Why do my muscles get sore after a workout?
Muscles get sore when an unusual effort, especially braking as on a downhill, damages tiny parts of the muscle fibers. The pain, called DOMS (delayed onset muscle soreness), starts 6 to 24 hours later, peaks between 1 and 3 days, then fades within about a week (Mizumura, 2016). Lactic acid is gone within an hour.
Simplified diagram, not to scale. Dotted curves are estimates based on published timelines; the percentages in the notes are measured.
Why do my muscles get sore after a workout?
A thigh muscle fiber, greatly magnified. Choose a situation, then tap a label on the drawing to find out what it is.
Sources: overstretched sarcomeres and muscle adaptation (Proske and Morgan, J Physiol, 2001); zigzag Z lines (Clarkson and Hubal, 2002); inflammation and repair (Peake et al., 2017); timelines and sensitized nerves (Mizumura and Taguchi, J Physiol Sci, 2016); 1st and 2nd downhill run (Byrnes et al., J Appl Physiol, 1985); how long the protection lasts (Nosaka et al., 2001). Drawing not to scale; scene timings and pain curve: estimates.
Keyboard: 1 to 3 situations, Space pause, L slow motion, R restart, ← → previous or next step.
Frequently asked questions about sore muscles
How long does muscle soreness last?
Muscle soreness usually lasts less than a week: it starts 6 to 24 hours after exercise, is at its worst between 1 and 3 days, then fades within about 7 days (Mizumura, 2016; Proske, 2001). After a usual workout, it stays mild and passes in a few days. After a very unusual and very intense effort, such as a first long downhill run, strength can take more than a week to come back (Paulsen, 2012). If the pain has not eased after a week, it is best to get medical advice (to be checked).
Can I exercise with sore muscles?
Yes, you can exercise with sore muscles, as long as you lower the intensity for 1 to 2 days (Cheung, 2003). Moving gently eases the pain, but only for a while. A sore muscle has less strength and a smaller range of motion: going back too hard, too soon, raises the risk of injury (Cheung, 2003). In a study of 109 people, strength was at its lowest right after exercise, then came back gradually over about ten days (Clarkson, 1992). So the muscle needs more time than the pain to recover.
Does stretching prevent sore muscles?
No, stretching before or after sports barely reduces muscle soreness. A Cochrane review of 12 studies, including a trial of 2,377 people, found a drop of about 1 point on a 100-point scale the next day, and 4 points at most over the week: too little to feel better (Herbert, 2011). Massage does better, especially 2 to 3 days later (Guo, 2017). A cold bath helps a little, but no more than a lukewarm bath, and these studies are of low quality (Bleakley, 2012).
Sore muscles or rhabdomyolysis: when should I worry?
See a doctor right away if, after exercise, your urine turns dark, reddish brown or tea-colored, especially with very painful and weak muscles: these are signs of rhabdomyolysis (MSD Manual). Damaged fibers then release a lot of myoglobin and CK into the blood, which can harm the kidneys; a blood test confirms the diagnosis. Fewer than 10% of people have all three signs at once (MSD Manual). A very swollen and hard muscle, or pain that gets worse instead of better, are also reasons to see a doctor (to be checked).
Do anti-inflammatories help sore muscles?
Anti-inflammatories help muscle soreness only a little, and inconsistently: taken once the pain has set in, they rarely help (Mizumura, 2016). Their effect also depends on the dose (Cheung, 2003). In rats, the pain involves substances that make nerves more sensitive, NGF and GDNF, which rise between 12 hours and 2 days after exercise (Mizumura, 2016). Inflammation is also part of muscle repair (Peake, 2017). Before taking any, it is best to ask a pharmacist or a doctor.
True or false?
Muscle soreness comes from lactic acid.
False. Lactate is back to its resting level in less than an hour, while soreness shows up the next day (Mizumura, 2016).
Your second workout leaves you less sore.
True. After 30 minutes of downhill running, blood CK rose by 340% the first time, and by only 63% for the same run 3 weeks later (Byrnes, 1985).
The more it hurts, the more damaged the muscle is.
False. In rats, fewer than 0.8% of the fibers were destroyed, and pain depended mostly on the speed and range of the stretch (Hayashi, 2017). In 10 men, after the same exercise, peak CK ranged from 236 to 25,244 units per liter (Nosaka and Clarkson, 1996).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
After an unusual workout, day by day
Pain, lost strength, swelling and CK in the blood do not follow the same rhythm. Pain peaks between 1 and 3 days; strength comes back more slowly. Estimated curves, in relative levels.
