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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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Related in: MedlinePlus

Representative trials from a young and an older adult exerting a constant force at 2% MVC with low (visual angle = 0.05°, left column) and high (visual angle = 1.5°, right column) magnification of visual feedback.A: Each subject performed a constant isometric contraction by abducting their left index finger against a force transducer. Subjects were instructed to match a line representing their force to a horizontal target line for 35 s. Visual feedback of the target line and exerted force was provided throughout the entire trial during visual feedback conditions. During no visual feedback trials, feedback was removed (no feedback area) after 15 s. B: Representative force output from a young and an older adult is shown. Data analysis was based on force output from 15–21 s (analysis area). Older adults exhibited greater variability of force with higher magnification of visual feedback (higher visual angles of 0.5° and 1.5°). C: Representative normalized power spectrum of the force output from 0–13 Hz in a young and an older adult during trials with low and high magnification of visual feedback. The majority of the power (∼85%) in the force output occurs from 0–1 Hz.
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pone-0055970-g001: Representative trials from a young and an older adult exerting a constant force at 2% MVC with low (visual angle = 0.05°, left column) and high (visual angle = 1.5°, right column) magnification of visual feedback.A: Each subject performed a constant isometric contraction by abducting their left index finger against a force transducer. Subjects were instructed to match a line representing their force to a horizontal target line for 35 s. Visual feedback of the target line and exerted force was provided throughout the entire trial during visual feedback conditions. During no visual feedback trials, feedback was removed (no feedback area) after 15 s. B: Representative force output from a young and an older adult is shown. Data analysis was based on force output from 15–21 s (analysis area). Older adults exhibited greater variability of force with higher magnification of visual feedback (higher visual angles of 0.5° and 1.5°). C: Representative normalized power spectrum of the force output from 0–13 Hz in a young and an older adult during trials with low and high magnification of visual feedback. The majority of the power (∼85%) in the force output occurs from 0–1 Hz.

Mentions: We manipulated the visual feedback condition (presence or absence of visual feedback), and the magnification of the visual feedback with a custom-written program in Matlab® (Math Works™ Inc., Natick, Massachusetts, USA). We achieved the specified visual angles (0.05°, 0.5°, 1.5°) by changing the ordinate scale, which altered the amplitude of the force fluctuations viewed by the subject on the screen (described above). A decrease in the size of the ordinate scale (zoom in) magnified the visual feedback of the force fluctuations (Figure 1A). Force fluctuations were magnified, therefore, with visual angle. The target force was indicated by a red horizontal line in the middle of the monitor and the force exerted by each subject was represented as a blue line, which progressed with time from left to right (see Figure 1 in Kennedy and Christou 2011). During the task, subjects maintained their position in the chair and were instructed to gradually push against the force transducer and increase their force (blue line on the monitor) to match the target force (red line) within 5 seconds. When the target was reached, subjects were instructed to maintain their force on the target as accurately and consistently as possible. Each trial lasted 35 s.


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)

Representative trials from a young and an older adult exerting a constant force at 2% MVC with low (visual angle = 0.05°, left column) and high (visual angle = 1.5°, right column) magnification of visual feedback.A: Each subject performed a constant isometric contraction by abducting their left index finger against a force transducer. Subjects were instructed to match a line representing their force to a horizontal target line for 35 s. Visual feedback of the target line and exerted force was provided throughout the entire trial during visual feedback conditions. During no visual feedback trials, feedback was removed (no feedback area) after 15 s. B: Representative force output from a young and an older adult is shown. Data analysis was based on force output from 15–21 s (analysis area). Older adults exhibited greater variability of force with higher magnification of visual feedback (higher visual angles of 0.5° and 1.5°). C: Representative normalized power spectrum of the force output from 0–13 Hz in a young and an older adult during trials with low and high magnification of visual feedback. The majority of the power (∼85%) in the force output occurs from 0–1 Hz.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0055970-g001: Representative trials from a young and an older adult exerting a constant force at 2% MVC with low (visual angle = 0.05°, left column) and high (visual angle = 1.5°, right column) magnification of visual feedback.A: Each subject performed a constant isometric contraction by abducting their left index finger against a force transducer. Subjects were instructed to match a line representing their force to a horizontal target line for 35 s. Visual feedback of the target line and exerted force was provided throughout the entire trial during visual feedback conditions. During no visual feedback trials, feedback was removed (no feedback area) after 15 s. B: Representative force output from a young and an older adult is shown. Data analysis was based on force output from 15–21 s (analysis area). Older adults exhibited greater variability of force with higher magnification of visual feedback (higher visual angles of 0.5° and 1.5°). C: Representative normalized power spectrum of the force output from 0–13 Hz in a young and an older adult during trials with low and high magnification of visual feedback. The majority of the power (∼85%) in the force output occurs from 0–1 Hz.
Mentions: We manipulated the visual feedback condition (presence or absence of visual feedback), and the magnification of the visual feedback with a custom-written program in Matlab® (Math Works™ Inc., Natick, Massachusetts, USA). We achieved the specified visual angles (0.05°, 0.5°, 1.5°) by changing the ordinate scale, which altered the amplitude of the force fluctuations viewed by the subject on the screen (described above). A decrease in the size of the ordinate scale (zoom in) magnified the visual feedback of the force fluctuations (Figure 1A). Force fluctuations were magnified, therefore, with visual angle. The target force was indicated by a red horizontal line in the middle of the monitor and the force exerted by each subject was represented as a blue line, which progressed with time from left to right (see Figure 1 in Kennedy and Christou 2011). During the task, subjects maintained their position in the chair and were instructed to gradually push against the force transducer and increase their force (blue line on the monitor) to match the target force (red line) within 5 seconds. When the target was reached, subjects were instructed to maintain their force on the target as accurately and consistently as possible. Each trial lasted 35 s.

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