Objectives and research hypothesis Physical inactivity is a major health concern that has been linked to a variety of chronic diseases, including obesity, diabetes, cancer, cardiovascular diseases, and mental disorders. Recent studies have shown that regular physical activity can decrease the risk of SARS-CoV-2 infection, and severe COVID-19 illnesses, as well as improve antibody response to vaccine. As such, the adoption of a physically active lifestyle carries potential health benefits and has even been referred to as a "miracle cure" by the Academy of Royal Medical Colleges. Despite the implementation of policies that aimed to encourage regular physical activity, the prevalence of insufficient physical activity in high-income countries has increased since 2001 (32% in 2001 vs. 37% in 2018). Given the limited impact of health policies on physical activity engagement, it is essential to explore other avenues of research that can contribute to understanding this high level of inactivity and driving innovative strategies for encouraging physical activity. In this context, the automatic attraction of individuals toward activities associated with low-effort exertion is thought to play a key role in physical inactivity. Physical activity involves exerting physical effort, i.e., intensifying physical energy to achieve certain goals, such as increasing the force to lift a heavy object. This physical intensification is associated with the phenomenological experience of energy exertion. Higher effort perception is thought to be aversively valued by inactive individuals, inhibiting their engagement in regular physical activity. However, there is a lack of knowledge regarding the neural correlates of effort perception and how they relate to physical inactivity. It is crucial to gain insights into these neural correlates, especially to enhance our comprehension of the significance of effort minimization in physical inactivity. This project aims to decrease effort perception and improve the valuation of effort, incentivize regular physical activity, and improve overall health outcomes.
Objective 1. Despite ongoing research, there is a lack of agreement on the neural mechanisms underlying effort perception as well as the role of sensorial feedback. Tasks EEG and fMRI aim to address this issue with original experimental methods in order to identify this neural mechanism.
Hypothesis 1. Following A) muscle vibration and B) Induced ischemic paralysis and anesthesia, we expect decreased effort perception associated with a lower cortical S1 activation, unchanged activation in premotor structures, and preserved functional connectivity between premotor regions and S1.
Objective 2. To unravel the neural interaction between efference copy and reafferent muscle spindle signals that contribute to effort perception Hypothesis 2. The neural correlates of effort perception involve interactions between premotor and sensory brain structures. Neural activation patterns of the brain regions implicated in effort perception vary depending on an individual's inclination to engage in physical activity.
Objective 3. Task 3 will examine the potential of non-invasive brain stimulation techniques (TMS) to reduce effort perception in turn increase its perceived value quantified with the CR100 scale, the outcome variable of this study.
Hypothesis 3. Vibration-induced desensitization of muscle spindles and the SMA cTBS reduce effort perception and improve the subjective value of physical effort.
Normal subjects all ranges age
Neurologic conditions that may bias the EEG or fMRI results such as epilepsy, tumors; stroke; which can be a casual MRI finding during the study.
Parallel
Transcranial Magnetic Stimulation Sham
DevicecTBS over SMA and cTBS over precuneus (control site)
Effort perception
Physical effort scale Category (C)-Ratio (R) (CR) scaling 100 or Borg centiMax® Scale (CR100) is a measure from 0 to 100 to rate the intensity of effort perception, where 0 means "nothing at all" (i.e. "no perception of effort at all") and 100 means "Maximal", that is, the maximal perception of effort experienced.
Resting-state and task fMRI functional connectivity
Task fMRI condition A) induce ischemic paralysis and anesthesia: an MRI-compatible two chamber cuff will be placed over participants' upper arm outside the scanner and inflated to 250 mmHg until total abolishment of light touch sensation below the elbow is achieved46. This generally takes 20-40 min B) Task fMRI control condition. They will perform voluntary isometric handgrip contractions at moderate and strong perceived effort intensities based on the CR100 with their dominant hand. These two intensities were chosen to assess the impact of perceived effort level on brain activity, while avoiding excessive head movement that could occur at higher intensities and controlling for the development of neuromuscular fatigue C) Resting-state fMRI: 10-min resting-state fMRI scan to assess functional connectivity between different brain regions.
EEG event related synchronization
ERSP analyses will allow us to examine changes in alpha (8-13 Hz) and beta (13-30 Hz) neural oscillations within predetermined regions of interest during spindle desensitization. This will be done trougth the application of vibration at the myotendinous junction of the biceps brachii using a custom-made vibrator. Following the successful methodology of the PI in PoC1 and 2, we will apply the vibration for a 10-min period with a frequency of 100 Hz and an amplitude of approximately 2 mm in the vibration condition.
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University Hospital, Grenoble
Lead sponsor
IRMage
Collaborator