| Hours after the workout | Pain (soreness) (dotted) | Lost strength (dotted) | Swelling (dotted) | CK in the blood (dotted) | What happens |
|---|---|---|---|---|---|
| End | 0 | 100 | 0 | 0 | The end of the workout |
| Day 1 | 45 | 88 | 25 | 8 | 24 h after the workout (day 1) |
| Day 2 | 100 | 78 | 50 | 45 | 48 h after the workout (day 2) |
| Day 3 | 82 | 68 | 72 | 80 | 72 h after the workout (day 3) |
| Day 4 | 45 | 58 | 90 | 100 | 96 h after the workout (day 4) |
| Day 5 | 20 | 48 | 100 | 95 | 120 h after the workout (day 5) |
| Day 6 | 7 | 38 | 92 | 70 | 144 h after the workout (day 6) |
| Day 7 | 2 | 30 | 80 | 45 | 168 h after the workout (day 7) |
Key points
- Nothing for the first few hours (Up to 24 h, Shown in humans)
After exercise, there are often 12 to 24 hours without pain; some people feel it as early as 6 to 8 hours (Proske, 2001). Source: Mizumura and Taguchi, "Delayed onset muscle soreness: involvement of neurotrophic factors", J Physiol Sci, 2016 - Not the fault of lactic acid (Up to 24 h, Shown in humans)
Lactate returns to its resting level in less than an hour, long before soreness sets in. Source: Mizumura and Taguchi, "Delayed onset muscle soreness: involvement of neurotrophic factors", J Physiol Sci, 2016 - The peak: between 1 and 3 days (From 24 h to 72 h, Shown in humans)
Pain is at its worst between 24 and 72 hours, often around 48 hours (Proske, 2001). Source: Hotfiel et al., "Advances in Delayed-Onset Muscle Soreness (DOMS): Part I: Pathogenesis and Diagnostics", Sportverletz Sportschaden, 2018 - Less strength for days (Throughout, Shown in humans)
In 109 people, after eccentric arm exercise, strength was at its lowest right afterward, then came back steadily over 10 days. Swelling peaked on day 5, and CK rose sharply on day 2. Source: Clarkson, Nosaka and Braun, "Muscle function after exercise-induced muscle damage and rapid adaptation", Med Sci Sports Exerc, 1992 - CK: highly variable (From 36 h, Shown in humans)
In 10 men, after the same arm exercise, peak CK ranged from 236 to 25,244 units per liter: a blood test does not tell you how sore you will be. Source: Nosaka and Clarkson, "Variability in serum creatine kinase response after eccentric exercise of the elbow flexors", Int J Sports Med, 1996 - Nerves made more sensitive (From 12 h to 72 h, Seen in animals)
In rats, NGF rises from 12 hours to 2 days after exercise, and GDNF from 12 hours to 1 day: these substances make pain nerve endings more sensitive. Source: Mizumura and Taguchi, "Delayed onset muscle soreness: involvement of neurotrophic factors", J Physiol Sci, 2016 - Pain does not measure the damage (From 12 h to 96 h, Seen in animals)
In rats, less than 0.8% of fibers were destroyed, and pain depended mostly on the speed and range of the stretch. Source: Hayashi et al., "Muscular mechanical hyperalgesia after lengthening contractions in rats depends on stretch velocity and range of motion", Eur J Pain, 2017 - Gone within a week (From 96 h, Shown in humans)
Sore muscles usually go away within 7 days. After a maximal and very unusual effort, full recovery can take more than a week (Paulsen, 2012). Source: Mizumura and Taguchi, "Delayed onset muscle soreness: involvement of neurotrophic factors", J Physiol Sci, 2016 - Estimated curves (Throughout, Hypothesis)
The shape of the curves follows published timelines; the heights are relative levels, not measurements. The CK peak around day 4 is to be verified.
Why does the second workout hurt less?
The same effort, repeated a few weeks later, causes much less soreness: this is the repeated bout effect. Measured percentages; estimated curves.
| Hours after the workout | Pain, 1st downhill run (dotted) | Pain, same downhill run 3 weeks later (dotted) | What happens |
|---|---|---|---|
| End | 0 | 0 | The end of the workout |
| Day 1 | 58 | 31 | 24 h after the workout (day 1) |
| Day 2 | 99 | 48 | 48 h after the workout (day 2) |
| Day 3 | 75 | 28 | 72 h after the workout (day 3) |
| Day 4 | 40 | 10 | 96 h after the workout (day 4) |
| Day 5 | 18 | 3 | 120 h after the workout (day 5) |
| Day 6 | 6 | 1 | 144 h after the workout (day 6) |
| Day 7 | 1 | 0 | 168 h after the workout (day 7) |
Key points
- The same run, 3 weeks later (Throughout, Shown in humans)
After 30 minutes of downhill running, blood CK rose by 340% the 1st time and by 63% the 2nd time. Pain, rated at 6, 18 and 42 hours, was worst at 42 hours. Source: Byrnes et al., "Delayed onset muscle soreness following repeated bouts of downhill running", J Appl Physiol, 1985 - How long does the protection last? (Throughout, Shown in humans)
In this trial, it still held at 6 weeks (CK +272% the 1st time, +62% the 2nd), but not at 9 weeks. For the arm muscles, it lasted at least 6 months and faded between 9 and 12 months (Nosaka, 2001). Source: Byrnes et al., "Delayed onset muscle soreness following repeated bouts of downhill running", J Appl Physiol, 1985 - Even the other leg benefits (Throughout, Shown in humans)
When one leg works, then the other 6 weeks later, the 2nd one has 42% less soreness, 62% less CK and loses 54% less strength. Source: Hody et al., "The susceptibility of the knee extensors to eccentric exercise-induced muscle damage is not affected by leg dominance but by exercise order", Clin Physiol Funct Imaging, 2013 - More sarcomeres (Throughout, Seen in animals)
In rats that run downhill, fibers gain about 11% more sarcomeres end to end: each one stretches less at the next workout. Source: Proske and Morgan, "Muscle damage from eccentric exercise: mechanism, mechanical signs, adaptation and clinical applications", J Physiol, 2001 - Several adaptations (Throughout, Shown in humans)
The nervous system, muscle tissue and the cells themselves adapt; no single explanation accounts for the effect on its own. Source: McHugh, "Recent advances in the understanding of the repeated bout effect", Scand J Med Sci Sports, 2003 - The surest way to limit them (Throughout, Shown in humans)
Start eccentric efforts with light workouts, then build up over 1 to 2 weeks. An effort at 50% of maximal strength causes much less damage than a maximal effort (Nosaka, 2002; Hody, 2019). Source: Cheung, Hume and Maxwell, "Delayed onset muscle soreness: treatment strategies and performance factors", Sports Med, 2003 - Estimated curves (Throughout, Hypothesis)
Only the percentages in the notes are measured. The curve for the 2nd downhill run is drawn about half as high, as an estimate.
Stretching, massage, cold: what really helps?
Large reviews of studies compare the methods. Stretching changes almost nothing; massage helps the most. Stretching curve based on the numbers; massage estimated.
| Hours after the workout | Doing nothing (dotted) | With stretching (dotted) | With massage (estimate) (dotted) | What happens |
|---|---|---|---|---|
| End | 0 | 0 | 0 | The end of the workout |
| Day 1 | 45 | 44 | 38 | 24 h after the workout (day 1) |
| Day 2 | 100 | 96 | 70 | 48 h after the workout (day 2) |
| Day 3 | 82 | 79 | 57 | 72 h after the workout (day 3) |
| Day 4 | 45 | 43 | 30 | 96 h after the workout (day 4) |
| Day 5 | 20 | 19 | 13 | 120 h after the workout (day 5) |
| Day 6 | 7 | 7 | 5 | 144 h after the workout (day 6) |
| Day 7 | 2 | 2 | 1 | 168 h after the workout (day 7) |
Key points
- Stretching: almost nothing (Throughout, Shown in humans)
12 studies, including a trial of 2,377 people: stretching before or after sports lowers pain by about 1 point out of 100 the next day, and by 4 points at most over the week. Too little to notice. Source: Herbert, de Noronha and Kamper, "Stretching to prevent or reduce muscle soreness after exercise", Cochrane, 2011 - Massage: the most effective (From 24 h to 96 h, Shown in humans)
In 11 studies (504 people), massage reduces soreness, especially 48 and 72 hours after. A review of 99 studies ranks it first among recovery methods (Dupuy, 2018). Source: Guo et al., "Massage alleviates delayed onset muscle soreness after strenuous exercise: a systematic review and meta-analysis", Front Physiol, 2017 - Cold baths: no better than lukewarm (Up to 96 h, Shown in humans)
17 small trials, 366 people, water below 59 °F (15 °C): a little less pain than resting, but no less than with lukewarm water, and the studies are of low quality. Source: Bleakley et al., "Cold-water immersion (cryotherapy) for preventing and treating muscle soreness after exercise", Cochrane, 2012 - Move gently (Throughout, Shown in humans)
Light exercise eases the pain, but only for a while. Lowering the intensity for 1 to 2 days helps avoid injury. Source: Cheung, Hume and Maxwell, "Delayed onset muscle soreness: treatment strategies and performance factors", Sports Med, 2003 - No miracle cure (Throughout, Shown in humans)
No treatment reliably makes sore muscles go away: they pass on their own. Source: Connolly, Sayers and McHugh, "Treatment and prevention of delayed onset muscle soreness", J Strength Cond Res, 2003 - Estimated curves (Throughout, Hypothesis)
The stretching curve follows the numbers from the Cochrane review. The massage curve is an estimate: studies give an effect size, not a drop in points.
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