Differences in muscle activity during hand-dexterity tasks between women with arthritis and a healthy reference group

Abstract

Background: Impaired hand function is common in patients with arthritis and it affects performance of daily activities; thus, hand exercises are recommended. There is little information on the extent to which the disease affects activation of the flexor and extensor muscles during these hand-dexterity tasks. The purpose of this study was to compare muscle activation during such tasks in subjects with arthritis and in a healthy reference group.

Methods: Muscle activation was measured in m. extensor digitorium communis (EDC) and in m. flexor carpi radialis (FCR) with surface electromyography (EMG) in women with rheumatoid arthritis (RA, n = 20), hand osteoarthritis (HOA, n = 16) and in a healthy reference group (n = 20) during the performance of four daily activity tasks and four hand exercises. Maximal voluntary isometric contraction (MVIC) was measured to enable intermuscular comparisons, and muscle activation is presented as %MVIC.

Results: The arthritis group used a higher %MVIC than the reference group in both FCR and EDC when cutting with a pair of scissors, pulling up a zipper and-for the EDC-also when writing with a pen and using a key (p < 0.02). The exercise "rolling dough with flat hands" required the lowest %MVIC and may be less effective in improving muscle strength.

Conclusions: Women with arthritis tend to use higher levels of muscle activation in daily tasks than healthy women, and wrist extensors and flexors appear to be equally affected. It is important that hand training programs reflect real-life situations and focus also on extensor strength.

Figure 1

Muscle activation was measured with surface EMG in m. extensor digitorum communis and m. flexor carpi radialis in the dominant hand while performing four hand exercises and four daily tasks: (a) squeezing the putty, (b) rolling the putty with a flat hand, (c) finger extension, (d) isolated opposition, digits II–V (daily activities), (e) writing with a pen, (f) locking a door with a key, (g) cutting with scissors, and (h) pulling up a zip. Consent was obtained from individuals for publication of the images.

Figure 2

Muscle activation in m. flexor carpi radialis (FCR) and m. extensor digitorum communis (EDC) when performing daily activities and hand exercises for patients with reumatoid arthritis (RA), hand osteoarthritis (HOA) and a healthy reference group (RG) presented as percentage of maximal voluntary isometric contraction (%MVIC) (box plot shows median and range; * and º show outliers). a) Muscle activity in FCR radialis when performing daily tasks (left-right): writing with a pen, locking a door with a key, cutting with scissors and pulling up a zipper. b) Muscle activity in EDC when performing daily tasks (left-right): writing with a pen, locking a door with a key, cutting with scissors and pulling up a zipper. c) Muscle activity in FCR when performing hand exercises (left-right): squeezing the dough, rolling the dough with a flat hand, finger extension and isolated opposition digit II-V. d) Muscle activity in extensor digitorum communis when performing hand exercises (left-right): squeezing the dough, rolling the dough with a flat hand, finger extension and isolated opposition digit II-V.