YR Sports Lab
This pain is easy to recognise, and the area is small enough to cover with one fingertip: the spot right below the kneecap. A few warm-up laps barely hurt, it starts aching dully when you kneel to pressure half guard, it stabs the moment your weight settles mid knee cut, and it bites again when you stand up after a long drive home. There is no swelling, no catching, no locking, and an X-ray usually shows nothing, so most people blame it on "too much kneeling", ride it out with ibuprofen, and only realise two years later that it never actually healed. A meta-analysis puts patellar tendinopathy prevalence at 18.3% in athletes versus just 0.1% in the general population, a difference of roughly 180-fold. More sobering still is a 15-year follow-up in which 53% of the athletes who had symptoms back then had eventually left their sport, against 7% of controls. This article uses PubMed literature to unpack where patellar tendon load really comes from in jiu-jitsu, how two tests separate it from other sources of knee pain, and why "rest" is the worst prescription for this injury.
1. What the patellar tendon is: the only channel for force transfer
Start with the anatomy, because it determines everything that follows. The patellar tendon (strictly speaking the patellar ligament) connects the inferior pole of the patella to the tibial tubercle and is roughly 4 to 5 cm long. Every bit of knee extension force generated by the quadriceps has to pass through the patella as a pulley and then through the patellar tendon to the tibia, with no second route. This tendon is both the outlet for force and the single-point bottleneck of the whole extensor mechanism.
The classic lesion in patellar tendinopathy is not the whole tendon but the deep proximal portion at the inferior pole of the patella, the posterior aspect of the short segment closest to the kneecap. There are mechanical reasons for that selectivity: in knee flexion the inferior pole shears and compresses the deep tendon fibres, and blood supply in that region is relatively sparse to begin with. It also explains why the tender spot is almost always confined to the same small area and why patients can point to it precisely.
Histologically, chronic patellar tendinopathy shows disorganised collagen, accumulation of glycosaminoglycans in the matrix, and ingrowth of new vessels and nerve endings, rather than the classic acute inflammatory cell infiltrate. This is exactly why the international literature renamed tendinitis as tendinopathy. That difference is not academic fussiness, it directly overturns the old "anti-inflammatories plus rest" prescription, because if inflammation is not the main driver, anti-inflammatory drugs and bed rest cannot reorganise disordered collagen.
2. Where patellar tendon load in jiu-jitsu comes from
The nickname for patellar tendinopathy in the literature is "jumper's knee", and its core population is volleyball and basketball players, with landing-phase high-speed energy storage as the mechanism. Jiu-jitsu has no landing impacts at all, so why does it hurt? The answer lies in two underrated variables: knee flexion angle and accumulated time.
Biomechanical studies agree that patellofemoral joint reaction force rises as knee flexion increases, growing steadily between 0 and 90 degrees. There are two reasons: the deeper the flexion, the more quadriceps force is needed to hold the position, and at the same time the angle between the quadriceps tendon and the patellar tendon narrows, increasing the resultant force pressing into the patella and its inferior pole. Both effects are repeatedly confirmed in biomechanical analyses of the squat, and most top positions in jiu-jitsu happen to park you in that high-load range for long stretches.
Bring that principle back to the mat and patellar tendon load in jiu-jitsu has four main sources. First, the static load of kneeling pressure: half guard pressure passing, the mid-transition position of the knee cut pass, and body lock pressure are all single- or double-knee deep-flexion loaded positions held for tens of seconds at a time. Second, weight shifting in knee on belly and transitions: the supporting leg has to make repeated micro-adjustments in deep flexion. Third, explosive knee extension in technical stand-ups and scrambles to the feet, the movement closest to the original jumper's knee mechanism. Fourth, direct contact pressure: kneeling on a hard mat presses the tendon and inferior pole against the floor, and this one is unique to jiu-jitsu, volleyball players never get it.
Why patellar tendon pain in BJJ gets misread as "too much kneeling"
The most common self-diagnosis in the gym is "the front of my knee hurts from kneeling, I just need better knee pads". That is half right: direct contact pressure genuinely provokes symptoms, and pads genuinely reduce the immediate discomfort. But it fails to explain three other phenomena, and those three are the fingerprint of tendinopathy.
