Effects of robot viscous forces on arm movements in chronic stroke survivors: a randomized crossover study.

Only 13 participants were analysed, and the study was not prospectively powered, so small or unstable effects are possible. One person consented but did not take part because of a second stroke, so the analysed group was smaller than the recruited group. Participants were chronic stroke survivors with Upper Extremity Fugl-Meyer scores from 15 to 50 and no significant contractures or Modified Ashworth scores above 3, so findings may not apply to more impaired or spastic patients. The intervention was a single visit with 5-minute blocks, and the study did not test functional recovery or long-term training. The main speed effect was temporary; after negative viscosity was removed, speed did not stay increased. One participant initially had difficulty stopping motion under negative viscosity because of weakness, although the data were ultimately used. Crossover order effects remain possible; order was significant for retention movement error. Spasticity was not controlled for in the analysis.

The supplied text states that the funder was the American Heart Association. No author conflict-of-interest declaration is provided in the supplied text.

Do not conclude that robot negative viscosity improves stroke arm function or produces lasting speed gains. The speed increase was only while the force was on, and speed did not remain increased after it stopped; functional recovery was not tested.