Estimation of minute ventilation by heart rate for field exercise studies.

The aim of this study was to develop predictive equations for minute ventilation based on heart rate, and to test the precision of the equations in two forms of endurance exercise. Eighteen men (age 27.8 ± 5.4 years old, maximal oxygen uptake 45.4 ± 8.3 ml·kg-1·min-1) performed a maximal progressive cycle test in which minute ventilation and heart rate were continually measured and further used to establish the proposed equations with quadratic and exponential adjustments. In the second and third laboratory visits, sixteen participants completed two cycling bouts, one high-intensity interval exercise and one low-intensity continuous exercise. The minute ventilation and heart rate were measured in both exercises and the validity of the equations tested. The Bland-Altman analysis showed agreement between the minute ventilation and estimated equations for interval and continuous exercise. There was no difference between the minute ventilation obtained from both equations and the minute ventilation directly measured during the interval exercise. However, the quadratic equation underestimated the minute ventilation during continuous exercise (p < 0.05). While both equations seem to be suitable to estimate minute ventilation during high-intensity interval exercise, the exponential equation is recommended for low-intensity continuous exercise.

Possibilidade da ocorrência dos 1º e 2º limiares ventilatórios em cargas de trabalho coincidentes, durante protocolos progressivos com incrementos de longa duração / Possibility of the occurrence of 1st and 2nd ventilatory thresholds at the same work rate during incremental test with long steps

Este estudo teve como objetivos, investigar a incidência do aumento abrupto na curva dos 1º e 2º limiares ventilatórios (LV) em cargas coincidentes, durante protocolo progressivo com incrementos de longa duração (8), e verificar com qual limiar de lactato (LL) os LV se aproximam, quando este fenômeno ocorre. 29 maratonistas e triatletas de nível regional, executaram protocolo estabelecido por Heck e col. (12). Os 1º e 2º LV (LV1 e LV2) foram identificados respectivamente, através de análises visuais das curvas dos VE/VO2 e VE/VCO2 em função do tempo. Os valores do lactato sangüíneo plotados em função da velocidade possibilitaram a identificação dos 1º e 2º LL através de análises visuais (LLi1 e LLi2), e através das concentrações fixas de 2,0 e 3,5 mM. l-1 (LL2,0 e LL3,5), respectivamente. 42% da amostra apresentaram LV1 e LV2 em cargas coincidentes (LVC). Nestes indivíduos, LVC foi maior que LLi1 e menor que LL3,5. Não houve diferenças entre LVC e LLi2, ou entre LVC e LL2,0. Os resultados indicam que os VE/VO2 e VE/VCO2 podem não determinar dois LV em protocolo progressivo com incrementos de longa duração. A aproximação dos LVC com os LL pode variar com os diferentes métodos empregados na identificação dos LL.

The purposes of this study were to examine the incidence of the abrupt increase in ventilatory thresholds (VT) at the same work rate, during incremental test with long steps and to observe to which lactate threshold (LT) the VT are close agreement when this phenomenon occur. Twenty-nine endurance runners performed Heck et al. protocol (12). The 1st and 2nd ventilatory thresholds (VT1 and VT2) were determined visually by curve of VE/VO2 e VE/VCO2 against time. The blood lactate against the speed allowed to determinate the 1st and 2nd lactate thresholds, accomplished by the visual inspection (VLT1 and VLT2) and by the blood lactate concentration of 2,0 and 3,5 mM.l-1 (LT2,0 and LT3,5), respectively. 42% of group showed VT1 and VT2 at the same speed (SVT). These subjects showed higher SVT than VLT1 and smaller SVT than LT3,5. There was no difference between SVT and VLT2, either between SVT and LT3,5. The results suggest that VE/VO2 and VE/VCO2 may not determine two VT, during incremental test with long steps. The agreement between the VT and LT may change regarding different methods used to establish the LT.