Force decline after low and high intensity contractions in persons with multiple sclerosis

Area of Science:

• Neurology
• Exercise Physiology
• Rehabilitation Science

Background:

• Muscle force decline during contractions is influenced by contraction intensity.
• In persons with multiple sclerosis (PwMS), understanding fatigue mechanisms is crucial for rehabilitation.

Purpose of the Study:

• To compare force decline and its contributing factors in PwMS during low and high intensity contractions.
• To investigate differences in fatigue mechanisms between PwMS and healthy controls.

Main Methods:

• Evaluated index finger abduction force and nerve stimulation-evoked force (RTw) in 19 PwMS and 19 controls.
• Participants performed intermittent contractions at 25% or 80% maximal voluntary contraction (MVC), with assessments of voluntary activation and RTw post-contraction sets.

Main Results:

• Low-intensity contractions led to greater voluntary activation decline and smaller RTw decline compared to high-intensity contractions.
• PwMS exhibited a smaller decline in RTw compared to controls, despite completing similar contraction sets.
• Female PwMS showed poorer voluntary activation, and low-intensity contractions correlated with perceived fatigue.

Conclusions:

• The mechanisms underlying force decline during submaximal contractions differ between PwMS and controls, despite similar overall fatigability.
• Fatigue and fatigability are associated during weak contractions in PwMS.