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Do isometric and isotonic exercise programs reduce pain in athletes with patellar tendinopathy in-season? A randomised clinical trial

Published:December 07, 2015DOI:https://doi.org/10.1016/j.jsams.2015.11.006

      Abstract

      Objectives

      Many athletes with patellar tendinopathy participate in sports with symptoms during or after activities. Current treatments do not decrease pain in-season; eccentric exercises in-season result in an increase in pain. This study examined if isometric and isotonic exercises relieved pain in competing athletes with patellar tendinopathy.

      Design

      Randomised clinical trial.

      Methods

      Jumping athletes with patellar tendinopathy playing at least three times per week participated in this study. Athletes were randomised into an isometric or isotonic exercise group. The exercise programs consisted of four isometric or isotonic exercise sessions per week for four weeks. Pain during a single leg decline squat (SLDS) on a Numeric Rating Scale (NRS; 0–10) was used as the main outcome measure; measurements were completed at baseline and at 4-week follow-up.

      Results

      Twenty-nine athletes were included in this study. Median pain scores improved significantly over the 4-week intervention period in both the isometric group (Z = −2.527, p = 0.012, r = −0.63) and isotonic group (Z = −2.952, p = 0.003, r = −0.63). There was no significant difference in NRS pain score change (U = 29.0, p = 0.208, r = 0.29) between the isometric group (median (IQR), 2.5 (1–4.5)) and isotonic group (median (IQR), 3.0 (2–6)).

      Conclusions

      This is the first study to show a decrease in patellar tendon pain without a modification of training and competition load and the first study to investigate isometric exercises in a clinical setting. Both isometric and isotonic exercise programs are easy-to-use exercises that can reduce pain from patellar tendinopathy for athletes in-season.

      Keywords

      1. Introduction

      Patellar tendinopathy, also known as jumper's knee, is an overuse injury of the patellar tendon that causes pain and dysfunction. It is a common injury in sports that involve explosive movements that load the extensor mechanism of the knee.
      • Lian O.B.
      • Engebretsen L.
      • Bahr R.
      Prevalence of jumper's knee among elite athletes from different sports—a cross-sectional study.
      High prevalence rates are reported in jumping sports such as volleyball and basketball (45% and 32% in elite athletes respectively).
      • Lian O.B.
      • Engebretsen L.
      • Bahr R.
      Prevalence of jumper's knee among elite athletes from different sports—a cross-sectional study.
      Many different modalities are used for the treatment of patellar tendinopathy, however treatments like injections, shockwave and surgery require athletes to cease sporting activities.
      • Muccioli G.M.M.
      • Zaffagnini S.
      • Tsapralis K.
      • et al.
      Open versus arthroscopic surgical treatment of chronic proximal patellar tendinopathy. A systematic review.
      • Van Ark M.
      • Van den Akker-Scheek I.
      • Meijer L.
      • et al.
      An exercise-based physical therapy program for patients with patellar tendinopathy after platelet-rich plasma injection.
      • Zwerver J.
      • Hartgens F.
      • Verhagen E.
      • et al.
      No effect of extracorporeal shockwave therapy on patellar tendinopathy in jumping athletes during the competitive season: a randomized clinical trial.
      Exercise may be the best treatment for tendinopathies as histopathological changes and clinical improvements in pain and function have been demonstrated.
      • Kjaer M.
      • Langberg H.
      • Heinemeier K.
      • et al.
      From mechanical loading to collagen synthesis, structural changes and function in human tendon.
      Most studies have been conducted using eccentric exercise protocols
      • Alfredson H.
      • Pietila T.
      • Jonsson P.
      • et al.
      Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis.
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Stanish W.D.
      • Rubinovich R.M.
      • Curwin S.
      Eccentric exercise in chronic tendinitis.
      and early studies showed positive results. However, eccentric exercises may not be effective when used in-season and might even make symptoms worse in athletes with patellar tendon pathology.
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Visnes H.
      • Bahr R.
      The evolution of eccentric training as treatment for patellar tendinopathy (jumper's knee): a critical review of exercise programmes.
      • Visnes H.
      • Hoksrud A.
      • Cook J.
      • et al.
      No effect of eccentric training on jumper's knee in volleyball players during the competitive season: a randomized clinical trial.
      Moreover, when eccentric exercise was used prophylactically in-season in asymptomatic soccer players with pathology on imaging, there was a higher risk of developing a jumper's knee.
      • Fredberg U.
      • Bolvig L.
      • Andersen N.T.
      Prophylactic training in asymptomatic soccer players with ultrasonographic abnormalities in Achilles and patellar tendons: the Danish Super League Study.
      Many athletes play with jumper's knee symptoms and pain negatively affects capacity to train and perform in matches. They cope with their injury because pain often decreases after warm-up but returns and is worse the day after activity. Isometric and isotonic exercises have the potential to decrease pain while continuing sport activities.
      • Naugle K.M.
      • Fillingim R.B.
      • Riley III, J.L.
      A meta-analytic review of the hypoalgesic effects of exercise.
      • Kongsgaard M.
      • Qvortrup K.
      • Larsen J.
      • et al.
      Fibril morphology and tendon mechanical properties in patellar tendinopathy: effects of heavy slow resistance training.
      Isotonic muscle contractions (heavy slow resistance training 3–5 times per week) resulted in a significant reduction in pain after a 12-week program.
      • Kongsgaard M.
      • Kovanen V.
      • Aagaard P.
      • et al.
      Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy.
      • Cannell L.J.
      • Taunton J.E.
      • Clement D.B.
      • et al.
      A randomised clinical trial of the efficacy of drop squats or leg extension/leg curl exercises to treat clinically diagnosed jumper's knee in athletes: pilot study.
      Isometric exercises have been found to decrease tendon pain in athletes with patellar tendinopathy in the short-term (45 min).
      • Rio E.
      • Kidgell D.
      • Cook J.
      Exercise reduces pain immediately and affects cortical inhibition in patellar tendinopathy.
      It is unknown if isometric exercises can decrease tendon pain over a longer period of time and if repeated isometric exercises are beneficial.
      The aim of this study was to examine whether isometric and isotonic exercises relieve pain in competing athletes with patellar tendinopathy. It was hypothesised that both isometric and isotonic exercises would decrease pain in athletes with patellar tendinopathy in-season and that isometric exercises would decrease patellar tendon pain more than isotonic exercises.

