• 1.

  Pain inhibits the athlete using the elastic (energy storage and release) capacity of the tendon, thereby compromising function and performance.18

• 2.

  Excessive training volume or too intense training involving the elastic function of tendons may induce tendon overload and are important factors in the onset of athletic tendinopathy.

• 3.

  Repeated training combined with too short resting periods can result in a net degradation of the matrix and lead to overuse injury.26

• 4.

  Managing tendinopathy in season centers around load management, these include strategies that control pain, both reducing aggravating loads and introducing pain-relieving loads.18

• 5.

  No medication or injectable treatment to date has been shown to alter tissue properties; only tendon load can stimulate remodeling.18

• 6.

  The only option for repeated failures to accommodate athletic load is a comprehensive rehabilitation program that can increase the load absorption ability of the tendon.18

• 7.

  Loads that reduce pain should be introduced as early as possible. Loading to decrease pain will maintain a load stimulus on the tendon that is critical to maintain cell function and matrix integrity.18

• 8.

  In painful (reactive, reactive on degenerative) tendons, isometric contraction with some load decreases pain for several hours.18 These loads can be repeated several times a day, using 40–60″ holds, 4–5 times, to reduce pain and maintain some muscle capacity and tendon load.18 In highly reactive and painful tendons, bilateral exercises, shorter holding time and fewer repetitions per day may be indicated.18 Literature supports the use of isometric work in painful conditions; sustained isometric fatiguing muscle contraction recruits segmental and/or extrasegmental descending inhibition mechanisms. The recruitment of descending inhibition results in mechanical hypoalgesia and increased pressure pain threshold in healthy individuals.18 Although there isn’t a golden standard for tendinopathy rehab,34 the guidelines (progression protocols) described in this article match the standards that other authors had previously presented and discussed.18,34,35 During the strength training sessions, the patients can use metronomes or phone apps, which provide a better control of the number of repetitions of each exercise. Adding these external stimuli has proven to maximize the effects of the workout and to prevent relapses34–36 and it must be taken into account.

• 9.

  Moderate to heavy loads with slow machine-based weights rarely cause pain.18 These exercises should be completed in the mid to inner range of the muscle-tendon unit to reduce compression at the tendon insertion.18

• 10.

  Provocative tests and objective scoring methods should be used to monitor tendon pain. As the VISA scales give substantial scores on pain during high-level activity, they are not responsive to short-term change and are best used on a month-to-month basis. Pain behavior the day after loading is the critical load response test. The athlete can monitor tendon response to training loads by completing a simple loading test every day at a similar time (avoid early morning except in the Achilles where morning pain and stiffness can be a good guide to progression).18

• 11.

  Perhaps it is the magnitude of the structural tendon response to a load what matters, as this appears to occur before pain arises or changes. An instrument that could quantify the response of a tendon to load would mean a huge advance in the management of tendinopathy.18

• 12.

  Kannus and Józsa examined 891 spontaneously ruptured tendons histologically and found that 864 (97%) of them had degenerative changes.37 If there's degeneration and tendon overload for a prolonged period, the whole tendon can become degenerative and may fail completely.38,39 Avoiding these pathological changes is the main prevention to prevent rupture of the Achilles tendon.40,41 So, in addition to improving the pain and the functional-capacity load tolerance, we must maintain or improve tendon structure to prevent tendon rupture.27

• 13.

  Mechanical loading seems to induce changes in gross morphology, mechanical properties as well as biochemical parameters of tendon tissue.42 It appears that both intense and regular exercise raise human collagen synthesis (Langberg et al., 1999,43 2000,44 200145; Miller et al., 200546), which suggests that human tendon tissue is more metabolically active in response to activity than what was previously believed.47 Intense exercise increased the formation of type I collagen during the recovery process, which suggests that intense physical loading leads to some kind of adaptation.48 Intense exercise in humans is followed by an increase of collagen synthesis and degradation. Over the first 24–36h, this response results in a net loss of collagen, but this is followed by a net synthesis 36–72h after exercise.26 An increased collagen synthesis is consistently observed as a part of the tendon adaptation response to mechanical loading,42 however the integration of new collagen into the matrix has not been shown. The COOH-terminal propeptide of type I collagen (PICP) is an indicator for collagen type I synthesis. PICP initially decreased after exercise and an increase in this marker of collagen synthesis was detected 72h after exercise.48 In healthy humans, both synthesis and degradation increased after 4 week of physical training, whereas after 11 weeks only the collagen synthesis, and not the collagen degradation, was chronically raised.48

The idea that the tendon can hypertrophy in response to mechanical loading suggests that there is a net formation of connective tissue.47 Both long-term (years) and relatively short-term (months) loading induce tendon hypertrophy. The degree of hypertrophy is rather small and seems to occur only in certain tendon regions.42 However, this appears to be true only in young people as collagen turnover after the age of 17 years is limited (Heinemeier et al., 2011).42

• 14.

  Persons who undergo regular training have a greater Achilles tendon cross-sectional area than other age-matched persons (Magnusson and Kjaer, 200349; Kongsgaard et al., 200550), which indirectly reflects a region-specific hypertrophy in response to long term loading,47 possibly during adolescent loading when the tendon is able to adapt structurally to load.

• 15.

  The potential region-specific adaptation to running appears to be far greater in men than in women. The ability of the tendon to adapt to regular loading is attenuated in women.47

• 16.

  A similar increase in collagen synthesis is seen that is independent of exercise volume (repetitions), which suggests that there is a ceiling effect in collagen synthesis.26

• 17.

