Dysfunctional neuro-muscular mechanisms explain gradual gait changes in prodromal spastic paraplegia

Table 1 The controller is based on Geyer and Herr [19] and has several components and states: constant actuation (C), muscle reflex, and pelvis tilt proportional-derivative (PD) primitives

	Early Stance	Late Stance	Pre-swing	Swing	Late swing
Eevent initiating gait state	GRF greater than threshold	Sagittal distance stance foot	Contralateral foot enters early stance	GRF lower than threshold	Sagittal distance swing foot
GLU	C, PD+	C, PD+	C	F+	F+
HAM	C, PD+	C, PD+		F+	F+
IL	C, PD-	C, PD-	C	PD+, L+/-(HAM)	PD+, L+/-(HAM)
VAS	C, F+	C, F+
GAS	F+, V+	F+, V+	F+, V+	V+	V+
SOL	F+, V+	F+, V+	F+, V+	V+	V+
TA	L+, F-(SOL), V+	L+, F-(SOL), V+	L+, F-(SOL), V+	L+, F-(SOL), V+	L+, F-(SOL), V+

Muscle reflex primitives are based on normalised muscle length (L) or force (F) feedback. In this study, we added positive velocity feedback (V+) to simulate hyperreflexia. Positive feedback (L+, F+, and V+) directly stimulates a muscle based on its on proprioceptive signals. Furthermore, negative force feedback from SOL may inhibit TA (F-(SOL)) and length feedback from HAM may inhibit IL (L±(HAM)). The active controller components depend on the five gait states: early stance, late-stance, pre-swing, swing (S) and late swing (state machine) and the states are switched when the specified events are detecte (second row of the table)

ISSN: 1743-0003