First, symptoms usually peak about 24 hours after training rather than during it. Second, pain temporarily eases after warming up, which fools people into thinking they can train through it, only for it to come back twice as hard afterwards. Third, the first step after sitting with the knee bent for a long time hurts most, which has nothing to do with mat contact and shows up hardest after a desk day or a drive.
These three features point to reduced tendon tolerance to load, not locally compressed soft tissue. Pads address the fourth load source, while the first three remain untouched. That is why people who only change equipment without changing training content usually see the symptoms return unchanged two or three months later.
3. Prevalence and prognosis: the numbers 18.3% and 53%
A systematic review and meta-analysis published in the Orthopaedic Journal of Sports Medicine in 2023 pooled 28 studies with 28,171 participants and is currently the largest synthesis of patellar tendinopathy epidemiology. It reported a prevalence of 18.3% (95% CI 14.6 to 22.1) in athletes, against just 0.1% (95% CI 0.1 to 0.2) in the general population. Incidence in athletes was 7% (95% CI 3.9 to 10).
| Population / subgroup | Prevalence | 95% CI | Source | Relevance to BJJ |
|---|---|---|---|---|
| Athletes (overall) | 18.3% | 14.6 to 22.1 | 2023 meta-analysis | BJJ not listed separately, not covered |
| Volleyball | 24.8% | 17.8 to 31.8 | 2023 meta-analysis | High-speed landing load, different mechanism |
| Basketball | 20.8% | 15.0 to 26.5 | 2023 meta-analysis | High-speed landing load, different mechanism |
| Soccer | 6.1% | 0.7 to 11.6 | 2023 meta-analysis | Prevalence drops clearly with less jumping |
| General population | 0.1% | 0.1 to 0.2 | 2023 meta-analysis | About one 180th of the athlete rate |
| Athletes aged 18 and over | 21.3% | 15.9 to 26.7 | 2023 meta-analysis | The core adult gym age bracket |
| Athletes under 18 | 10.1% | 5.7 to 14.5 | 2023 meta-analysis | Difference between groups significant (P = .004) |
| Male / female athletes | 17% / 11.2% | 13 to 20.9 / 7 to 15.4 | 2023 meta-analysis | Difference not significant (P = .070) |
*Figures compiled from publicly available abstracts, retrieved July 2026. The same meta-analysis notes that prevalence derived from patient-reported questionnaires (25.4%) was clearly higher than from clinical assessment alone (12.1%), P = .004, meaning the assessment method itself materially shifts the number, so treat cross-study comparisons with care.
One thing has to be stated honestly: there is currently no study of patellar tendinopathy prevalence in Brazilian jiu-jitsu practitioners. The numbers above cannot be transplanted straight onto the gym. The closest knee data we have is a cross-sectional study published in 2021 that surveyed 198 amateur and professional jiu-jitsu practitioners aged 18 to 60 using a reference morbidity questionnaire. It found that 29.8% had experienced a knee injury, of which the medial collateral ligament accounted for 38%, sprain mechanisms for 86%, and conservative management for 65%, with 88% having had only a single knee injury.
The key point about that dataset is that it is uniformly acute sprain-type injury, with overuse tendinopathy not counted separately. That is precisely the problem: jiu-jitsu injury surveys mostly ask in terms of "events", and patellar tendinopathy has no discrete injury event because it accumulates day by day, so it is structurally missed by this kind of questionnaire. The reasonable inference is that the real number of people in the gym with patellar tendon pain is higher than any jiu-jitsu injury statistic shows.
As for prognosis, the follow-up study by Kettunen et al. published in the American Journal of Sports Medicine in 2002 offers an unsettling long-term picture: among athletes diagnosed with jumper's knee at the time, 53% had left sport 15 years later, versus only 7% of asymptomatic controls. Only 20 jumper's knee cases and 16 controls responded (the 53% has a denominator of 17), so statistical precision is limited and the figure should not be used as an actuarial probability. But it does establish one thing: patellar tendinopathy is not the kind of injury that simply resolves if you keep training, and its natural course when ignored can run very long.
4. Confirming it really is the tendon: two tests and one questionnaire
Anterior knee pain has more than one source. Patellofemoral pain syndrome, prepatellar bursitis, infrapatellar fat pad impingement and adolescent tibial tubercle apophysitis all hurt nearby. Clinically, three things separate patellar tendinopathy from the rest.
