On Monday morning, you lower yourself into your chair at work and have to brace both hands on the armrests. The fronts of your thighs are stiff and aching, and every spot you press is sore. Last Saturday afternoon was your first trail run (a run on dirt paths and mountain tracks): fifteen kilometers of red-earth path looping around a few hills outside the city. On the climbs you were out of breath, at times pushing on your knees to keep going. The descents felt much easier; you let your legs go and even passed a few people in the group. That evening your legs felt only as tired as after a long run on the road. The soreness started on Sunday, and by this morning even squatting to tie your shoelaces makes you wince.
People moving from the road to the trail usually worry about the hills they have to climb. Yet it is the downhills that tend to make the thighs hurt. Climbing tires the heart and lungs right then and there. Running downhill makes the thigh muscles do a job they are not used to, and the price only shows up after a night’s sleep. Soreness like your Monday morning is usually harmless, fades on its own, and with the right training it is milder next time. What needs watching is a different kind of muscle pain, which can also come after a long descent and which, if not recognized early, can harm the kidneys.
Legs on the brakes all the way down
Going uphill, the thigh muscles shorten to lift the body, as when you step up a stair. Going downhill, it is the reverse. Gravity pulls the body forward, the knee bends as the foot lands, and the front thigh muscles have to tense to brake while they themselves are being stretched. This kind of contraction, tensing while lengthening, is called an eccentric contraction. Put simply, the front of the thigh is on the brakes the whole way down, braking with every step.
Eccentric contraction uses less energy, which is why the downhill feels easy and your breathing settles. The clinical kinesiology textbook Brunnstrom notes that most muscle injuries happen in these braking, eccentric phases, and that prolonged downhill running is linked to damage in both the muscle fibers and the connective tissue. In our view, it is exactly that pleasant feeling of letting your legs go on a descent that makes many people run down too fast from their very first session.
City roads rarely have a downhill longer than an overpass, while trail races have descents that run for several kilometers at a stretch. So people already used to long distances on the road can still end up with sore thighs like a beginner after their first trail run.
Pain that arrives after a night
The soreness in the opening scene is called delayed onset muscle soreness, or DOMS. It begins about 24 hours after exercise and can last up to 10 days (Brunnstrom). Travell and Simons, in their book on muscle pain in the lower limbs, describe the pain building gradually and peaking at around one to three days. The pain is usually spread across the whole muscle rather than concentrated at one point, with stiffness, difficulty bending the knee fully, and thigh muscles that feel weaker when they have to support your weight. Anyone who has made the New Year pilgrimage up Yen Tu mountain may remember the feeling: climbing the stone steps leaves you breathless, but the next day at home, the thighs hurt most each time you step down.
At that point, many people reach for a strip of anti-inflammatory painkillers. Travell and Simons note that most studies find this group of drugs does little or nothing to ease muscle soreness after exercise. After a long race in hot weather, while the body is still short of water, these drugs also reduce blood flow to the kidneys (Jameson and colleagues, 2018). Delayed onset muscle soreness goes away on its own, so your only job is to give the muscles time to recover, and not to schedule the next hard hill session while your thighs are still sore.
The next descent hurts less than the first
The thigh muscles learn very quickly from the first bout of soreness. Physiologists call this the repeated bout effect: after one downhill run, the next downhill run causes less soreness and less muscle damage. Reviewing the research, Assumpção and colleagues (2013) found that a single downhill run reduced the signs of muscle damage in the following session. The study by Tallis and colleagues (2024) was smaller. A group of female distance runners not used to running hills ran downhill twice; the second time, soreness in the calves, the front of the thighs and the back of the thighs was milder. Brunnstrom also writes that once the muscle has recovered, repeating the same eccentric movement does not bring back the pain of the first time, and the muscle gradually adapts.
Applying these findings to preparing for a trail race is our own inference, because no trial has been done on race runners themselves. From that inference comes a simple way to train: start running downhill on short stretches, then build up gradually over the weeks before the race.
- Begin with a few short, gentle downhill stretches, run slowly;
- Next time, lengthen the descent or add one more repeat, once your thighs are no longer sore from the previous session;
- Count a hill session as a hard session, and do not put it right next to a long run or a fast run;
- Add only one change at a time: if you have added hills, do not change shoes yet.
