Thursday afternoon at the gym, you squat with a bar weighing almost as much as you do, five full reps, and stand up with ease. On Saturday morning’s long run, your running buddy films a short clip at the eighteenth kilometer and posts it to the group. Every time your left foot lands, your right hip drops a little and your left knee caves inward. In the clip from the second kilometer, your form is still upright.
The whole group says your glutes are weak and you should train them more. That muscle is strong enough to push the bar; it is just that by the eighteenth kilometer, the nervous system is no longer giving it enough of the work. Applied Kinesiology (AK, a method of testing muscle strength by hand to read the state of the body) calls this a muscle working below threshold, meaning it goes weak when muscle tested. Tam Duc Clinic uses in-depth AK to find out why a muscle falls into that state, and also checks the supplements runners are taking.
Strong enough to push the bar, yet unable to lock
Manual muscle testing does not measure lifting strength. The doctor places your leg in a position and then pushes gently and steadily. A muscle that is working normally locks, holding the position. A muscle working below threshold (inhibited muscle) does not lock, and the leg is pushed out of position even though the muscle is still big. In his AK textbook on the lower body, Cuthbert describes muscles that at first cannot lock on the manual test (p. 108). The fault lies in the nerve signal more than in the muscle fibers.
On the same page, he notes that a muscle tested lying down may be strong and only fail to hold once the person is standing and bearing weight. When only a few individual muscles go weak, they usually match the exact place where the patient complains of pain. That is why the clip from the eighteenth kilometer is worth more than one muscle test on the examination table.
The work shifts to the muscle next door
You still finish the run, because the movement system always has a detour. Cuthbert cites Edgerton and colleagues (1996): when a muscle is inhibited, meaning the nervous system calls it into action less, other groups of motor nerve cells (motor neurons) are called on more to compensate, and that compensation can lead to further injury (p. 108). As the clinic understands it, the painful spot is often where a muscle is carrying the extra load, while the muscle that has switched off stays silent.
Walther sorts the causes of a muscle switching off by the three sides of the health triangle: structure, chemistry, mind (p. 11). Cuthbert divides them into three similar groups, and each group can be assessed separately with AK testing (p. 177).
A topic that changes a muscle’s strength
The mental side is the one most often overlooked. When the patient thinks about something that hurt them, an indicator muscle (a strong muscle the doctor uses as a reference for testing) tests weak; among the muscles, the clavicular part of the pectoralis major (the part of the chest muscle attached to the collarbone) reflects emotion more clearly than any other (Walther, Synopsis, p. 426). The doctor changes the topic while examining. If the muscle goes weak just as the conversation touches on your teenage child, the stress very likely lies in that area (p. 427).
Emotional stress can also keep the adrenal glands in a state of prolonged underperformance, together with the sartorius and gracilis working below threshold. If that is the root, Walther observes that the glands hardly respond until the emotional stress has been resolved (p. 433). The sartorius and gracilis support the inner side of the knee. When these two muscles are weak, the pelvis tends to shift backward, and even after it is mobilized it easily slips back again (p. 464–465). For athletes, he regards competition as a major stress even when it is a stress people enjoy, especially when combined with extreme heat and training sessions that go on to exhaustion (p. 200).
Schmitt, in the Summer 1988 proceedings of the International College of Applied Kinesiology (ICAK), placed the emotional part of pain in the limbic system, the network of brain areas that handles emotion, specifically the orbitofrontal cortex (the brain area just above the eye sockets) and the cingulate gyrus (p. 305). The clinic uses an in-depth AK technique to check for stress in the frontal lobe, limbic system and cingulate gyrus. The doctor often uses it when your running form on video gets worse in exactly the weeks of heavy training and poor sleep, or when a painful spot keeps coming back even though the structure has already been corrected.
Last year’s ankle sprain still has something to say
On the structural side, the clinic looks first at the proprioceptors, the tiny sensors in the joints, muscles and tendons. When they misreport, the nervous system adjusts the muscles according to wrong information.
Freeman and Wyke, as cited by Walther, found that stimulating the receptors in the ankle ligaments changes the activity of the calf muscles and the tibialis anterior. People whose joint capsule injury has healed may still have long-lasting abnormalities in the postural reflexes of the muscles that cross that joint (Synopsis, p. 60). The tissue has healed; the signal has not.
Schmitt (1999) explains why the fault stays. Throughout healing, the pain receptors fire continuously, and the cerebellum adapts and then keeps that state as the “new normal” (ICAK 1999–2000, p. 137–139). Walther calls this an encoded memory. It throws off posture, changes the order in which muscles contract, and changes the way you walk (Synopsis, p. 186), and while it remains, treatment results are hard to maintain (p. 184).
