It has been reported that respiratory frequency (F) serve 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. Vo
2 at AT were determined by four differnt methods, which detect the point of 1)nonlinear increase in V
E, V
CO2, and increase in V
E/Vo
2 Without increasing in V
E/V
CO2 (AT-v), 2) nonlinear increase in F (visual estimation : AT-
V_F), 3) inflection in F by multisegment linear regression (AT-
C_F), 4) inflection with omitting above RC point as with 3) (AT-
CF2)' The mean Vo
2 at AT-
V_F (40.8±9.2ml/kg/min) and AT-
C_F (42.7±9.9ml/kg/min) was significantly higher compared with AT-
V (28.2±l0.4ml/kg/min) and not RC (42.3±10.0ml/kg/min). It would be possible that AT-
V_F and AT-
C_F indicated RC, but not AT. There were no significant differences between AT-
CF2 (28.2±l0. 9ml/kg/min) and AT-
V, and a highly positive correlation (r=0.79, p<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.
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