Muscle soreness: why it happens and what studies show about heat, massage and movement

Two physiologists at Monash University in Melbourne summarized what happens during braking muscle work. Untrained people become stiff and sore the day after, because muscle fibers are damaged. The authors see disruptions at the level of the sarcomeres, the smallest units that generate force inside the muscle fiber, as the likely starting point.

For you, this means: when braking, individual tiny links in your muscle fiber can be overstretched. That is where the soreness comes from.

A team led by Schwane and Armstrong had seven people run on a treadmill for 45 minutes each, once on the flat and once downhill at a ten percent decline. Only after the downhill run did they develop marked muscle soreness in the buttocks, thighs and lower legs, and the muscle enzyme CK in the blood was 351 percent higher after 24 hours. After the level run, which was performed at a higher intensity, no statistically significant muscle soreness occurred.

For you, this means: it is not effort alone that matters, but the type of load. Braking and going downhill challenge the muscle in a particular way.

A German team led by Hotfiel from the University of Erlangen-Nuremberg, with contributors including the German Sport University Cologne, summarized the current knowledge on muscle soreness. Today, the main mechanism is considered to be damage to the finest structures of the muscle cells after unaccustomed or eccentric exercise, followed by protein breakdown, programmed cell death and a local inflammatory response. Because these processes unfold gradually, the discomfort comes with a delay and typically peaks after 48 to 72 hours.

For you, this means: the pain on day two is not a new injury. It is the delayed echo of yesterday.

In 1983, the research group led by Schwane and Armstrong tested the lactate question directly. They measured blood lactate before and during a 45-minute run, once on the flat and once downhill, and then recorded muscle soreness for 72 hours. During the level run, lactate rose markedly, but no muscle soreness followed. During the downhill run, lactate never rose, and yet the soreness came.

For you, this means: in this study, lactate and muscle soreness went separate ways. The authors concluded that lactic acid is not related to delayed onset muscle soreness.

The physiologist Brooks from the University of California, Berkeley, summarized what lactate does in the body. It used to be considered a waste product. It is now known that it is produced continuously, even when there is enough oxygen. It is passed between cells and serves as an important energy source, as a starting material for new glucose and as a signaling molecule.

For you, this means: lactate is more like fuel that gets passed on than slag that stays behind in the muscle.

A team led by Peake from Queensland University of Technology in Brisbane summarized what goes on in the muscle after unaccustomed, braking exercise. Inflammation used to be considered harmful to recovery. Today it is regarded as an integral part of rebuilding and renewing the muscle, as long as it stays well regulated. In animal experiments, various immune cells, including scavenger cells, helped rebuild the tissue. Whether the same happens in humans after exercise has not yet been sufficiently studied.

For you, this means: the brief, local inflammation after training is more construction crew than arsonist.

A research team led by Mizumura and Taguchi studied, mainly in rats, how the typical pain on pressure and movement develops. They observed the pain one to three days after braking muscle work, even without damage visible under the microscope and without signs of inflammation. Nerve growth factors such as NGF and GDNF were involved. They are produced by muscle fibers and their stem cells and can make the pain sensors more sensitive, triggered among other things via the messenger substance bradykinin and the enzyme COX-2.

For you, this means: how much it hurts does not reliably reveal how big the damage is. In humans, this pathway has not yet been conclusively demonstrated.

Researchers from Brigham Young University in the US, National Taiwan Normal University and Edith Cowan University in Australia compiled how this repeated bout effect comes about. They assume that several adaptations work together: in the nervous system, in the mechanical properties of the muscle, in the remodeling of the connective tissue scaffold around the fibers and in biochemical signaling pathways. Many details are not yet understood.

For you, this means: the protection develops on several levels at once, from the nervous system to the connective tissue.

A team led by Nosaka in Yokohama had 35 male students perform the same hard, braking arm exercise twice, six, nine or twelve months apart. After six months, the second bout of soreness was milder, and swelling and muscle enzymes rose less. After six and nine months, strength recovered faster. After twelve months, no protective effect could be detected anymore.

For you, this means: your muscle can remember a load for months. For most measures, the protection lasted at least six months.

At National Chiayi University in Taiwan, a team led by Chen and Nosaka compared 30 untrained men. One group performed a light braking arm exercise at 40 percent of their maximal strength four times, two weeks apart, before the hard session came. Even these light sessions caused considerably less discomfort than a first hard session, and they protected against the later hard session just as well as a hard preliminary bout.

For you, this means: protection can also be gentle. A gradual increase can have the same effect as a painful start.

In a follow-up study from Taiwan with 65 untrained men, groups performed a very light braking exercise at only ten percent of maximal strength, between two days and three weeks before a hard session. The protection was clear when the light exercise had been done two days to one week earlier, and it weakened by the second week. After three weeks it had largely disappeared. Only the muscle soreness was still somewhat milder.

