Functional ability and muscle force in healthy children and ambulant Duchenne muscular dystrophy patients

doi:10.1016/j.ejpn.2005.06.004

European Journal of Paediatric Neurology

Volume 9, Issue 6, November 2005, Pages 387-393

https://doi.org/10.1016/j.ejpn.2005.06.004 Get rights and content

Summary

Neuromuscular disorders are characterised by progressive muscle weakness, which in time causes functional impairment. To quantify the extent of disease progression, muscle force and functional ability can be measured. Which of these parameters changes most depends on the disease stage.

In a previous study, we reported normal values for muscle force obtained by hand-held dynamometry in healthy children aged 4–16 years. In the present study, we report normal values for timed functional tests in healthy children aged 4–11 years.

These normal values were compared with values obtained in 16 ambulant patients with Duchenne muscular dystrophy (DMD) aged 5–8 years to study the extent of functional impairment.

In ambulant patients with DMD, we found that muscle function assessed by timed functional tests (running 9 m and rising up from the floor) and muscle force assessed by hand-held dynamometry were severely impaired. However, a small reduction of muscle force was accompanied by a large reduction in functional ability. Therefore, in our group of ambulant patients with DMD, timed functional testing was the most sensitive parameter to determine the extent of disease progression. Timed functional testing may therefore be considered as an additional outcome measure in drug trials to evaluate the effects of therapy in ambulant patients with DMD and possibly in other neuromuscular disorders.

Introduction

Neuromuscular disorders (NMD) are characterised by progressive muscle weakness and can present themselves at any time from birth through adulthood. With progressing muscle weakness, functional ability will eventually become impaired.

Muscle strength and functional ability are often determined by testing methods such as the Medical Research Council-scale in which muscle strength can be classified in a 6-point scale or by visual assessment, respectively.

Because these methods are to some extent subjective, many centres also employ additional quantitative testing methods such as hand-held dynamometry1, 2, 3, 4 to quantify muscle strength.

To determine the extent of muscle weakness and functional impairment, to monitor the effects of therapy or to determine disease progression objectively, normal values for muscle force and functional ability are needed. Which of these parameters should preferably be used depends on the disease stage. We suggest that a decrease in muscle force is only noticed after the loss of muscle force is so extensive that activities of daily living (ADL) become hampered. Typically, in the early stages of DMD when patients are ambulant and ADL function is still normal, we expect that dynamometry would already show a decrease in muscle force. In the advanced stages of DMD when patients are non-ambulant, most functional abilities will be lost although some residual force may still be measured by dynamometry.

We hypothesise that in ambulant patients with DMD, large changes in functional ability can be observed, whereas muscle force, although severely affected, deteriorates at a much slower rate.

We previously established reference values for muscle force in normal children.² In this study, we additionally report normal values for timed functional tests in healthy children aged 4–11 years.

Furthermore, we determine which parameter changes most in ambulant DMD patients by comparing normal values for muscle force and functional ability with values obtained in 16 ambulant patients with DMD aged 5–8 years.

Section snippets

Subjects and methods

Healthy children aged 4–11 years and ambulant patients with DMD aged 5–8 years, who participated in a randomised controlled prednisone trial,⁵ were included in this study. Anthropometric measurements (height and weight) were taken and timed functional testing (running 9 m and rising up from a supine position on the floor to a standing position as fast as possible) was performed. All tests were carried out in shorts and t-shirts and with bare feet. Timed tests were measured in seconds by using a

Statistics

Differences between boys and girls for timed functional tests were calculated by using Student's t-test or the non-parametric Mann–Whitney test for independent group samples when data were not distributed normally. Because some neuromuscular disorders such as DMD are only found in boys, we did not pool the values for both genders.

Normality was tested by the Shapiro–Wilk test. Significance was accepted if two-sided p-values were below 5%. Pearson correlation coefficients (r) were calculated in

Results

Sixty-six healthy boys (mean age 7.4 years, SD 2.3) and 57 healthy girls (mean age 7.4 years, SD 2.2) were included. They were equally distributed over each age group comprising one year (Table 1). The mean age of the 16 ambulant patients with DMD was 6.25 years (SD 0.93 years). Height and weight of the patients with DMD was distributed normally and within normal range.

Mean values for both timed functional tests are presented in Table 1. As mean values were not distributed normally, we used the

Discussion

To quantify the extent of functional impairment in DMD muscle force or functional ability can be measured. Which of these parameters changes most depends on the degree of force loss.

We hypothesised that functional testing changes more than muscle force testing in intermediate disease stages, where large changes in functional ability can be observed, whereas muscle force, although severely affected, deteriorates only slightly. Therefore, functional testing may be used as an additional parameter

Acknowledgements

This study was financially supported by the ‘Prinses Beatrix Fonds’, The Netherlands. Projectnumber: MAR99-0219.

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Original articleFunctional ability and muscle force in healthy children and ambulant Duchenne muscular dystrophy patients

Summary

Introduction

Section snippets

Subjects and methods

Statistics

Results

Discussion

Acknowledgements

Neuromuscul Disord

Neuromuscul Disord

Neuromuscul Disord

Eur J Paediatr Neurol

Original article
Functional ability and muscle force in healthy children and ambulant Duchenne muscular dystrophy patients