Analysis of vertical ground reaction force variables during a Sit to Stand task in participants recovering from a hip fracture

Abstract

Background: A Sit to Stand task following a hip fracture may be achieved through compensations (e.g. bilateral arms and uninvolved lower extremity), not restoration of movement strategies of the involved lower extremity. The primary purpose was to compare upper and lower extremity movement strategies using the vertical ground reaction force during a Sit to Stand task in participants recovering from a hip fracture to control participants. The secondary purpose was to evaluate the correlation between vertical ground reaction force variables and validated functional measures.

Methods: Twenty eight community dwelling older adults, 14 who had a hip fracture and 14 control participants completed the Sit to Stand task on an instrumented chair designed to measure vertical ground reaction force, performance based tests (Timed up and go, Berg Balance Scale and Gait Speed) and a self report Lower Extremity Measure. A MANOVA was used to compare functional scales and vertical ground reaction force variables between groups. Bivariate correlations were assessed using Pearson Product Moment correlations.

Findings: The vertical ground reaction force variables showed significantly higher bilateral arm force, higher uninvolved side peak force and asymmetry between the involved and uninvolved sides for the participants recovering from a hip fracture (Wilks' Lambda=3.16, P=0.019). Significant correlations existed between the vertical ground reaction force variables and validated functional measures.

Interpretation: Participants recovering from a hip fracture compensated using their arms and the uninvolved side to perform a Sit to Stand. Lower extremity movement strategies captured during a Sit to Stand task were correlated to scales used to assess function, balance and falls risk.

Copyright © 2010 Elsevier Ltd. All rights reserved.

Figures

Figure 1

The instrumented chair incorporated 4 force plates to measure vertical ground reaction forces under the seat, chair, right lower extremity and left lower extremity.

Figure 2

The following figures are an example of a single participant trial A. The summed vertical ground reaction forces(vGRF) under the right and left lower extremity(vGRFbilateal) and arms (vGRFarms) are shown. Task initiation and the end of the rising phase was determined from vGRFbilateral. Seat off, which determines the transition point between the preparation and rising phases, was determined from the seat force plate (vGRFseat). The rate of force development (RFDbilateral) was calculated as the slope from 25 to 50 % of the force value at seat off. The arms impulse was the area under the vGRFarms. B. The unilateral measures of vGRFinvolved/uninvolved were determined from the left and right force plates. For the preparation phase the RFD invovled/uninvolved was calculated similar to RFD bilateral. Symmetry during the rising phase was calculated as the area between the vGRFinvolved and uninvolved throughout the rising phase.

Figure 3

Scatter plot of bilateral rate of force development (vGRFbilateral) and the Lower Extremity Measure (LEM). Blue circles represent elderly control group and red squares represent hip fracture group.