HEART-RATE THRESHOLD RELATED TO LACTATE TURN POINT AND STEADY-STATE EXERCISE ON A CYCLE ERGOMETER

The aim of this study was to investigate heart rate threshold (HRT) related exercise intensities by means of two endurance cycle ergometer tests using blood lactate concentration [La], pulmonary ventilation (V-E), oxygen uptake (VO2), heart rate (HR) and electromyogram (EMG) activity of working muscle. Firstly, 16 healthy female students [age, 21.4 (SD 2.8) years; height, 167.1 (SD 5.1) cm; body mass 62.7 (SD 7.1) kg] performed an incremental exercise test (10 W each minute) on an electrically braked cycle ergometer until they felt exhausted. The HRT and lactate turn point (LTP) were assessed by means of computer-aided linear regression break point analysis from the relationship of HR or [La] to power output. No significant difference was found between HRT and LTP for all the variables measured. Secondly, two endurance tests (ET) of 20 min duration were performed by 7 subjects. The first (ET I) was performed at an exercise intensity which was about 10% lower than the power output at HRT [61.2 (SD 3.1)% maximal oxygen uptake (VO2max)], the second (ET II) at an exercise intensity about 10% higher than the power output at HRT [79.2 (SD 3.4) % VO2max]. The parameters measured showed a clear steady state in ET I. All mean values were lower than values at HRT [power, 138.7 (SD 18.9) W; HR, 172.1 (SD 4.7) beats.min(-1); VO2, 2.2 (SD 0.3) l.min(-1); V-E, 54.0 (SD 9.1) l.min(-1); [La], 3.7 (SD 1.1) mmol.l(-1); EMG, 81.1 (SD 24.0) mu V] except HR which was the same. No parameters showed a steady state (except EMG activity) in ET II. No subject was able to maintain the exercise for the whole 20 min in ET II [mean time to cessation of the exercise was 10.4 (SD 3.7) min]. At the end of ET II all variables measured were significantly higher (P < 0.05) than in ET I (except EMG activity) [HR, 184.3 (SD 5.2) and 172.1 (SD 8.7) beats.min(-1); V-E: 75.2 (SD 11.7) and 49.6 (SD 8.4) l.min(-1); VO2, 2.9 (SD 0.7) and 2.1 (SD 0.5) l.min(-1); [La], 7.0 (SD 1.8) and 3.3 (SD 2.2) mmol.l(-1); EMG, 86.3 (SD 28.7) and 75.9 (SD 21.5) mu V]. Although no exercise, at HRT exactly was performed, we assume that maximal steady state lay in between ET I and ET II.