title: Motor control differs for increasing and releasing force.
abstract: Control of the motor output depends on our ability to precisely increase and release force. However, the influence of aging on force increase and release remains unknown. The purpose of this study, therefore, was to determine whether force control differs while increasing and releasing force in young and older adults. Sixteen young adults (22.5 ± 4 yr, 8 females) and 16 older adults (75.7 ± 6.4 yr, 8 females) increased and released force at a constant rate (10% maximum voluntary contraction force/s) during an ankle dorsiflexion isometric task. We recorded the force output and multiple motor unit activity from the tibialis anterior (TA) muscle and quantified the following outcomes: 1) variability of force using the SD of force; 2) mean discharge rate and variability of discharge rate of multiple motor units; and 3) power spectrum of the multiple motor units from 0-4, 4-10, 10-35, and 35-60 Hz. Participants exhibited greater force variability while releasing force, independent of age (P < 0.001). Increased force variability during force release was associated with decreased modulation of multiple motor units from 35 to 60 Hz (R(2) = 0.38). Modulation of multiple motor units from 35 to 60 Hz was further correlated to the change in mean discharge rate of multiple motor units (r = 0.66) and modulation from 0 to 4 Hz (r = -0.64). In conclusion, these findings suggest that force control is altered while releasing due to an altered modulation of the motor units.
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Seoung Hoon
authors.initials: SH
authors.lastname: Park
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: MinHyuk
authors.initials: M
authors.lastname: Kwon
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Danielle
authors.initials: D
authors.lastname: Solis
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and.
authors.forename: Neha
authors.initials: N
authors.lastname: Lodha
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and Department of Physical Therapy, University of Florida, Gainesville, Florida eachristou@hhp.ufl.edu.
authors.forename: Evangelos A
authors.initials: EA
authors.lastname: Christou
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D000842:Ankle / Q000502:physiology; D004576:Electromyography; D030141:Feedback, Psychological; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009048:Motor Skills / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010775:Photic Stimulation; D055815:Young Adult
keywords: decomposition electromyogram; force variability; motor unit activity