      2. Methods

      This study was a randomised trial of two interventions—participants were randomly assigned to one of two exercise intervention groups. The study was approved by the Monash University Human Research Ethics Committee (MUHREC), Australia (CF12/0230–2012000067). All participants provided written informed consent. This trial was registered in the Australian New Zealand Clinical Trial Registry (ACTRN12613000871741).
      Participants were volleyball and basketball players (16–32 years) playing or training at least three times per week, presenting with patellar tendinopathy diagnosed by an experienced physiotherapist. Inclusion criteria consisted of focal tendon pain at the inferior or superior pole of the patella and a history of exercise associated knee pain at the same spot. Exclusion criteria were existence of other knee pathology, previous patellar tendon rupture, previous patellar tendon surgery, inflammatory disorders, metabolic bone diseases, type II diabetes, use of fluroquinolones or corticosteroids in the last 12 months, known familial hypercholesterolemia and chronic pain conditions.
      Players from Victorian volleyball leagues and basketball leagues who played or trained at least three times per week were approached at their game or training venue. After baseline measurements were performed, participants were given an exercise program. Participants were randomised to an exercise program by the draw of a sealed opaque envelope from 40 identical envelopes that were randomised using a randomisation table created by computer software (20 in each group). The program was demonstrated (including repetition maximum testing) at the gym where they were going to perform their exercises. Every week participants were followed-up in person or by phone, asking participants if they encountered any problems with the exercise program. After the 4-week exercise program baseline measurements were repeated.
      Both groups performed a 4-week exercise program with exercises performed four times per week. The isometric and isotonic exercise program were matched for time under tension and rest. Pilot testing was used to ensure that the protocols were matched for rate of perceived exertion. The isometric exercise consisted of 5 × 45 s single leg isometric contractions of each leg on a leg extension machine. Isometric contractions were performed at 80% of maximal voluntary contraction with a knee joint angle of 60°. Isotonic exercise consisted of four sets of eight repetitions of single leg isotonic contractions of each leg on a leg extension machine. Isotonic contractions consisted of a 3-s concentric phase immediately followed by a 4-s eccentric phase and were performed on 80% of 8 repetitions maximum. After performing the exercises for each leg, participants rested for 15 s before continuing with the first leg again. Weight was increased by 2.5% every week if possible. If pain was experienced during an exercise or if participants were not able to complete their repetitions with proper execution (e.g., shaking during the contraction), they were instructed to lower the weight for the following repetitions and complete the entire session (equal time under tension). Audio files that counted the timing of the exercises were provided for use during their exercises to standardise the speed of repetition and rest and therefore time under tension for all participants.
      The primary outcome measure was pain during a single leg decline squat (SLDS) scored on a numeric rating scale (NRS) (0–10), which is a provocative clinical test to monitor tendon pain.
      • Purdam C.R.
      • Cook J.L.
      • Hopper D.M.
      • et al.
      Discriminative ability of functional loading tests for adolescent jumper's knee.
      • Zwerver J.
      • Bredeweg S.W.
      • Hof A.L.
      Biomechanical analysis of the single-leg decline squat.
      A 2-point difference on the NRS was considered to be a minimal clinical important difference (MCID).
      • Salaffi F.
      • Stancati A.
      • Silvestri C.A.
      • et al.
      Minimal clinically important changes in chronic musculoskeletal pain intensity measured on a numerical rating scale.
      The VISA-P, a questionnaire on pain and function of the knee,
      • Visentini P.J.
      • Khan K.M.
      • Cook J.L.
      • et al.
      The VISA score: an index of severity of symptoms in patients with jumper's knee (patellar tendinosis).
      was also completed. The score on the VISA-P ranges from 0 to 100, 100 being a completely asymptomatic and fully functioning athlete. The MCID of the VISA-P was considered to be 13 points.
      • Hernandez-Sanchez S.
      • Hidalgo M.D.
      • Gomez A.
      Responsiveness of the VISA-P scale for patellar tendinopathy in athletes.
      Participants were asked about their average tendon pain compared to the beginning of the exercise program on a global rating of change scale from very much worse (−4) to very much better (+4). A diary was also provided to the participants, in which they reported completed exercise sessions. These data were used to calculate adherence to the exercise program. All outcome measures were administered at baseline and four weeks later at the end of the program. Only the worst knee was used in the analysis of the data in athletes with bilateral patellar tendinopathy. NRS pain scores on the SLDS had a non-normal distribution, and non-parametric tests were used to test for differences. A Wilcoxon signed rank test was conducted to test for differences between baseline and follow-up measurements for NRS pain score during SLDS within each group. A Mann–Whitney U-test was used to test for differences between the isometric and isotonic intervention group. As secondary analyses, the same tests were performed for the VISA-P score. Analyses were conducted using IBM SPSS Statistics 20 software and an alpha of 0.05 was considered significant.

      3. Results

      Participants were included in the trial between August 2013 and July 2014 (Fig. 1). Thirteen participants were randomised to the isometric group and 16 to the isotonic group. Group characteristics did not differ at baseline (Table 1) and mean adherence to the exercise program was 81%. Median pain scores improved significantly over the 4-week intervention period within the isometric group (Z = −2.527, p = 0.012, r = −0.63) and within the isotonic group (Z = −2.952, p = 0.003, r = −0.63) (Table 2).There was no significant difference in NRS pain score change (U = 29.0, p = 0.208, r = 0.29) between the isometric group (median (IQR), 2.5 (1–4.5)) and isotonic group (median (IQR), 3.0 (2–6)) (Table 2). Median VISA-P scores also improved significantly over the 4-week intervention period within the isometric group (Z = −2.201, p = 0.028, r = −0.55) and within the isotonic group (Z = −2.952, p = 0.003, r = −0.66). The median change in VISA-P was 9 points (3–25). There was no significant difference in VISA-P score change (U = 39.5, p = 0.965, r = −0.01) between the isometric group and isotonic group (Table 2). The median perceived global rating of change (−4 to +4) for tendon pain at follow-up compared to pre-intervention was +2.3 (2.0–3.0).
      Figure thumbnail gr1
      Fig. 1Flow chart of participants included in the trial.
      Table 1Characteristics of the population.
      CharacteristicsIsometric group (n = 13)Isotonic group (n = 16)Total (n = 29)
      Age, year

      mean ± SD (range)
      22.9 ± 4.9 (16–30)23.1 ± 4.7 (17–32)23.0 ± 4.7 (16–32)
      Sex (male/female)12/115/127/2
      Duration of symptoms, months