The last two points follow the advice of Joyce and Lewindon (2016) to increase load gradually and avoid two high-load sessions back to back. The repeated bout effect only makes the muscles less sore next time; it does not make your ankles any steadier on loose rock.
Urine the color of cola
There is one kind of muscle pain after a descent that you must not wait out. When too much muscle breaks down, substances from the muscle cells spill into the blood and can damage the kidneys. This is called rhabdomyolysis. The internal medicine textbook Harrison and CMDT (a reference on diagnosis and treatment in internal medicine, updated every year) list the usual settings: long downhill running, hot weather, people taking cholesterol-lowering statins, and people with sickle cell trait (an inherited feature of the red blood cells).
| Delayed onset muscle soreness | Rhabdomyolysis | |
|---|---|---|
| Muscles | Sore, stiff, painful when bending the knee or going down steps | Swollen, severely painful, far worse than ordinary tiredness |
| Urine color | Normal | Dark like cola, or red |
| Amount of urine | Normal | Less than usual |
| What to do | Rest and wait for it to pass | See a doctor right away; test the muscle enzyme (CK) and kidney function |
The sources we checked give no separate muscle enzyme threshold for runners. After a long race, muscle enzymes can rise even in people who only have ordinary muscle soreness (Brunnstrom), so test results need to be read by a doctor together with your symptoms; do not compare them yourself with numbers found online.
Middle-aged runners who take a statin and plan to run a long, hilly race should tell the doctor who prescribed it before signing up. Prolonged exertion, especially eccentric work, raises the risk of muscle disease and rhabdomyolysis in people taking this drug (Papadakis and colleagues, 2022; Jameson and colleagues, 2018). Do not stop the medicine on your own in order to run.
Feet on the trail
Trails have rocks, roots and wet leaves, and injuries in trail runners are concentrated in the feet. When Viljoen and colleagues (2021) pooled the studies on trail runners, the foot topped the list of injury sites, followed by the knee, lower leg, thigh and ankle. The common problems were abrasions, blisters, muscle strains, cramps and sprains, and the data were mostly collected on race day. For the ankle alone, two figures are worth noting. In ultra runners (races longer than a marathon), the ankle accounts for about one third of injuries (Kakouris and colleagues, 2021). For trail running, the meta-analysis of ankle sprains by Hansoulle and colleagues (2024) gives a rate of about one quarter. The pooled studies vary widely, and we have not checked them in detail, so we treat this only as a signal.
If you twist your ankle and cannot walk 4 steps on your own, or if it hurts to press on the back edge or tip of the ankle bone, the base of the 5th metatarsal (the base of the foot bone on the little-toe side), or the navicular (the small bone that sticks out on the inner edge of the top of the foot), you need an X-ray according to the Ottawa rules (Magee). For an ankle that has been sprained before and is still loose, the clinical practice guideline on ankle sprains published in the journal JOSPT (Martin and colleagues, 2021) most strongly recommends two things to prevent another sprain: wearing a brace, and balance training combined with training your sense of joint position.
Races high in the mountains
Many trail races in the northern mountains and the Central Highlands of Vietnam are run at altitudes of 1,500–3,000 m. Altitude sickness mainly occurs above 2,500 m, but it has also been recorded at 1,500–2,500 m, and it usually appears 6–10 hours after going above 2,000 m. Harrison lists ascending quickly and having had altitude sickness before as the main risk factors; exertion is also a factor, but poor fitness is not, so a fit runner can get altitude sickness like anyone else. Preventive medicines such as acetazolamide are prescription drugs, so if you plan to run a high-altitude race, ask a doctor beforehand.
The sinews of the thigh, and what the clinic does
Traditional medicine calls the tendons and muscles that carry the body’s effort the sinews, and holds that “the Liver governs the sinews” (肝主筋, gān zhǔ jīn), meaning the Liver (the liver as understood in traditional medicine) is in charge of these tendons and muscles. The textbook of basic theory of Chinese medicine quotes the chapter Liu Jie Zang Xiang Lun (六节藏象论 / 六節藏象論, On the Six Periods and the Visceral Manifestations) of the classic Su Wen (素问 / 素問, Basic Questions): the fullness of the Liver shows in the sinews (其充在筋). “The Liver stores blood” (肝藏血, gān cáng xuè), meaning the Liver keeps the blood in store. When blood is sufficient, the sinews are nourished; when Liver blood is lacking, “the sinews and vessels lose their nourishment” (筋脉失养 / 筋脈失養, jīn mài shī yǎng), that is, the tendons and muscles are not fed well enough, and the hands and feet go numb easily (Basic Theory of Chinese Medicine, 中医基础理论 / 中醫基礎理論, p. 219, 225).
