Effect Of Unweighting Assistance On Sit-to-stand Mechanics

Document Type

Article

Publication Date

5-2016

Publication Title

Medicine & Science in Sports & Exercise Supplemental

DOI

10.1249/01.mss.0000486486.64511.b9

ISSN

1530-0315

Abstract

Being able to rise from a chair is an important activity of daily living and often a determinant for independence in older adults. Older adults who have difficulty rising from a chair may benefit from training devices that provide adjustable unweighting assistance.

PURPOSE: To determine the effects of four levels of unweighting assistance on sit-to-stand (STS) mechanics.

METHODS: Healthy men (n=5) and women (n=9) aged 18-35 years completed five repetitions of the stand-sit-stand cycle using a STS training device (Sit2Stand Trainer, Biodex Inc., Shirley, NY) with assistance comparable to 40%, 50%, 60%, and 70% of body weight. For the current analysis, only the motion from sitting to standing was investigated. Subjects performed the repetitions using a self-selected pace at 5 second intervals. Feet, shanks, thighs, pelvis, and trunk kinematic data and ground reaction forces under the right foot were collected and used to determine total rise time, timing of peak joint velocities, and phases of the STS movement. Inverse dynamics were then used to calculate ankle, knee, and hip net joint moment impulses (NJMI) during two phases: lift off to peak dorsiflexion and peak dorsiflexion to end of movement.

RESULTS: Assistance level had no significant (P>.05) effect on total rise time and timing of peak joint velocities. Assistance level by joint by phase analysis revealed a significant three-way interaction (P=.005). Post hoc interaction contrasts by phase revealed a significant assistance level by joint interaction (P<.001) during lift off to peak dorsiflexion. Subsequent trend analysis demonstrated significant linear NJMI reduction for hip (P=.036, d=1.30) and increase for ankle (P=.017, d=1.51) with greater assistance. From peak dorsiflexion to end of movement, there was a significant linear decrease in NJMI across all three joints (P=.010, d=2.36).

CONCLUSIONS: STS movement timing was similar across the four assistance levels, however, the effects on NJMI were different for the two phases. From lift off to peak dorsiflexion, with greater assistance, torques at the hip were decreased with a concurrent increase at the ankle. From peak dorsiflexion to end of movement, greater assistance produced similar decreases across all three joints. Future research will begin replicating this study using older adults.

Comments

© 2016 American College of Sports Medicine

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