      mean ± SD (range)
      30.8 ± 26.1 (1–84)39.6 ± 39.1 (1–120)35.8 ± 33.8 (1–120)
      BMI, kg/m2

      mean ± SD (range)
      23.7 ± 2.0 (19.8–26.5)24.2 ± 3.7 (18.9–34.7)24.0 ± 3.0 (18.9–34.7)
      Unilateral/bilateral symptoms6/77/913/16
      Table 2Main outcome measures at baseline and follow-up for the intervention groups and total population.
      MeasurementsIsometric groupIsotonic groupTotal
      NRS pain SLDS—baseline median (IQR)6.3 (5.3–7.0)

      n = 8
      5.5 (4.0–6.0)

      n = 11
      6.0 (4.0–7.0)

      n = 19
      NRS pain SLDS—4 week median (IQR)4.0 (2.0–5.0)
      Minimal clinical important difference from baseline.
      ,
      Significant difference from baseline (p<0.05).


      n = 8
      2.0 (1.0–3.0)
      Minimal clinical important difference from baseline.
      ,
      Significant difference from baseline (p<0.05).


      n = 11
      2.0 (2.0–3.8)
      Minimal clinical important difference from baseline.
      ,
      Significant difference from baseline (p<0.05).


      n = 19
      VISA-P—baseline median (IQR)66.5 (59.5–75.8)

      n = 8
      69.5 (55.0–75.8)

      n = 10
      69.5 (58.3–75.3)

      n = 18
      VISA-P—4 week median (IQR)75.0 (72.5–87.0)
      Significant difference from baseline (p<0.05).


      n = 8
      79.0 (67.0–86.0)
      Significant difference from baseline (p<0.05).


      n = 10
      77.5 (70.8–86.5)
      Significant difference from baseline (p<0.05).


      n = 18
      Number of exercise performed per week median (IQR)3.0 (2.5–3.9)

      n = 9
      3 (2.75–3.75)

      n = 11
      3.1 (2.8–3.8)

      n= 20
      Tendon pain change compared to pre-intervention on GRC (−4 to +4), median (IQR)+2.5 (.5–3.0)

      n = 9
      +2 (2–3)

      n = 11
      +2.3 (2.0–3.0)

      n = 20
      GRC = global rating of change scale; IQR = Inter quartile range.
      * Significant difference from baseline (p< 0.05).
      a Minimal clinical important difference from baseline.