  The fact that pro collagen expression is regulated the same way in the tendon regardless of the type of muscle contraction (eccentric, isometric or concentric) supports the belief that the collagen protein synthesis response is regulated by fibroblast strain.26

• 18.

  With regard to tendon mechanical properties, increased tendon stiffness is generally observed in response to large volumes of loading.42

• 19.

  Studies suggest that appropriate loading during rehabilitation of tendinopathy is the most important treatment method.19 Exercise prescription can target matrix reorganization and collagen synthesis, reduce tenocyte activity, affect tendon compliance or have an analgesic effect.19 The way the absorption of energy is distributed across the kinetic chain is important and each tendinopathy requires a holistic approach in terms of rehabilitation.15 Each component of the rehabilitation program, in particular loading, must be handled in relation to the nature, speed and magnitude of the forces applied to the muscle/tendon/bone unit in order to achieve the goals of the particular management stage (Table 1), without causing an exacerbation of the pathological state or pain. When planning a rehabilitation strategy, it is crucial to find an approach that addresses the re-education of muscle function instead as considering the tendon as an isolated unit. While early stimulus of the muscle tendon unit is typically focused on isometric muscle activation, which may include muscle stimulation, most programs advocate the progression to higher loads as guided by symptom presentation.19 Progression beyond the early isolated strength and hypertrophy loading requires functional conditioning of the muscle-tendon unit, adjusting tendon load through faster eccentric work prior to starting skill specific re-education such as landings, before introducing sports specific challenges such as sprinting and cutting.19 Consideration of the cortical effects of exercise on the motor cortex are critical.

  Table 1.

  Treatments and considerations for different tendinopathy stages.27

  Pathology	Treatment	Considerations
  Reactive tendinopathy	Load management (reduction). Assessment and modification of intensity, duration, frequency and type of load is the key clinical intervention.	1. The tendon shows no adaptation to load→back to the load used before the symptoms 2. Isometrics
  Tendon dysrepair	Process of adaptation to load→load management and exercise.	Progression of strength work: Isometrics 2. Slow dynamic functional work (first progressing the strength, then the speed) 3. Add endurance as required 4. Progressing the compression 5. Energy storage and release loads
  Degenerative tendinopathy	Process of adaptation to load→load management and exercise.	Progression of strength work: Isometrics Slow dynamic functional work (first progressing the strength, then the speed) Progressing the compression High load elastic (plyometric work)
  Reactive on degenerative	Settle the reactive tendon first and then address the degenerative component	The reactive tendinopathy settles relatively quickly

• 1.

  Removing the cause of reactive or reactive on degenerative tendinopathy (usually unaccustomed load)

• 2.

  Reduce the pain through reduction of high loads

• 3.

  Introducing isometric loads that reduce pain at early stages

• 4.

  Adapt the training volume and resting periods to the amount that the tendon can safely handle at that moment

• 5.

  Increasing load capacity of the tendon up to that required by the person by improving the structural and/or mechanical properties of the tendon

• 6.

  At the end of the progression the athlete should be able to use the elastic capacity of tendon and have regained function of the kinetic chain suitable for performance

• 1.

  Load management (reductions) removes the cause of reactive or reactive on degenerative tendinopathy.23 Assessment and modification of the intensity, duration, frequency and type of load is the key clinical intervention.23 Intensity seems to be the most important feature; therefore this is the first factor we should modify by removing intensity peaks (i.e. sprinting, sets, Fartlek, fast changes of direction, explosive jumping). Frequency is a very flexible value that we can use to adapt the load (more or less resting hours between workouts depending on the pain level of the next day). Volume seems to be the less aggressive feature, if there is enough time of rest among workouts, therefore at early stages we can keep the volume of training and change intensity and frequency. If pain increases the day after the workout we need to assess if the person should maintain regular training or adapt their training. Sometimes the athlete may need a different approach than the rest of the group (alternate days, half track, specific work,...). The change on the Numeric Pain Scale (NPS) value the day after the workout tells us if the load is tolerated. Daily NPS: NPS should not raise on the loading test the day after training.

• 2.

  Isometric exercises reduce the pain in the early phase of rehabilitation or while managing an athlete in season. Isometrics must be heavy (up to 70% maximal voluntary isometric contraction) for the musculotendinous unit and be held for a long time (up to 45s).51,52

• 3.

  How the tendon responds to the training volume and rest periods indicates if the amount of load is within the load that the tendon can safely handle. During early stages of rehabilitation high energy storage loads should not be repeated in less than 48h. Adapting the training according to the NPS observed the next day: If NPS increases keep 72h rest between workouts, if NPS does not increase, keep 48h rest between workouts, if NPS decreases it is possible to increase the frequency or intensity of high load training.

• 4.

  To Increase load capacity of the tendon up to that required by the person by improving either structural or mechanical properties of the tendon, we must increase load absorption ability of the musculotendinous unit and the kinetic chain, through progressive loading. Mechanical properties of tendon, including tendon compliance, are improved later in rehabilitation by retraining landings, running, changing pace or direction, jumps (energy storage loads). Eccentric exercises incorporated in all the loads proposed in this paper seems to be the best way to stimulate remodeling of tissue.

• 5.

  The ultimate goal is that the athlete should be able to use the elastic capacity of tendon and have regained function of the kinetic chain suitable for performance. Functional exercises and individual technical exercises that involve high loads at maximum speed, to apply high force and achieve high velocity, maximum expression of force in sports where tendon have to show their ability to store and release energy in functional and asymptomatic form.