A long descent, with the thighs braking for several kilometers, is when the sinews work hardest. Even so, muscle soreness one or two days after your first hill session needs no medicine. The doctor pays more attention to people who, after every trail race, get calf cramps and numb legs, have pale nails and lips, and, in women, scanty periods. Once low potassium, low sodium, drug effects such as from diuretics or statins, nerve disease and venous insufficiency have been ruled out, traditional medicine may place that person in the pattern of Liver blood deficiency with the sinews undernourished (肝血虚、筋失养 / 肝血虛、筋失養, gān xuè xū, jīn shī yǎng). The formulas textbook (Formulas of Chinese Medicine, 方剂学 / 方劑學) records Bu Gan Tang (补肝汤 / 補肝湯, Liver-Supplementing Decoction) for blood failing to nourish the sinews, with numb hands and feet and calf cramps (p. 184). After the examination, the doctor may prescribe a decoction in ready-to-drink 50 ml pouches aimed at nourishing the blood and softening the sinews, cooked in a separate batch for each person. This use follows the classics; no one has yet run a trial on runners. If you are about to run a race with doping control, tell the doctor at the start, before anything is prescribed.
The small brake behind the knee
The front of the thigh does not brake alone. Behind the knee lies the popliteus, a small muscle that keeps the thighbone from sliding forward on the tibial plateau, that is, the top surface of the shinbone. Walther, author of the Applied Kinesiology textbooks (AK, a way of testing the strength of each muscle by hand to read the state of the body), notes that this job matters most when running downhill: with each landing, the body weight travelling down the shaft of the thighbone pushes its end forward, the popliteus holds it back, and it can be overloaded by exactly this work (Walther, Synopsis, p. 468).
The popliteus often works below threshold, meaning it tests weak, when the foot and ankle send up faulty signals. Freeman and Wyke found that receptors in the ankle ligaments, the tiny nerve endings that sense the position and tension of a joint, can control the muscles of the lower leg; people whose joint capsule injury has healed may still have abnormal postural reflexes in the muscles around that joint. According to AK, a small bone of the foot or ankle out of place also stimulates these receptors wrongly (p. 60). Cuthbert cites McVey (2005): a painless stimulus to the joints of the foot and ankle is enough to strongly inhibit the muscles of that region (p. 85). A trail tips the ankle back and forth for kilometer after kilometer. With prolonged pronation, that is, the arch of the foot rolling inward, the tibia rotates inward more, and the popliteus has to carry even more load (Walther, p. 468).
Trail runners with pain on the outer side of the knee first have the painful point located. A sharp pain confined to the attachment of the popliteus differs from the widespread pain of the iliotibial band (the long band of tendon running down the outer side of the thigh), and has to be told apart from a ligament tear, a cyst or the lateral meniscus (p. 468), which need ultrasound or imaging when suspected. The doctor then tests the popliteus and does the shock absorber test: a quick force is applied to the sole of the foot or the ankle joint, and a strong muscle is retested; if a joint is out of place, that muscle weakens for a moment (Walther, p. 61). At that joint, the doctor restores the signal and then retests the popliteus. During recovery, Walther advises runners to run only on flat ground.
When to see a doctor
See a doctor the same day if either of these happens:
- Urine as dark as cola or red, severely swollen and painful muscles, or passing little urine after a long descent or a hot day;
- You twist your ankle on the trail and then cannot take 4 steps on your own, or it hurts to press on the ankle bone, the base of the 5th metatarsal or the navicular.
In the mountains, if you are short of breath even at rest, coughing or confused, get down to a lower altitude first, then seek medical care. If the pain is concentrated at one point on a bone, stop running and see a doctor. If cramps and numb legs come back after every trail race, or your knee or ankle keeps giving way on the trail, book an appointment.
Those aching thighs in the chair at work on Monday morning, as long as your urine is still normal, are muscles that have just got used to a new job. In a few days the soreness will fade. On next week’s trail run, slow down on that same descent and run only part of it. Lengthen it gradually over the following weeks, so that by race day your thighs have met that hill many times.