First, locating the tenderness. In patellar tendinopathy the tender point sits at the inferior pole of the patella, in a small and consistent area. If the worst point is at the joint line, the medial or lateral patellar border, or behind the patella, look elsewhere.
Second, the Royal London Hospital test. With the knee extended, palpate along the patellar tendon from proximal to distal to find the tender point, then flex the knee to 90 degrees and press the same spot; the test is positive if tenderness clearly decreases in flexion. The rationale is that quadriceps tension in flexion tightens the tendon and "hides" the lesion in the deeper layer where it is harder to reach. Maffulli et al. reported in 2017, using high-resolution ultrasound as the reference standard, a sensitivity of 88% and specificity of 98% for this test, with manual palpation in the same group at 98% sensitivity and 94% specificity, and recommended using both. Note that the study included 15 affected and 15 control participants, so the sample is small and the values should be read as directional.
Third, the single-leg decline squat. Standing on a decline board of roughly 25 degrees, perform a single-leg half squat; the decline angle concentrates load onto the patellar tendon. People with poor load tolerance typically start hurting at around 30 degrees of knee flexion. The value of this test is not only diagnostic, it also works as a daily self-monitoring baseline: do it at the same time of day to the same depth, record the pain score out of 10, and use the trend to judge whether this week's load progression is right.
To quantify symptoms, use the VISA-P questionnaire (Victorian Institute of Sport Assessment for Patellar tendinopathy). It is a self-completed 0 to 100 scale where 100 means completely pain-free with no limitation in function or sport, and lower scores mean worse symptoms. The interpretation commonly used in clinical research is that a change of more than 13 points counts as a meaningful improvement; anything smaller may just be noise in the instrument. For anyone rehabbing on their own, the practical value is that it converts "I think it's a bit better" into a comparable number, and filling it in every 4 weeks is enough.
5. Why "rest" is the worst prescription: the evidence for HSR
The most counterintuitive point in tendinopathy management is that complete rest makes things worse. Tendon mechanical properties depend on loading; prolonged unloading reduces stiffness and tolerance, so by the time you return to training the threshold is even lower than before you stopped. Current management therefore does not remove load, it converts load into a controlled, progressive and measurable form.
The most frequently cited evidence here is the randomised, assessor-blinded trial by Kongsgaard et al. published in Scandinavian Journal of Medicine and Science in Sports in 2009. The study recruited 39 male patients with patellar tendinopathy, randomised to three 12-week interventions: corticosteroid injection (CORT), eccentric decline squat training (ECC), and heavy slow resistance training (HSR), with assessment at week 0, week 12 and 6-month follow-up.
| Intervention | Result at 12 weeks | 6-month follow-up | Imaging change (12 weeks) | Practical reading |
|---|---|---|---|---|
| Corticosteroid injection (CORT) | VISA-P and pain improved | Improvement lost (P < 0.05) | Swelling −13%, neovascularisation −52% | Effective short term, not sustained |
| Eccentric decline squat (ECC) | VISA-P and pain improved | Improvement maintained | No significant change | Effective, but more painful during training |
| Heavy slow resistance (HSR) | VISA-P and pain improved | Maintained, highest satisfaction | Swelling −12%, neovascularisation −45% | Improves symptoms, pathology and collagen turnover |
*Compiled from the publicly available abstract of that study, retrieved July 2026. All three groups improved on VISA-P and VAS at 12 weeks (P < 0.05), and the difference emerged at 6-month follow-up: ECC and HSR held, CORT regressed. The sample was all male and only 39 participants, so extrapolation to female practitioners should be cautious.
The message of that table is clear: the three approaches look similar at 12 weeks, and the difference only shows up six months out. Corticosteroid injection relieves pain fastest but had slipped back to baseline at follow-up, while both exercise interventions held their gains. The research team also recorded the highest treatment satisfaction in the HSR group, alongside improved tendon pathology and increased collagen turnover.
From a practical standpoint, HSR has one more key advantage over eccentric training: it is just ordinary strength training. Squats, leg press, hack squats; the movements themselves contain both concentric and eccentric phases, you simply slow the tempo down and load them heavier. For a jiu-jitsu practitioner already lifting, that means rehab does not require carving out extra time, only converting the existing lower-body day into the rehab protocol, and adherence is far higher as a result.
