Effects Of Exercise-Induced Muscle Damage On Neuroplasticity And Stiffness

Musculoskeletal injuries are one of the leading causes of disability within the general population. Acutely, injury can cause pain, inflammation, and feelings of stiffness impacting the nervous system as well as the muscle to control the injured segment. However, studying injuries in an acute environment can pose challenges with respect to controls and timing of measurement. Exercise-induced muscle damage (EIMD) is also known to alter muscular stiffness and cause pain acutely; therefore, it was the goal of this thesis to examine if EIMD could describe mechanical and neural changes in vivo. Changes in muscle architecture, tendon stiffness, reflexive inhibition, and intracortical inhibition were observed over 72 hours following EIMD. Twelve untrained subjects took part in a muscle damage protocol of eccentric calf contractions (10 sets of 10 repetitions at 75% of one repetition maximum) on an isokinetic dynamometer. They were then tested for pennation angle and fascicle length via ultrasound, tendon stiffness using the tendon displacement method, reflexive inhibition by the Hoffman reflex (HReflex), and intracortical inhibition as determined by cortical silent period (CSP). v Testing took place before muscle damage, 10 minutes, 24 hours, and 72 hours after muscle damage. No significance was found in any measure despite a significant increase in pain; however, large effect sizes were observed of decreased CSP at 110% of motor threshold (µp 2=0.302) and decreased fascicle length (µp 2=0.163). These results though are underpowered for both CSP (p=0.135) and fascicle length (p=0.114). From this, it can be said that resting muscle tone could have been altered. More investigation is needed to confirm these effects. Further, examination across different muscle groups would help to further these conclusions.