Tendons are mechanically responsible for transmitting forces from muscles to bones, allowing postural control and the full spectrum of human movements. Daily life activities such as walking, running, jumping, sitting, and squatting involve a highly coordinated action by the central nervous system, muscles, and tendons to plan, initiate, control, and execute different movements efficiently. In these functions, tendons are exposed to some of the higher mechanical demands in the human body. Thus, the ability of tendons to bear these loads originates from a unique structural organisation and adaptability to respond to mechanical forces by adjusting their load-bearing capacity.
Sudden exposure to elevated mechanical stress may put tendons at risk of damage, therefore mechanical loading can be viewed as a state of switch between functional tendon remodelling and the development of chronic tendon disease (tendinopathy).
Tendinopathy describes a variety of pathological changes to the tendon, leading to pain and reduced function. The essence of tendinopathy is a failed healing response characterised by abnormalities in the tendon’s microstructure, macrostructure, composition, and cellularity. In the last two decades, the number of people suffering from tendinopathy has increased worldwide, affecting athletic and non-athletic individuals of all ages. Interestingly, the presentation of tendinopathy varies widely between different parts of the body according to age, sex, type of physical activity, occupational setting, etc.
For the first study of my PhD, I will determine the morphological and mechanical properties of the Achilles tendon and calf muscles at rest and during low force isometric contractions using B-mode ultrasonography and elastography techniques. Additionally, we will measure neuromuscular properties of the calf muscles during isometric and dynamic contractions using surface high-density surface electromyography (HD-sEMG). Until now, most studies investigating the neuromuscular impairments induced by Achilles tendinopathy have focused on the changes in global electromyography amplitude, which is an indirect estimate of neural activity; motor unit recordings via HD-sEMG will give us more comprehensive information about the neural strategies employed by the central nervous system to control muscle force.
In my second study, I will examine the morphological and mechanical adaptations of the Achilles tendon and calf muscles to a 6-weeks eccentric or concentric exercise protocol in individuals with non-insertional Achilles tendinopathy. Furthermore, after applying these exercise protocols, I will determine the neuromuscular adaptations of the calf muscles during isometric and dynamic contractions. Although eccentric exercise has been widely used for the treatment of Achilles tendinopathy, evidence of histological changes following a program of eccentric exercise is lacking, and the mechanisms by which this type of exercise may help to reduce symptoms is unclear. Therefore, this investigation will increase our understanding of the neuromuscular mechanisms underlying Achilles tendinopathy and improve our knowledge of therapeutic alternatives to manage this condition.