Previous research investigating endurance sports from a physiological perspectivehas mainly used constant or graded exercise protocols, although the nature ofsports like cross-country skiing and road cycling leads to continuous variations inworkload. Current knowledge is thus limited as regards physiological responses tovariations in exercise intensity. Therefore, the overall objective of the present thesiswas to investigate cardiovascular and metabolic responses to fluctuations inexercise intensity during exercise. The thesis is based on four studies (Studies I-IV);the first two studies use a variable intensity protocol with cardiorespiratory andblood measurements during cycling (Study I) and diagonal skiing (Study II). InStudy III one-legged exercise was used to investigate muscle blood flow duringvariable intensity exercise using PET scanning, and Study IV was performed toinvestigate the transition from high to low exercise intensity in diagonal skiing,with both physiological and biomechanical measurements. The current thesisdemonstrates that the reduction in blood lactate concentration after high-intensityworkloads is an important performance characteristic of prolonged variableintensity exercise while cycling and diagonal skiing (Studies I-II). Furthermore,during diagonal skiing, superior blood lactate recovery was associated with a highaerobic power (VO2max) (Study II). Respiratory variables such as VE/VO2, VE/VCO2and RER recovered independently of VO2max and did not reflect the blood lactate oracid base levels during variable intensity exercise during either cycling or diagonalskiing (Studies I-II). There was an upward drift in HR over time, but not inpulmonary VO2, with variable intensity exercise during both prolonged cyclingand diagonal skiing. As a result, the linear HR-VO2 relationship that wasestablished with a graded protocol was not present during variable intensityexercise (Studies I-II). In Study III, blood flow heterogeneity during one-leggedexercise increased when the exercise intensity decreased, but remained unchangedbetween the high intensity workloads. Furthermore, there was an excessiveincrease in muscular VO2 in the consecutive high-intensity workloads, mainlyexplained by increased O2 extraction, as O2 delivery and blood flow remainedunchanged. In diagonal skiing (Study IV) the arms had a lower O2 extraction thanthe legs, which could partly be explained by their longer contact phase along withmuch higher muscle activation. Furthermore, in Study IV, the O2 extraction in botharms and legs was at the upper limit during the high intensity workload with nofurther margin for increase. This could explain why no excessive increase inpulmonary VO2 occurred during diagonal skiing (Study II), as increased O2extraction is suggested to be the main reason for this excessive increase in VO2(Study III).

Made available in DSpace on 2016-06-02T19:30:11Z (GMT). No. of bitstreams: 1 TeseRDO.pdf: 756445 bytes, checksum: dd46098f781f2c54d8f4d7f9d1c6bb92 (MD5) Previous issue date: 2003-04-25 / Universidade Federal de Sao Carlos / Tropical fish generally inhabit environments with high temperatures and low dissolved oxygen. Along the evolutionary process several species developed mechanisms of air-breathing in order to compensate the oxygen demands caused by the aquatic hypoxia. These mechanisms required anatomical, physiological and biochemical adaptations. Studies on the effects of hypoxia and temperature changes on fish involve the comprehension of the cardio-respiratory mechanisms of compensation. The present study was addressed to determine the cardio-respiratory and air-breathing responses of jeju, Hoplerythrinus unitaeniatus, which utilize the swimming bladder as an organ for accessory respiration in the air, submitted to gradual hypoxia after acclimation to 15, 20, 25 and 30oC. The oxygen uptake ( &VO2 ), gill ventilation ( G V& ) breathing frequency (fR), ventilation volume (VT) and the O2 extraction from the ventilatory current (EO2) were obtained for specimens of jeju (Wt = 209,7 ± 5 g) by flow-trough respirometry. The