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Research project


Research project: To compare the effectiveness of progressive tendon-loading exercises (PTLE) with eccentric exercise therapy (EET) in patients with patellar tendinopathy.

What we do

About our project

A research team, led by Dr. Robert-Jan de Vos (sports physician) and Dr. Edwin Oei (musculoskeletal radiologist) and coordinated by Dr. Stephan Breda (resident radiology) at Erasmus MC, completed a randomised clinical trial for athletes with patellar tendinopathy.

This large project took more than 4 years to complete, and was funded by the American National Basketball Association (NBA) and GE Healthcare.

Patellar tendinopathy is a common chronic tendon injury that is characterized by load-related pain in the patellar tendon. As many as 45% of elite athletes in jumping sports like basketball and volleyball suffer from patellar tendinopathy. This often results in prolonged sport absence, which hampers an individual’s athletic performance and the health-related benefits of physical activity.

Eccentric exercise therapy (EET) has strong evidence of effectiveness for patellar tendinopathy and is also supported in medical guidelines. However, EET is pain-provoking and the therapeutic effects on pain and functional outcome are debated when applied during the competitive season. These limitations could be overcome by performing progressive tendon-loading exercises (PTLE) within the limits of acceptable pain.

Our aim was to compare the effectiveness of progressive tendon-loading exercises (PTLE) with eccentric exercise therapy (EET; usual care before the start of the project) in patients with patellar tendinopathy.

Methods of our project


In a stratified, investigator-blinded, block-randomised trial, 76 athletes with clinically diagnosed and ultrasound-confirmed patellar tendinopathy were included.

Patients were randomly assigned to PTLE within the limits of acceptable pain (interventional treatment) or pain-provoking EET (control treatment) during 24-weeks.

The PTLE protocol consisted of the following phases:
Stage 1: daily isometric exercises (single-leg leg-press or leg-extension, 5 repetitions of 45-second mid-range (60° knee flexion) quadriceps isometric hold at 70% of maximum voluntary contraction).

Isometric exercise

Stage 2: isometric exercises of stage 1 on every first day, and new isotonic exercises performed on every second day. The isotonic exercises were also performed as a single-leg leg-press or leg-extension, and started with 4 sets of 15 repetitions between 10-60° of knee flexion and slowly progressed to 4 sets of 6 repetitions with increasing load and knee angles between almost full extension and 90° flexion. 

Isotonic exercise

Stage 3: plyometric (energy-storage) loading and running exercises (jump squats, box jumps and cutting manoeuvers) on every third day, starting with 3 sets of 10 repetitions using both legs and slowly progressed to 6 sets of 10 repetitions using one leg. Isometric and isotonic exercises were continued on every first and second day, respectively. 
Stage 4: sport-specific exercises, which were characteristic for the type of sport (e.g. basketball, volleyball). Patients were instructed to gradually return to sport-specific training, performed every 2-3 days to allow for recovery from high tendon-loading exercises. In this stage, the isometric exercises of stage 1 were continued on days that the sport-specific exercises were not performed. 

Plyometric exercise 1

Plyometric exercise 2

Plyometric exercise 3

Plyometric exercise 4

Plyometric exercise 5

Progression to each subsequent stage was defined using individualised progression criteria, based on the level of pain experienced during a pain provocation test that consisted of one single-leg squat. If the VAS-score was 3 or less and exercises of the stage were performed for at least one week, progression to the next stage was advised. When all the exercises in stage 4 were performed within the limits of acceptable pain (VAS score ≤ 3 points), return to competition was recommended. In this phase, stage 1 and 2 maintenance exercises were advised twice per week.

The primary end point was clinical outcome assessed with the validated Victorian Institute of Sports Assessment (VISA-P) questionnaire after 24 weeks. Secondary outcomes included the return to sports rate, subjective patient satisfaction and exercise adherence.

Between January 2017 and July 2019, a total of 272 applications from potentially eligible athletes with suspected patellar tendinopathy were screened, of which 101 athletes were invited for eligibility assessment. Twenty-seven of these athletes were excluded, leaving 76 eligible patients remaining for inclusion.
The population (mean age, 24 years, 76% male) consisted of patients with mostly chronic patellar tendinopathy (median symptom duration 2 years). Most patients (82%) underwent prior treatment for patellar tendinopathy but failed to recover fully. 38 patients were randomised to the PTLE-group and 38 patients to the EET-group. 
The improvement in VISA-P score was significantly better for PTLE than for EET after 24 weeks (28 vs.18 points, adjusted mean between-group difference, 9 (95% confidence interval, 1 to 16); P=.023). There was a trend toward a higher return to sports rate in the PTLE-group (43% vs. 27%, P=.13). No significant between-group difference was found for subjective patient satisfaction (81% vs. 83%, P=.54) and exercise adherence between the PTLE-group and EET-group after 24 weeks (40% vs. 49%, P=.33).

In patients with patellar tendinopathy, PTLE resulted in a significantly better clinical outcome after 24 weeks than EET. PTLE are superior to EET and are therefore recommended as initial conservative treatment for patellar tendinopathy.


Funds & Grants

This research received a grant from the American National Basketball Association (NBA) and GE Healthcare.


J. Zwerver, Centre for Human Movement Sciences, Medical Centre Groningen, Groningen, The Netherlands.

E. Visser, Sportgeneeskunde Rotterdam, The Netherlands


The results of this Randomised Clinical Trial have been published in the highly rated “British Journal of Sports Medicine” – and available as open access.

Our team