A common method to evaluate the energy cost of walking is the oxygen consumption measurement with a metabolimeter, but it is expensive and time-consuming. The physiological cost index (PCI) is easy to calculate, is low cost, and doesn’t require high-tech equipment. It estimates energy expenditure during walking as a ratio of heart rate and self-selected walking speed, and previous studies have reported that PCI is reliable in individuals with lower-limb amputations, but only if there is a walking impairment, according to an open-access study published in December in the Canadian Prosthetics and Orthotics Journal.

The latest study evaluated the correlation between PCI and energy cost of walking (ECW) in active individuals with traumatic transtibial amputations and no residual limb problems or comorbidities in different walking conditions. A secondary aim was to evaluate if the correlation can determine ECW from PCI values.

Researchers calculated metabolic data, heart rates, and walking speeds of 90 male participants as they walked overground, on a treadmill with no slope, and on a treadmill at 12 percent slope during a six-minute walk test.

The research team found a significant correlation between ECW and PCI in participants walking overground and on the 12 percent slope, but found only a poor to moderate correlation around the trendline. No significant correlation was found walking on the treadmill with no slope. The Bland-Altman plot analysis the researchers conducted suggests that is not possible to evaluate ECW directly from PCI, according to the study’s authors.

They concluded that PCI is a reliable alternative measure of energy expenditure during walking in active individuals with transtibial amputations when performing overground or at high intensity on a treadmill; PCI is therefore useful only for monitoring a within-subject assessment.