Old surgical wounds are the same. Garten found that interference fields, places where mechanoreceptors and pain receptors behave abnormally, are mostly scars (Applied Kinesiology, 2016, p. 8). In athletes, Stark names the feet, the dura mater (the membrane wrapping the brain and spinal cord) and the breathing and chest region as the most important sources of disruptive signals behind repeated injuries (ICAK 2024–2025, p. 17–18).
For signal faults, the clinic uses the Injury Recall Technique (IRT) and Palomar’s P-DTR method (Proprioceptive Deep Tendon Reflex). The doctor uses muscle testing to find the pair of receptors that are misreporting, stimulates both places at the same time, then taps a deep tendon reflex so the nervous system restarts the signal (Palomar, p. 13–17). This is combined with gentle movement of the joint involved. P-DTR is for functional disorders; fractures and torn tendons belong to imaging and specialists.
Muscles in the thigh, organs in the abdomen
The chemical side leads to one of the founding observations of AK. Goodheart, the founder of AK, saw that a weak clavicular pectoralis major often goes with stomach disorders, the quadriceps with the small intestine, and the tensor fasciae latae with the large intestine. Stimulating the organ’s neurolymphatic reflex points (Chapman) or neurovascular reflex points (Bennett) made the matching muscle strong again; later, the meridians were added (Walther, Synopsis, p. 14). Walther’s table, narrowed to the muscles runners need most:
| Muscle | Job in running | Organ or gland in AK | Also check |
|---|---|---|---|
| Sartorius, gracilis | Support the inner knee | Adrenal glands | Vitamin C, pantothenic acid (vitamin B5) |
| Gastrocnemius, soleus, tibialis posterior | Push the body forward, hold up the arch of the foot | Adrenal glands | Foot pronation, race season |
| Quadriceps | Straighten the knee, absorb the body’s weight on landing | Small intestine | Vitamin D, B vitamins |
| Tensor fasciae latae | Stabilize the outer hip and knee | Large intestine | Weak on both sides: consider iron deficiency |
| Gluteus medius, gluteus maximus, piriformis | Keep the pelvis level on one leg | Reproductive organs | Vitamin E |
| Hamstrings | Brake the thighbone when running downhill | Gallbladder | Vitamin A |
| Peroneal group | Keep the ankle from rolling | Bladder | Calcium, B vitamins; cut down on coffee |
This table is a guide to what to test, not a basis for prescribing (Synopsis, p. 310–333). Walther himself sets out its limits. An organ can be diseased while the muscle stays strong, because the body has adapted; and a weak muscle may be due to a local problem. The muscle–organ link is only meaningful alongside other diagnostic methods (p. 14), so a muscle that tests weak is a prompt for further checks, not yet a conclusion about the organ.
The three sides often intertwine. Extended pronation of the foot often goes with adrenal stress, which Walther believes may work through the tibialis posterior, a muscle both related to the adrenal glands and responsible for holding the ankle (p. 515). The knee that caves inward at the eighteenth kilometer may be a matter of both your shoes and your sleep.
A little on the tip of the tongue
The doctor places a little of the substance being tested on your tongue, sometimes only having you hold it in your mouth or smell it, without swallowing, and then retests the muscle related to the organ under suspicion. In an example Walther gave back in 1981, when the liver has a problem, the sternal part of the pectoralis major tests weak; if tasting vitamin A makes the muscle strong, that substance can be applied. Harmful substances make the muscle go weak, such as alcohol with the sartorius and gracilis in someone whose adrenal glands are underperforming (Basic Procedures, p. 46).
In the clinic’s experience, this kind of check is useful for people under stress, or people short of nutrients: their blood values are still within the normal range but not enough for the body to run well. The doctor keeps to several points Walther stressed:
- The list of nutrients for each muscle is not comprehensive, and finding a weak muscle is not yet a reason to give something; it has to be tested on that very person (Basic Procedures, p. 46);
- A muscle getting stronger is not necessarily good in the long run: in someone with low blood sugar, tasting sugar can make the latissimus dorsi strong (p. 46);
- Dehydration distorts the test; some people have almost every muscle weak, and one glass of water brings them back (Synopsis, p. 162);
- Sedatives, birth control pills, diuretics, and drugs that suppress or stimulate the nervous system can make an AK examination give false information (Basic Procedures, p. 51).
If a gland does not respond to its own nutrients, the patient places one hand on that gland’s reflex area and the other hand on each of the other glands in turn, to find the gland that is pulling it down (p. 46). The clinic does not test by having you hold the bottle, and does not use muscle testing to set doses.
