Up to about 5 out of 10, settled within an hour; numbness means change something nowEmerging evidence
This guide uses the foot and ankle hubs' rule. Some discomfort during exercise is fine. Aim for pain you would call mild to moderate, no more than about 5 out of 10, that settles within an hour, with no more swelling or stiffness the next morning. If it's worse the next day, do a little less (a smaller range, fewer reps, a lighter band), not nothing.
The exceptions: pain in one spot on a bone should be pain-free, because it could be a stress fracture; burning, tingling or numbness means stop that movement; and if your feet are numb, pain won't warn you, so check your skin after exercise.
If pain climbs day after day, or you notice a warning sign, stop and get it checked. The 5 out of 10 figure is an editorial starting point that matches this site's other pain guides, not a tested rule.
For numbness, our numb feet when cycling guide's paragraph applies: Burning, tingling or numbness isn't a pain score: stop any movement that brings on burning or shooting pain, tingling or numbness between the toes, and change it rather than push through. Pain in one spot on a bone should be pain-free, because it could be a stress fracture. If your feet are numb, pain won't warn you, so check your skin after exercise and after every ride.
With Morton's neuroma, stop any movement that brings on burning or shooting pain, tingling or numbness between the toes, and change it rather than push through.
On the elliptical (our suggestion, built on the same rule): judge each session by its last few minutes, by how your feet feel 10 minutes after you step off, and, with heel pain, by your first steps the next morning. An ache up to about 5 out of 10 that settles within an hour is fine; NHS inform's ball of the foot advice uses the same 0 to 5 limit and says a little activity is better than nothing. When numbness, tingling or burning starts, shift your weight back through your heels, wiggle your toes, ease the resistance, or step off and loosen your laces. If it fades within a few minutes, carry on with the changes below; if it lasts after the session, comes back every session despite the changes, or is in both feet off the machine, see a GP, as the NHS advises for pins and needles that keep coming back. If your feet are numb, check your skin after every session. Pain at one spot on a bone, a hot, swollen foot, a cold, pale foot and any new problem with diabetes aren't pain-rule questions: see the warning signs.
Sources 52, 7, 47, 20