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

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 +/- 90 min/d vs 1028 +/- 85 min/d), (2) took significantly fewer steps and spent fewer minutes at moderate (66 +/- 31 min/d vs 94 +/- 30 min/d) and high step rates (43 +/- 30 min/d vs 72 +/- 38 min/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. (c) 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation