Up to about 5 out of 10, settled within an hour; with leg symptoms, walk in intervalsEmerging evidence
For the exercises, this guide uses the back hub's rule. Some discomfort during exercise is fine, and it doesn't mean you are doing damage. Aim for pain you would call mild to moderate, no more than about 5 out of 10. It should settle within an hour or so, and your back should be no worse the next morning. If it is worse, do less next time (fewer reps, a smaller range, a lighter load), not nothing.
Leg symptoms are the exception: stop or shrink any movement that sends pain, pins and needles or numbness further down your leg. If leg symptoms move back towards your spine, that is a good sign, even if your back aches a little more for a while.
If pain climbs day after day, or you notice any warning sign, stop and get it checked. The 5 out of 10 figure matches this site's other pain guides and hasn't been tested in a back pain trial; NHS inform's back exercises use the same limit (keep pain within 0 to 5 out of 10, and no worse the morning after), and in trials of long-lasting muscle and joint pain, exercise that allowed some pain did no harm.
Walking with ordinary back pain (our suggestion): the same limit. Walk at a pace and distance where your back stays at 5 out of 10 or less and settles within an hour; split longer walks, and add a few minutes every 2 or 3 walks.
Walking with the stenosis pattern (our spinal stenosis guide's rule, from NHS inform and an NHS spinal service): walking is safe while symptoms remain manageable, and the spinal service says harm to the nerves is unlikely when pain is felt. Walk until the leg symptoms start to build, then sit or lean forward until they ease, and go again; your walking time should creep up. Leg weakness that is getting worse, or numbness around the genitals or bottom, is never an interval: it's a warning sign.
Calf, thigh or buttock ache that goes when you stand still isn't this rule: get it checked by a GP. Once narrowed arteries are diagnosed, the walking programme deliberately walks into the pain, as our calf pain when walking guide explains.
Sources 26, 27, 4, 5, 10, 13