Fatigability in Patients With Multiple Sclerosis During Maximal Concentric Contractions.

OBJECTIVE: To compare quadriceps fatigability during maximal concentric contractions in persons with multiple sclerosis (MS) and healthy subjects.

DESIGN: Observational study.

SETTING: Hospital rehabilitation department.

PARTICIPANTS: Persons with MS (n=38) and healthy subjects (n=14) were included (N=52). Torque of the knee flexor and extensor muscles and fatigability of the knee extensor muscles were evaluated using an isokinetic device. Surface electromyographic activity of the rectus femoris, vastus lateralis, biceps femoris, and semitendinosus muscles was recorded.

INTERVENTIONS: None.

MAIN OUTCOME MEASURE: Muscle fatigability (torque fatigue index).

RESULTS: The torque fatigue index was lower in persons with MS than in healthy subjects, but when torque was normalized to maximal isometric peak torque, persons with MS and healthy subjects finished the fatigue protocol at exactly the same level of relative strength (50% of the maximal isometric peak torque). Moreover, the reduction in torque was primarily because of a reduction in neuromuscular efficiency, with no changes of coactivation of antagonist muscles.

CONCLUSIONS: Although fatigue is a disabling symptom of MS, persons with MS develop less muscle fatigability than healthy subjects during repeated maximal concentric contractions, but they end up at the same level of relative strength.