For you, this means: gentle protection needs to be maintained. After longer breaks, the soreness can return.

A team at Northern Arizona University wanted to know whether building muscle requires noticeable damage. One group was slowly accustomed to braking cycling over three weeks and showed hardly any signs of muscle damage. The other started with a strenuous session and had CK levels more than five times as high, along with marked muscle soreness. Afterwards, both trained for eight weeks with the same total work, and the gains in muscle size and strength were the same: 25 and 26 percent more strength.

For you, this means: building muscle can begin without noticeable damage. In this study, the soreness brought no advantage.

Researchers from the University of São Paulo and McMaster University followed ten young men through ten weeks of strength training and repeatedly took tissue samples from the thigh. In the first week, muscle damage and protein synthesis were highest, but this early building work was not related to later muscle growth. Only after three and ten weeks, when the damage had decreased considerably, did protein synthesis go hand in hand with growth.

For you, this means: at the beginning, your muscle seems to put a lot of energy into repair rather than growth. Growth tends to come once the damage gets smaller.

A team from the University of Poitiers in France analyzed 99 studies on recovery methods after exercise. Active recovery, massage, compression garments, water immersion, contrast baths and cold reduced muscle soreness to a small to large extent. For the other methods examined, no change was found. Massage performed best for muscle soreness and perceived fatigue, and massage and cold also dampened inflammatory markers most clearly.

For you, this means: among the well-studied methods, it is human hands, of all things, that lead the field.

A research group from Shanghai University of Sport and Wenzhou Medical University pooled eleven studies with 504 participants. With massage, muscle soreness was lower after 24, 48 and 72 hours than without, most clearly after 48 and 72 hours. In addition, maximal strength recovered better, and the muscle enzyme CK in the blood was lower.

For you, this means: massage may do more than make the soreness more bearable. In these studies, it was also associated with better strength.

At McMaster University in Canada, eleven young men received ten minutes of massage on one thigh after a strenuous session, while the other thigh was left untreated. In tissue samples, the massage dampened the inflammatory switch NF-kB and the production of the inflammatory messengers TNF-alpha and IL-6, while signals for the formation of new mitochondria increased. The massage had no effect on lactate or glycogen in the muscle.

For you, this means: massage does not seem to work by flushing things out, but through signals inside the cell. Eleven participants, however, are not many.

A team from Lanzhou University in China analyzed 32 randomized trials with 1,098 participants on heat and cold for muscle soreness. Heat eased pain within the first 24 hours and also afterwards, most clearly with heat packs. Cold, applied within one hour after exercise, reduced pain during the first 24 hours, after which no clear effect was discernible, and there was no statistically significant difference between heat and cold.

For you, this means: both can bring relief. Heat seems to last a little longer, but according to this analysis there is no clear winner.

In two small randomized trials from San Diego, 67 healthy people deliberately induced muscle soreness in the lower back with vigorous braking exercises. A heat wrap worn for four hours before and four hours after training reduced pain intensity after 24 hours by 47 percent compared with the control group. As a treatment between hour 18 and hour 42, the heat wrap provided 138 percent greater pain relief after 24 hours than a cold pack.

For you, this means: mild, steady warmth over several hours can noticeably dampen soreness, at least in the back. The authors themselves describe it as a small study.

A Cochrane review from the University of Ulster in Northern Ireland pooled 17 small studies with 366 participants on cold water baths below 15 °C. Compared with rest, muscle soreness was lower after 24, 48, 72 and 96 hours, although the studies were of low quality. Compared with warm baths or contrast baths, there was no difference.

For you, this means: cold can bring relief, but it is not superior. In the few direct comparisons, a warm bath did no worse.

A team from the University of Queensland in Brisbane had 21 active men do strength training twice a week for twelve weeks, each time followed by ten minutes of either a cold water bath or active recovery. Strength and muscle mass increased more with active recovery, and only in this group did the fast muscle fibers grow, by 17 percent. In tissue samples, the cold water bath dampened the activation of muscle stem cells and of signaling pathways that steer muscle growth.

For you, this means: if building muscle is your goal, it's better not to make the cold bath a routine right after strength training. Whether cold at other times has the same effect was not examined in this study.

At Edith Cowan University in Australia, 14 people performed a hard braking exercise once with each arm. In the four days that followed, one arm moved daily with 600 light, almost effortless bending and straightening movements, while the other did not. Directly after the light movement, muscle soreness and tenderness were about 40 percent lower, but the effect did not last, and overall the muscle did not recover any faster.

For you, this means: movement can turn down the pain for the moment. In this study it did not speed up remodeling, but it can make your day easier.

The Cochrane review led by Herbert from the George Institute for Global Health in Sydney analyzed twelve studies on stretching before or after exercise. Stretching before exercise reduced muscle soreness on the following day by an average of half a point on a scale from 0 to 100, stretching afterwards by about one point, and similarly small effects appeared up to three days later. Even in a large field study with 2,377 participants who stretched before and after exercise, the difference in the worst muscle soreness of a week was only about four points, which the authors classify as very small.

