The program is performed 3 times per week using resistance equipment in a fitness center. Each session consists of three 2-legged loaded quadriceps and lower limb kinetic chain exercises. The patients complete 3 or 4 sets in each exercise with a 2- to 3-minute rest between sets and a 5-minute rest period between the 3 exercises.

The number of repetitions decreases, and load gradually increases, every week. The repetitions and loads are as follows: 3 times, 15-repetition maximum (15RM ), in week 1; 3 times, 12RM , in weeks 2 to 3; 4 times, 10RM , in weeks 4 to 5; 4 times, 8RM , in weeks 6 to 8; and 4 times, 6RM , in weeks 9 to 12.

The program is performed 3 times per week using resistance equipment in a fitness center. Inertial flywheel resistance is a type of strength training; which is based on the increasing demands on eccentric action (breaking) after a concentric action (acceleration), due to the inertial load caused during the return movement. The patients complete 12 repetition máximum (RM) with moment inertia 0.05 m² from week 1-6 and 8 repetition máximum (RM) with moment inertia = 0.10 m² from week 6-12.

To compare the effectiveness of the inertial flywheel resistance program versus slow heavy resistance in patients with chronic patellar tendinopathy

Self-administered questionnaire. Consists of 8 items; 6 are used to evaluate pain levels or disability in daily activities and specific functional tests and 2 provide information regarding ability to play sport. Response options for each item are provided on a numeric rating scale (from 0 to 10), with higher scores indicating lower levels of pain or disability for all items other than 7 and 8, for which options have weighted scores.

Self-reported patient-specific outcome measure assess functional change, primarily in patients presenting with musculoskeletal disorders. Patients are asked to identify up to 3 important activities they are unable to perform or are having difficulty with as a result of their problem. In addition to identifying the activities, patients are asked to rate, on an 11-point scale, the current level of difficulty associated with each activity. Following the intervention, patients are asked again to rate the activities previously identified.