Possibility that extensors respond faster than flexors for the
metacarpophalangeal joints in individuals with severe-to-moderate
stroke-caused impairment: A pilot study
Abstract
Damage in the corticospinal system following stroke produces imbalance
between flexors and extensors in the upper extremity including the
fingers, eventually leading to flexion-favored postures. The
substitution of the reticospinal tract for the damaged corticospinal
tract is known to excessively activate flexors of the fingers while the
fingers are voluntarily being extended. Here, we questioned whether the
cortical source or/and neural pathways of the flexors and extensors of
the fingers are coupled and what factor of impairment influences finger
movement. In this study, a total of 7 male participants with hemiplegic
stroke conducted isometric flexion and extension at the MCP joints in
response to auditory tones. We measured activation and de-activation
delays of the flexor and extensor of the MCP joints on the paretic side,
as well as, force generation and co-contraction between the flexor and
extensor. All participants generated greater torque in the direction of
flexion (p=0.017). Regarding co-contraction, coupled activation of the
extensor is also made during flexion in the similar way to coupled
activation of the flexor made during extension. As opposite to our
expectation, we observed that during extension, the extensor showed
marginally significantly faster activation (p=0.66) while it showed
faster de-activation (p=0.038), in comparison to activation and
de-activation of the flexor during flexion. But movement smoothness was
not affected by those factors. Our results imply that the cortical
source and neural pathway for the extensors of the MCP joints are not
coupled with those for the flexors of the MCP joints and extensor
weakness mainly contributes to the asymmetry between flexors and
extensors.