Background & Objectives :�Heart rate deflection point (HRDP) plays an important role in predicting anaerobic threshold and monitoring athletes training schedule. Despite some research, the physiological mechanisms involved in occurrence of the HRDP remains to be fully elucidated. The objective of this study was to survey of the agreement between Heart Rate Deflection Point (HRDP) and the Potassium Turn Point (KTP) in young athlete men.

  Methods :�Thirty young men athlete volunteer (Mean ± SD age= 20 ± 1.21 years height = 176 ± 7.34 Cm and weight = 6.58 ± 5.66 Kg) were selected as subjects. Hofmann protocol was used to cause the HRDP. One week later and after determining the HRDP by using the S.Dmax method, subjects performed Hofmann protocol again and blood samples were taken from left forearm vein in five phases, simultaneously. The amount of potassium was measured directly by the Flamephotometer.

  Results :�According to the results of study, the HRDP and KTP were occurred in average in 78% HRmax and 79% HRmax, in all of the subjects, also there was a highly agreement between HRDP and KTP (158 3.84 vs. 159 3.88 b/min). HRDP & KTP were occurred in third phase, simultaneously.

  Conclusion: Based on these results, exercise induced increase in serum potassium during Hofmann incremental cycle ergo-meter testing protocol can be one of the mechanisms of the occurrence of HRDP.