In our 20s, most of us, myself included, wore post-workout soreness like a badge of honor. It was the ultimate proof we had pushed our bodies to the limit and a sure sign we were on our way to building real muscle . But there is a dangerous line between building new muscle and triggering a catastrophic internal breakdown.

When you push far past your threshold, whether powering through a marathon , your latest HYROX race, or an intense lifting session after time off, excessive stiffness is not always just fatigue. It can be a clear sign you’ve overtrained, and if you’ve gone too far, you could put yourself at serious risk of rhabdomyolysis.

Often called “rhabdo,” the condition occurs when overworked muscle fibers disintegrate and release toxic cellular proteins straight into your bloodstream.…