Journal of Neurophysiology · 2010 · 154 citations · 51 references
Gait AnalysisMuscle FunctionNeuromuscular CoordinationMovement BiomechanicsMotor ControlMuscle SynergiesKinesiologyElderly PeopleApplied PhysiologyHealth SciencesSpinal Cord InjuryRehabilitationMotor Control StrategiesAge-related ModificationsMotor PrimitivesPathological GaitNeuroscienceMusculoskeletal InteractionCentral Nervous SystemHuman MovementMedicineSpinal Cord Activity
Spinal cord neural circuits drive muscle activation during locomotion by integrating descending signals and peripheral sensory input, a relationship that may be altered by aging. The study aimed to determine how aging affects muscle synergies and spinal cord activity during walking. Researchers recorded activity of 12 ipsilateral leg muscles in 7 young and 7 elderly participants across six walking cadences, extracted muscle synergies, and mapped motoneuronal activity in the lumbosacral enlargement. Results showed that motor primitive timing and muscle loading synergies were unchanged with age, but spinal maps varied with cadence, with elders exhibiting higher, scattered activity throughout the gait cycle and young subjects showing well‑defined bursts, indicating that spinal integration of biomechanical demand, peripheral afference, and descending inputs differs between age groups.
Recent findings have shown that neural circuits located in the spinal cord drive muscular activations during locomotion while intermediating between descending signals and peripheral sensory information. This relationship could be modified by the natural aging process. To address this issue, the activity of 12 ipsilateral leg muscles was analyzed in young and elderly people (7 subjects per group) while walking at six different cadences (40-140 steps/min). These signals were used to extract synergies underlying muscle activation and to map the motoneuronal activity of the pools belonging to the lumbosacral enlargement (L(2)-S(2)). The comparison between the two groups showed that neither temporal patterning of motor primitives nor muscles loading synergies seemed to be significantly affected by aging. Conversely, as the cadence increased, spinal maps differ significantly between the groups, showing higher and scattered activity during the whole gait cycle in elders and well-defined bursts in young subjects. The results suggested that motor primitives lead the synchronization of muscle activation mainly depending on the biomechanical demand of the locomotion; hence they are not significantly affected by aging. Nevertheless, at the spinal cord level, biomechanical requirements, peripheral afference, and descending inputs are differently integrated between the two groups, probably reflecting age-related changes of both nervous system and motor control strategies during locomotion.
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