Influence of muscle glycogen on the origin of fatigue in different domains of intensity

Author(s)

Carlos Augusto Kalva Filho

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-03-21

Examining board members

Marcelo Papoti; Claudio Alexandre Gobatto; Rinaldo Roberto de Jesus Guirro; Eduardo Kokubun

• Advisor: Marcelo Papoti

Abstract

During efforts with low muscle glycogen (B-Glic), fatigue is classically related to peripheral factors, such as energy unavailability. However, the B-Glic situation also induces systemic changes, which can decrease the muscle activation by the nervous system (i.e., central fatigue). Considering these two strands of thought, this thesis aimed to investigate the possible influences of muscle glycogen on the origin of fatigue in different domains of intensity. To test the different origins of fatigue, we used techniques such as twitch interpolation (TI) and transcranial magnetic stimulation (TMS). In addition, we tested whether the B-Glic situation may be responsible for the decrease in the activation of the motoneurons (i.e., central fatigue), mainly by the action of circulating tryptophan (TrP). Basically, we tried to evaluate the origin of fatigue in efforts with B-Glic, induced by previous exercise, and after the recovery of this substrate (R-Glic), through a diet with high carbohydrate levels. In the first experiment, 11 participants underwent depletion effort, 24-hour with solution application containing (10% Maltodextrin; R-Glic) or not (placebo, B-Glic) carbohydrates, and a high-intensity intermittent effort (6x 1 min to 120% of VO2PICO, separated by 3 min of passive recovery). In this experiment, the glycogen content was estimated by ultrasound. The main results demonstrate that i) glycogen is preserved in efforts with B-Glic and ii) the fatigue has peripheral origin regardless of the previous glycogen content. In another experiment we investigated the origin of fatigue in prolonged exertion and its relationships with the blood concentrations of TrP, this time we performed a 5-day period for glycogen depletion (exercises and diet with low amounts of carbohydrates (0.3 ± 0,2 g.kg-1. Day-1)). The R-Glic situation was induced by three days of rest and diet with high amounts of carbohydrate (4.5 ± 1.7 g.Kg-1.day-1). In this experiment, glycogen levels were determined by muscle biopsy (B-Glic: 0.6 ± 0.2 mg.l00mg-1; B-Glic: 4.5 ± 1.6 mg.l00mg-1; p = 0.001). The effort performed at 80% of VO2PICO (2x15 min, followed by an exhaustive effort at this intensity, E30Tlim) demonstrated a pronounced peripheral fatigue in B-Glic efforts, which did not occur for the R-Glic effort. Concentrations of TrP were correlated with parameters of central fatigue (r = - 0.87) only in the B-Glic situation. In addition, the percentage variation of the force evoked by the TMS magnetic stimuli was significantly correlated with the percentage variation of the TrP (r = 0.89). The longer effort with lower intensity (2x20 min at 70% of VO2PICO, followed by an exhaustive exercise at 80% of VO2PICO; E40Tlim) showed a more pronounced peripheral fatigue when performed with B-Glic. The results of the TMS technique demonstrated that the R-Glic situation induced significant decreases in amplitude, time between peaks and in the force evoked by magnetic stimuli. Significant correlations were observed between the time of silence after the second constant effort and the concentrations of TrP (r = 0.94). The peak-to-peak time at rest was also correlated with TrP concentrations (r = 0.93). Thus, it can be concluded that the origin of fatigue in efforts with different amounts of glycogen is influenced by the intensity of exercise performed. Specifically, fatigue in B-Glic efforts has peripheral origin in intermittent high-intensity efforts and in moderate-duration efforts has a mixed (E30Tlim) or peripheral (E40Tlim) character. The central origin of the fatigue emerges only in the E30Tlim, when the effort is realized in the R-Glic situation (AU)

• FAPESP's process: 16/09339-9 - CHARACTERISTICS OF FATIGUE IN EFFORTS WITH LOW MUSCLE GLYCOGEN PERFORMED IN DIFFERENT INTENSITIES: A DOUBLE-BLIND AND RANDOMIZED STUDY
• Grantee: Carlos Augusto Kalva Filho
• Support Opportunities: Scholarships in Brazil - Doctorate