title: Modulation of force below 1 Hz: age-associated differences and the effect of magnified visual feedback.
abstract: Oscillations in force output change in specific frequency bins and have important implications for understanding aging and pathological motor control. Although previous studies have demonstrated that oscillations from 0-1 Hz can be influenced by aging and visuomotor processing, these studies have averaged power within this bandwidth and not examined power in specific frequencies below 1 Hz. The purpose was to determine whether a differential modulation of force below 1 Hz contributes to changes in force control related to manipulation of visual feedback and aging. Ten young adults (25±4 yrs, 5 men) and ten older adults (71±5 yrs, 4 men) were instructed to accurately match a target force at 2% of their maximal isometric force for 35 s with abduction of the index finger. Visual feedback was manipulated by changing the visual angle (0.05°, 0.5°, 1.5°) or removing it after 15 s. Modulation of force below 1 Hz was quantified by examining the absolute and normalized power in seven frequency bins. Removal of visual feedback increased normalized power from 0-0.33 Hz and decreased normalized power from 0.66-1.0 Hz. In contrast, magnification of visual feedback (visual angles of 0.5° and 1.5°) decreased normalized power from 0-0.16 Hz and increased normalized power from 0.66-1.0 Hz. Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05). Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05). Specifically, older adults exhibited greater normalized power from 0-0.16 Hz and lesser normalized power from 0.66-0.83 Hz. The changes in force modulation predicted the changes in the variability of force with magnification of visual feedback (R(2) = 0.80). Our findings indicate that force oscillations below 1 Hz are associated with force control and are modified by aging and visual feedback.
authors: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.
authors: Emily J
authors: EJ
authors: Fox
authors: Harsimran S
authors: HS
authors: Baweja
authors: Changki
authors: C
authors: Kim
authors: Deanna M
authors: DM
authors: Kennedy
authors: David E
authors: DE
authors: Vaillancourt
authors: Evangelos A
authors: EA
authors: Christou
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D005221:Fatigue; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D053580:Muscle Strength; D011597:Psychomotor Performance / Q000502:physiology*; D055815:Young Adult