6. The 12-week HSR block and the four-stage loading progression
The HSR protocol in the literature is fairly consistent in structure: three bilateral exercises (squat, leg press, hack squat), three times a week, 3 to 4 sets of each per session, with 2 to 3 minutes rest between sets. Tempo is the single most important detail: 3 seconds concentric, 3 seconds eccentric, 6 seconds per rep, so the tendon gets enough time under tension. Load starts at 15RM and progresses every two to three weeks, reaching 6RM by week 12.
| Week | Sets × load | Tempo | Sessions per week | Matching adjustment on the mat |
|---|---|---|---|---|
| Week 1 | 3 sets × 15RM | 3 s concentric + 3 s eccentric | 3 | Cut the share of rounds spent in kneeling pressure and knee cuts |
| Weeks 2 to 3 | 3 sets × 12RM | 3 s concentric + 3 s eccentric | 3 | Technique classes as usual, reduce free rolling volume |
| Weeks 4 to 5 | 4 sets × 10RM | 3 s concentric + 3 s eccentric | 3 | Add top-position work back gradually, guided by decline squat scores |
| Weeks 6 to 8 | 4 sets × 8RM | 3 s concentric + 3 s eccentric | 3 | Introduce low-volume technical stand-ups and scrambles to the feet |
| Weeks 9 to 12 | 4 sets × 6RM | 3 s concentric + 3 s eccentric | 3 | Return to normal rolling volume, drop lifting to 2 maintenance sessions a week |
*RM (repetition maximum) is the heaviest load you can lift for that number of reps, so 15RM is a weight you can move at most 15 times. The mat-side arrangements in the table are practical mappings based on load-management principles, not part of the original study protocol.
Alongside that main progression, clinicians use a four-stage framework to decide what to do right now. Stage one is isometrics, used for pain relief in the symptomatic phase: a common dose is single-leg knee extension at a mid-range angle of 30 to 60 degrees, held for 45 seconds at roughly 70% of maximal voluntary contraction, 5 sets, 2 to 3 times a day. In the crossover trial by Rio et al. published in the British Journal of Sports Medicine in 2015, volleyball players who completed this isometric block saw pain drop from an average of 7 to 0 and stay there for at least 45 minutes, with reduced cortical inhibition and about a 19% increase in maximal voluntary contraction. Note the study had only 6 participants, so individual responses may vary widely, and it is best treated as a "worth trying, use it if it works" analgesic tool.
Stage two is the HSR isotonic loading described above, introduced once pain sits at or below 3 out of 10. Stage three is energy storage loading, meaning plyometrics and fast stretch-shortening work, generally recommended only once you have a strength base of roughly 3 times body weight on the double-leg press (or about 1.5 times body weight single-leg), and done every third day so the tendon gets adequate recovery between exposures. Stage four is return to sport, at which point you still need two stage-two sessions a week or tendon tolerance drifts back down.
Patellar tendon load management for jiu-jitsu practitioners: fitting rehab into the training you already do
1. Use the "24-hour rule" to decide how you train tomorrow. Pain during the session may go up to 3 out of 10, but the day after is what matters: symptoms must return to the previous day's baseline within 24 hours, and morning stiffness must not worsen. Do one single-leg decline squat at the same time each day and score it, then use that number rather than a feeling to decide whether to add or cut volume.
2. Change "time in position" before "sessions per week". Patellar tendon load in deep flexion accumulates with time. Rather than skipping a session, shorten how long you stay in kneeling pressure positions, speed up the knee cut transition, and stop parking in half guard when side control would settle the situation. Cut the exposure time, not the training frequency.
3. On the worst days, open with isometrics. Before class, do 5 sets of 45-second single-leg isometric knee extensions so the 45-minute analgesic window covers the first half of the technique session. This is not treatment, it is a bridge that lets you keep accumulating load.
4. Treat tempo as part of the prescription. What makes HSR HSR is the 6-second rep, not just the weight. Use a timer or count under your breath, 3 seconds up and 3 seconds down, and drop the load rather than speed it up. This is the most common failure point in self-directed training.
5. Pads handle contact pressure, training handles tolerance, and neither substitutes for the other. Padded knee protection reduces the direct pressure on the inferior pole when kneeling and is worth using long term, but it will not raise the tendon's ability to handle deep flexion and explosive extension, and only loading does that.
- Fill in VISA-P every 4 weeks: only a change greater than 13 points counts as real progress, and anything smaller is no reason to rush a change to the protocol.
