Study on the limitation for detecting anaerobic threshold by respiratory frequency]

It has been reported that respiratory frequency (F) serves to determine anaerobic threshold (AT). The purpose of this study was to investigate whether the method detecting AT by using F is influenced by the subject's condition such as the existence of sport experiences. Ten healthy adults volunteered to perform progressive cycle ergometer exercise with workloads increased by 30-W (female:20-W) every 2 min at 60 rpm. VO2 at AT were determined by four different methods, which detect the point of 1)nonlinear increase in VE, VCO2, and increase in VE/VO2 without increasing in VE/VCO2 (AT-v), 2) nonlinear increase in F (visual estimation: AT-VF), 3) inflection in F by multisegment linear regression (AT-CF), 4) inflection with omitting above RC point as with 3) (AT-CF2). The mean VO2 at AT-VF (40.8 +/- 9.2 ml/kg/min) and AT-CF (42.7 +/- 9.9 ml/kg/min) was significantly higher compared with AT-V (28.2 +/- 10.4 ml/kg/min) and not RC (42.3 +/- 10.0 ml/kg/min). It would be possible that AT-VF and AT-CF indicated RC, but not AT. There were no significant differences between AT-CF2 (28.2 +/- 10.9 ml/kg/min) and AT-V, and a highly positive correlation (r = 0.79, p less than 0.05) was observed between them. It was recognized that F reached a plateau at AT in four of the subjects. The error between AT-V and AT-CF2 was observed individual variations and the error between them within 5% was observed in only one subject. These results suggest that F is inadequate as an indicator of the AT, because F may be influenced by entrainment of breathing and pedalling frequency.