Tonics are medicines too
The older people in the family often repeat that saying, and it holds true for runners. The table below sums up what recent reviews and guidelines show.
| Supplement | Current evidence | Tests to go with it | What AK can add |
|---|---|---|---|
| Caffeine | Benefits endurance at moderate doses; not banned | Usually not needed | Walther advises cutting down on coffee with adrenal stress (Synopsis, p. 514) |
| Nitrate (beetroot) | Small benefit, which disappears in very well-trained athletes (Maughan and colleagues, 2018; Gao and colleagues, 2021) | None | The muscle’s response on tasting |
| Iron | Beneficial when there is a true deficiency | Ferritin (a measure of stored iron), transferrin saturation (the share of the iron carrier in the blood that is carrying iron), complete blood count | Repeated muscle testing; a tensor fasciae latae weak on both sides suggests getting tested |
| Vitamin D, calcium | A large trial in female military recruits found fewer stress fractures (bones cracking gradually from repeated loading) | 25(OH)D (a blood test for vitamin D) | Quadriceps and tensor fasciae latae on tasting vitamin D |
| Magnesium | A Cochrane review (Garrison and colleagues, 2020) found no trials for exercise-related cramps | As ordered by the doctor | The muscle’s response; not a reason to take it to prevent cramps |
| Sodium, salt tablets | May be needed in long, hot races; salt tablets cannot prevent low blood sodium if you keep drinking too much water | Blood sodium if you have ever been confused after a run | Sodium–potassium balance |
| Collagen, gelatin with vitamin C | May help during tendon loading exercise; not proven to prevent injury | None | The response of the muscles around the tendon |
| High-dose vitamins C and E | Regular use may blunt some of the beneficial changes the body makes on its own from training (small trials) | None | No need to test |
| Glandular products, “endurance-boosting” extracts, products of unknown origin | Weak or conflicting evidence; doping risk | None | Muscle testing cannot detect banned substances |
Many of the products that AK books suggest testing are concentrates made from animal glands and organs, and some contain hormones and require a prescription (Walther, Basic Procedures, p. 48). For runners in races with doping control, the clinic does not use them when the product has no certification.
An athlete who is tested bears absolute responsibility for the substances in their body, even when taken unknowingly. Third-party certification such as Informed Sport or NSF Certified for Sport lowers the risk but does not remove it entirely, and WADA (the World Anti-Doping Agency) does not certify any product (Maughan and colleagues, 2018). The Australian Institute of Sport (AIS) puts DHEA, Tribulus, maca, bitter orange and synephrine in the “do not use” group.
When not to wait for muscle testing
If you have pain concentrated at one point on a bone that is getting clearer, groin pain when bearing weight, dark urine after a long run, confusion or vomiting after a race, or chest pain or dizziness in the middle of a run, you need to see a doctor or get emergency care first. If iron deficiency is suspected, you need a ferritin test; if low sodium is suspected, a blood sodium test; if a stress fracture is suspected, magnetic resonance imaging (MRI). Walther stresses that nutritional testing results must always be checked against clinical examination and standard lab tests (Synopsis, p. 159).
From the video to the examination table
The examination starts with your story: race season, sleep, past ankle sprains, old surgical scars, every supplement you are taking. If there are signs that call for imaging or lab tests, the doctor orders them right away. Muscle testing is done in positions as close as possible to running, such as standing on one leg or stepping up onto a high step. The clinic does not do muscle testing on a treadmill.
If the glutes do not lock, the doctor looks for the reason. You place a hand on the ankle you once sprained, or on an old surgical scar, and the muscle is tested again; AK calls this step therapy localization. For joints, the doctor pushes gently in each direction and then retests, which is called a challenge. Treatment includes restimulating the signal, tapping tendon reflexes, light contact on reflex points, and mobilizing the joint in exactly the direction the challenge indicated. The clinic does not do massage, acupressure or massage-style stretching, nor electroacupuncture. After treatment, the doctor retests exactly those muscles while they are bearing weight.
If the four examinations (the four methods of traditional diagnosis: looking, listening and smelling, asking, taking the pulse) show a clear pattern in traditional medicine, such as qi and blood deficiency (气血虚 / 氣血虛, qì xuè xū; a shortage of both vital strength and blood) after a long race season, the doctor may also prescribe a decoction in ready-to-drink 50 ml pouches, cooked separately for your pattern. If you race with doping tests, let the doctor know in advance so the prescription avoids herbs that carry a risk.
Next week, your buddy will hold up the phone again at the eighteenth kilometer. That dropping right hip may be a matter of sleep, or it may be an old signal in the ankle that has not yet been reset. The Thursday afternoon barbell sessions carry on regardless.
If you have a video like that, or a pain that keeps returning at the same kilometer, book a visit with Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine). The examination will start from that very video. Book a consultation.
