What Happens When Tendons Become Painful

Welcome back to our 3-part series on tendon health. In Part 1, we covered what tendons are, how they function, and their role in movement. Today, we’re diving into what happens when tendons stop pulling their weight and start causing trouble.

If you’ve ever had a nagging Achilles pain, shoulder discomfort that overstays its welcome, or knee pain from running or jumping, someone might have thrown around words like tendinitis or tendinopathy. Let’s break that down into more digestible terms.

What Is Tendinopathy, Really?

Tendinopathy is the umbrella term for tendon pain and dysfunction that affects your ability to perform activities. The current scientific understanding recognizes that tendinopathy is more complex than simple inflammation or degeneration. Instead, it represents a continuum of structural and functional changes in response to loading patterns.

Modern research has moved away from the old inflammation “-itis” versus degeneration “-osis” debate. This is because studies show that most of the histologic findings (think under the microscope) in tendinopathy do not actually show much true inflammation. Instead, there are more signs of attempted repairs: small microtears, disorganized fibers, and tissue trying (but not always succeeding) to heal.

You don’t need to worry too much about which “-itis” or “-osis” is on your report. What matters is how it’s showing up in your body. Tendon dysfunction usually looks like pain during or after activity, swelling or thickening of the tendon, stiffness in the morning or after rest, or that “ugh, I used to be able to do this” feeling when trying to lift, jump, or move like you used to.

Just to clarify, tendinopathy is different from an acute tendon rupture, which usually happens suddenly with significant force—think Golden State Warriors Kevin Durant in the 2019 NBA playoffs—and typically requires immediate medical attention.

The Tendon Continuum: A Modern Understanding

Researchers now understand that tendon problems do not fall into neat boxes but exist on a spectrum, or continuum. In the early stage, called reactive tendinopathy, the tendon often swells and thickens after being overloaded, but this stage can improve quickly if the stress is managed. If the overload continues, the tendon may enter a dysrepair stage, where its healing process gets messy and fibers become disorganized while the tendon stays thickened. In the most advanced stage, degenerative tendinopathy, parts of the tendon show breakdown and failed healing. The good news is that tendons are not stuck in one place. They can move forward or backward along this spectrum depending on how they are cared for, especially in the early stages.

What Causes Tendinopathy?

Tendinopathy can sneak up on you slowly or hit you fast, and there’s usually more than one factor at play. Tendinopathy is divided into two types: primary and secondary.

Primary Tendinopathy

This is the most common type. It usually happens when tendons are unhappy with the workload we’re putting on them. That could mean:

• Too much load (hello, weekend warrior)
• Too little load (hello, desk job)
• Age-related changes in tissue resilience
• Less-than-ideal movement patterns 
• Or just life stacking up over time without adequate recovery

Maybe you started a new workout, or maybe you’ve been compensating for a stiff joint without realizing it. Either way, the tendon says “nope” and begins to operate inefficiently.

Secondary Tendinopathy

This type happens when a medical condition sets the stage for tendon irritation. Some common culprits:

• Metabolic conditions like diabetes (affects collagen cross-linking and healing)
• Inflammatory conditions such as rheumatoid arthritis or lupus
• Medications including fluoroquinolone antibiotics and some statins
• Hormonal changes that can affect tissue properties
• Genetic factors that influence collagen structure

If you fall into this category, recovery is absolutely possible, but treatment may need to be more carefully progressed and consider these underlying factors.

So, What’s Going On Inside the Tendon?

Imagine your healthy tendon as a strong, well-organized rope that handles tension with ease. Now picture what happens when that rope starts to break down. The collagen fibers lose their neat, parallel structure and become disorganized. Your body tries to step in and help by sending scar tissue, swelling, and even extra blood vessels and nerve endings, which unfortunately can make the tendon more painful. The tendon thickens as part of this repair attempt, but it is not necessarily stronger. At the same time, the tendon cells, called tenocytes, release chemicals such as PGE2 in response to altered loading, which makes the tendon more sensitive to stress and movement. All of these changes are the tendon’s way of trying to adapt and heal, but when the demand placed on it is greater than its ability to adjust, pain and dysfunction can result.

Why Does Tendon Pain Vary So Much?

Tendons can be moody. One day you feel fine and the next you might be hobbling around like you just ran a marathon in flip-flops. Pain is not just about damage to the tendon itself, but also about how your nervous system processes signals. Sometimes nearby structures like a bursa or fat pad are irritated and add to the discomfort. The tendon might also be slightly inflamed, overloaded, or stiff from too little use. On top of that, factors contribute to the manifestation of pain like stress, sleep, and even your mood. Pain actually comes from the brain, not directly from the tendon itself, which is why two people with the exact same MRI can have very different experiences. One person might be sprinting while the other struggles to walk.

Why Rest Alone Doesn’t Fix It

It seems logical to think that if something hurts, you should stop using it. Unfortunately, that approach alone does not work well for tendons. Too much rest actually makes them weaker, stiffer, and more sensitive. What tendons really need is carefully applied movement that encourages healing. The load has to be controlled so it is not too much or too little, and it needs to progress gradually over time so the tendon can build its strength and tolerance again. In other words, successful recovery requires a thoughtful rehab plan rather than a vacation from movement. Tendons are complex, resilient, and a little sensitive, and when they are not happy, they let you know. The encouraging part is that with proper understanding and a comprehensive approach, they can return to doing their job.

In Part 3, we’ll talk about what physical therapy actually does to help painful tendons. Spoiler alert: it’s not just about stretching.

And if your tendon is currently complaining, don’t panic. Help is out there and recovery is very much possible. Reach out to us at Beacon PT so we can aid you in your recovery.

Sources

Scott A, Rees JD. Basic Science and Pathophysiology of Tendons. In: Simoneau GG, ed. Physical Therapy Management of Tendinopathies. Academy of Orthopaedic Physical Therapy, APTA, Inc.; 2022:5-25.