Visual Feedback Attenuates Force Fluctuations Induced by a Stressor

Publisher Website
Google Scholar
Abstract
Purpose: The fluctuations in force during a steady contraction can be influenced by age, vision, and level of physiological arousal. The aim of this study was to determine the effects of a stressor on the force fluctuations and information transmission exhibited by young, middle-aged, and older adults when a pinch-grip task was performed with and without visual feedback. Methods: Thirty-six men and women (19–86 yr) participated in a protocol that comprised anticipatory (30 min), stressor (15 min), and recovery periods (25 min). The stressor was a series of noxious electrical stimuli applied to the dorsal surface of the left hand. Subjects sustained a pinch-grip force with the right hand at 2% of the maximal voluntary contraction force. The normalized fluctuations in pinch-grip force (coefficient of variation), information transmission (log2 signal:noise), and the spectra for the force were quantified across the 70-min protocol. Results: Removal of visual feedback exacerbated the force fluctuations (3.83 ± 3.15 vs 2.82 ± 1.64%) and reduced the information transmission (5.01 ± 0.86 vs 5.34 ± 0.71 bits) only during the stressor period. The effect was similar for all age groups. Older adults exhibited greater force fluctuations and lower information transmission compared with young and middle-aged adults, especially during the stressor period. The impairments in fine motor performance during the stressor were associated with an enhancement of the power at 1–2 Hz in the force spectrum (R2 = 0.41–0.52). Conclusion: Removal of visual feedback increased the force fluctuations and decreased information transmission during a stressor period, which suggests that integration of visual feedback can attenuate the stressor-induced enhancement of synaptic input received by the motor neuron pool.