Tendons and Tendinopathy
- Storm Baynes-Ryan
- Nov 7
- 6 min read
Updated: Nov 12
Intro
What is a Tendon?
Tendons are what attach muscles to bones. They are the white “sinew” at the end of muscles, and transmit forces from the muscle to the bone and joint - stabilising the joint, or greating movement. They also, importantly, create elasticity and bounce, decreasing the work of the muscle e.g. the achilles.
The lower limb tendons can withstand high levels of force e.g. the foot tendon (and the whole body) needs to withstand between 1.5-2 x body weight (walking), up to 6-7 x body weight (running) -14 x body weight (gymnastics) when running and jumping (multiply your weight by any of those numbers by an activity level force and feel amazed at what your body can withstand.)
The structure of tendons is highly aligned collagen – and the structure varies depending on the purpose e.g. finger flexor and toe extensor tenons are long and ropey, the elbow tendons for those same muscles are broader and flatter, the rotator cuff tendons are curved and have a pulley system involved, and the achilles is long, thick, ropey (with it’s fibres parallel to each other but a semi spiral (!) and stores and releases energy in an elastic way. The body is an amazing and complex thing.
The microscopic makeup is a lot like wool - including the crimping, which is where the elastic recoil is thought to come from.
That's probably enough anatomy. Even for me!
So... what's the problem?
What about when they hurt?
Tendons are thought to go through four different phases of change.
Stage ONE
The first stage happens in the first 2 days after loading, and there is an increase in size, with increased water noted inside the tendon. It is not known whether this is pathological or a part of the normal recovery process of loading and adaptation.
My take: The human body is so intelligent, that if we load it (smartly, and judiciously) it will adapt.
What to do about it: load your body, be smart about it, and make sure you load it more than you are currently, but don't push too hard (your training should be for a lifetime) and make sure you allow for rest.
Stage TWO
The second phase is where we get early irritation. It's when we fall on our knee, or hit our elbow, or spend a day doing tasks that are outside of our normal tolerance.
The tendon can get sore, and if it's not too much for the tendon, it will settle with being smart about ongoing loading. This phase is ideal to be done at 20 days when the clever chemicals involved in healing and growth change from one kind to another.
Key takeaway - when it first starts hurting, settle that sucker down.
What to do about it: do as much as you can without increasing your pain more than 2/10 and make sure it settles properly. You WILL need to adapt your life in the meantime, as this stage is the most easily reversible. The other option is to ignore it and move to ... the next stage
Stage THREE
The third phase is early degeneration. This phase is reactive - the tendon has been loaded beyond it's capacity to heal and hasn't had the chance to recover. There are changes to function even if you don't feel pain, including the ability to create force, and absorb load. This stage is reversible, but requires work.
What to do about it: Activity modification is a part of it, but a specific strengthening programme prescribed by a knowledgable physiotherapist, based on findings in your assessment can be helpful. Isometric and eccentric loading are the most popular ways to get started, but a full rehab programme also needs to include concentric and plyometric and ballistic loading for full recovery.
Key Takeaway: this is where the rubber hits the road. Your decisions now impact whether you will have a tendon that recovers it's function, or whether you move down to --- Stage four.
Stage FOUR
The fourth phase is tendon degeneration: when it's getting dire - there are changes that are not reversible - the damaged portion of the tendon does not react to forces through it, and does not change - it cannot absorb force and has no elasticity. This in itself is a problem, but alongside, this can also create increased force - beyond the loss of capacity - in the uninjured tendon, which can then create a tendon that has "normal" tendon and degeneration, which then transitions into a reactive tendon.
Key Takeaway: according to the science, you are unlikely to ever get resolution of the spots of degeneration, but, you can adapt the rest of the tendon so the remainder can take the load required for life. There are ways to work around the tendon and gradually build up compensatory patterns to make sure you can live your life.
What to do about it: Go and see your physiotherapist, get a training programme and stick to it, knowing that it will take some time to notice changes, and that there will be things happening in the background that you won't know about, especially at the start, because you are likely to have a combination of Stage 2-4 within that tendon. There will need to be a combination of things done for you, and ideally your programme will be individualised.
NOTE: 97% of tendon ruptures have signs of prior degeneration on inspection.
Conclusion
Tendons are an astonishing structure that create elastic recoil, absorb forces and distribute them. They can adapt and respond to the world around them, up until a certain point, in which case they stop and the rest of the tendon has to be loaded more to "take up the slack". Some of this is reversible with consistent and clever rehabilitation programmes, and some programmes need to build up compensatory patterns to improve function.
What else you can do:
If you have concerns about your tendons, (think tennis elbow, Achilles tendon, front of knee pain, tennis elbow/golfers elbow, grumbling shoulders) and your pain is more than 3/10 and it's interfering in your daily life, it's a really good idea to get it managed earlier rather than later. It's literally more likely to make it reversible than something we have to work around.
Other Bits and Pieces
Email me storm@thatfarmingphysio.com to make an appointment to make a plan together.
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If you have any concerns, and want individualised advice, please contact me via email, storm@thatfarmingphysio.com
References:
Ground reaction forces Estimating Running Ground Reaction Forces from Plantar Pressure during Graded Running | MDPI
Structure - Tendon Physiology and Mechanical Behavior: Structure–Function Relationships - ScienceDirect
Nilsson, J. (1989). Ground reaction forces at different speeds of human locomotion. Acta Physiologica Scandinavica, 136(2), 217-227. PubMed+1
McNair, P. J. (1999). Normative data of vertical ground reaction forces during landing from a jump. (Technical Report) Journal of Science and Medicine in Sport, 2(2), 100-112. sciencedirect.com
Seegmiller, J. G., & McCaw, S. T. (2003). Ground reaction forces among gymnasts and recreational athletes in drop landings. Research Quarterly for Exercise and Sport, 74(3), 319-323. PMC
Ortega, D. R. et al. (2010). Analysis of the Vertical Ground Reaction Forces and Impulses in Male and Female Ground Reaction Forces in Drop Landings. Journal of Bone & Mineral Research (Special Issue). PMC article. PMC
Kluitenberg, B. et al. (2012). Comparison of vertical ground reaction forces during running on an instrumented treadmill and overground running. BMC Musculoskeletal Disorders, 13, 104. BioMed Central
La Greca, S. et al. (2024). The ground reaction force-time profile of drop vertical jumps: effect of instruction on landing mechanics. Frontiers in Sports and Active Living, 6, 1474537. Frontiers
Pavei, G., et al. (2019). Race walking ground reaction forces at increasing speeds. Symmetry, 11(7), 873. MDPI
Suzuki, M., Ishida, T., Matsumoto, H., et al. (2025). Relationship Between Vertical Ground Reaction Force and Acceleration from Wearable Inertial Measurement Units During Single-Leg Drop Landing After Anterior Cruciate Ligament Reconstruction. Applied Sciences, 15(3), 1583. MDPI
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