If you’ve ever started a new exercise program, returned to training after time off, or tried a movement pattern your body wasn’t used to, you know the feeling: a deep, diffuse ache that arrives 24 to 48 hours after training and makes sitting down and standing up feel like acts of negotiation.

That’s delayed onset muscle soreness — DOMS. And it’s one of the most misunderstood phenomena in fitness.

What DOMS Actually Is

DOMS is not caused by lactic acid buildup, despite what you may have heard. That myth has been thoroughly debunked. Lactic acid clears from the bloodstream within an hour of exercise and plays no role in the soreness you feel the next day.

The current scientific understanding is that DOMS results from micro-tears in muscle fibers — particularly during eccentric (lengthening) muscle contractions — that trigger a local inflammatory response. This inflammation brings fluid, immune cells, and repair signals to the damaged tissue. The soreness, stiffness, and tenderness you feel are byproducts of that repair process.

In other words: DOMS is your body in the process of rebuilding.

Why Eccentric Exercise Causes More Soreness

Eccentric contractions — the lowering phase of a squat, the descent of a push-up, the lowering of a weight — generate more mechanical stress on muscle fibers than concentric (shortening) contractions at the same load. This is why downhill running produces severe DOMS in people who can run uphill for miles without soreness, and why a slow, controlled lowering phase in any exercise will produce more soreness than a quick drop.

This also explains why DOMS tends to be most severe when you first start training or try new exercises — your muscles haven’t developed tolerance to the specific stress being imposed.

DOMS Is Not a Measure of Workout Quality

This is perhaps the most important thing to understand about DOMS: it does not correlate with training effectiveness. Some of the most productive workouts produce minimal soreness. Some workouts that leave you barely able to walk the next day produce suboptimal results.

Soreness is a measure of novelty — how unfamiliar the stimulus was to your body. As your body adapts to a given exercise, the same workout produces less DOMS. That’s not a sign that it stopped working. It’s a sign that you’ve adapted, which is exactly what strength training is designed to produce.

What Helps With DOMS

The most effective intervention for DOMS is low-intensity movement. Active recovery — a walk, light yoga, easy cycling — increases blood flow to affected tissues and accelerates the clearance of inflammatory byproducts. It doesn’t eliminate soreness, but it meaningfully reduces duration and severity.

Protein intake supports muscle repair. If you’re training consistently and experiencing ongoing soreness, check that you’re consuming adequate protein — especially in the 24 hours after a hard session.

Sleep is when the majority of muscle repair and adaptation occurs. Growth hormone release peaks during deep sleep, and muscle protein synthesis continues elevated for 24–48 hours post-training. Protecting sleep is one of the highest-leverage recovery interventions available.

Cold water immersion, contrast therapy, and massage have all shown modest benefits in research — but their effects are mainly on perceived soreness rather than actual tissue repair. Use them if they help you recover psychologically and physically between sessions.

Should You Train While Sore?

Mild to moderate soreness is generally fine to train through, particularly if you’re training different muscle groups than the ones that are sore. Severe soreness — the kind that significantly limits your range of motion or makes normal movement difficult — is a signal to rest or reduce intensity until it resolves.

Training the same severely sore muscles at high intensity before they’ve recovered can impair the adaptation process and increase injury risk. Listen to the degree of soreness, not just whether soreness is present.

The Bottom Line

DOMS is normal, expected, and not something to chase or fear. It’s a sign of stimulus. The goal of training is not to be perpetually sore — it’s to create a consistent, progressive stimulus that your body adapts to over time. Rest, eat well, sleep enough, and show up again when you’re ready.