The impact of muscle-tendon degeneration on functional ability in healthy and pathological populations

Locomotion is an important function of our lives. It is fundamental for the physical and psychological well-being of humans. The bioenergetics and biomechanics of walking could be altered by the onset of a pathological condition, thus negatively affecting the quality of life of this population. Muscles and tendons are involved in each human movement, such as walking, since the force generated by muscle contraction is transmitted to the bone through tendons, generating joint movement. Muscles consume oxygen to generate energy to restore the ATP necessary for muscle contraction. Since tendons are collagenous structures, they don’t directly affect oxygen consumption. Still, during walking, the Achilles tendon conserves some of the energy during heel strike. Then, it returns it at the toe-off, reducing activity for the triceps surae muscles. Thus, muscle-tendon properties and mechanics should be assessed to understand their influence on pathological gait. However, different pathologies lead to different peripheral alterations, and identifying them could help find specific strategies to counteract muscle-tendon alteration and improve walking energetics and biomechanics. In this thesis, muscle-tendon behaviour was investigated for the following aims: 1) to investigate a possible effect of an altered glucose environment on tendon structure and walking ability, 2) to investigate muscle and tendon mechanical alterations in diabetic patients and how they affect the biomechanics and energetics of walking; 3) to determine a possible effect of a minute oscillation stretching training on muscle-tendon function and walking capability in diabetic people; 4) to investigate the role of muscle architecture on maximal torque production in PD patients; 5) to investigate the alterations of muscle behaviour in PD patients and their effect on the ability to produce torque rapidly. Altered (yet not pathological) levels of HbA1c are associated with alterations in Achilles tendon characteristics and walking mechanics (Study 1). Similar results are observed in Study 2: diabetic patients (well-controlled and physically active) are characterized by alterations in Achilles tendon characteristics (e.g. an increase in stiffness), which limit the ankle ROM during locomotion; these alterations, however, do not impact the energetics of walking, compared to healthy controls. The MOS training protocol (Study 3) allows for reversing these differences by reducing tendon stiffness at the ankle level (without affecting muscle stiffness); in turn, this allows for an increase in ankle ROM during walking, improving walking mechanics (increasing stride length) and energetics (reducing the energy cost). An impaired mechanical output is observed in the more affected limb of PD patients, along with an altered muscle behaviour during contraction (Study 4). The reduced ability to produce torque rapidly in these patients is related to lower muscle activation, altered muscle behaviour and muscle mechanical properties (i.e. stiffness) (Study 5).