If your thighs have hurt for more than ten days without easing, your urine has changed color, or you take cholesterol medicine and are aiming for your first trail race, remember to put the strip of medicine you are taking in your bag when you come in. Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine) will go over your medicine and any muscle enzyme results with you, then check whether your popliteus and ankles are ready for the next descent. Book a consultation.
Worth keeping
- On your first trail run, go slowly on the descents; do not let your legs go;
- Practice downhills on short stretches, and lengthen them only once your thighs are no longer sore from the previous session;
- Soreness all over the thighs one or two days after a hill session goes away on its own; no anti-inflammatory painkillers are needed;
- After a long descent, look at the color of your urine; if it is as dark as cola, see a doctor the same day;
- If you take a statin, ask your doctor before signing up for a long, hilly race;
- Have a doctor read your post-race muscle enzyme results together with your symptoms; do not compare them yourself with numbers found online;
- In high-mountain races, even fit runners can get altitude sickness; if you want preventive medicine, ask a doctor beforehand.
References
Sources in English
- Assumpção CO, Lima LC, Oliveira FB, Greco CC, Denadai BS. 2013. Exercise-induced muscle damage and running economy in humans. ScientificWorldJournal. 2013:189149. doi:10.1155/2013/189149. PMID: 23431253.
- Cuthbert S. 2013. Applied Kinesiology: Clinical Techniques for Lower Body Dysfunctions. Gangasas. p. 85.
- Hansoulle T, Peters-Dickie JL, Mahaudens P, Nguyen AP. 2024. Do we underestimate the frequency of ankle sprains in running? A systematic review and meta-analysis. Phys Ther Sport. 68:60-70. doi:10.1016/j.ptsp.2024.06.009. PMID: 38963954.
- Houglum PA, Bertoti DB. Brunnstrom’s Clinical Kinesiology. p. 182, 186.
- Jameson JL, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J, editors. 2018. Harrison’s Principles of Internal Medicine. 20th ed. New York: McGraw-Hill Education. p. 2145–2149, 3286, 3379–3380, 3384–3386, 3391.
- Joyce D, Lewindon D, editors. 2016. Sports Injury Prevention and Rehabilitation: Integrating Medicine and Science for Performance Solutions. London: Routledge. p. 213, 232, 417–421.
- Kakouris N, Yener N, Fong DTP. 2021. A systematic review of running-related musculoskeletal injuries in runners. J Sport Health Sci. 10(5):513-522. doi:10.1016/j.jshs.2021.04.001. PMID: 33862272.
- Magee DJ, Manske RC. 2021. Orthopedic Physical Assessment. 7th ed. St. Louis (MO): Elsevier. p. 82, 1353.
- Martin RL, Davenport TE, Fraser JJ, Sawdon-Bea J, Carcia CR, Carroll LA, et al. 2021. Ankle Stability and Movement Coordination Impairments: Lateral Ankle Ligament Sprains Revision 2021. J Orthop Sports Phys Ther. 51(4):CPG1-CPG80. doi:10.2519/jospt.2021.0302. PMID: 33789434.
- Papadakis MA, McPhee SJ, Rabow MW, et al., editors. 2022. CURRENT Medical Diagnosis and Treatment 2022. New York: McGraw-Hill. p. 378, 536, 870.
- Tallis J, McMorrow C, Shelley SP, Eustace SJ. 2024. Repeated Bout Effect of Downhill Running on Physiological Markers of Effort and Post Exercise Perception of Soreness in Trained Female Distance Runners. Sports (Basel). 12(6). doi:10.3390/sports12060169. PMID: 38921863.
- Travell JG, Simons DG. 1992. Myofascial Pain and Dysfunction: The Trigger Point Manual. Vol. 2: The Lower Extremities. Baltimore (MD): Williams & Wilkins. p. 571.
- Viljoen CT, Janse van Rensburg DC, Verhagen E, van Mechelen W, Tomás R, Schoeman M, et al. 2021. Epidemiology of Injury and Illness Among Trail Runners: A Systematic Review. Sports Med. 51(5):917-943. doi:10.1007/s40279-020-01418-1. PMID: 33538997.
- Walther DS. 2000. Applied Kinesiology: Synopsis. 2nd ed. Pueblo (CO): Systems DC. p. 60, 61, 468.
Sources in Chinese
- 李冀, 连建伟, 主编. 方剂学. 第 184 页.
- 王新华, 主编. 中医药学高级丛书 · 中医基础理论. 第 219、225 页.
