Patellar tendonitis (jumper’s knee) is one of the most frustrating sports injuries because it often appears without warning. You might feel fine during training, only to be hit with knee pain later and by that point, your tendon has already been under stress.
So why does patellar tendonitis really happen, and what can you do about it?
Let’s unpack the hidden causes step by step.
To really understand how to prevent flare-ups, you’ll want to look at the deeper risk factors and stages of injury.
What Is Patellar Tendonitis and Why It Matters
Patellar tendonitis, often called jumper’s knee, is a painful condition that affects the tendon connecting the kneecap (patella) to the shinbone (tibia). This tendon plays a key role in activities like jumping, running, and squatting by transmitting the power of the thigh muscles.
You may also hear it described as patellar tendinitis, patellar tendinopathy, patellar tendonosis, or jumper’s knee.
All of these terms refer to the same problem: an overuse injury of the patellar tendon that ranges from mild irritation to chronic degeneration.
The confusing part is that you might not feel pain until tissue damage has already occurred. To learn how this hidden progression works, see the section on the “tendinopathy continuum” below.
Common Causes of Patellar Tendonitis (Beyond Just Jumping)
The root cause is mechanical overload. Tendons are made of collagen fibers that adapt slowly compared to muscles. When training or activity increases too quickly, the tendon cannot keep up in strength gains.
But one-time overload is not the only cause of patellar tendonitis. Other typical causes include:
- Repetitive jumping and sprinting (main jumper’s knee causes)
- Training too much too often (cumulative overload over time)
- Rapid increases in training intensity or volume (tendon’s load tolerance exceeded)
- Sudden return to sport after time off (rest period led to tendon weakness)
- Direct trauma to the tendon (impact can cause local tissue changes)
This mismatch between muscle strength and tendon adaptation explains why even strong athletes can develop tendonitis.
Self-check:
Did your knee pain start after a sudden change in training load, like a tournament, a heavy squat cycle, or after returning from a break?
If yes, that’s the classic setup for tendon overload.
Interesting facts from research:
- In patellar tendonitis, healthy tissue often sits right next to degenerated patches where cells have died and the tendon matrix is disorganized, which explains why recovery can be so unpredictable.1
- Rest also causes tendon degeneration2, with 14 days of complete rest leading to a 9.8% decrease in stiffness (23 days: 29.3%!)3
This data shows that “overuse” is an oversimplification when it comes to explaining patellar tendonitis. To understand this injury, you need to look deeper.
Why Patellar Tendonitis Happens in Athletes
The most common reasons why athletes get patellar tendonitis are:
- Excessive weekly training load with too little rest
- Being a single-sport athlete
- Abrupt return to sports after 3+ weeks of time off (think a vacation, injury, busy period at work or at home, etc.)
- Just doing your sport, without taking care of your body (weakness and tightness lead to altered mechanics, which then contributes to tendon overload)
- Ignoring early warning signs and training through pain
Athletes whose sports involve repeated explosive movements of the legs are at higher risk. Here’s an overview:
- Running: Long-distance runners often stress the tendon through repetitive loading.
- Squats and weight training: Deep squats and heavy strength work can overload the tendon if progress is too fast.
- Basketball and volleyball: Frequent jumping and landing are classic triggers for jumper’s knee.
Across all sports, up to 22% of elite athletes report patellar tendon pain at some point in their career. While it is more common in jumping sports, it can also happen in runners, cyclists, and CrossFitters.
However, keep in mind that jumper’s knee was slightly more common in non-athletes (9.8% vs. 8.8% of injuries) than in athletes.4 So even if you’re not an athlete, you can still get patellar tendonitis.
Risk Factors That Make Patellar Tendonitis Worse
Several factors can increase the likelihood or severity of tendon problems:
- Overuse without enough rest (patellar tendonitis overuse)
- Age: older tendons are less adaptable and slower to heal (the influence of age on patellar tendonitis can be neutralized with the right strategies)
- Training errors: poor load management, sudden spikes in intensity
- Biomechanical issues: muscle imbalances or tightness, weakness in certain muscles, poor movement patterns
- Intrinsic risk factors such as diabetes can also predispose someone to tendon injuries5
- Training on hard surfaces, like concrete courts
These are just some examples of factors that can increase your risk of developing patellar tendonitis. Unfortunately, there are too many to explain everything in a short article such as this one. If you want to know everything about how you can reduce your risk of tendonitis setbacks, join this free course.
