Some soreness early on is normal — EMS works muscle hard and in ways your body isn’t used to, so the first few sessions can leave you sore for 1–3 days, similar to (sometimes a bit more than) a tough gym session. It eases as you adapt over the first several weeks.

What’s not normal is extreme soreness, heavy swelling, weakness that doesn’t improve, or dark, cola-colored urine — those can be signs of overdoing it (rhabdomyolysis) and mean you should ease right back and get checked out. See the pinned safety notice.

To keep normal soreness in check: start easy, ramp intensity slowly, hydrate well, get some protein in, and don’t stack two hard sessions back to back.