Validation of a clinically feasible activity monitor which measures body postures and movements in adults with lower-limb amputation who wear a prosthesis

Purpose: A simple single-unit activity monitor (Activ8), which is based on a tri-axial accelerometer, measures specific body postures and movements, and has potential for research and clinical practice to monitor and optimize physical behavior of people with chronic conditions. However, the validity of the Activ8 in people with lower-limb amputation is unknown. Studying validity in this specific group is needed because they often have postures and movements that differ from the normal population, and which might affect validity. Therefore our study aimed to validate the Activ8 to measure body postures and movements in people with a lower-limb amputation. Methods: Thirty people with a unilateral lower-limb amputation and who are able to walk with a prosthesis completed two activity protocols in a simulated home setting: one with basic activities (only one posture or movement) and one with functional activities from daily living. Outcomes of the Activ8 (used in thigh-fixed position and pocket position) were compared to outcomes of video observation (the reference method). Primary analyses focused on the agreement in duration of merged measures of physical activity (walking, running, cycling, standing) and sedentary behavior (lying/sitting) with the Activ8 used in thigh-fixed position. Additional analyses included the detection of specific types of physical activity, the effects of amputation level and cause, and the validity of the Activ8 in pocket position. Results: Overall percentage time differences between Activ8 (thigh-fixed position) and video observation for merged measures of physical activity and sedentary behavior outcomes were −2.7% and 2.3%, respectively. These percentages were −1.6% and 1.3% for the basic protocol, and −3.9% and 3.6% for the functional protocol, respectively. For specific postures and movements, differences were larger (ranging from −12.6% to 7.1%). Conclusion: The Activ8 activity monitor has acceptable validity to measure physical activity and sedentary behavior in people with a unilateral lower-limb amputation.