I was not self employed back in the day but worked in vet clinical. Benefits were non-existant. 1/4 of my income went to paying for a medical coverage plan. Taxes went towards workmans comp, which covered time off I needed after a minor surgery. Because of this I exited the clinical community with zero savings or long term funds.
trainers are no different. They must pay their taxes and it would be best they invest in a medical policy via ACA or their state health insurance org so that they have medical coverage. If they are injured they need to have paid into state taxes which cover their temporary disability and they should be looking towards long term retirement security via a serious insurance policy.
much like anyone else, if you think that your social security benefits will cover you in your golden years, you are sorely mistaken.
the bottom line you really are not going to be spending your income on glamorous vacations and posh ponies, you really need to plan for a huge disaster. The disaster may not even be a fall from a horse. That pesky lump in your breast probably should not be ignored etc etc etc
dont rely on Go Fund Me to cover your disaster