In contrast, the following factors do not increase risk of patellar tendonitis:
- Gender differences between sports categories and sex were not statistically significant6
- Height, weight, and BMI do not influence risk (ibid., one caveat: study was on elite athletes)
- Patellar tendon abnormalities on ultrasound do not predict risk7
The problem is that once pain begins, the condition often lingers. Research shows that patellar tendonitis can last from 3 months up to 15 years.8 That’s why taking the right steps early on is so important, as stories such as this one show:
“I am a cyclist and was having knee problems for over two years and I was told the only solution was surgery. I followed your exercises and now my knees are just fine. My cycling is now normal, no more pain! I am 72 years old and cycle competitive. I can only thank You very much for your assistance.”
— Per Pedersen-Hoien
How Overuse and Training Load Lead to Jumper’s Knee
When you train hard, your muscles adapt quickly, but tendons lag behind. This creates a dangerous window where the muscle can produce more force than the tendon can tolerate.
If you progress training gradually, the tendon has time to strengthen. But sudden increases in load can push the tendon into overload. This can be something like weekend tournaments, heavy squat cycles, multiple training sessions without recovery, as well as being more physically active during vacation or performing unusual movements at work.
This explains why patellar tendonitis often appears after overtraining, jumping, an intense workout schedule, or a change in movement habits: your activities exceeded the tendon’s current load tolerance and tendonitis has set in. How you react will determine how long your recovery time will be.
Role of Biomechanics and Muscle Imbalance
Poor movement mechanics can contribute to overload of the patellar tendon even at moderate training volumes. Examples include:
- Weak glutes or hamstrings causing the quadriceps to take over
- Limited ankle mobility increasing stress on the knee
- Tight quadriceps or hip flexors pulling excessively on the tendon
Corrective strategies like targeted stretches, eccentric quadriceps exercises, and structured rehab programs help restore balance and reduce tendon strain. To prevent setbacks, a comprehensive treatment plan for patellar tendonitis should always address load tolerance deficits (= tendon weakness), as well as other intrinsic and extrinsic risk factors.
During my research on the injury, I’ve uncovered over 40 factors that can increase the risk of patellar tendonitis. Unless you address them, your risk of setbacks will always remain higher than normal. This is something I cover in the free Tendonitis Insights course at the bottom of this page.
Why Patellar Tendonitis Keeps Coming Back
Many athletes experience recurring pain. Reasons include:
- Continuing to play through pain, worsening tendon degeneration
- Incomplete rehab that strengthens muscles but not the tendon
- Chronic structural changes in collagen fibers (patellar tendonosis)
- Returning to high-load sports too early
- Leaving too many of the 40+ hidden risk factors unaddressed
This cycle explains why patellar tendonitis often becomes chronic. Breaking it requires proper load management, progressive tendon rehab, patience, and a comprehensive approach that fixes all causes while strengthening the tendon safely.
Take Control of Patellar Tendonitis
Get the step-by-step answers in my free Tendonitis Insights Course: simple self-tests, the biggest training mistakes to avoid, and smart recovery strategies athletes use to stay pain-free.
My work is recommended by doctors and has produced thousands of success stories. The next one may be yours.
[1] J. L. Cook and C. R. Purdam, “Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy,” British Journal of Sports Medicine 43, no. 6 (2009): 411.
[2] James H.-C. Wang, Qianping Guo, and Bin Li, “Tendon Biomechanics and Mechanobiology—A Minireview of Basic Concepts and Recent Advancements,” Journal of Hand Therapy 25, no. 2 (2012): 138.
[3] De Boer, Maarten D. et al., “Time course of muscular, neural and tendinous adaptations to 23 day unilateral lower-limb suspension in young men,” The Journal of physiology 583, no. 3 (2007): 1091.
[4] Marienke van Middelkoop et al., “Knee complaints seen in general practice: active sport participants versus non-sport participants,” BMC Musculoskeletal Disorders 9, no. 1 (2008): 167.
[5] A. Del Buono et al., “Tendinopathy and inflammation: some truths,” International journal of immunopathology and pharmacology 24, 1 Suppl 2 (2011): 46.
[6] Michael Cassel et al., “Incidence of Achilles and Patellar Tendinopathy in Adolescent Elite Athletes,” International Journal of Sports Medicine 39, no. 09 (2018): 729.
[7] Marcey Keefer Hutchison et al., “Low prevalence of patellar tendon abnormality and low incidence of patellar tendinopathy in female collegiate volleyball players,” Research in Sports Medicine 28, no. 2 (2020): 166.
[8] M. Kongsgaard et al., “Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy,” Scandinavian Journal of Medicine & Science in Sports 19, no. 6 (2009), http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0838.2009.00949.x/full.
[9] Melanie L. Plinsinga et al., “Evidence of Nervous System Sensitization in Commonly Presenting and Persistent Painful Tendinopathies: A Systematic Review,” Journal of Orthopaedic & Sports Physical Therapy 45, no. 11 (2015): 864.
