title: Postural challenge affects motor cortical activity in young and old adults.
abstract: When humans voluntarily activate a muscle, intracortical inhibition decreases. Such a decrease also occurs in the presence of a postural challenge and more so with increasing age. Here, we examined age-related changes in motor cortical activity during postural and non-postural contractions with varying levels of postural challenge. Fourteen young (age 22) and twelve old adults (age 70) performed three conditions: (1) voluntary contraction of the soleus muscle in sitting and (2) leaning forward while standing with and (3) without being supported. Subthreshold transcranial magnetic stimulation was applied to the soleus motor area suppressing ongoing EMG, as an index of motor cortical activity. The area of EMG suppression was ~60% smaller (p<0.05) in unsupported vs. supported leaning and sitting, with no difference between these latter two conditions (p>0.05). Even though in absolute terms young compared with old adults leaned farther (p=0.018), there was no age effect or an age by condition interaction in EMG suppression. Leaning closer to the maximum without support correlated with less EMG suppression (rho=-0.44, p=0.034). We conclude that the critical factor in modulating motor cortical activity was postural challenge and not contraction aim or posture. Age did not affect the motor control strategy as quantified by the modulation of motor cortical activity, but the modulation appeared at a lower task difficulty with increasing age.
authors.affiliation: University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands. Electronic address: s.papegaaij@umcg.nl.
authors.forename: Selma
authors.initials: S
authors.lastname: Papegaaij
authors.affiliation: University of Fribourg, Department of Medicine, Ch. du Musée 8, CH-1700, Fribourg, Switzerland.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Taube
authors.affiliation: University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands.
authors.forename: Helco G
authors.initials: HG
authors.lastname: van Keeken
authors.affiliation: University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands.
authors.forename: Egbert
authors.initials: E
authors.lastname: Otten
authors.affiliation: Université Libre de Bruxelles, Faculty for Motor Sciences, Laboratory of Applied Biology, CP 640, Route de Lennik 808, 1070 Brussels, Belgium.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Baudry
authors.affiliation: University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands; Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle-upon-Tyne NE1 8ST, United Kingdom.
authors.forename: Tibor
authors.initials: T
authors.lastname: Hortobágyi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D004576:Electromyography; D005221:Fatigue / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult
keywords: Aging; Balance; Intracortical inhibition; Postural activation; Transcranial magnetic stimulation; Voluntary activation