- Do not do deep eccentrics in the symptomatic phase: decline eccentric squats work, but they hurt more during training, so start with isometrics and HSR when symptoms are bad.
- Bilateral before unilateral: the progression suggested in the literature is to stabilise bilateral movements first, then move to single-leg versions, deepening the flexion angle as pain tolerance allows.
- Be extra careful during weight cuts: low energy availability conflicts with the anabolic demands of tendon repair, so when a pre-competition cut overlaps with rehab, slow the loading progression down.
7. Turning the literature into one actionable judgement
Pulling the evidence together gives a fairly compact rule: patellar tendon pain is not a "something pressed on it" problem, it is a "not enough tolerance" problem. Pads, tape and anti-inflammatories address the former, which is why they make today easier without changing where you are in three months; HSR addresses the latter, at the cost of 12 weeks of discipline and with the payoff of the improvement that still held at 6-month follow-up in the Kongsgaard trial.
Three limitations deserve an honest label. First, neither the prevalence nor the treatment evidence in this article was generated in a jiu-jitsu population: the 18.3% comes from athlete samples dominated by volleyball, basketball and soccer, and the HSR protocol comes from 39 male patients with patellar tendinopathy. Second, the loading mechanism in jiu-jitsu is not identical to jumping sports, and neither prolonged deep-flexion holds nor direct contact pressure was specifically tested in the source literature. Third, the 53% dropout figure comes from a long-term follow-up with only 20 jumper's knee responders and 16 controls, so the direction is credible but the number should not be treated as precise. This article is therefore positioned as "a reasonable plan consistent with current tendon loading science", not as a protocol validated by a randomised controlled trial in jiu-jitsu athletes.
Pain you can cover with one finger deserves a 12-week plan
Put all the data side by side and patellar tendinopathy occupies an awkwardly symmetrical position in jiu-jitsu: it is the easiest injury to overlook and also one of the injuries with the clearest solution in the literature. There is no swelling, no catching, and imaging is often normal, so it is almost never captured in injury statistics; yet the tendon loading science accumulated over the past fifteen years has made 12 weeks of progressive strength training one of the few conservative approaches supported by randomised controlled trials with effects that hold out to six months.
Reasoning backwards from Kettunen's 53% dropout rate, the real cost of this injury is not any single painful session but the way it slowly changes how a person trains: first you avoid pressuring half guard, then you avoid every pass that requires kneeling, and finally your technical repertoire shrinks to the handful of moves that do not hurt. Technical atrophy usually arrives earlier than the pain does, and it is harder to reverse.
So the next time it stings below the kneecap while you are kneeling on someone, you do not need to leave the mat immediately, and you also should not spend two years proving to yourself that it will not resolve on its own. Locate it with a finger, do one single-leg decline squat and record the score, fill in a VISA-P, then turn the next 12 weeks of lower-body days into 6-second-per-rep strength training. Tendons do not get stronger because you rest, they get stronger because you load them the right way.
FAQ
Can I keep training jiu-jitsu with patellar tendon pain?
In most cases yes, but you have to train by rules rather than by feel. The current consensus on tendon load management is this: keep pain during the session at or below 3 on a 10-point scale, and symptoms must return to the previous day's baseline within 24 hours, with no worsening of morning stiffness or first-step pain. If you meet both conditions you can keep your mat time, you simply need to cut back the share of kneeling pressure positions and deep squat-style stand-ups. Stopping completely is counterproductive, because tendon load tolerance is maintained by loading, and prolonged unloading only raises the bar you have to clear when you come back.
Are patellar tendinopathy, jumper's knee and patellar tendinitis the same thing?
Jumper's knee and patellar tendinopathy describe the same clinical problem, but the old label "tendinitis" is no longer recommended. Biopsy studies show that the dominant changes in chronic tendinopathy are disorganised collagen, matrix proliferation and ingrowth of vessels and nerves, not the classic inflammatory cell infiltrate, which is why the international literature replaced tendinitis with tendinopathy. The naming difference has practical consequences: if inflammation is not the main driver, anti-inflammatories, ice and rest alone cannot fix the underlying problem, and what you need is progressive reloading.
Do patellar straps or knee pads help with tendon pain in BJJ?
