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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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Modulation of power below 1 Hz for young and older adults with magnification of visual feedback.The top row shows a representative force output low-passed at 1 Hz for a young and an older adult during the lowest (0.05°) and highest (1.5°) visual angle. The bottom row demonstrates the power spectrum of force from 0–1 Hz for the same subjects. Age-associated differences in the modulation of force oscillations below 1 Hz are evident.
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pone-0055970-g006: Modulation of power below 1 Hz for young and older adults with magnification of visual feedback.The top row shows a representative force output low-passed at 1 Hz for a young and an older adult during the lowest (0.05°) and highest (1.5°) visual angle. The bottom row demonstrates the power spectrum of force from 0–1 Hz for the same subjects. Age-associated differences in the modulation of force oscillations below 1 Hz are evident.

Mentions: We examined how the modulation of force oscillations below 1 Hz in young and older adults contributed to the increase in the variability of force with magnification of visual feedback. Specifically, we used a regression model to predict the changes in the CV of force from no visual feedback to the highest visual angle from the changes in absolute and relative power in specific frequencies below 1 Hz. We used the highest visual angle (1.5°) because age-associated differences in the variability of force were the greatest at this angle (Figure 2). Furthermore, the modulation of force below 1 Hz is different for young and older adults (Figure 5). These age-associated differences appear to be exacerbated from the lowest to the highest amount of visual feedback. As is evident from the representative sample in Figure 6, the variability of force did not change with magnification of visual feedback for the young adults but it increased substantially for the older adults. In addition, the absolute and relative power of frequencies below 1 Hz appears to be different for the two age groups (Figure 5). For the absolute power spectrum, the change in CV of force at the highest visual angle was predicted (R2 = 0.68, adjusted R2 = 0.66; P<0.001; Figure 7A) by a multiple-regression model that included the absolute power from the 0–0.08 Hz bin only. This regression model suggests that a reduction in CV of force with magnification of visual feedback was associated with a decrease in absolute power from 0–0.08 Hz. For the normalized power spectrum, the change in CV of force at the highest visual angle was predicted (R2 = 0.8, adjusted R2 = 0.73; P<0.05; Figure 7B) by a multiple-regression model that included the normalized power at 0.16 Hz, 0.33 Hz, 0.5 Hz, 0.66 Hz, and 0.83 Hz. This regression model suggests that a greater change in CV of force with magnification of visual feedback was associated with greater relative power at 0.16 Hz (part r = 0.43), 0.5 Hz (part r = 0.49), and 0.83 Hz (part r = 0.48), and lesser relative power at 0.33 Hz (part r = −0.48) and 0.66 Hz (part r = −0.45).


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)

Modulation of power below 1 Hz for young and older adults with magnification of visual feedback.The top row shows a representative force output low-passed at 1 Hz for a young and an older adult during the lowest (0.05°) and highest (1.5°) visual angle. The bottom row demonstrates the power spectrum of force from 0–1 Hz for the same subjects. Age-associated differences in the modulation of force oscillations below 1 Hz are evident.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3569433&req=5

pone-0055970-g006: Modulation of power below 1 Hz for young and older adults with magnification of visual feedback.The top row shows a representative force output low-passed at 1 Hz for a young and an older adult during the lowest (0.05°) and highest (1.5°) visual angle. The bottom row demonstrates the power spectrum of force from 0–1 Hz for the same subjects. Age-associated differences in the modulation of force oscillations below 1 Hz are evident.
Mentions: We examined how the modulation of force oscillations below 1 Hz in young and older adults contributed to the increase in the variability of force with magnification of visual feedback. Specifically, we used a regression model to predict the changes in the CV of force from no visual feedback to the highest visual angle from the changes in absolute and relative power in specific frequencies below 1 Hz. We used the highest visual angle (1.5°) because age-associated differences in the variability of force were the greatest at this angle (Figure 2). Furthermore, the modulation of force below 1 Hz is different for young and older adults (Figure 5). These age-associated differences appear to be exacerbated from the lowest to the highest amount of visual feedback. As is evident from the representative sample in Figure 6, the variability of force did not change with magnification of visual feedback for the young adults but it increased substantially for the older adults. In addition, the absolute and relative power of frequencies below 1 Hz appears to be different for the two age groups (Figure 5). For the absolute power spectrum, the change in CV of force at the highest visual angle was predicted (R2 = 0.68, adjusted R2 = 0.66; P<0.001; Figure 7A) by a multiple-regression model that included the absolute power from the 0–0.08 Hz bin only. This regression model suggests that a reduction in CV of force with magnification of visual feedback was associated with a decrease in absolute power from 0–0.08 Hz. For the normalized power spectrum, the change in CV of force at the highest visual angle was predicted (R2 = 0.8, adjusted R2 = 0.73; P<0.05; Figure 7B) by a multiple-regression model that included the normalized power at 0.16 Hz, 0.33 Hz, 0.5 Hz, 0.66 Hz, and 0.83 Hz. This regression model suggests that a greater change in CV of force with magnification of visual feedback was associated with greater relative power at 0.16 Hz (part r = 0.43), 0.5 Hz (part r = 0.49), and 0.83 Hz (part r = 0.48), and lesser relative power at 0.33 Hz (part r = −0.48) and 0.66 Hz (part r = −0.45).

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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