Tendinitis in Athletes: Causes and the Link to Training Load and Drugs

Tendon pain sidelines athletes in nearly every sport: the runner with an aching Achilles, the volleyball player with jumper's knee, the climber or tennis player with a sore elbow. It is usually called "tendinitis," though researchers now prefer "tendinopathy" because inflammation is not the main story. This article explains why tendons become painful, how training load drives the problem and which medications and performance drugs can make tendons more vulnerable.

Tendinitis or tendinopathy?

Tendons connect muscle to bone and transmit large forces. They are made mostly of type I collagen arranged in parallel bundles, with relatively few cells and a limited blood supply. That structure makes tendons strong but slow to adapt and heal.

The term "tendinitis" implies inflammation. In 2002, Khan and colleagues argued in the BMJ that chronic tendon pain usually shows degenerative changes, disorganized collagen, increased ground substance and new blood vessels, rather than classic inflammatory cells. They proposed abandoning the "tendinitis myth" in favor of "tendinopathy."

Newer research suggests that inflammatory signaling does play a role, especially early, but it differs from the acute inflammation of a sprain. That is one reason anti-inflammatory drugs offer only short-term relief in many cases.

Cook and Purdam proposed a continuum model in which tendons move from reactive tendinopathy, an acute response to overload, through tendon disrepair to degenerative tendinopathy. Each stage may respond differently to treatment, and tendons can move back toward health with appropriate loading.

Training load as the main driver

The most common cause of tendinopathy is a mismatch between the load placed on the tendon and its capacity to adapt. Tendons respond to loading by increasing collagen synthesis, but that process is slow. Kjaer and colleagues showed that collagen synthesis rises after exercise, while breakdown also increases, and net gains take time.

Typical load errors include sudden increases in running mileage, adding hill or plyometric training, returning too fast after a break, changing surfaces or footwear and competition congestion with insufficient recovery. Tendons that store and release energy, such as the Achilles and patellar tendons, are especially sensitive to such changes.

• Rapid increases in training volume or intensity
• New explosive or jumping activities
• Reduced rest between demanding sessions
• Age-related reductions in tendon capacity
• Excess body weight and metabolic conditions such as diabetes
• Previous tendon injury

Complete rest is also not ideal. Tendons that are unloaded lose strength, and when activity resumes they may be even more vulnerable. Effective management usually involves modifying, not eliminating, load.

Medications that affect tendons

Fluoroquinolone antibiotics, such as ciprofloxacin and levofloxacin, carry an FDA boxed warning for tendinitis and tendon rupture, most often affecting the Achilles. Risk is higher in people over 60, those taking corticosteroids and transplant recipients, but athletes are not immune. Lewis and Cook reviewed the evidence and advised that athletes on these drugs reduce high-load training and avoid new loading during treatment and for some weeks afterward.

Corticosteroid injections can relieve pain quickly, but long-term outcomes may be worse. In a randomized trial by Coombs and colleagues in tennis elbow, people who received a corticosteroid injection had poorer one-year outcomes and more recurrences than those given placebo. Repeated injections into or near tendons can weaken them and are associated with rupture.

Statins have been linked to tendon problems in case reports and some observational studies, although the absolute risk appears low. Systemic corticosteroids, used for asthma, autoimmune disease or misused for recovery, impair collagen synthesis.

Anabolic steroids and other performance drugs

Anabolic-androgenic steroids increase muscle strength faster than tendons can adapt. Animal studies suggest they alter collagen structure and make tendons stiffer and less able to absorb energy. Case reports describe ruptures of the biceps, triceps, pectoral and quadriceps tendons in steroid users, often during heavy lifting.

Growth hormone misuse has been promoted in some circles as tendon-protective because it stimulates collagen synthesis. However, the evidence in humans is limited, and the risks of misuse, including insulin resistance, joint pain and cardiomyopathy, are substantial. Growth hormone is prohibited under the WADA Code.

Unapproved peptides marketed for "tendon healing," such as BPC-157, lack human clinical trials. The FDA has raised safety concerns about such compounds in compounding, and they appear on WADA's prohibited list. Their quality and contents are unregulated.

The common thread is that drugs which accelerate muscle gains or mask pain can encourage athletes to load tendons beyond their capacity, while doing nothing to protect tendon structure.

Evidence-based management

The foundation of tendinopathy treatment is progressive loading. Alfredson and colleagues showed that a 12-week program of heavy eccentric calf exercises allowed many patients with chronic Achilles tendinopathy to return to running. Heavy slow resistance and isometric exercises are also effective, depending on the tendon and stage.

Load management means reducing aggravating activities while maintaining tolerable exercise. Pain during or after activity that settles by the next morning is often acceptable; pain that increases day to day suggests the load is too high.

Other measures, such as shockwave therapy, braces or platelet-rich plasma injections, have variable evidence and are best used as adjuncts. NSAIDs can help with short-term pain but do not repair the tendon.

Seek medical attention for sudden severe pain, a popping sensation, inability to bear weight or a visible gap in the tendon, which may indicate rupture and require urgent assessment.

Conclusions of the Editorial Team

Most tendon pain in athletes is tendinopathy driven by load exceeding the tendon's capacity to adapt, rather than simple inflammation. Gradual progression and structured strengthening programs are the most effective treatments.

Some medications and drugs increase risk: fluoroquinolone antibiotics, repeated corticosteroid injections, systemic steroids and anabolic steroids. Unapproved peptides promoted for tendon healing lack evidence and are prohibited in sport.

For further reading, see our articles on Achilles tendon rehabilitation, corticosteroid injections in sports medicine and how anabolic steroids affect connective tissue.

References

1. Khan KM, Cook JL, Kannus P, Maffulli N, Bonar SF. Time to abandon the "tendinitis" myth. BMJ. 2002;324(7338):626–627.
2. Cook JL, Purdam CR. Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy. Br J Sports Med. 2009;43(6):409–416.
3. Kjaer M, Langberg H, Heinemeier K, et al. From mechanotransduction to extracellular matrix and back again. Scand J Med Sci Sports. 2009;19(4):500–510.
4. Alfredson H, Pietilä T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med. 1998;26(3):360–366.
5. Coombs BK, Bisset L, Brooks P, Khan A, Vicenzino B. Effect of corticosteroid injection, physiotherapy, or both on clinical outcomes in patients with unilateral lateral epicondylalgia: a randomized controlled trial. JAMA. 2013;309(5):461–469.
6. Lewis T, Cook J. Fluoroquinolones and tendinopathy: a guide for athletes and sports clinicians and a systematic review of the literature. J Athl Train. 2014;49(3):422–427.