Differential activation of lumbar and sacral motor pools during walking atdifferent speeds and slopes

Differential activation of lumbar and sacral motor pools duringwalking at different speeds and slopes.J Neurophysiol122: 872–887,2019. First published July 10, 2019; doi:10.1152/jn.00167.2019.—Organization of spinal motor output has become of interest forinvestigating differential activation of lumbar and sacral motor poolsduring locomotor tasks. Motor pools are associated with functionalgrouping of motoneurons of the lower limb muscles. Here we exam-ined how the spatiotemporal organization of lumbar and sacral motorpool activity during walking is orchestrated with slope of terrain andspeed of progression. Ten subjects walked on an instrumented tread-mill at different slopes and imposed speeds. Kinetics, kinematics, andelectromyography of 16 lower limb muscles were recorded. Thespinal locomotor output was assessed by decomposing the coordi-nated muscle activation profiles into a small set of common factorsand by mapping them onto the rostrocaudal location of the motoneu-ron pools. Our results show that lumbar and sacral motor pool activitydepend on slope and speed. Compared with level walking, sacralmotor pools decrease their activity at negative slopes and increase atpositive slopes, whereas lumbar motor pools increase their engage-ment when both positive and negative slope increase. These findingsare consistent with a differential involvement of the lumbar and thesacral motor pools in relation to changes in positive and negativecenter of body mass mechanical power production due to slope andspee