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Modulation of force below 1 Hz: age-associated differences and the effect of magnified visual feedback.

Fox EJ, Baweja HS, Kim C, Kennedy DM, Vaillancourt DE, Christou EA - PLoS ONE (2013)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.

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.

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The effect of visual angle and frequency bins below 1 Hz.A: The absolute power as a function of frequency bins during the three different visual angles. The age and visual angle main effects and associated interactions were not significant. B: The normalized power during the two visual feedback conditions. Magnification of visual feedback at the highest visual angle (1.5°) compared with the lowest visual angle (0.05°) significantly decreased force oscillations from 0–0.16 Hz and increased power from 0.83–1.0 Hz. Visual feedback at a moderate visual angle (0.5°) compared with the lowest visual angle (0.05°) increased power at 0 Hz and decreased power from 0.83–1.0 Hz. Asterisk (*) indicates significant difference (P<0.05) between the highest (1.5°) and lowest (0.05°) visual angle. A cross (+) indicates significant difference (P<0.05) between the moderate (0.5°) and lowest (0.05°) visual angle.
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pone-0055970-g004: The effect of visual angle and frequency bins below 1 Hz.A: The absolute power as a function of frequency bins during the three different visual angles. The age and visual angle main effects and associated interactions were not significant. B: The normalized power during the two visual feedback conditions. Magnification of visual feedback at the highest visual angle (1.5°) compared with the lowest visual angle (0.05°) significantly decreased force oscillations from 0–0.16 Hz and increased power from 0.83–1.0 Hz. Visual feedback at a moderate visual angle (0.5°) compared with the lowest visual angle (0.05°) increased power at 0 Hz and decreased power from 0.83–1.0 Hz. Asterisk (*) indicates significant difference (P<0.05) between the highest (1.5°) and lowest (0.05°) visual angle. A cross (+) indicates significant difference (P<0.05) between the moderate (0.5°) and lowest (0.05°) visual angle.

Mentions: For the absolute power spectrum there was a significant frequency main effect (F6,72 = 4.3, P<0.01). The interaction between visual feedback angle and frequency was not significant (P = 0.69; Figure 4A). Visual inspection of the data demonstrated that magnification of visual feedback increased absolute power from 0.66 to 0.83 Hz. For the normalized power spectrum there was a significant visual feedback angle×frequency interaction (F12,216 = 3.79, P<0.001; Figure 4B). Based on visual inspection of this interaction, magnification of visual feedback decreased relative power from 0 to 0.16 Hz and increased relative power from 0.66 to 1.0 Hz. Post hoc analyses (Tukey HSD) demonstrated that when subjects received visual feedback at the highest visual angles (0.5° and 1.5°) compared with the lowest visual angle (0.05°) they decreased power in their force output from 0–0.16 Hz (P<0.05) and increased power from 0.83 to 1.0 Hz (P<0.05).


Modulation of force below 1 Hz: age-associated differences and the effect of magnified visual feedback.

Fox EJ, Baweja HS, Kim C, Kennedy DM, Vaillancourt DE, Christou EA - PLoS ONE (2013)

The effect of visual angle and frequency bins below 1 Hz.A: The absolute power as a function of frequency bins during the three different visual angles. The age and visual angle main effects and associated interactions were not significant. B: The normalized power during the two visual feedback conditions. Magnification of visual feedback at the highest visual angle (1.5°) compared with the lowest visual angle (0.05°) significantly decreased force oscillations from 0–0.16 Hz and increased power from 0.83–1.0 Hz. Visual feedback at a moderate visual angle (0.5°) compared with the lowest visual angle (0.05°) increased power at 0 Hz and decreased power from 0.83–1.0 Hz. Asterisk (*) indicates significant difference (P<0.05) between the highest (1.5°) and lowest (0.05°) visual angle. A cross (+) indicates significant difference (P<0.05) between the moderate (0.5°) and lowest (0.05°) visual angle.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3569433&req=5

pone-0055970-g004: The effect of visual angle and frequency bins below 1 Hz.A: The absolute power as a function of frequency bins during the three different visual angles. The age and visual angle main effects and associated interactions were not significant. B: The normalized power during the two visual feedback conditions. Magnification of visual feedback at the highest visual angle (1.5°) compared with the lowest visual angle (0.05°) significantly decreased force oscillations from 0–0.16 Hz and increased power from 0.83–1.0 Hz. Visual feedback at a moderate visual angle (0.5°) compared with the lowest visual angle (0.05°) increased power at 0 Hz and decreased power from 0.83–1.0 Hz. Asterisk (*) indicates significant difference (P<0.05) between the highest (1.5°) and lowest (0.05°) visual angle. A cross (+) indicates significant difference (P<0.05) between the moderate (0.5°) and lowest (0.05°) visual angle.
Mentions: For the absolute power spectrum there was a significant frequency main effect (F6,72 = 4.3, P<0.01). The interaction between visual feedback angle and frequency was not significant (P = 0.69; Figure 4A). Visual inspection of the data demonstrated that magnification of visual feedback increased absolute power from 0.66 to 0.83 Hz. For the normalized power spectrum there was a significant visual feedback angle×frequency interaction (F12,216 = 3.79, P<0.001; Figure 4B). Based on visual inspection of this interaction, magnification of visual feedback decreased relative power from 0 to 0.16 Hz and increased relative power from 0.66 to 1.0 Hz. Post hoc analyses (Tukey HSD) demonstrated that when subjects received visual feedback at the highest visual angles (0.5° and 1.5°) compared with the lowest visual angle (0.05°) they decreased power in their force output from 0–0.16 Hz (P<0.05) and increased power from 0.83 to 1.0 Hz (P<0.05).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.

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.

Show MeSH
Related in: MedlinePlus