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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 change in CV of force with magnification of visual feedback for young and older adults.The change in CV of force at each visual angle was calculated relative to the no visual feedback condition. On average, older adults exhibited significantly greater change in the CV of force across all visual angles. The greatest age differences in the change of the CV of force occurred at the moderate and high visual angles.
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pone-0055970-g002: The change in CV of force with magnification of visual feedback for young and older adults.The change in CV of force at each visual angle was calculated relative to the no visual feedback condition. On average, older adults exhibited significantly greater change in the CV of force across all visual angles. The greatest age differences in the change of the CV of force occurred at the moderate and high visual angles.

Mentions: During this experiment young and older adults exhibited similar MVC before (young: 25.0±12.0 N; older: 25.0±4.1 N; P>0.5) and after (young: 24.8±10.7 N; older: 25.3±4.7 N; P>0.5) the experimental session [15]. This indicates that the experimental protocol did not induce any fatigue in our subjects. Furthermore, as we have previously reported [15], older adults exhibited greater CV of force compared with young adults, especially during the highest visual angle condition (young vs. older; 0.05°: 5.62±1.01 vs. 6.30±1.34; 1.5°: 5.59±1.17 vs. 9.03±2.48). For this study, we focused on low-force contractions (2% MVC) and examined the change in CV of force for each visual angle relative to no visual feedback condition. On average, older adults exhibited greater change in the CV of force than young adults (F1,18 = 4.3, P = 0.05). Based on the pattern of data, which is evident from Figure 2, the age-associated differences in the change of CV of force were greater for the largest visual angle (1.5°). Thus, because the protocol did not induce fatigue in the subjects, these findings indicate that the differences in the variability of force were independent of the subjects’ strength. Furthermore, these findings suggest that magnification of visual feedback exacerbated the age associated differences in the variability of force (Figures 1 and 2).


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 change in CV of force with magnification of visual feedback for young and older adults.The change in CV of force at each visual angle was calculated relative to the no visual feedback condition. On average, older adults exhibited significantly greater change in the CV of force across all visual angles. The greatest age differences in the change of the CV of force occurred at the moderate and high visual angles.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0055970-g002: The change in CV of force with magnification of visual feedback for young and older adults.The change in CV of force at each visual angle was calculated relative to the no visual feedback condition. On average, older adults exhibited significantly greater change in the CV of force across all visual angles. The greatest age differences in the change of the CV of force occurred at the moderate and high visual angles.
Mentions: During this experiment young and older adults exhibited similar MVC before (young: 25.0±12.0 N; older: 25.0±4.1 N; P>0.5) and after (young: 24.8±10.7 N; older: 25.3±4.7 N; P>0.5) the experimental session [15]. This indicates that the experimental protocol did not induce any fatigue in our subjects. Furthermore, as we have previously reported [15], older adults exhibited greater CV of force compared with young adults, especially during the highest visual angle condition (young vs. older; 0.05°: 5.62±1.01 vs. 6.30±1.34; 1.5°: 5.59±1.17 vs. 9.03±2.48). For this study, we focused on low-force contractions (2% MVC) and examined the change in CV of force for each visual angle relative to no visual feedback condition. On average, older adults exhibited greater change in the CV of force than young adults (F1,18 = 4.3, P = 0.05). Based on the pattern of data, which is evident from Figure 2, the age-associated differences in the change of CV of force were greater for the largest visual angle (1.5°). Thus, because the protocol did not induce fatigue in the subjects, these findings indicate that the differences in the variability of force were independent of the subjects’ strength. Furthermore, these findings suggest that magnification of visual feedback exacerbated the age associated differences in the variability of force (Figures 1 and 2).

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