Itchysphincter said:
Very painful for some people, insignificant for others. He’ll have no choice but to rest for a few days. Tell him to eat nothing but ibuprofen and drink water (not really, but definitely stay of refined processed foods until the inflammation settles down at the very least). Once he’s able to move get going and in a few weeks pay for a personal trainer and get on the weights to build strength. Others will say chiropractor or osteopath but that will only treat the symptom not the cause.
Deadlifts helped me when I was suffering, lightweights of course and only started once I was pain free of course, planks helped as well as they strengthen the inner core muscles around the spine, apart from the occasional twinge and stiffness, I haven't had an issue with my back, for a good few yrs.
I should add is that I was never diagnosed with a slipped disc, my back issues were classed as mechanical back pain, muscles around spine going into a spasm.