDSS] mean = 4.0, SD = 1.4) and 12 women without MS (control group) initiated gait at their preferred speed. MS participants attained a slower anterior velocity because of smaller anterior center of mass displacements and took longer to complete the initiation of gait than the control group. MS participants exhibited a smaller posterior shift in center of pressure during GI and stepped with a longer dual support time than the control group. However, these changes may be due to differences in initiation velocity. Relative timing analysis showed invariance in postural and locomotor phases of gait initiation between groups. The MS group showed different coordination between anterior-posterior and medio-lateral center of pressure components while increasing temporal margins to the posterior and lateral stability boundaries in comparison with the control group. Overall, during gait initiation at their preferred speed the MS participants adopted a functional strategy that produces lower speed and reduced proximity to the stability boundaries prior to stepping.