Fatiguing Arm Exercise Following Stroke

This study investigates the effects of sub-maximal exercise to task-failure (e.g., fatigue) with the less involved, or so-called non-paretic hand, in people who have experienced a stroke. In previous work the investigators found that non-paretic hand exercise to task-failure increased excitability of the motor cortex in the more involved hemisphere and produced behavioral improvements in the unexercised paretic hand. Importantly, the magnitude of increased brain excitability is greater than what has been observed following brain stimulation with either repetitive transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) and lasts longer. This approach could be implemented in the clinical setting and could be accessible to a greater number of people than brain stimulation. The investigators' goals in the current study are to: repeat previous findings in a different group of participants and investigate the neural mechanisms that produce brain and behavioral facilitation in order to inform development of this approach for clinical implementation.

The long-term goal is to restore upper extremity (UE) motor function following stroke. The overall objective of this proposal is to improve the investigators' understanding of neural mechanisms contributing to inter-limb and inter-hemispheric transfer following non-paretic limb exercise to task failure. The investigators will use transcranial magnetic stimulation to probe acute adaptations in cortical excitability, intracortical and inter-hemispheric circuits that accompany behavioral facilitation of the paretic hand. The work proposed in this two year project will enable the investigators to obtain three data elements critical to complete the working hypothesis: . Changes in intracortical and interhemispheric inhibition in both hemispheres following non-paretic limb exercise to task-failure. . Behavioral effects using a motor task involving manipulation and dexterity. . Determine the persistence and consistency of neural and behavioral facilitation.

Repeated sub-maximal gripping exercise with the less affected hand to task-failure - followed by repeated measurements (5) during recovery period

SICI is a neurophysiologic measure of intra-cortical inhibition, obtained using transcranial magnetic stimulation (TMS) measured here in the ipsilesional hemisphere (IH) at each point to determine how it is modulated in response to task-failure. SICI is quantified as a ratio where values <1 reflect inhibition and >1 disinhibition or relative excitation. In health, SICI is ~0.5. Thus if SICI = 0.8, while <1 it would indicate less inhibition than expected in health. Transient change in SICI from 0.8 to 1.1 over the course of this experimental paradigm would reflect a period of relative excitation in response to the exercise paradigm.

baseline, post task-failure (minutes to an hour), every 45 min up to 3.5 hours post-task-failure (7 points total)

SICI is a neurophysiologic measure of intra-cortical inhibition, obtained using transcranial magnetic stimulation (TMS) measured here in the ipsilesional hemisphere (IH) at each point to determine how it is modulated in response to task-failure. SICI is quantified as a ratio where values <1 reflect inhibition and >1 disinhibition or relative excitation. In health, SICI is ~0.5. Thus if SICI = 0.8, while <1 it would indicate less inhibition than expected in health. Transient change in SICI from 0.8 to 1.1 over the course of this experimental paradigm would reflect a period of relative excitation in response to the exercise paradigm.

The BBT measures motor function/dexterity, scored as the number of blocks transferred in 1 minute. Here function of the paretic hand was measured at each time point: baseline, post-task failure, 45min post, 90min post, 135min post, 180min post, 225min post-task failure to determine the change in paretic hand BBT performance following exercise to task-failure. Scores are numeric ranging from 0 (no blocks transferred) to whatever the participant is able to achieve. Healthy age-matched adults without motor disability score in the range of 60 (+/- 10) blocks transferred in 1 minute.

baseline, post task-failure (requires variable timeline from minutes to an hour), every 45 min up to 3.5 hours post-task-failure (7 points total)

The BBT measures motor function/dexterity, scored as the number of blocks transferred in 1 minute. Here function of the paretic hand was measured prior to exercise at each of 8 repeated sessions conducted twice weekly for 4 weeks to determine the change in paretic hand BBT performance following repeated sessions of exercise to task-failure. Scores are numeric ranging from 0 (no blocks transferred) to whatever the participant is able to achieve. Healthy age-matched adults without motor disability score in the range of 60 (+/- 10) blocks transferred in 1 minute.

Inclusion Criteria: individuals at least 6 months post-stroke in the cortical or sub-cortical distribution with residual upper-extremity hemiparesis Non-Veteran Participants are eligible Exclusion Criteria: multiple strokes strokes in both hemispheres brainstem/medullary/cerebellar stroke seizure disorder metal implants in head or neck pacemaker or other implanted device inability to produce any measurable grip force