Amputees use 30% more energy than able-bodied people when doing simple tasks like walking. Their prosthetics are supposed to help them, but a team of engineers from the University of Central Florida (UCF) and University of Michigan has found that most transtibial amputees don’t have their prosthetic on the right power setting. This could result in them exerting more energy than necessary.

A UCF engineering professor recently published a study in Scientific Reports that shows that people with transtibial amputations -- the loss of a limb below the knee -- may improve their walking ability if they change the power setting on their devices. Source: UCF: Karen Norum

Most transtibial amputees are given passive-electric prostheses, which store and release energy when they touch the ground. They don’t perform the same positive net ankle work that uses muscle shortening contractions to walk and only provide 1/8^th the power that an able-bodied person’s gastrocnemius and soleus muscles exert. This means the user has to exert more energy when walking in order to lift the prosthesis.

Powered ankle prostheses use actuators to reduce these increased metabolic costs. BiOM, a powered ankle prosthesis that most amputees use, was used in the study. BiOM has a visual display that allows wearers to customize the power setting to their liking.

But just how much power is the right amount? This question plagues many amputees. Too little power results in high metabolic costs, but too much could result in knee hyperflexion and increased energy absorption in the knee. The UCF researchers aimed to find out what the right amount of power is.

The team tested the BiOM prosthesis on 10 people with transtibial amputations. They measured the metabolic cost of transport (COT) while using it at various power settings as participants walked on a treadmill.

The study found that the perfect power setting is not the same as the power an able-bodied person uses to walk. The perfect power setting is higher, in order to decrease the excess energy that the amputee uses.

"The key finding of this study was that none of the subjects had the minimum metabolic cost when they walk with unimpaired individuals' work or power. When they had greater power, then the impaired individuals actually reduced metabolic cost," said Hwan Choi, an assistant professor in the UCF Department of Mechanical and Aerospace Engineering and co-lead author of the study.

The study also found that power settings greater than 50% reduced COT. The setting that minimized energy cost was double the net ankle work of a biological ankle. The perfect power setting for an amputee is just over the amount of power they would use if they had a biological ankle, leg or foot. Amputees that follow this rule have a greater chance of staying active, improving life quality and preventing health problems.

The study was published in Scientific Reports.