Use of step activity monitoring for continuous physical activity assessment in boys with Duchenne muscular dystrophy

Abstract

McDonald CM, Widman LM, Walsh DD, Walsh SA, Abresch RT. Use of step activity monitoring for continuous physical activity assessment in boys with Duchenne muscular dystrophy. Arch Phys Med Rehabil 2005;86:802–8. Objectives To evaluate the StepWatch Activity Monitor (SAM) as a quantitative measure of community ambulation, to investigate activity patterns and heart rate of ambulatory boys with Duchenne muscular dystrophy (DMD), and to correlate the step activity with measures of body composition and strength. Design Case-control study. Setting General community and laboratory. Participants Sixteen ambulatory boys with DMD and 20 male controls (age range, 5–13y). Interventions Not applicable. Main outcome measures Laboratory determinations of body composition, knee extension strength, and minute-by-minute step rate and heart rate during 3 days of community activity. Results During the 3 days of activity, DMD subjects, when compared with controls, (1) had significantly more inactive minutes (1096±90min/d vs 1028±85min/d), (2) took significantly fewer steps and spent fewer minutes at moderate (66±31min/d vs 94±30min/d) and high step rates (43±30min/d vs 72±38min/d), (3) had higher resting heart rate (110±12 beats/min vs 94±7 beats/min) and lower increase in heart rate with increased step rate, and (4) had lower maximum heart rates (164±24 beats/min vs 208±16 beats/min). Percentage of body fat and knee extension strength correlated with total step activity in the DMD group but not in the control group. Conclusions Step-rate monitoring with the SAM provides useful outcome measures with which to evaluate the activity of ambulatory boys with DMD. Their heart rate did not increase with activity to the same degree as observed in the control group.