      4. Discussion

      This study showed a clinically important decrease in pain in athletes with patellar tendinopathy during a season with both isometric and isotonic exercises. The VISA-P also showed a significant improvement over time (close to MCID), which indicates that not only pain but also function of the knee improved in this population. No significant difference between the isometric and isotonic exercise group was found. In the field of tendinopathy, where exercise is the primary and most effective treatment available,
      • Zwiers R.
      • Wiegerinck J.I.
      • van Dijk C.N.
      Treatment of midportion Achilles tendinopathy: an evidence-based overview.
      • Larsson M.E.
      • Käll I.
      • Nilsson-Helander K.
      Treatment of patellar tendinopathy—a systematic review of randomized controlled trials.
      relatively few studies have been conducted on exercise programs for patellar tendinopathy.
      • Malliaras P.
      • Barton C.J.
      • Reeves N.D.
      • et al.
      Achilles and patellar tendinopathy loading programmes.
      Improvements in pain have been reported when resistance exercise/training is used as rehabilitation. Kongsgaard et al.
      • Kongsgaard M.
      • Kovanen V.
      • Aagaard P.
      • et al.
      Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy.
      showed a similar improvement in pain after 12 weeks of heavy slow resistance training as our study. After six weeks of the heavy slow isotonic exercise rehabilitation program, Cannell et al.
      • Cannell L.J.
      • Taunton J.E.
      • Clement D.B.
      • et al.
      A randomised clinical trial of the efficacy of drop squats or leg extension/leg curl exercises to treat clinically diagnosed jumper's knee in athletes: pilot study.
      also found a decrease in pain. Other studies have focussed on eccentric exercises as rehabilitation, and these exercise protocols also relieved pain in non-competing athletes.
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Jonsson P.
      • Alfredson H.
      Superior results with eccentric compared to concentric quadriceps training in patients with jumper's knee: a prospective randomised study.
      • Young M.A.
      • Cook J.L.
      • Purdam C.R.
      • et al.
      Eccentric decline squat protocol offers superior results at 12 months compared with traditional eccentric protocol for patellar tendinopathy in volleyball players.
      Eccentric exercise in-season may have no effect or even worsens patellar tendinopathy symptoms.
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Visnes H.
      • Bahr R.
      The evolution of eccentric training as treatment for patellar tendinopathy (jumper's knee): a critical review of exercise programmes.
      • Visnes H.
      • Hoksrud A.
      • Cook J.
      • et al.
      No effect of eccentric training on jumper's knee in volleyball players during the competitive season: a randomized clinical trial.
      The findings of our study using isotonic and isometric exercise are in contrast with eccentric exercises in-season.
      An important difference between the exercise programs in our study compared to previous studies investigating eccentric exercises on a decline board,
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Visnes H.
      • Bahr R.
      The evolution of eccentric training as treatment for patellar tendinopathy (jumper's knee): a critical review of exercise programmes.
      • Kongsgaard M.
      • Kovanen V.
      • Aagaard P.
      • et al.
      Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy.
      is that eccentric exercises on a decline board were designed to provoke pain in the tendon.
      • Purdam C.R.
      • Jonsson P.
      • Alfredson H.
      • et al.
      A pilot study of the eccentric decline squat in the management of painful chronic patellar tendinopathy.
      • Zwerver J.
      • Bredeweg S.W.
      • Hof A.L.
      Biomechanical analysis of the single-leg decline squat.
      Since participants in this study were still participating in basketball or volleyball matches and training sessions (exposing their tendons to a high tendon load), provocative loads for the patellar tendon should be avoided. An essential part of the exercises performed in our study is that the exercises are a high load for the muscle, however not in a way that that is provocative to the tendon and may increase pain.
      • Cook J.L.
      • Purdam C.R.
      The challenge of managing tendinopathy in competing athletes.
      The dosage (e.g., number of repetitions, days per week and duration of a contraction) and type of exercise are important characteristics of an exercise program. A high percentage of repetition maximum (RM) has been used in our study for the isometric (80% 1RM) as well as the isotonic exercises (80% 8RM). Beneficial effects from rehabilitation for tendons require high load per repetition.
      • Arampatzis A.
      • Peper A.
      • Bierbaum S.
      • et al.
      Plasticity of human Achilles tendon mechanical and morphological properties in response to cyclic strain.
      Furthermore, a high percentage of RM in leg extension exercises has been shown to improve muscle strength and neural activation.
      • Kubo K.
      • Ikebukuro T.
      • Yata H.
      • et al.