air-breathing frequency (fRA) and time spent in air-breathing (TRA) were determined by means of an experimental chamber specially constructed for this purpose. Independently of the acclimation temperature, jeju responded to hypoxia as an oxyregulator, i. e., the species was able to keep constant &VO2 in response to graded hypoxia until reach a critical oxygen tension (PcO2). The mean &VO2 values at each acclimation temperature, before reaching the PcO2, were: 47 ± 0,8 mlO2.kg-1h-1 (15°C), 82 ± 0,3 mlO2.kg-1h-1 (20°C), 104 ± 2,6 mlO2.kg-1h-1 (25°C) and 112 mlO2.kg-1h-1 (30°C). The PcO2 for each acclimation temperature were 28, 33, 41 e 52 mmHg, respectively. The increased reductions on PcO2 as acclimation temperatures rose from 15 to 30oC showed that this species presents partial compensation (or type 3 compensation) to temperature increases. Jeju increased the G V& to compensate the graded hypoxia due to higher increments on VT than in fR. This kind of compensation, however, was not enough to keep a constant EO2, which decreased gradually in response to graded hypoxia in all acclimation temperature. At 25 and 30°C the fH were significantly higher than at 15 and 20oC. Hypoxic bradicardia was not recorded at 15 and 20oC and at 25 and 30°C it only occurred below the PcO2. The different PcO2 were also the threshold for the development of accessory air-breathing in all acclimation temperatures. Increases in both fRA and TRA were inversely proportional to the water PO2 reductions and directly proportional to the acclimation temperature. / Peixes de água doce tropical vivem em ambientes de altas temperaturas e baixas concentrações de O2. Isto resultou, ao longo do processo evolutivo, na necessidade da tomada do ar atmosférico em várias espécies de peixes, a fim de compensar seus requerimentos metabólicos, o que requereu modificações anatômicas, fisiológicas e bioquímicas. Estudos sobre o efeito da hipóxia e da variação da temperatura ambiental nos peixes devem envolver o conhecimento dos mecanismos de compensação cardiorespiratória. Assim, o objetivo deste estudo foi determinar as respostas cardiorespiratórios e da respiração aérea de jeju (Hoplerythrinus unitaeniatus), que utiliza a bexiga natatória como órgão acessório de troca gasosa, após período de aclimatação nas temperaturas de 15, 20, 25 e 30°C e submetido à hipóxia gradual. As medidas do consumo de O2 ( &VO2 ), ventilação branquial ( G V& ), freqüência respiratória (fR), volume ventilatório (VT) e extração de O2 da corrente ventilatória (EO2) foram obtidas de exemplares de jeju (Wt = 209,7 ± 5 g) por meio de respirometria de fluxo constante. A freqüência (fRA) e o tempo da respiração aérea (TRA) também foram determinados utilizando-se de uma câmara especialmente desenvolvida para esta finalidade. Independentemente da temperatura de aclimatação, H. unitaeniatus comportou-se como um oxi-regulador, mantendo uma &VO2 constante por amplos intervalos de reduções de O2 até atingir a tensão crítica de O2 (PcO2). Nas diferentes temperaturas a &VO2 foi de 47 ± 0,8 mlO2.kg-1h-1 a 15°C, 82 ± 0,3 mlO2.kg-1h-1 a 20°C, 104 ± 2,6 mlO2.kg-1h-1 a 25°C e 112 mlO2.kg-1h-1 a 30°C. As PcO2 nas respectivas temperaturas foram de 28, 33, 41 e 52 mmHg. A redução crescente das PcO2 mostrou que esta espécie apresenta uma compensação parcial ou do tipo 3 aos aumentos crescentes na temperaturas de aclimatação. O jeju aumentou a G V& em resposta à hipóxia gradual valendo-se de maiores incrementos no VT do que na fR. Entretanto, este tipo de compensação não foi suficiente para manter uma constante EO2, a qual decresceu gradualmente em função da hipóxia. A fH a 25 e 30°C foi significativamente mais elevada do que a 15 e 20°C. A bradicardia hipóxica só foi registrada nas temperaturas de 25 e 30°C e somente ocorreu em tensão abaixo das respectivas PcO2. As PcO2 foram o limiar para o início da respiração aérea acessória em todas as temperaturas estudadas. Os aumentos na fRA, assim como da TRA foram inversamente proporcionais às reduções da PO2 da água e diretamente proporcionais às temperaturas de aclimatação.