5 research outputs found
Acute effects of small changes in bicycle saddle height on gross efficiency and lower limb kinematics
P. 784-791El objetivo del presente estudio fue evaluar los efectos agudos de pequeños cambios en la altura del sillĂn de bicicleta sobre la eficiencia bruta y cinemática de las extremidades inferiores. Ciclistas bien entrenados (n = 14) realizaron una prueba de pedaleo sub-máximo (~ 70-75% del VO2max) a cadencia constante (90 rpm). ConsistiĂł en tres series aleatorias de 6 minutos con la altura de sillĂn preferida, 2% más alta y 2% más baja. La eficiencia bruta (GE) fue significativamente menor y el consumo de oxĂgeno (VO2) fue significativamente mayor levantando el sillĂn (GE = 19.9 ± 1.5%; VO2 = 43.8 ml.kg-1.min-1) que al bajarlo (GE = 20.4 ± 1.3%; VO2 = 42.8 ml.kg-1.min-1). Adicionalmente, un cambio de 0.8% en GE (20.6 ± 1.6 a 19.8 ± 1.6%, p < 0.05) se observĂł al comparar las posiciones donde se obtuvieron los mejores y peores GE. TambiĂ©n se observĂł un efecto significativo en la cinemática de las extremidades inferiores (p <0.05) al efectuar pequeños cambios en la altura del sillĂn. Las diferencias entre las posiciones de silla de montar más bajas y más altas, en las articulaciones de cadera, rodilla y tobillo fueron un aumento de la extensiĂłn (~ 4, 7 y 8Âş, respectivamente), una disminuciĂłn de la flexiĂłn (~3, 4 y 4Âş respectivamente) y, en consecuencia, un aumento del rango de movimiento (~1, 3 y 4Âş respectivamente). Los resultados del presente estudio indican que pequeños cambios en la altura del sillĂn afectaron a GE y a la cinemática de las extremidades inferiores. Los cambios observados en la cinemática de las extremidades inferiores podrĂan justificar, en parte, los cambios de GES
The effect of nitric oxide donors on human performance
Tesi qualificada amb un EXCEL.LENT "Cum Laude", per a l'obtenciĂł del tĂtol de doctor per la Universitat de Barcelona amb menciĂł europea[eng] Nitric oxide or nitrogen monoxide (NO) is a tiny free radical gas. The discovery of this intriguing molecule has revolutionized physiology and pharmacology research during the last 20 years. Currently, it is known that NO is endogenously synthesized by several molecules and tissues via two pathways: the synthase-dependent pathway and the synthase-independent pathway. In the first, the amino acid L-arginine is the main donnor of NO synthesis. In the second, inorganic nitrate is the main substrate for the synthesis of this molecule. Interestingly, both pathways are directly connected. While the synthase-dependent pathway is oxygen dependent, the synthase-independent metabolic route is greatly facilitated under hypoxia conditions. Thus, these mechanisms of NO production regulate levels of NO in the tissues. An adequate production of NO is important because it plays an essential role in mechanisms related with vasodilatation and blood flow distribution. Additionally, NO modulates other important functions in the human body such as mitochondrial respiration and immune mechanisms. For all these reasons, the interest for dietary NO donors have increased during the last years. It has been suggested that the consumption of food rich in L-arginine or in inorganic nitrate may enhance NO availability in the human body. This hypothesis has not been unnoticed in exercise physiology. In fact, it has been suggested that supplementation with NO donors may improve the cardio-respiratory response, as well as the tolerance to endurance exercise in humans. However, there is a lack of studies analyzing this issue. Therefore, the aim of this doctoral thesis was to assess the effect of L-arginine and inorganic nitrate in the cardio-respiratory and metabolic response of healthy humans.