      Effects of training on muscle and tendon in knee extensors and plantar flexors in vivo.
      The leg extension machine was used to isolate the load through the quadriceps muscle and patellar tendon as much as possible. Despite the positive effect of exercise for tendinopathy, both in research labs and in the clinic, the precise mechanism of effect, optimal dosage and loading strategy has not yet been determined and further research is required.
      Previous studies investigating short-term effects of isometric and isotonic exercises on (tendon) pain
      • Naugle K.M.
      • Fillingim R.B.
      • Riley III, J.L.
      A meta-analytic review of the hypoalgesic effects of exercise.
      • Rio E.
      • Kidgell D.
      • Cook J.
      Exercise reduces pain immediately and affects cortical inhibition in patellar tendinopathy.
      have found a decrease in pain post exercise. Isometric exercises resulted in a significant decrease in tendon pain and cortical inhibition (present at elevated levels in patellar tendinopathy); pain relief lasted for at least 45 min after isometric exercises, while a much smaller decrease in pain and no change in cortical inhibition was found after isotonic exercises.
      • Rio E.
      • Kidgell D.
      • Cook J.
      Exercise reduces pain immediately and affects cortical inhibition in patellar tendinopathy.
      In contrast to these studies on the acute effects of isometric and isotonic exercise, our study found no difference between isotonic and isometric exercise after four weeks. Previous studies suggest it may be that isometric exercises have a greater effect in reducing acute pain, while isotonic exercise may cause a more gradual decrease in pain.
      • Cannell L.J.
      • Taunton J.E.
      • Clement D.B.
      • et al.
      A randomised clinical trial of the efficacy of drop squats or leg extension/leg curl exercises to treat clinically diagnosed jumper's knee in athletes: pilot study.
      • Rio E.
      • Kidgell D.
      • Cook J.
      Exercise reduces pain immediately and affects cortical inhibition in patellar tendinopathy.
      How exercises affect pain is still unclear. An ongoing debate about pain in (patellar) tendinopathy exists; it is still unclear if pain is physiological or pathophysiological or a combination in patellar tendinopathy.
      • Rio E.
      • Moseley L.
      • Purdam C.
      • et al.
      The pain of tendinopathy: physiological or pathophysiological?.
      Our study has an important contribution to the conservative management of patellar tendinopathy, in particular for in-season athletes with patellar tendinopathy. It also confirms the recent shift in the literature away from isolated eccentrics for the rehabilitation of patellar tendinopathy.
      • Woodley B.L.
      • Newsham-West R.J.
      • Baxter G.D.
      Chronic tendinopathy: effectiveness of eccentric exercise.
      • Scott A.
      • Docking S.
      • Vicenzino B.
      • et al.
      Sports and exercise-related tendinopathies: a review of selected topical issues by participants of the second International Scientific Tendinopathy Symposium (ISTS) Vancouver 2012.
      The shift away from isolated eccentric exercises does not seem to be exclusive for patellar tendinopathy, a similar shift in the literature seems to take place in other tendinopathies as well.
      • Habets B.
      • Cingel R.
      Eccentric exercise training in chronic mid-portion Achilles tendinopathy: a systematic review on different protocols.
      • Kulig K.
      • Reischl S.F.
      • Pomrantz A.B.
      • et al.
      Nonsurgical management of posterior tibial tendon dysfunction with orthoses and resistive exercise: a randomized controlled trial.
      • Silbernagel K.G.
      • Thomee R.
      • Eriksson B.I.
      • et al.
      Continued sports activity, using a pain-monitoring model, during rehabilitation in patients with Achilles tendinopathy: a randomized controlled study.
      More high quality research in this field is needed to find the best treatment strategy for every phase of tendinopathy.
      • Cook J.L.
      • Purdam C.R.
      Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy.
      The current study had relatively small numbers in the intervention groups. Despite small group sizes, we found significant improvements in pain scores in both groups. There were no data on which to base an a priori sample size calculation, as this was the first study to compare these exercise programs. The group sizes in this study are similar to other studies investigating exercise programs for patellar tendinopathy.
      • Malliaras P.
      • Barton C.J.
      • Reeves N.D.
      • et al.
      Achilles and patellar tendinopathy loading programmes.
      The 4-week follow-up was relatively short as the study was designed to investigate if an (initial) decrease in patellar tendon pain could be achieved in competing athletes. Another limitation was that sessions were not supervised and no random checks for compliance in the gym were performed. This was a real-life study, supervision of all patients was therefore not feasible and it reflects what is done in clinical practice. The chance to successfully implement the exercise programs in practice with a high adherence of the patient might also be greater than in studies with a more controlled environment.

