BACKGROUND: The second heart rate (HR) turn point has been extensively studied, however there are few studies determining the first HR turn point. Also, the use of mathematical and statistical models for determining changes in dynamic characteristics of physiological variables during an incremental cardiopulmonary test has been suggested. OBJECTIVES: To determine the first turn point by analysis of HR, surface electromyography (sEMG), and carbon dioxide output ( ) using two mathematical models and to compare the results to those of the visual method. METHOD: Ten sedentary middle-aged men (53.9±3.2 years old) were submitted to cardiopulmonary exercise testing on an electromagnetic cycle ergometer until exhaustion. Ventilatory variables, HR, and sEMG of the vastus lateralis were obtained in real time. Three methods were used to determine the first turn point: 1) visual analysis based on loss of parallelism between and oxygen uptake ( ); 2) the linear-linear model, based on fitting the curves to the set of data (Lin-Lin ); 3) a bi-segmental linear regression of Hinkley' s algorithm applied to HR (HMM-HR), (HMM- ), and sEMG data (HMM-RMS). RESULTS: There were no differences between workload, HR, and ventilatory variable values at the first ventilatory turn point as determined by the five studied parameters (p>0.05). The Bland-Altman plot showed an even distribution of the visual analysis method with Lin-Lin , HMM-HR, HMM-CO2, and HMM-RMS. CONCLUSION: The proposed mathematical models were effective in determining the first turn point since they detected the linear pattern change and the deflection point of , HR responses, and sEMG.

Considerando a crescente utilização da técnica de nado ondulatório submerso (NO SB) durante a saída e as viradas nas provas de nado crawl, o presente estudo objetivou determinar a força dos membros inferiores em nado ondulatório (FMI NO) e suas correlações com as performances máximas do NO SB e na superfície (NO SP). Para isso 19 nadadores com idade de 15,2±0,6 anos filiados a federação aquática paulista foram submetidos a um esforço máximo de 30s de FMI NO, atados a um dinamômetro contendo células de carga como elemento sensor primário. A tensão detectada pelo dinamômetro, devido aos esforços dos nadadores, foi amplificada por uma fonte de extensometria. Os valores obtidos foram enviados ao computador armazenados na freqüência de 200Hz e suavizados utilizando o filtro "butterworth" de quarta ordem com freqüência de corte de 3 Hz. Com a utilização da reta de calibração pode-se converter valores de tensão (mV) em unidades de força (N) pelo programa Matlab 5.3, possibilitando assim a determinação dos valores médios de FMI NO. Posteriormente os nadadores realizaram esforços máximos de 15 m de NO SB e de 25 m NO SP. As possíveis relações entre esses três esforços, foram analisadas utilizando o teste de correlação de Pearson com nível de significância pré-fixado para P<0,05. Verificamos valores de 53,85±11,45N, 1,19±0,14 m.s-1 e 1,76±0,26 m.s-1 para a FMI NO, NO SB e NO SP, respectivamente. A FMI NO apresentou significativas correlações com a NO SB (r=0,80) e NO SP (r=0,76). Os resultados do presente estudo sugerem a utilização da FMI NO na avaliação e predição do NO SB e NO SP de nadadores treinados. No entanto mais pesquisas são necessárias para verificar a sensibilidade da FMI NO aos efeitos específicos do treinamento em natação.

Considering the crescent utilization of the underwater dolphin kick (NO SB) techniques during the beginning and the turns of front crawl events, the main purpose of the present study was to determine the dolphin kick force (FMI NO) in tethered swimming and its correlations with the maximal performance determined in NO SB and in dolphin kick with a commercial board (NO SP). Nineteen male swimmers with mean age of 15.2±0.6 years and affiliated with Sao Paulo Aquatic Federation participated in the present study. The athletes were submitted a 30-s maximal effort of dolphin kick tethered to a dynamometer with strain gages (load cells) as a primary sensor element. The tension detected by the dynamometer due the swimmers’ efforts was amplified by an extensometer font. The results obtained during the efforts were sent to a computer using an interface and were stored in a data acquisition program at 200 Hz. After these procedures, the results were smoothed using the "butterworth" filter of fourth order with 3-Hz frequency. Using the calibration straight line, the values were converted into force units (N) by the Matlab 5.3 program. This conversion allowed the determination of the dolphin kick mean force in tethered swimming (FMI NO). Then, the swimmers performed a 15-m maximum effort of underwater dolphin kick (NO SB) and another 25-m maximum effort of dolphin kick using a commercial board (NO SP). The relationships between these three maximum efforts were analyzed using the Pearson’s correlation coefficient. A significance level of 5% was chosen. The mean ± standard deviation of FMI NO, NO SB and NO SP were 53.85 ± 11.45N, 1.19 ± 0.14 m.s-1, and 1.76 ± 0.26 m.s-1, respectively. The FMI NO presented significant correlations with NO SB(r= 0.80) and NO SP (r= 0.76). According to the results of the present study, the use of FMI NO to evaluate and predict the NO SB and NO SP of expert’s swimmers is suggested. However, more studies are necessary to verify the sensibility of the FMI NO to specific effects into the swimming training.