How proven a technique is cupping for sports recovery?

Not proven at all. Most cupping benefits are likely Placebo effects.

History Of Cupping: A Massage Therapeutic Supposed to Restore Balance To The Body's Humors As Per The Ancient Medical Theory Of Humorism Popularized By Galen

Cupping is an ancient vacuum pressure technique. Its reports stretch back thousands of years from sources as varied as Egypt, China, Iran to Arabia (where it's called Hijama) to Europe, Korea and even Mongolia. Continuing to exist outside mainstream medicine the world over, high profile clients like Jennifer Aniston, Gwyneth Paltrow, Lena Dunham and now Michael Phelps raised its public profile in the 2000s and beyond. Yet cupping's benefits lack rigorous scientific evidence. This may be because over the centuries, as scientific medicine took root, cupping got relegated to the sidelines, practiced not by licensed physicians but by support staff and of course quacks. Consider late medieval England for example. Though hardly the bastion of rational, evidence-based medicine, even this era considered cupping an alternative, the purview not of physicians but of barber-surgeons, who apart from being licensed to cut hair, were allowed to perform minor superficial interventions such as cupping and leeching (1).

Cupping got its start from the ancient medical theory of the four humors, blood, phlegm, black and yellow bile. The theory gave each humor two qualities. Blood was hot and wet, phlegm was cold and wet, black bile was cold and dry, and yellow bile was hot and dry (1). According to medieval European medicine, cupping-generated vacuum was supposed to extract 'vicious' humor, i.e., humor that was in imbalance (see below from 2). Obviously they didn't know that blood circulates through the pumping action of the heart, which discredits the notion of balance between different bodily humors controlling health.

However, if cupping does provide some health benefits especially for musculoskeletal diseases, the critical knowledge gap is not knowing how. Improve blood flow? Lymph flow? Modulate nerve physiology? One or all of the above? One more important than the rest? Not currently known.

Problems With Cupping

I. Cupping Lacks Rigorous, Scientific Studies, & Standardized Training & Credentialing

• Lacks rigorous, well-controlled studies on large numbers of subjects, i.e., studies with sufficient statistical power to allow inferences about mechanism of action. Since 2000, hundreds of studies including randomized clinical trials have examined cupping's effects on problems ranging from local (chronic muscle pain, fibromyalgia, herpes zoster) to systemic issues (blood pressure). However, being poorly designed, i.e., lacking rigorous controls or sufficient numbers or failing to assess adverse outcomes, most of them add little value so conclusive data's still missing.
• Since a sham wet cupping technique doesn't exist (3), an additional technical limitation is being unable to blind the study. In other words, even in a randomized clinical trial, those getting wet cupping know. This can introduce Placebo effects.
• Lack of systematic, formal, standardized training and credentialing. In many countries cupping doesn't require a medical degree or even a license. Often quacks with neither knowledge of medicine nor safe, aseptic techniques perform cupping. No surprise then that burns and infections can ensue. With the Chinese government introducing guidelines in 2010 to standardize cupping therapy across China (4), maybe at least safety will improve.

II. Cupping’s Lack Of Standardized Training & Credentialing Creates Unnecessary Risk

• Examining six databases on English language reports between 2000 and 2011, an analysis of adverse events following cupping found 10 ranging from mild (keloid scarring, burns and bullae) to more serious (acquired hemophilia A, stroke, factitious panniculitis, reversible cardiac hypertrophy and iron deficiency anemia) (5).
• Another systematic review of scientific databases between 2000 and 2016 found a total of 979 cupping studies. Discarding the majority because of various flaws, it ended up reviewing only 25 (~2.6%; 6 randomized clinical trials, 16 single case reports, 3 case series). It found adverse events related to dry cupping in 15 studies and in 8 to wet cupping (6). Scars and burns were most frequent (see below from 6).

Bibliography

1. Lindemann, Mary. Medicine and society in early modern Europe. Cambridge University Press, 1999.

2. A History Of Medicine. Dr. Jenny Sutcliffe, Nancy Duin. Morgan Samuels Editions, 1992. http://global-help.org/publicati...

3. Aleyeidi, Nouran A., et al. "Effects of wet-cupping on blood pressure in hypertensive patients: a randomized controlled trial." Journal of integrative medicine 13.6 (2015): 391-399. http://www.jcimjournal.com/artic...

4. Gao, S. Z., and B. Liu. "Study on standardization of cupping technique: elucidation on the establishment of the National Standard Standardized Manipulation of Acupuncture and Moxibustion, Part V, Cupping." Zhongguo zhen jiu= Chinese acupuncture & moxibustion 30.2 (2010): 157.

5. Xu, Shifen, et al. "Adverse events of acupuncture: a systematic review of case reports." Evidence-Based Complementary and Alternative Medicine 2013 (2013). http://downloads.hindawi.com/jou...

6. Al-Bedah, Abdullah Mohammad, et al. "Safety of Cupping Therapy in Studies Conducted in Twenty One Century: A Review of Literature." https://www.researchgate.net/pro...

https://www.quora.com/How-proven-a-technique-is-cupping-for-sports-recovery/answer/Tirumalai-Kamala