Heart rate variability threshold in different ergometric protocols / Limiar de variabilidade da freqüência cardíaca em diferentes protocolos ergométricos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The heart rate variability (VFC) decreases gradually during progressive exercise, which tends to stabilization in intermediate loads. Initially, the possibility of identification of a threshold of this variable (LiVFC1), assumed as demarcating of the transition of the vagal withdrawal for the predominance of the sympathetic activity in the control of the FC was demonstrated. Later, a possibility of a second point of transition was presented (LiVFC2). The objective of this research was to obtein more evidences of validity of the determination of this LiVFC, verifying the influence of the protocol of test in the diverse employed methods. Twenty one healthy subjects (24,8 5,2 years; 76,7 11,4 kg; 178,8 7,8 cm) were submitted randomly to three experimental tests in an ergometer cycle: PAi5w/i; PB30w/1 and PC45w/3. The VFC - SD1 index of the Poincaré plots - (Polar S810i) and blood lactate concentrations was measured (YSI@1500 Sport). Determination of LiVFC1 was considered by these methods: 1) LiVFCLIM - SD1 minor the 3 ms; 2) LiVFCTUL - difference between the SD1 of two consecutive stages <1 ms; of LiVFC2: 1) LiVFC2LIM - subdivision of curve of VFC in two straight lines, from the LiVFCLIM. The lactate thresholds was identified from the following method for LL1 : 1) LLINADIR - smaller value equivalent of [La] /load; 2) LL1FIXO - 2 mmol.1-1 for LL2: 1) LL2THO - previous load to two consecutive increases, higher or equal the1 mmol.1-; 2) LL2FIXO - 4 mmol-1-1. In analysis intra-protocol for the first threshold of transition (LT1), it was verified that the referring load to the LiVFCLIM method was similar between the protocols; whereas, in the LiVFCTUL the values of PC45w/3 was greater and different of the PA15w/1 (p≤ 0,05). Moreover, it was verified, that as much under effect of the increment and/or duration of stage, the LiVFC1 followed the alterations in the LL1. The distinct methods of LT1, it was observed that are in comparable levels in the PA15w/ı(r = 0,45 - 0,47; p≤ 0,05) and in the PB30w/1. On the other hand, the second threshold of transition (LT2), the load in the LjVFC2LIM presented higher values in the PB30w/1 compared with PA15w/ı (p ≤ 0,05). To testing it influences the distinct protocols, the LiVFC2 LIM varied contrary direction the alterations in the LL2. The diverse methods of the LT2 differ in the three protocols, but they present moderate degree of association (r = 0,43 - 0,72). These data show that, the spite of the evidences of that the LiVFCLIM is not dependent protocol, is necessary caution in the use of this as an indicator of aerobic fitness, which had low the association to the LL1 . On the other hand, the LiVFC2LIM suffers modifications because the alteration in the amplitude and duration of the protocols, however, shows enough discriminatory power of the aerobic fitness, that exactly situated in distinct intensity of the LL2.

ASSUNTO(S)

heart rate variability threshold anaerobic threshold limiar anaeróbio limiar de variabilidade da freqüência cardíaca protocolos de exercício incremental educacao fisica protocols incremental exercise lactate threshold limiar de lactato

ACESSO AO ARTIGO

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