      Conclusion

      This study was, to our knowledge, the first to find positive results for athletes with patellar tendinopathy without modification of the training and competition load and it was the first study to investigate isometric exercises in a clinical setting. Both isometric and isotonic exercise programs can reduce pain and improve function in athletes with patellar tendinopathy in-season.

      Practical implications

      • This study shows that isometric and isotonic exercises can decrease pain in athletes with patellar tendinopathy in-season.
      • The exercises are easy to perform and also have the advantage over conventional eccentric training that they are less time-consuming for the athlete.
      • The programs should be applied in a situation in which an athlete has pain in-season or in the first weeks after a patient comes to a sports medicine/physiotherapy clinic with patellar tendinopathy symptoms.
      • Pain decrease in the relatively short term possibly increases the adherence of patients with a program and reduces the chance of transition to invasive and more expensive treatments.

      Acknowledgements

      The first author has been supported by Foundation “De Drie Lichten”, “Wetenschappelijk College Fysiotherapie” and “Anna Foundation | NOREF” in The Netherlands for this project. This study has also been supported by the Australian Institute of Sport. Prof Cook was supported by the Australian centre for research into sports injury and its prevention (ACRISP), which is one of the International Research Centres for the Prevention of Injury and Protection of Athlete Health supported by the International Olympic Committee (IOC). Prof Cook is a NHMRC practitioner fellow (ID 1058493).

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