Rate of force development and relaxation scaling factors are highly sensitive to detect upper extremity motor impairments in multiple sclerosis

Clinical assessment of upper extremity in multiple sclerosis is mainly limited to 9-hole peg test (9-HPT), which is commonly criticized due to its limited sensitivity. There is a need for sensitive outcome measures for the assessment of motor symptoms in individuals with multiple sclerosis (iMS). We evaluated our recently developed brief force pulse protocol to simultaneously quantify the motor control of hand function and neuromuscular quickness in iMS. Additionally, we compared the sensitivity of the studied outcome measures with 9-HPT in detecting the differences between iMS and controls. Twelve iMS and 12 controls grasped a grip- (GF; perpendicular force) and load-force (LF; tangential force) measuring handle and produced around 100 isometric LF pulses to various submaximal levels by pushing down on it as quickly as possible, followed by quick relaxation. The GF-LF ratio quantified the motor control of hand function. The slopes of linear regressions between peak forces and corresponding peak rates of force development (rate of force development scaling factor; RFD-SF) and relaxation (rate of force relaxation scaling factor; RFR-SF) quantified the control of neuromuscular quickness. All of the selected variables were different between groups (all p-values