Perception of effort during an isometric contraction is influenced by prior muscle lengthening or shortening

Abstract

Purpose: Following a shortening or lengthening muscle contraction, the torque produced in the isometric steady state is distinctly lower (residual torque depression; rTD) or higher (residual torque enhancement; rTE), respectively, compared to a purely isometric contraction at the same final muscle length and level of activation. This is referred to as the history dependence of force.When matching a given torque level, there is greater muscle activation (electromyography; EMG) following shortening and less activation following lengthening. Owing to these differences in neuromuscular activation, it is unclear whether perception of effort is altered by the history dependence of force. Methods: Experiment 1 tested whether perception of effort differed between the rTD and rTE state when torque was matched. Experiment 2 tested whether perception of effort differed between the rTD and rTE state when EMG was matched. Finally, experiment 3 tested whether EMG differed between the rTD and rTE state when perception of effort was matched.Results: When torque was matched, both EMG and perception of effort were higher in the rTD compared to rTE state. When EMG was matched, torque was lower in the rTD compared to rTE state while perception of effort did not differ between the two states. When perception of effort was matched, torque was lower in the rTD compared to rTE state and EMG did not differ between the two states. Conclusion: The combined results from these experiments indicate that the history dependence of force alters one's perception of effort, dependent on the level of motor command.

Pharmacological blockade of muscle afferents and perception of effort: a systematic review with meta-analysis

“…Therefore, as perception of effort is not reduced, muscle afferent feedback cannot be considered as a sensory signal processed by the brain to generate the perception of effort. This result reinforces the potential of using the perception of effort intensity as a psychophysiological index of the motor command [24, 27, 88–90], as traditionally performed in the neuroscience, cardiovascular physiology and kinesthesia literatures [24, 25, 27, 91].…”

“…We therefore recommend, similarly to others [14, 29, 133], that researchers and clinicians instruct and familiarize their participants to rate their perception of effort specifically by excluding other exercise-related perception(s) from their sense of effort. This is also crucial for researchers investigating the perception of effort as a psychophysiological marker of the magnitude of the motor command [e.g., 88, 90] and using muscle pain as a psychophysiological marker of feedback from group III-IV muscle afferents [e.g., 136, 137].…”

Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-analysis

“…Therefore, as perception of effort is not reduced, muscle afferent feedback cannot be considered as a sensory signal processed by the brain to generate the perception of effort. This result reinforces the potential of using the perception of effort intensity as a psychophysiological index of the motor command [24,27,[88][89][90], as traditionally performed in the neuroscience, cardiovascular physiology and kinesthesia literatures [24,25,27,91].…”

“…For example, Zenon et al [121] demonstrated that disrupting the supplementary motor area via continuous theta burst transcranial magnetic stimulation decreases perception of effort. Other studies demonstrated a close relationship between perception of effort and physiological variables known to be strongly influenced by the motor command, such as the respiratory frequency [122] or the electromyographic signal [90].…”