For you, this means: according to this analysis, stretching does not bring about a clinically meaningful reduction in muscle soreness in healthy adults.

A more recent meta-analysis led by the University of Porto, covering ten randomized trials with 229 participants, came to a similar result. Compared with passive recovery, stretching after exercise changed neither the recovery of strength nor muscle soreness after 24, 48 or 72 hours. The authors advise against currently recommending post-exercise stretching as a recovery measure, because the available data do not support it.

For you, this means: stretch if it feels good or if you want to improve your mobility. As a remedy for muscle soreness, it is overrated.

In a randomized trial at the University of Sydney, 52 adults walked backwards downhill for 30 minutes on an inclined treadmill, an exercise designed to induce muscle soreness. Those who had warmed up beforehand with ten minutes of brisk uphill walking had, on average, 13 millimeters less muscle soreness on a 100-millimeter scale after 48 hours. A cool-down after the exercise, by contrast, did not change muscle soreness.

For you, this means: a few minutes of warming up before unaccustomed exercise can reduce soreness somewhat. The effect is not large, but it costs you little.

A team at Georgia State University in Atlanta analyzed 41 human and animal studies on anti-inflammatory painkillers after acute muscle injuries. Overall, the drugs reduced strength loss, muscle soreness and the muscle enzyme CK to a small to moderate extent. The authors see this as an argument for short-term use in humans. In animal studies, however, the drugs appeared rather unfavorable at later time points after the injury.

For you, this means: painkillers are not taboo. The question is what you might be trading for them.

At the University of Arkansas, 24 young men received, after a hard braking session for the thighs, either the maximum over-the-counter daily dose of ibuprofen, 1,200 milligrams, or of paracetamol (acetaminophen), 4,000 milligrams, or a placebo. Under placebo, muscle protein synthesis rose by 76 percent after 24 hours. Under the two painkillers, it did not rise significantly. In this study, the drugs did not reduce perceived muscle soreness more than the placebo.

For you, this means: in this study, the painkillers dampened building processes in the muscle without noticeably easing the soreness.

At the Karolinska Institute in Stockholm, 31 young women and men trained their thighs for eight weeks and took either 1,200 milligrams of ibuprofen or 75 milligrams of acetylsalicylic acid, a very low dose, every day. The thigh muscle grew by 3.7 percent in the ibuprofen group and by 7.5 percent with the low dose, and in some measures strength also increased less under ibuprofen. The authors advise young people who want to build strength and muscle against excessive use of anti-inflammatory drugs.

For you, this means: regular high doses over weeks could slow muscle growth.

A team led by Lipman from Stanford University studied runners in desert races of 80 kilometers who received ibuprofen or a placebo during the race. Acute kidney injury developed in 52 percent of the ibuprofen group and 34 percent of the placebo group, which works out to one additional case for roughly every five to six people treated. The difference fell short of statistical significance, but the authors still advise caution with these drugs during long endurance efforts.

For you, this means: during long, sweaty efforts, a painkiller can put additional strain on the kidneys.

A team at the Center for Human Sleep Science at the University of California, Berkeley, investigated how sleep loss changes pain. After a sleepless night, the pain threshold dropped. In the brain, the region that processes bodily sensations reacted more strongly to pain, while regions that evaluate and regulate pain reacted more weakly. In everyday life, too, even small night-to-night fluctuations in sleep quality went along with more or less pain the next day.

For you, this means: sleep is also pain management. The everyday data show a temporal association, and the lab experiments make it plausible.

At Deakin University in Australia, 13 young adults, seven men and six women, spent one night without sleep and one night with normal sleep in random order. After the sleepless night, muscle protein synthesis was 18 percent lower, the stress hormone cortisol 21 percent higher and testosterone 24 percent lower. A single night was enough to shift metabolism toward breakdown.

For you, this means: sleep is building material for remodeling. A short night can measurably slow down the building process.

Researchers at the US Army Research Institute of Environmental Medicine analyzed 27 studies on protein supplements around training. Taken before, during or after a single session, they did not reliably reduce muscle soreness or signs of muscle damage. Benefits were more likely when protein was taken regularly after daily training, and most evident when overall energy or protein intake was too low.

For you, this means: the shake right after training is no magic potion against soreness. What matters more is that you eat enough over the day and get enough protein.

A Cochrane review from Sheffield Hallam University analyzed 50 placebo-controlled studies with 1,089 participants on high-dose antioxidants, taken as supplements or as enriched foods. Statistically, muscle soreness was somewhat lower at several time points. All differences, however, were well below the threshold at which a difference is considered meaningful in everyday life.

For you, this means: high-dose antioxidants did not reduce soreness to an extent you would notice in everyday life.