Corticospinal responses to patellar tendon pain and the effects of externally paced strength training

2017-02-27T05:33:54Z (GMT) by Rio, Ebonie
Patellar tendinopathy (PT) is most commonly characterised by localised, load-dependent pain at the proximal attachment of the tendon to the patella. The quadriceps is the muscle group that loads the patellar tendon, and the corticospinal control of the quadriceps, including corticospinal excitability (CSE) and short-interval intra-cortical inhibition (SICI) was quantified in this work using transcranial magnetic stimulation. An understanding of the corticospinal control of the quadriceps and the effects of strength training in people with PT was important because: 1) the mechanisms by which tendons become painful remain poorly understood as no local nociceptive driver has been identified; 2) other musculoskeletal pain conditions are associated with changes to motor control; 3) there may be primary motor cortex (M1) changes that contribute to chronicity and recalcitrance to treatment and 4) exercise, known to be a powerful modulator of the M1, is the mainstay of treatment for PT, yet the analgesic and corticospinal responses to exercise, in particular the modes of strength training in PT is unknown and may influence rehabilitation of people with PT. A comprehensive literature review highlighted that the clinical presentation of tendon pain exhibits features of both physiological and pathophysiological pain and that possible changes to the M1 in people with tendon pain warranted investigation (Chapter 2). Chapter 3 investigated the CSE in jumping athletes with, (separated into those with PT or other anterior knee pain [AKP]), and without AKP. Athletes with PT displayed greater CSE than controls and those with other AKP, however no differences were detected between the control group and other AKP group. This study improved our understanding of the CSE relating to different sources of knee pain (with similar, but different clinical presentations) and may direct better treatment approaches. There are few non-invasive interventions that reduce tendon pain. Chapter 4 demonstrated that externally paced isometric contractions of the quadriceps muscle group had a greater analgesic effect than externally paced isotonic quadriceps muscle contractions. Importantly, pain reduction was paralleled by a reduction in cortical inhibition, and therefore that muscle performance (evidenced by increased quadriceps torque) was improved following isometric muscle contractions. The clinical implications of these findings are important as the findings show that isometric muscle contractions may be used to reduce pain in people with PT without a reduction in muscle performance. In Chapter 5, two strength training programs, isometric and isotonic quadriceps muscle contractions that used external pacing to control the timing of the movement, were compared for their immediate analgesic effect in a 4-week withinseason randomised clinical trial. Both protocols were efficacious for inseason athletes to reduce pain; however, the isometric intervention demonstrated significantly greater immediate analgesia throughout the trial, which may increase the ability to load the patellar tendon. Chapter 6 reviewed knowledge about changes to the M1 and motor control in tendinopathy, identified parameters shown to induce neuroplasticity in strength training such as the use of external pacing, aligned these principles with current tendon loading protocols and proposed future direction for tendon rehabilitation. These studies demonstrated that PT was associated with substantial differences in the corticospinal control of the quadriceps. Externally paced strength training was capable of not only modifying tendon pain, but excitability and inhibitory control of the quadriceps. Changes to corticospinal control would logically alter tendon load and therefore may be important in reducing recalcitrance or symptom recurrence. An improved understanding of the methods that optimise neuroplasticity of the M1 may be an important progression in how the clinical prescription of exercise based rehabilitation in tendinopathy for pain modulation and potentially restoration of the corticospinal control of the muscle-tendon complex. 

Awards: Winner of the Mollie Holman Doctoral Medal for Excellence, Faculty of Medicine, Nursing and Health Sciences, 2015.