The effects of changing pace on metabolism and stroke characteristics during high-speed breaststroke swimming

Performances often vary between the heats and finals of breaststroke swimming competitions possibly because the swimmers try to conserve their energy, or for other tactical reasons. Additionally, coaches might advise either a 'positive' or 'even' pace race strategy during the final. The effect of such pacing changes on metabolism (blood lactate, heart rate, ventilation), ratings of perceived exertion, stroke kinematics and turning times have not been investigated. Nine male competitive breaststroke swimmers swam three paced (Aquapacer™) 200-m trials, 48 h apart and in random order, at 98%, 100% and at an attempted 102% of their maximal 200-m time-trial speed. Responses in metabolic variables were similar between the 98% and 100% trials, but higher post-exercise blood lactate concentrations and respiratory exchange ratios were observed following the 102% trial. As the pace of trials increased, stroke rate was found to increase proportionately with stroke count. However, during the latter stages of the 100% trial, a disproportionate increase in the stroke count was observed, which led to a significant pacing error. This feature was more obvious in the 102% trial, where participants demonstrated 'positive pacing' and reported higher ratings of perceived exertion than for the 98% trial. During the early stages of the trials, turning times were initially shorter the faster the pace of the trial; however, as the trials progressed, this pattern was found to reverse. We conclude that a slight reduction in pace during near maximal breaststroke swimming altered kinematic but not post-exercise metabolic responses, while an increase in pace led to positive pacing and an increase in both kinematic responses and anaerobic metabolism

Fatores intrínsecos do custo energético da locomoção durante a natação Factores intrínsecos del desgaste energético de locomoción durante la natación Intrinsic factors of the locomotion energy cost during swimming

A quantidade de energia metabólica gasta em transportar a massa corporal de um sujeito por unidade de distância tem sido definida como custo energético da locomoção, ou especificamente para natação, o custo de nado. As diferenças no custo de nado entre os indivíduos parecem ser influenciadas por dois principais fatores, a resistência hidrodinâmica e habilidade técnica do nadador. O menor custo de nado apresentado pelas mulheres tem sido atribuído a menor resistência hidrodinâmica decorrente de menor tamanho corporal, maior percentagem de gordura e melhor posicionamento horizontal. Porém, essas diferenças no custo de nado entre homens e mulheres desaparecem quando corrigidos para o tamanho corporal. Em relação às crianças, o maior custo de nado comparado com o dos adultos quando corrigidos para o tamanho corporal pode ser explicado principalmente por menor habilidade técnica apresentada por elas. Para indivíduos com as mesmas características antropométricas, melhor habilidade técnica e maior tamanho da superfície de propulsão, associados a aumento na eficiência propulsiva, podem reduzir o custo de nado. Quando se comparam os diferentes estilos, o mais econômico é o crawl seguido pelo de costas em qualquer velocidade de nado. O borboleta é o estilo menos econômico a baixas velocidades (< 0,8m·s¹). Entretanto, acima dessa velocidade o peito passa a ser o estilo menos econômico.<br>La cantidad de energía metabólica gastada en transportar la masa corporal de un individuo por unidad de distancia ha sido definida como el desgaste energético de locomoción, o específicamente para la natación, el desgaste de nado. Las diferencias en el desgaste de nado entre los individuos parecen ser influenciadas por dos principales factores, la resistencia hidrodinámica y la habilidad técnica del nadador. El menor desgaste de nado presentado por las mujeres ha sido atribuido a una menor resistencia hidrodinámica proveniente de un menor tamaño corporal, mayor porcentaje de grasa, y mejor posicionamiento horizontal. Sin embargo, estas diferencias en el desgaste de nado entre hombres y mujeres desaparece cuando se corrige el tamaño corporal. En relación a los niños, el mayor desgaste de nado comparado a los adultos cuando se corrige el tamaño corporal puede ser explicado principalmente por una menor habilidad técnica presentada por los mismos. Para individuos con las mismas características antropométricas, una mejor habilidad técnica y mayor tamaño de superficie de propulsión, asociados a un aumento en la eficacia de propulsión, pueden reducir el desgaste de nado. Cuando se comparan los diferentes estilos, el más económico es el de pecho seguido por el de espalda a cualquier velocidad de nado. El estilo mariposa es el estilo menos económico a bajas velocidades (< 0,8 m·s-1). A pesar de esto, por encima de esta velocidad el estilo pecho pasa a ser el estilo menos económico.<br>The amount of metabolic energy spent in transporting the body mass of the subject over a unit of distance has been defined as the energy cost of locomotion, or regarding to swimming, cost of swimming. The differences in the cost of swimming between the individuals seem to be influenced by two main factors, the hydrodynamic resistance and technical skill of the swimmer. The lower cost of swimming showed by females has been attributed to a smaller hydrodynamic resistance due to their smaller size, larger percentage fat and more streamlined position. However, the difference in cost of swimming between males and females disappears when correcting for body size. With regard to children, the higher energy cost of swimming when correcting for body size may be caused by the lower swimming technique showed by them. For individuals with the same anthropometric characteristics, the better swimming technique and larger size of propelling surface, associated with higher propelling efficiency, may decrease the energy cost of swimming. When comparing different types of strokes, the most economical stroke is crawl, followed by backstroke, irrespective the swimming velocity. Butterfly is the less economical at low velocities (< 0.8 m·s¹). However, above that velocity the breaststroke become the less economical stroke