To develop this aim, three studies and one review were carried out. In the first, it was found that L-arginine supplementation during three days at several doses, between 5.5 and 20.5 g/day was not effective to increase plasma markers of NO, as well as the cardio-respiratory and metabolic response during endurance test. In the second study we found that acute dose of inorganic nitrate supplementation (10 mg/kg of body mass) raised significantly plasma levels of nitrate and nitrite. However, this effect did not report an improvement in the cardio-respiratory response at low-to-moderate intensities of exercise. However, at maximal work loads of exercise dietary nitrate induced significantly reduction of oxygen consumption (VO2peak) compared with placebo. Other cardio-respiratory parameters, as well as blood lactate concentration did not differ between nitrate and placebo. In addition, exercise performance measured as time to exhaustion during an incremental test did not increase compared with placebo. All these findings together suggested that at higher intensities of exercise energy production became more efficient after inorganic nitrate ingestion. Accordingly, in the third study it was analyzed the effect of dietary inorganic nitrate ingestion for three days during endurance exercise in a cycle ergometer at high intensity (time-trial of 40-min). Results of this study showed that nitrate supplementation did not increase significantly plasma levels of nitrite, as well as enhance performance in healthy subjects. Interestingly, a significant, negative correlation was found between change in nitrite and endurance capacity measured as VO2peak during the exercise test. These results indicated that the effect of dietary nitrate ingestion was lower in subjects with high cardiovascular capacity compared with subjects with poor tolerance capacity to endurance exercise. This fact is very important, since it is known that endurance training increase values of VO2peak in sedentary population and this fact is correlated with lower incidence of cardiovascular diseases. These and other important conclusions of these studies are included in the last work of this thesis which was a review article.[cat] L’òxid nĂtric (NO) Ă©s un radical lliure alliberat per diverses molècules i teixits en l’organisme humĂ . El descobriment d’aquesta intrigant molècula ha revolucionat la recerca en el camp de la fisiologia i la farmacologia durant els Ăşltims 20 anys. Actualment, es coneix que la alliberaciĂł de NO per part de les cèl•lules endotelials estimula el procĂ©s de vasodilataciĂł. A mĂ©s, tambĂ© es coneix que aquesta molècula es un important regulador de la respiraciĂł mitocondrial i del sistema immunològic. Totes aquestes funcions han generat un gran interès per els precursors nutricionals de NO. En l’à mbit de la fisiologia de l’exercici fĂsic s’ha suggerit que la suplementaciĂł amb alguna d’aquestes substancies (L-arginina o nitrat inorgĂ nic) pot millorar la tolerĂ ncia a l’exercici fĂsic de resistència. No obstant, hi ha molta controvèrsia en els resultats dels estudis que han analitzat aquesta hipòtesi. Per tant, l’objectiu principal d’aquesta tesi doctoral va ser analitzar els efectes dels principals precursors de NO, L-arginina i nitrat inorgĂ nic, en la resposta cardiorrespiratòria i metabòlica durant l’exercici fĂsic de carĂ cter aeròbic en humans. Per dur a terme aquest objectiu es van realitzar 3 estudis i una revisiĂł bibliogrĂ fica. Els principals resultats d’aquests estudis van mostrar que la suplementaciĂł de L-arginina en diferents dosis no va ser efectiva per augmentar el marcadors plasmĂ tics de NO, aixĂ com, la resposta cardiorrespiratòria i metabòlica durant un exercici fĂsic aeròbic en intensitats moderades. En referència als nitrat inorgĂ nic, es va observar que la suplementaciĂł augmenta els nivells d’aquests compostos en plasma. No obstant, aquest fet no es va correlacionar amb una millora de la tolerĂ ncia a l’exercici fĂsic de resistència. A mĂ©s, es va observar una correlaciĂłn negativa i significativa entre l’augment dels nitrits plasmĂ tics i la potència aeròbica mĂ xima (VO2max). Tots aquests resultats van ser Ă mpliament tractats en l’últim treball (revisiĂł bibliogrĂ fica) d’aquesta tesi. En resum, l’ingesta nutricional de L-arginina i/o nitrat inorgĂ nic no resulta efectiva per millorar la resposta cardiorrespiratòria i la tolerĂ ncia a l’exercici fĂsic de resistència en humans sans i entrenats fĂsicament