Oxygen uptake kinetics and bioenergetics profile at maximal and supramaximal intensities in swimming

• Autor(a) principal: Almeida, T.
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.5/30082
• topic: Oxygen Uptake Kinetics; Bioenergetics; Swimming; Maximal Aerobic Velocity; Interval Training; Cinética do Consumo de Oxigénio; Bioenergética; Velocidade Aeróbia Máxima; Treino Intervalado; Natação; Domínio/Área Científica::Ciências Médicas::Outras Ciências Médicas

The aim of this work was to investigate and describe the swimmers oxygen uptake kinetics (V̇O2K) and bioenergetic profiles at different maximal and supramaximal intensities in order to provide new insights about the impact that competitive and training efforts have on swimmers physiology. For that purpose, several physiological parameters were measured throughout the different tests performed by the swimmers before, during and after exercise, such as V̇O2, heart rate, blood lactate concentration and rate of perceived exertion (RPE). All tests were conducted using a breath-by-breath apparatus connected to a swimming snorkel for pulmonary gas sampling and an underwater visual pacer displayed at the bottom of the pool for velocity control. The V̇O2K parameters were calculated through mono or bi-exponential modelling and by a new growth rate method. For the analysis of the bioenergetic profiles we considered: the aerobic system determined as the time integral of the net V̇O2 during exercise; the anaerobic lactic system calculated by the net [La-] at the end of exercise; and the anaerobic alactic system determined by the analyses of the fast component of the V̇O2 recovery curve. Four main studies embody the fundamental part of this thesis. They were designed to: 1) characterize swimming competitive events; 2) test the tolerance to the maximal aerobic velocity (MAV) at continuous vs. interval training (IT) sets; 3) test two different work-intervals (medium and long) in IT sets performed at the MAV; and 4) test the impact of different intensities applied on similar IT sets, testing also the effects of short and medium work-intervals. For each study, swimmers first performed a discontinuous incremental test in order to access the second ventilatory threshold (VT₂), maximal oxygen uptake (Peak-V̇O2) and maximal aerobic velocity ( MAV). This allowed to set the reference markers for the application of the remaining tests that were performed at maximal and supramaximal intensities, varying according to intensity (constant vs. maximal trials) and total distance performed (continuous vs. intermittent). In study 1, three simulated swimming events (50, 100 and 200 meters maximal trials) showed a tendency, as the distance of the event increases and the exercise intensity decreases, of a slower V̇O2K response but higher oxidative responses, while the aerobic participation increased and the anaerobic decreased, presenting a cross-over in the 100 meters event. Study 2 showed that athletes could hold the MAV intensity for ~256 seconds, with less proficient swimmers getting higher times to exhaustion (TLim). Furthermore, performing this intensity intermittently (100 meters bouts with 15 seconds breaks) lead to significantly longer TLim and consequently swimmers spent a considerable longer time near the V̇O2 maximal values. Study 3 showed that, independently of performing medium or long work-intervals (100 vs. 200 meters bouts), the physiological impact on swimmers is similar and capable to tax the aerobic mechanism to its maximal values. When normalized for the same overall distance (first 800 meters) the RPE showed that swimmers could easily perform the shorter work-interval getting the same physiological benefits than with longer work-interval. Study 4 showed that, whilst training with short distance bouts (50-m), 5 to 10% of increase in the intensity could rise the oxidative rate ~6 to 13% higher, and improve ~20 to 46% the tolerance to swimming in the severe domain (i.e., above VT₂). In addition, the results recommend an increase of, at least, 5% of the intensity to an IT set performed with 50 meters bouts to match the results obtained with 100 meters bouts. Overall, the studies demonstrated that higher oxidative rates, amplitudes of the V̇O2K, MAV’s and aerobic and total anaerobic participations seemed to be associated with better swimming performances. At MAV, the IT sets seemed to bring more benefits for the aerobic capacity development than the continuous workout and increasing the intensity of a short work-interval IT set above MAV is advisable for a more taxing effect on the aerobic metabolism. When comparing work-intervals it seems that a significant improvement occurs from increasing the sets repetition from 50 to 100 meters bouts, however no further physiological benefits occur from the 100 to the 200 meters bouts. Our investigation confirms that the analysis of the V̇O2K parameters as well as profiling swimmers bioenergetics, especially in the intensities associated with training and competitive events, are important aspects for a true understanding of human sports performance.