Patellar tendinopathy is a common condition affecting a variety of individuals. Characteristics of this condition involve pain on the anteromedial aspect of the knee between patella and tibial tuberosity[1-7]. Additionally, research has shown mechanical properties of tendons can become dysfunctional in individuals with tendinopathies[ 1-4, 8-10]. Eccentric exercise is an intervention believed to specifically target tendons via the tension loading of musculotendinous units in an elongated position[11-15]. Moreover, eccentric exercise has long been held as the gold standard in managing patellar tendinopathies.

While many hold eccentric exercise as the gold standard, research has yet to show whether other forms of exercise are equally or possibly more beneficial. Additionally, the question still remains whether other forms of exercise change pain levels in addition to eccentric exercise. Recent research appears to dissuade the belief that eccentric exercise truly triumphs other forms of exercise in addressing pain and/or tendon mechanical properties[8, 11, 16].

Isometric exercise, for example, can theoretically improve tendon properties, as the muscle unit must generate significant tension on a tendon at a fixed load, thus improving tendon stiffness. While eccentric exercise theoretically should increase loading of the tendon, in reality, the muscle is simply contracting to decrease velocity of the weight lowering[17]. In concentric-based exercise, the muscle must produce sufficient force to overcome load, and so, transfer of the force through its tendinous unit to the bone. The physiological function of concentric exercise, therefore, could yield an improved outcome of tendon properties and pain, as the tendon should experience less repetitive strain[18].

This systematic review sought to investigate the relationship between various forms of exercise with pain and function of patellar tendinopathies. The purpose of this review is identifying the most effective exercise for addressing (1) pain, (2) tendon properties, or (3) both. There has not been a systematic review conducted on this topic recently, and newer research on this topic has emerged. Due to that fact, we believe this systematic review was critical to perform at this time.

A literature review was performed across four databases: MEDLINE Complete, PubMed, CINHAL Complete, and Journal of Science and Medicine in Sports. The search limits required peer-reviewed articles, full text availability, timeline of 2018-2022, and written in English. Selection criteria included RCTs, subjects 18＋ years old, and intervention including eccentric exercises. Each article was evaluated to have greater than a 6/10 on the PEDro scale by investigators.

Of the 145 articles identified during research, only 11 met the standard for further investigation, and only 8 met our selection criteria. All 8 studies were randomized control trials with sample sizes ranging from 20-76 participants(n＝378) who all had pain at the inferior pole of the patella or were diagnosed via ultrasound for patellar tendinopathy. The average PEDro score for this review was 8.75/12. The following peerreviewed articles were examined for patella tendinopathy. Breda et al. found that the progressive tendon-loading exercise therapy (PTLE) significantly decreased patellar tendon stiffness after 12 and 24 weeks[11]. Compared to the eccentric exercise therapy (EET), both groups showed significant improvements in their VISA-P scores at 12 and 24 weeks, however the PTLE group showed larger improvements overall. In Breda SJ et al., they found that both the PTLE and EET groups showed significant improvements in VISA-P scores at 24 weeks but favored the PTLE group. The return to sports was not statistically significant at 12 or 24 weeks for either group. VAS pain scores were also significantly lower in the PTLE group at 24 weeks compared to the EET group[16].

In Lee W-C et al. they could not find that combining exercise and extracorporeal shock wave therapy was more effective than eccentric exercise alone[8]. Lopez- Royo et al. found that eccentric exercise combined with percutaneous needle electrolysis group demonstrated significant improvements 1 month post treatment and improved symptoms for 10＋ years compared to the eccentric group only. They also found that dry needling or percutaneous needling combined with eccentric training were not statistically significant when compared to eccentric therapy alone[19]. Acaroz et al discovered that maximal voluntary isometric contractions displayed increased muscle activation throughout the quadriceps muscle group[20].

Macdonald et al. demonstrated that eccentric exercises combined with concentric hip strengthening was not more effective than eccentric exercise alone[21]. Both groups showed significant improvements in LEFS and VISA-P scores at 24 weeks. The eccentric group was found to have improved triple hop jump distance scores at 4 and 12 weeks unlike the combination group. In Abian-Vicen, they used 80% 1RM single leg squat to measure improvement. Groups were broken down into no treatment, 6 second eccentric holds and 3 second eccentric holds. It was found that neither the 6 second-hold or 3 second-hold group produced statistically significant increases in muscle strength or recruitment. Therefore, the authors concluded that hold time was nebulous and that eccentric strengthening was effective versus the control group in this patient population[22].

All the participants in the chosen studies were between the ages of 18 and 50 years old with a diagnosis of patellar tendinopathy. All but one study looked at VISA-P as an outcome measure for the evaluation of symptom severity, knee function, and athletes’ ability to play sports. Additional outcome measures analyzed in the studies included pain via the VAS, quality of life via the SF-26, return to sport, patellar tendon stiffness, and patient satisfaction. All the articles had an intervention of eccentric exercise therapy(EET) for the treatment of the participants’ patellar tendinopathy. Each article compared EET to a combination of treatments. Different combinations that were analyzed included EET with progressive tendon loading exercise therapy(PTLE), EET with dry needling( DN), EET with percutaneous needle electrolysis (PNE), EET with extracorporeal shock wave therapy (ESWT), and EET with concentric hip muscle strengthening. The majority of the articles stated the combination of interventions had no significant difference in outcomes compared to EET alone. All groups showed significant improvements in outcome measures, but no significant differences between combinations and EET. The only exception is when comparing EET with PTLE. There were two articles comparing these intervention groups, and both of those articles found the same results. It was found that both EET and PTLE groups showed significant improvements, but the PTLE group showed better improvements in multiple different outcome measures, including VISA-P, patellar tendon stiffness, and VAS ratings, all following 24 weeks of treatment.

Eccentric exercise has long been held as the gold standard treatment for patellar tendinopathies[7, 9]. Therefore, the findings supporting the benefits of eccentric exercise alone weren’t surprising. However, it was surprising that combination treatments didn’t result in more improvement than EET alone as it was expected for multiple treatments in addition to eccentric exercise to show more improvements. It was also interesting that the intervention of PTLE showed better improvements compared to EET, which goes against EET being the best treatment for patellar tendinopathy. Overall, EET is a beneficial treatment of patellar tendinopathy. PTLE may be an even better treatment for patellar tendinopathy than EET, but further research is needed to support this. Additional research should also include a combination intervention of PTLE with EET to determine if the combination of those would produce better results.

There were limitations in some of the articles that also would suggest a need for further research. One article only included males in their study, and other articles included mostly male participants, affecting the generalizability to females with patellar tendinopathy. There were also three articles that potentially had bias by there being a lack of blinding and having one person conduct all treatments with a preference for one working over the other(s). Further research can pick up on these limitations which would allow for more significant interpretation and generalization of the findings. There were also strengths to this systematic review, including the selection of only randomized control trials, which allowed for more reliable interpretation of results. It was also beneficial to look at multiple different types of combination treatments with EET to broaden the findings and have a better feel on the comparative benefits of eccentric exercise alone.

There is moderate to strong mixed evidence to show the effect of eccentric exercise in combination with other interventions decreases patellofemoral pain and increased functional mobility in individuals with patellofemoral tendinopathy. However, additional benefits of eccentric exercise in combination with supplemental interventions compared to eccentric exercise alone need to be studied. Progressive tendon-loading exercise therapy showed more significant improvements in outcome measures compared to eccentric exercise therapy and requires further research to back this finding.

We have no acknowledgements.

We declare no conflict of interest.

Ethical approval was not required for this systematic review. All authors followed the PEDRo guidelines during the article search process.