AbstractThe amount of people that practice sports activity has increased in recent years. However, the percentage of sedentarism in Chile is still devastating. Furthermore, several studies have related sedentarism with the dropout rate within the first weeks of physical activity. One of the leading causes of this dropout is muscle damage and pain after eccentric contractions, which could manifest through independent neuromuscular changes according to each muscle’s structural morphology. Some research has currently reported a muscular group of the human body that could resist post-exercise damage, unlike what is observed in other muscles. This is the medial gastrocnemius (MG), a muscle with particular anatomy and function, requested in many daily activities. However, there is no clarity about the neuromuscular adaptations underlying this phenomenon. On the other hand, non-invasive tools, such as surface electromyography (sEMG) have allowed searching for new findings based on possible neuromuscular changes, linked to the myoelectrical activity and the effect of the exercise, using, for example, analysis of the sEMG signals in the time and frequency domain. Some studies focused on processing the sEMG signal intend to respond to possible neuromuscular changes caused by eccentric exercise. These studies use variables such as median frequency (MF) of the signal’s power spectral density, muscle fiber conduction velocity (MFCV), amplitude of the sEMG signal, among other. However, there is little evidence about changes in the GM after eccentric exercise. Based on the above, this research’s main aim was to study the use of spectral analysis and muscle conduction velocity to describe possible neuromuscular changes in the recording of high-density sEMG of the MG, in sedentary people.
Starting from a non-randomizer experimental study (previously developed), the myoelectrical activity of the MG in sedentary subjects was registered using high-density sEMG, before (PRE), two hours (2H), forty-eight hours (48H), and seven days (7D) after one session of eccentric exercise. Each volunteer developed an exercise protocol requesting the plantar flexor muscles. The MF and MFCV were estimated using a non-parametric spectral analysis (Welch), and an optimization algorithm based on the maximum likelihood principle and the Newton method, respectively. The results ended in preparation of two articles. The first described the relevance of the window size used to estimate the MF. This article suggested a range between 256ms and 4096ms when using the Welch method. The second article determined possible neuromuscular changes based on the analysis of the MF and MFCV, after a protocol eccentric exercise for the MG. The data show a decrease in both variables after 2H post-exercise in sedentary people. At the same time, no significant changes were found after 48H and 7D. This could reflect only acute changes in response to the periarticular tissue inflammation and not a neuromuscular change in the MG, the opposite behavior observed in other human body muscles.
|Date of Award||Dec 2020|
|Original language||Spanish (Chile)|
|Supervisor||Alejandro Weinstein (Supervisor) & Rodrigo Salas (Supervisor)|