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, 5-13 y). 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.

Utility of a step activity monitor for the measurement of daily ambulatory activity in children.

OBJECTIVES: To evaluate the reliability and validity of the StepWatch Activity Monitor (SAM) as a reliable and valid measurement tool for assessing ambulatory activity in able-bodied children and to assess the ambulatory activity of able-bodied children. DESIGN: Descriptive study. SETTING: General community. PARTICIPANTS: Ninety-seven able-bodied children, aged 6 to 20 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Anthropometric parameters, calibration of a step activity monitor to ensure accuracy, and 3 days of simultaneous heart rate and step activity monitoring. RESULTS: The SAM had an accuracy of 99.87% compared with the observer-counted steps and was shown to be valid and reliable when compared with heart rate monitoring. The subjects in all age groups (6-10 y, 11-15 y, 16-20 y) spent most of their active time at low step rate but took the fewest steps at this rate. Although the least amount of time was spent at high step rate, it accounted for the most steps. The 6- to 10-year-old group took more total steps per day than any of the other groups. Boys spent significantly more time at high step rate than girls in all age groups (mean for boys, 66+/-4 min/d; girls, 47+/-4 min/d). CONCLUSIONS: The SAM is an accurate, valid, and useful tool for measuring continuous, time-based step activity during real-world community activity for children and adolescents.