A patellar strap can help symptoms in the short term, but it does not replace loading. Its proposed mechanism is altering force distribution across the tendon and providing proprioceptive feedback, and some people report lower perceived pain while wearing one, which is symptom management rather than tissue repair. Jiu-jitsu adds a practical layer: straps and rigid braces can snag the gi or bother your partner during rolls, and some gyms and competitions restrict equipment. The pragmatic order is to use padded knee pads to cut the direct contact pressure of kneeling while keeping HSR training as the main intervention.
How long does patellar tendinopathy take to get better?
Judging by the standard protocols in the literature, count in blocks of at least 12 weeks. In the randomised controlled trial by Kongsgaard et al. published in Scandinavian Journal of Medicine and Science in Sports in 2009, all three intervention arms ran for 12 weeks, and the heavy slow resistance (HSR) group maintained its improvement at both 12 weeks and 6-month follow-up with the highest satisfaction. Clinically the VISA-P questionnaire is used for tracking, and a change of more than 13 points is considered a meaningful improvement. If VISA-P has barely moved after 12 weeks of consistent training, the diagnosis or the loading dose needs to be re-examined.
When should I see a doctor instead of rehabbing on my own?
If you cannot actively extend the knee, the kneecap has visibly ridden up, or you heard a snap, see a doctor immediately to rule out tendon rupture. Other situations that need professional assessment include: pain located at the joint line or the medial or lateral side rather than the inferior pole of the patella, recurrent joint swelling and effusion, clear catching or locking, night pain and pain at rest, fever with redness, heat and swelling, and local tenderness over the tibial tubercle in adolescents. These patterns point to meniscus damage, intra-articular pathology, infection or growth plate problems, and they are managed completely differently from patellar tendinopathy.
References
1. Nutarelli S, et al. (2023). Epidemiology of patellar tendinopathy in athletes and the general population: a systematic review and meta-analysis. Orthop J Sports Med;11(6):23259671231173659. PubMed 37347023 (28 studies, 28,171 participants; prevalence 18.3% in athletes versus 0.1% in the general population, volleyball 24.8%, basketball 20.8%, 21.3% in those aged 18 and over versus 10.1% under 18, the source of the prevalence table in this article)
2. Eustaquio JMJ, et al. (2021). Knee injuries prevalence in Brazilian jiu-jitsu: epidemiological study. Acta Ortop Bras;29(6):327-330. PubMed 34849099 (Cross-sectional survey of 198 amateur and professional jiu-jitsu practitioners, 29.8% knee injury rate, with the medial collateral ligament at 38%, sprain mechanisms at 86% and conservative management at 65%, supporting the argument that BJJ knee injury statistics are uniformly acute sprains and miss overuse cases)
3. Kettunen JA, et al. (2002). Long-term prognosis for jumper's knee in male athletes. A prospective follow-up study. Am J Sports Med;30(5):689-92. PubMed 12239003 (15-year follow-up; 53% (9 of 17) of the jumper's knee group left their sporting career because of knee problems versus 7% (1 of 14) of controls; only 20 jumper's knee cases and 16 controls responded, so the small sample means the values are directional)
4. Maffulli N, et al. (2017). The Royal London Hospital Test for the clinical diagnosis of patellar tendinopathy. Muscles Ligaments Tendons J;7(2):315-22. PubMed 29264343 (With high-resolution ultrasound as the reference standard: Royal London test sensitivity 88% and specificity 98%, manual palpation sensitivity 98% and specificity 94% (P = 0.01), the source of both test values and the recommendation to use them together)
5. Kongsgaard M, et al. (2009). Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy. Scand J Med Sci Sports;19(6):790-802. PubMed 19793213 (39 male patients with patellar tendinopathy randomised to corticosteroid injection, eccentric decline squat or heavy slow resistance training for 12 weeks each; corticosteroid was good short term but poor long term, while heavy slow resistance training was effective both short and long term, the basis for the 12-week prescription and the 6-month follow-up difference described here)
6. Rio E, et al. (2015). Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. Br J Sports Med;49(19):1277-83. PubMed 25979840 (Single-blind randomised crossover trial in 6 volleyball players; isometric contractions reduced single-leg decline squat pain from 7.0 ± 2.04 to 0.17 ± 0.41 for at least 45 minutes and raised maximal voluntary contraction by 18.7 ± 7.8%, the source of the "open with isometrics during symptomatic phases" advice here; sample of only 6)