Sore vs. Injured: How to Read Muscle Soreness

Almost everyone who trains has felt it: the deep, achy stiffness that shows up a day or two after a hard session or a new activity. Stairs become a negotiation. Getting out of a chair takes a moment. This is delayed onset muscle soreness, or DOMS, and it is one of the most common — and most misunderstood — sensations in physical activity. The important question is rarely "does this hurt?" It is "what kind of hurt is this?" Learning to read that difference is one of the more useful skills an active person can develop.

What DOMS actually is

Delayed onset muscle soreness typically appears 12 to 24 hours after unfamiliar or intense exercise, peaks somewhere around 24 to 72 hours, and resolves within a few days.¹ It is most strongly linked to eccentric contractions — the lengthening actions muscles perform when you lower a weight, run downhill, or decelerate. The classic explanation of "lactic acid buildup" is a myth; lactate clears within an hour of finishing exercise. The current understanding is that DOMS reflects micro-level mechanical stress to muscle fibres and connective tissue, followed by a local inflammatory and repair response.^1,2

Here is the reassuring part: DOMS is part of how muscle adapts and gets more resilient. The "repeated bout effect" describes how a single session of unfamiliar exercise dramatically reduces soreness after the next similar session, sometimes for weeks.² In other words, soreness after a new stimulus is expected, and your body is already adjusting so it happens less next time.

The character and timeline of normal soreness

Ordinary muscle soreness has a recognizable fingerprint:

• Diffuse, not pinpoint. It is spread across the belly of a muscle group, not localized to one small spot you can cover with a fingertip.
• Symmetrical or predictable. It shows up in the muscles you actually worked, often on both sides.
• Tender and stiff, and it eases as you move. A gentle warm-up usually reduces it.
• It follows the timeline. It builds over a day or two and then steadily improves.

A true injury tends to read differently: pain that is sharp, localized to a specific structure, or tied to a distinct moment ("I felt it go"). Warning signs that deserve more attention include swelling or bruising, a joint that feels unstable or catches, pain that is worse the next day rather than better, numbness or pins and needles, or a localized bony tenderness that does not behave like muscle. Pain that keeps escalating past 72 hours, rather than settling, is a signal worth respecting. This is also where understanding the broader idea of hurt versus harm is genuinely useful — not all pain means damage, but the pattern matters.

The traffic-light model: acceptable soreness

In tendon rehabilitation, clinicians use a simple, evidence-informed framework often called the monitored or "acceptable" soreness model. It was validated in research on patellar and Achilles tendon loading, where completely avoiding load slows recovery but overloading flares symptoms.^3,4 The idea translates well to general training:

• Green (go): Soreness or discomfort during and after activity stays at a low level — roughly a 3 or less out of 10 — and settles back to baseline by the next morning. This is acceptable. Carry on.
• Amber (modify): Soreness sits in the moderate range, or lingers into the next day but is trending down within 24 hours. This is a cue to adjust — reduce volume, load, or intensity — rather than stop entirely.
• Red (back off): Pain is sharp, high, or worse the following morning, and it is not settling within 24 hours. This is the signal to pull back and reassess.

The practical rule that ties this together: judge how you feel the next morning, not just in the moment. Symptoms that return to baseline within 24 hours generally indicate the tissue tolerated the load.^3,4

Modify before you stop

This is where a favourite principle applies: "There are no bad exercises — only too much too soon."⁵ Most soreness that scares people is not a reason to abandon activity — it is information asking for a smaller dose. Rather than jumping from full effort to complete rest, the middle path is usually best: keep moving, reduce the load, shorten the session, or swap a provocative movement for a gentler one. Gentle activity, adequate protein, and sleep do more for recovery than lying still. Passive treatments can feel good, but the research consistently points to graded, progressive loading — not rest and modalities alone — as what actually rebuilds capacity. That rehab-first mindset is exactly how the Boreal team approaches training niggles.

Soreness is not the enemy. It is feedback. When you can read its timeline and character, and use a simple traffic-light check the next morning, you can keep training through the normal ups and downs — and recognize the smaller number of times when something genuinely needs a closer look.

References

1. Cheung K, Hume PA, Maxwell L. Delayed onset muscle soreness: treatment strategies and performance factors. Sports Med. 2003;33(2):145-164.
2. Hyldahl RD, Chen TC, Nosaka K. Mechanisms and mediators of the skeletal muscle repeated bout effect. Exerc Sport Sci Rev. 2017;45(1):24-33.
3. Silbernagel KG, Thomée R, Eriksson BI, Karlsson J. Continued sports activity, using a pain-monitoring model, during rehabilitation in patients with Achilles tendinopathy: a randomized controlled study. Am J Sports Med. 2007;35(6):897-906.
4. Malliaras P, Cook J, Purdam C, Rio E. Patellar tendinopathy: clinical diagnosis, load management, and advice for challenging case presentations. J Orthop Sports Phys Ther. 2015;45(11):887-898.
5. Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50(5):273-280.