Worth keeping
- Ask a running buddy to film a few seconds of your running form at the start and in the final stretch of a long run, and keep both clips;
- Write down past ankle sprains, falls and operations, even ones from many years ago;
- Photograph the labels of every supplement and medicine you are taking, and send them to the doctor before the visit;
- On the day of the visit, drink water and eat your meals as usual; do not come on an empty stomach;
- If you plan to take iron or vitamin D, get ferritin and 25(OH)D tests first;
- If you race with doping control, use only products with third-party certification, and tell the doctor before anything is prescribed.
References
Sources in English
- Australian Institute of Sport (AIS). AIS Sports Supplement Framework (Groups A–D).
- Cuthbert S. 2013. Applied Kinesiology: Clinical Techniques for Lower Body Dysfunctions. Gangasas. p. 108, 177 (citing Edgerton et al., 1996).
- Gao C, Gupta S, Adli T, Hou W, Coolsaet R, Hayes A, et al. 2021. The effects of dietary nitrate supplementation on endurance exercise performance and cardiorespiratory measures in healthy adults: a systematic review and meta-analysis. J Int Soc Sports Nutr. 18(1):55. doi:10.1186/s12970-021-00450-4. PMID: 34243756.
- Garrison SR, Korownyk CS, Kolber MR, Allan GM, Musini VM, Sekhon RK, et al. 2020. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 9(9):CD009402. doi:10.1002/14651858.CD009402.pub3. PMID: 32956536.
- Guest NS, VanDusseldorp TA, Nelson MT, Grgic J, Schoenfeld BJ, Jenkins NDM, et al. 2021. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 18(1):1. doi:10.1186/s12970-020-00383-4. PMID: 33388079.
- Hoffman MD, Stuempfle KJ. 2015. Muscle Cramping During a 161-km Ultramarathon: Comparison of Characteristics of Those With and Without Cramping. Sports Med Open. 1(1):24. doi:10.1186/s40798-015-0019-7. PMID: 26284165.
- Lappe J, Cullen D, Haynatzki G, Recker R, Ahlf R, Thompson K. 2008. Calcium and vitamin d supplementation decreases incidence of stress fractures in female navy recruits. J Bone Miner Res. 23(5):741-9. doi:10.1359/jbmr.080102. PMID: 18433305.
- Maughan RJ, Burke LM, Dvorak J, Larson-Meyer DE, Peeling P, Phillips SM, et al. 2018. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 52(7):439-455. doi:10.1136/bjsports-2018-099027. PMID: 29540367.
- Palomar Lever J. Proprioceptive-Deep Tendon Reflex (P-DTR) [introductory brochure]. p. 13–17.
- Paulsen G, Cumming KT, Holden G, Hallén J, Rønnestad BR, Sveen O, et al. 2014. Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. J Physiol. 592(8):1887-901. doi:10.1113/jphysiol.2013.267419. PMID: 24492839.
- Pengelly M, Pumpa K, Pyne DB, Etxebarria N. 2025. Iron deficiency, supplementation, and sports performance in female athletes: A systematic review. J Sport Health Sci. 14:101009. doi:10.1016/j.jshs.2024.101009. PMID: 39536912.
- Ristow M, Zarse K, Oberbach A, Klöting N, Birringer M, Kiehntopf M, et al. 2009. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci U S A. 106(21):8665-70. doi:10.1073/pnas.0903485106. PMID: 19433800.
- Schmitt WH. 1988. Functional Neurology of Pain. ICAK Collected Papers, Summer 1988. p. 305.
- Schmitt WH Jr. 1999–2000. A Neurological Rationale for Injury Recall Technique. ICAK-USA Collected Papers 1999–2000. p. 137–139.
- Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. 2017. Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. Am J Clin Nutr. 105(1):136-143. doi:10.3945/ajcn.116.138594. PMID: 27852613.
- Stark. 2024–2025. ICAK Collected Papers 2024–2025. p. 17–18.
- Walther DS. 1981. Applied Kinesiology. Vol. I: Basic Procedures and Muscle Testing. Pueblo (CO): Systems DC. p. 46, 48, 51.
- Walther DS. 2000. Applied Kinesiology: Synopsis. 2nd ed. Pueblo (CO): Systems DC. p. 11, 14, 60, 159, 162, 184, 186, 200, 310–333, 426–427, 433, 514–515.
- World Anti-Doping Agency (WADA). 2026. The 2026 Prohibited List (in force 1 January 2026). Available from: https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf.
Sources in German
- Garten H. 2016. Applied Kinesiology: Funktionelle Myodiagnostik in Osteopathie und Chirotherapie. 1. Aufl. München: Elsevier. S. 8.
