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Introduction
Tendinopathy (tendon pain and dysfunction) in athletes is difficult to manage. Eccentric exercise, which is the most commonly prescribed exercise for the treatment of tendinopathy, 1-4 is often painful to complete. 5 Tendinopathy is especially problematic in the competitive season, when there are constant time and performance pressures. 6 Where eccentric exercise has been completed in the competitive season, there has been poor adherence due to increased pain, and either no benefit 7 or worse outcomes. 8 Athletes are reluctant to cease sporting activity to complete eccentric exercise programmes 9 and they may be more compliant with exercise strategies that reduce pain to enable ongoing sports participation.
Exercise-induced pain relief would have several clinical benefits. First, athletes may be able to manage their pain with exercises either immediately prior to or following activity. Second, exercise is non-invasive and without potential pharmacological side effects or sequelae of long-term use that are associated with some interventions. Third, exercises that reduce pain are likely to have greater adherence. Therefore, alternative muscle contraction types, other than eccentric exercises, warrant investigation.
Isotonic exercise (heavy, slow, concentric and eccentric resistance training) has been shown to be as effective as eccentric only exercise in patellar tendinopathy (PT) for tendon pain and activity participation; 1 10 however, the immediate effect of isotonic exercise on pain has not been studied. Isometric muscle contractions have been shown to reduce pressure pain thresholds in normal participants, 11 12 but have not been investigated in tendon pain. The pain inhibition following a local isometric contraction, demonstrated in previous studies of normal participants, is widespread; 12 this indicates central nervous system (CNS) involvement and warrants investigation.
The effect of exercise on the motor cortex may be modulated in the presence of pain. Exercises that are painful to complete may change motor control and cause cortical reorganisation, as pain itself is known to alter cortical representation. 13
This may contribute to persistence of tendon pain through the continuation of aberrant motor patterns. In the CNS, the primary regions involved in motor control are the primary motor cortex and corticospinal tract, which activate the motor neurone pool and control motor function. Changes in motor output, however, are a combination of changes in the excitatory and inhibitory neural pathways. This...