Metabolic Cost and Physical Activity in Sedentary Adults With a Unilateral Transtibial Amputation as Compared to Controls

Up to 48% of adults following a lower-limb amputation will die within the upcoming year. Lack of physical activity (exercise) contributes to high death rates. It is recommended that younger (and middle-aged) adults without a health condition walk 10,000 steps/day to reduce the risk of chronic health conditions, while recommendations are 7,100 steps per day for older adults and those with chronic health conditions. Adults with a lower-limb amputation walking about 21-43% of the recommended 7,100 steps/day. Step activity monitors, such as the StepWatch (a research-grade accelerometer) and the FitBit (a commercially-available monitor) provide a means of evaluating physical activity, which is important since patients tend to over-estimate their level of physical activity. Activity monitor use, however, may not be possible in every healthcare practice setting, as monitors may cost $100-$600 and someone must remove the data from the monitor, interpret the data, and enter the data into the patient's medical record. Therefore, physical activity questionnaires, where the patient self-reports their physical activity, are ideal in a clinical setting. Unfortunately, to date, there has been little research looking at the accuracy of physical activity questionnaires in patients with lower-limb amputations and how these questionnaires measure up to data obtained from step activity monitors.

In addition to 7,100 steps/day, adults with mobility-limiting, chronic conditions (including individuals with lower-limb amputations) should participate in ≥150 minutes of moderate-intensity physical activity per week, with activity in ≥10 minutes per bout. Moderate-intensity activity has been defined as 3 metabolic equivalents (METs). One MET is equal to the amount of oxygen one consumes at rest, so 3 METs means that one is consuming 3 times the amount of oxygen one would consume at rest. In healthy adults without a medical condition this equates to walking 2.6-2.7 mph or 100 steps/minute, while for adults with an amputation of the leg below-the-knee (i.e. a transtibial amputation), 1.47 mph or 86 steps/minute has been reported to equal 3 METs. Maximal walking speeds for adults with lower-limb amputations, specifically those who have lost their limb due to poor blood circulation may be ≤1.67 mph, so one must question if walking 1.47 mph for an extended time is possible for these patients. Investigators believe that 1.47mph is greater than 3 METs for adults with a lower-limb amputation who have other medical issues, such as diabetes and peripheral vascular disease, and who are deconditioned and not participating in physical activity.

It is important to know what speed (mph) and cadence (steps/minute) equals 3 METs in adults with a lower-limb amputation with other medical conditions who are currently inactive. Investigators believe that these patients represent the vast majority of patients that healthcare providers encounter and must council regarding increasing physical activity levels. Providers need to know what speed and cadence is equal to 3 METs for inactive patients with limb loss with other medical conditions, so that providers can appropriately advise their patients and prescribe exercise.

Walking exercise may occur over-ground or on a treadmill. When an individual with a lower-limb amputation is walking over-ground, their right-to-left side walking pattern will be more asymmetrical (uneven) when compared to when they are walking on a treadmill. When walking is more symmetrical side-to-side (even), the patient may have to expend more energy. Energy expenditure can be assessed as the amount of oxygen consumed, which can be obtained while wearing a mask that evaluates the participant's breathing while walking. Among adults with a lower-limb amputation, energy expenditure studies have generally used treadmills to look at energy expenditure. Over-ground versus treadmill conditions, however, are different, and as such, what equals 3 METs (speed, cadence) in each walking condition may vary.

Further, no studies have compared the energy cost of walking in adults who are inactive with a lower-limb amputation to age-, sex-, and body mass index (computed from height and weight) -matched adults without an amputation. While studies have evaluated the impact of aging and limb length of the amputated limb on energy expenditure, few have evaluated modifiable factors that may impact energy expenditure among adults with lower-limb amputation. Similarly, little research has explored modifiable factors that may impact physical activity levels.