Walking activity in a large cohort of boys with Duchenne muscular dystrophy

Abstract

Introduction: In this study we explored walking activity in a large cohort of boys with Duchenne muscular dystrophy (DMD).

Methods: Step activity (monitored for 7 days), functional ability, and strength were quantified in ambulatory boys (5-12.9 years of age) with DMD and unaffected boys. Ambulatory status was determined 2 years later.

Results: Two to 5 days of activity monitoring predicted weekly step activity (adjusted R² = 0.80-0.95). Age comparisons revealed significant declines for step activity with increasing age, and relationships were found between step activity with both function and strength (P < .01). Our regression model predicted 36.5% of the variance in step activity. Those who were still ambulatory after 2 years demonstrated baseline step activity nearly double that of those who were no longer walking 2 years later (P < .01).

Discussion: Step activity for DMD is related to and predictive of functional declines, which may be useful for clinical trials.

Keywords: accelerometry, daily steps, Duchenne muscular dystrophy, functional ability, physical activity, walking.

FIGURE 1

Comparison of step activity in steps per day (mean ± standard deviation) across four age groups from a large sample of boys with Duchenne muscular dystrophy (n = 70): 5 to 6.9 years (n = 18) = 7033 ± 1957 steps; 7 to 8.9 years (n = 20) = 5055 ± 1889 steps; 9 to 10.9 years (n = 20) = 4443 ± 1587 steps; and 11 to 12.9 years (n = 12) = 3385 ± 1522 steps. Dashed line represents the mean and gray area represents the standard deviation for the step activity of 10 healthy control participants. 6MWD, 6-minute walk test distance; KE, knee extensor muscle group; PF, plantar flexor muscle group

FIGURE 2

Relationship between step activity, functional abilities, and strength in boys with DMD. A, 6MWD, distance walked for 6-minute walk test. B, Ten-meter walk/run, time to traverse 10 meters. C, Four stairs, time to ascend 4 steps. D, Supine Up, time to rise from the floor. E, KE peak torque, normalized knee extensor strength. F, PF peak torque, normalized plantar flexor muscle strength. Spearman correlations used for all variables. **Correlation significant at the P < 0.01 level

FIGURE 3

Comparison of step activity (mean steps/day ± SD) across: A, Three groups of boys with DMD based upon the distance walked in the 6-minute walk test: 0 to 300 meters (n = 9) = 3170 ± 1782; 301 to 400 meters (n = 33) = 5388 ± 1764; >400 meters (n = 19) = 5806 ± 2515. B, Two groups of boys with DMD, those who lost the ability to ambulate within 2 years (n = 11) = 3112 ± 1166 steps, and those who were still walking 2 years after assessing step activity (n = 25) = 6162 ± 2290 steps. Amb, ambulant (those still walking); LOA, lost ability to ambulate