The relationship of lower-limb muscle force to walking ability in patients with amyotrophic lateral sclerosis

The purpose of this study was to determine the level of muscle force associated with ability to walk in the community without assistance, in the community with assistance, or at home only in individuals with amyotrophic lateral sclerosis (ALS).

Percentage of predicted maximal muscle force (%PMF) of lower-extremity muscles was determined, and walking ability was categorized in 118 patients with ALS during periodic visits to the Neuromuscular Research Unit. Data were derived from consecutive visits in which subjects demonstrated declines in walking ability. Means for %PMF of each muscle group and a limb average were calculated at each consecutive visit.

The mean lower-extremity average %PMF was: (1) 54.01% (SD=12.76%) for subjects who walked independently in the community and 50.19% (SD=14.38%) during the next visit when these same subjects required assistance in the community (difference=3.82%, 95% confidence interval [CI]= 2.45-5.19);(2) 37.52% (SD=15.17%) during the last visit that subjects walked with assistance in the community and 32.18% (SD=13.83%) during the next visit when they walked only at home (difference=5.33%, 95% CI=3.61-7.06); and (3) 19.12% (SD=9.08%) during the visit when subjects were last able to ambulate at home versus 13.70% (SD=7.36%) when they became unable to walk (difference=5.42%, 95% CI=2.97-7.96).

The findings suggest there are required levels of lower-extremity muscle force for various categories of walking ability. Variations in forces within and between categories of walking ability, however, indicate the complexity of this relationship.