The physiological cost of restricted weight bearing

By R.W. Westerman, P. Hull, R.G. Hendry, and J. Cooper, Selly Oak Hospital, University Hospital Birmingham HS Foundations Trust, Birmingham, United Kingdom

Reprinted with permission from INJURY, International Journal of the Care of the Injured (2008) 39, 725-727.

Summary

Background: To identify the energy cost of placing restrictions on weight-bearing status.

Methods: Measurement of the physiological cost index (PCI) for 11 healthy volunteers carrying out three types of mobilization over a 100 m course in a physiology laboratory: normal walking fully weight bearing (FWB); non-weight bearing (NWB) and feather touch weight bearing (FTWB). NWB and FTWB were performed using a walking frame for support. FTWB was defined as mobilization with the foot flat, as in normal gait, but with less than 100 N force generated through the limb.

Results: Both NWB and FTWB developed significantly greater PCI than normal walking. There was no physiological cost benefit of FTWB over NWB, p = 0.67, but FTWB was perceived by all participants to be less tiring.

Conclusions: Restricting weight-bearing status significantly increases energy expenditure; the PCI. FTWB may be a more tolerable form of restricted weight bearing, although the PCI does not reflect this perception.

These findings should be borne in mind when recommending such restrictions in clinical practice and encouraging a patient to mobilize early and effectively.

Keywords: weight bearing, physiological cost, PCI, fracture, rehabilitation

Introduction
Mobilization following a fracture will always be difficult. Both operatively and non-operatively managed patients with pelvic or lower limb injuries require some degree of weight­bearing restriction.

This study set out to assess the physiological cost caused by restricting an individual's weight-bearing status, and compared it to fully weight bearing (FWB).

Non-weight bearing (NWB) requires no weight to be placed through the limb on the affected side. Feather-touch weight bearing (FTWB) requires the majority of a patient's body weight to be supported with crutches or a walking frame whilst touching the foot of the affected limb to the ground with a force of no greater than 100 N in our study. The FTWB is thought to be less strenuous and encourage compliant mobilization without compromising their fracture site or fracture fixation.

Exertion was assessed using the physiological cost index (PCI). PCI was defined by MacGregor (1979) as follows:
PCI (beats/m) = walking heart rate - resting rate (beats/min) walking speed (m/min)
and has since been validated and shown to correlate well with other methods of determining energy expenditure by Bailey and Ratcliffe ( 1995) among others, to assess energy expenditure in situations such as this. The participant should be able to move at the speed they find most comfortable, and establish a stead% -state heart rate whilst mobilizing.

Participants and methods
A group of 11 able-bodied hospital staff was recruited, nine males and two females. with an age range of 25 to 47. Each was required to complete three different tasks: a baseline of FWB, NWB with a walking frame and FTWB with a walking frame. The order of each task was varied to avoid bias.