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The Tale of Two Tendons

As a physical therapist, I rightfully get a lot of questions about injuries. Friends, family members, and sometimes people I barely know are never short of musculoskeletal injury inquiries. For my active workout friends, these questions normally stem around a “tendonitis” or tendon issue that is limiting their ability to lift, run, etc. I want to take a dive into tendon injuries and what to do and what NOT to do to fix them.

First of all, what the heck is a tendon anyway? A tendon is a connective tissue connecting a muscle belly to a bony attachment. This is different than a ligament, as a ligament connects bone to bone. The tendons primary job is to transfer force from a muscular contraction to a bone and allow for joint movement. Think of a tendon as a “force highway”. Tendons commonly become inflamed due to the repetitive stress as muscles shuttle force down the highway and as bones relay force back to muscle for absorption. Tendons become painful/inflamed when the amount of travel (force) exceeds what the tendon is used to and there’s a metaphorical crash on the highway.

So what can you do about it?

There are a few key concepts to consider with tendon health and rehabilitation.

1. Tendon’s respond only to LOAD. The biggest mistake that people make is assuming that resting a tendon will allow it to heal. Let’s go back to our highway analogy. If there’s a major crash and they shut down the highway, what happens? First of all, they have time to clean up the mess and get the cars out the way. This is good! However, one other crucial thing happens. Traffic piles up for miles and miles. The second the road opens, the highway is overwhelmed and is primed for another accident. This is the cycle that many people fall into. They have a tendon injury, they rest, the pain decreases, they start activities again, and they re-injure and repeat. Sound familiar?

Research teaches us a different pathway for tendon rehabilitation. A 2015 systematic review by the Journal of Sports Medicine-Open found that across studies “Tendons are highly responsive to increased mechanical loading and adapt through changes of their mechanical, material, and morphological properties.” This means that we don’t need to close the road, we need to build a few more lanes. By systematically and strategically loading a tendon, you allow it to lay down additional collagen and increase its’ cross sectional area. This process makes the tendon more resilient and allows for greater force transfer tolerance in the future.

2. The 4/10 rule. Now just because we’re not closing down the highway, doesn’t mean we don’t want to clean up the crash. This is where the 4/10 rule comes in to play. The 4/10 rule is simply that we want to keep pain levels during rehabilitation, exercise, and for 24 hours following activities at a 4/10 intensity or less. This is crucial for a couple of reasons. It allows room to load the tendon, but only in activities/exercises that are minimally painful. It allows the tendon to progress from a state of constant pain/inflammation while simultaneously allowing the building up of the tendon. It gives valuable feedback on what we should and shouldn’t do.

Let’s say you went to PT and performed some targeted exercises with a pain level of 2/10. However, later that evening your tendon pain was 7/10 and stayed “flared up” for 12 hours. This fails the 4/10 rule and exercises need to be regressed and slowly built up. On the other hand, if the tendon responds well it gives clearance to progress the rehab program and continue following the 4/10 rule until completion.

3. Stay the course. Due to being less vascular than muscle tissue, tendons can take a little longer to heal. Patience is key as research suggests the time frame is usually around 12 weeks. There are ways to make the most out of each stage of recovery. In the early stages, focus on isometric training to minimize tendon irritation. Isometrics are simply sustained muscle contractions without movement. This allows the tendon to strengthen without the repetitive stress. Isometrics have also been shown to improve pain which is crucial in the early stages.

Following the 4/10 rule you can confidently progress from isometrics to concentric/eccentric movements and progressive loading. Best evidence supports slow tempo heavy training of >80% of 1 rep max for the achilles and patellar tendons and is a concept used on many other tendons as well. Point being, don’t be afraid to go heavy as long as you are monitoring pain during and after activity. Remember, we have highway lanes to build and that doesn’t happen without some labor. Roads aren’t built in a day, and neither are your tendons.

Finally, be patient and slow to return to plyometric activities. Plyometrics include activities like running, jumping, and other dynamic movements. Plyometrics require the greatest amount of force transference from your tendon and can cause significant irritation if performed too soon. Make sure your tendon is ready before “jumping” back in. Think about this: if your goal is to run 1 simple mile, that mile consists of 5280 feet. If you stride 3 feet per stride, that is 1760 strides per mile and 880 individual impacts per foot. If you have an achilles tendon injury, you need to make sure that tendon is prepped for 880 reps of force transference before you embark on that mile! This is why proper progression is so important and why working with a rehab professional is so beneficial. Too much too fast and we end up right back at the highway fender bender.

If you’re dealing with a tendon injury, you have a choice to make. Are you going to shut down the highway or put in the work to build a few more lanes? Unfortunately, most often people end up on the first path and caught in an inflammatory hamster wheel. Our medical system encourages this with the use of boots, slings, braces, and the “take 6 weeks off” method that is grossly unnecessary and harmful in the long term. If you are not post-operative, there is no reason to ever wear a boot/brace for a overuse tendon injury. Instead, let’s focus on building a strong and resilient body that is prepped and ready for life. Let’s be patient and understand that a few weeks of diligent work now can impact you for years to come. Let’s stop taking the easy way out. Let’s build a highway and go wherever we want to go.

Stay Kinetic Friends.


Sports Med Open. 2015 Dec; 1: 7. Published online 2015 Mar 27. doi: 10.1186/s40798-015-0009-9.


Dr. Levi Kerby is a physical therapist, orthopedic certified specialist, and owner of Kinetic Performance and Rehab in Winston-Salem, NC. He enjoys fly fishing, guitar, various forms of fitness, and treating active and motivated individuals.

If you're dealing with an injury or pain, you can contact Kinetic Performance and Rehab directly below.

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