Quantifying associated reactions in the paretic arm in stroke and their relationship to spasticity

(1) To present a measurement protocol for assessing associated reactions (AR) in the paretic arm and (2) to use it to investigate the pattern of AR and its association with spasticity.

Inpatient rehabilitation unit.

Associated reactions in 49 adults with stroke were measured in terms of force generated, electrical muscle activity and wrist movement in the paretic arm using hand dynamometry, surface electromyography and electrogoniometry respectively. Simultaneous recording of the effort used to elicit the associated reaction was made using a second hand dynamometer. The magnitude and persistence of AR was compared with the clinical assessment of spasticity (using the modified Ashworth Scale, MAS).

There was poor correlation between peak AR and MAS, suggesting that AR are not confined to patients with severe spasticity. Co-activation of forearm flexors and extensors was evident during the AR. AR fluctuated during a single period of effort in some patients. Only 12 out of 31 patients who maintained uniform effort over the measurement period produced a uniform AR. AR often persisted for some time after effort had ceased. Eight were classified as minimal (median AR 0.23 N), 25 as mild (median AR 2.7 N), 11 as moderate (median AR 6.4 N) and 3 as severe (median AR 11.0 N). AR tended to persist in patients with higher MAS although this result was not statistically significant.

The magnitude, profile and persistence of AR varied considerably between individuals. Associated reactions were present in people with minimal spasticity. As this technique allows the magnitude of AR to be quantified in relation to effort it has the potential to be a useful outcome measure in clinical trials evaluating the treatments (e.g. physiotherapy) directed at reducing associated reactions.