Interesting scientific paper on this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3265077/

The research done to date supports the concept that grounding or earthing the human body may be an essential element in the health equation along with sunshine, clean air and water, nutritious food, and physical activity.

Apparently, it’s all to do with the vast supply of electrons found on the surface of the Earth.

Earthing / grounding is correlated with better sleep and reduced pain – as a result of either walking barefoot outside, or just sitting barefoot outside.

The graphs below show cortisol levels before and after grounding.

Subjects were grounded during sleep on a specialised mattress –

Image Source

How does this relate to combat sports?

Good question –

Recovery.

Recovery is often the limiting factor in terms of training load.
Anything that reduces cortisol levels and potentially increases energy levels is a must for mixed martial arts fighters.

It’s easy to do as well, just eat outside when possible, with your bare feet on the floor