Variable stimulation patterns for poststroke hemiplegia.

Neuromuscular electrical stimulation can improve motor function in those affected by paralysis, but its use is limited by a high rate of muscular fatigue. Variable stimulation patterns have been examined in young adults with and without spinal cord injury, but much less investigation has been devoted to studying the effects of variable stimulation patterns administered to older adults or those paralyzed by stroke. Significant changes occur in the neuromuscular system with age that may affect the response to variable stimulation patterns. We administered three, 3-min intermittent stimulation patterns to the median nerves of 10 individuals with hemiplegia from stroke and 10 age-matched able-bodied adults: (1) constant 20 HZ, (2) a pattern that began at 20 HZ and progressively increased to 40 HZ in the latter half of the task, and (3) a 20-HZ pattern that switched to a 20-HZ doublet pattern after 90 s. In the able-bodied group the doublet pattern produced significantly higher force time integrals (FTI) (1409.72 +/- 3.15 N s) than the 20-40-HZ pattern (1067.46 +/- 1.15 N s) or the 20-HZ pattern (831 +/- 1.87 N s). In the poststroke individuals the doublet pattern also produced the highest FTI (724.04 +/- 2.02 N s), and there was no significant difference between the 20-40-HZ (636.42 +/- 1.65 N s) and 20-HZ (583.64 +/- 3.02 N s) patterns. These results indicate that protocols that incorporate doublets in the later stages of fatigue are effective in older adults and in older adults with paralysis from stroke.