The Impact of Cast Walker Design on Metabolic Costs of Walking and Perceived Exertion

Cast walkers (CWs) are often prescribed to offload diabetic foot ulcers (DFUs). However, their mass, the degree of ankle immobilization and the limb length discrepancy they induce may increase the energetic demands of walking, contributing to lower adherence and poorer healing. The purpose of this study was to evaluate the effects of different commercially available CW options on the metabolic costs and perceived exertion of walking, and on related spatiotemporal kinematics, in healthy young participants as an initial step to understanding factors that impact adherence in patients with DFUs.

Participants walked on an instrumented treadmill at a standardized speed for six minutes under five footwear conditions: (1) athletic shoes only (control); (2) ankle-high CW on the dominant limb with athletic shoe on the contralateral limb; (3) condition two with an external lift on the athletic shoe; (4 and 5) conditions two and three with a knee-high CW. Condition 1 was performed first, after which the CW conditions were randomized. During all conditions, a portable calorimeter recorded gas exchange on a breath-by-breath basis. The metabolic cost of transport (MCoT) was quantified as the mean oxygen consumed per meter walked per kilogram body mass, after accounting for standing. After walking, participants reported perceived exertion using the Borg Rating of Perceived Exertion scale (RPE). From the treadmill data, we extracted the mean step width (SW) as well as absolute values for symmetry indices (SIs) for step length (SL) and step time (ST), all of which have associations with MCoT. For each outcome, linear mixed models compared each CW condition with the control and tested for effects of CW height (ankle-high vs. knee-high) and of the lift.

A total of 14 healthy young adults without diabetes participated. MCoT, RPE and SW were significantly higher for all CW conditions compared to the control, with less consistent results for asymmetry measures. MCoT was not significantly different across CW height or lift condition although an unexpected interaction between limb and CW height n was observed; MCoT was lower in the knee-high CW with vs. without a lift but did not change in the ankle-high CW based on lift status. Similarly, neither SW nor SIs changed in expected fashions across conditions. In contrast, RPE was significantly lower using the ankle- vs. knee-high CW and when using a lift vs no lift, with no significant interaction.

Although metabolic costs were unaffected by CW design changes, which may reflect the absence of anticipated changes in kinematics that impact MCoT, perceived exertion was reduced through such changes. Unanticipated biomechanical changes may reflect a complex interaction among a number of competing factors that dictate behavior and MCoT. The differing results in perception of exertion and metabolic costs might be due to participants' perceived exertion being sensitive to the collective impact of interacting biomechanical factors, including those not quantified in this study. Future work should seek to directly evaluate the impact of CW design changes in patients with DFU and the relationship to adherence.