Objectives: It is known that exercise induces cardio-respiratory autonomic modulation. The aim of this study was to assess the cardio-pulmonary fitness by ultra-short heart rate variability. Materials and Methods: Study population was divided into 3 groups: Group-1 (n = 40) consisted of military sports man. Group-2 (n = 40) were healthy age-matched sedentary male subjects with normal body mass index [BMI = 19 - 25 kg/m 2 ). Group-3 (n = 40) were healthy age-matched obese male subjects [BMI > 29 kg/m 2 ). Standard deviation of normal-to-normal QRS intervals (SDNN) was recorded over 15 minutes. Bruce protocol treadmill test was used; and, maximum oxygen consumption (VO 2max) was calculated. Results: When the study population was divided into quartiles of SDNN (first quartile: < 60 msec; second quartile: > 60 and < 100 msec; third quartile: > 100 and <140 msec; and fourth quartile: >140 msec), progressive increase was found in VO 2max; and, SDNN was significantly linked with estimated VO 2max. Conclusion: In conclusion, the results of this study demonstrate that exercise training improves cardio-respiratory autonomic function (and increases heart rate variability). Improvement in cardio-respiratory autonomic function seems to translate into a lower rate of long term mortality. Ultra-short heart rate variability is a simple cardio-pulmonary fitness test which just requires 15 minutes, and involves no exercise such as in the treadmill or cycle test.
Key words: Exercise, fitness, heart rate variability, standard deviation of normal-to-normal QRS intervals.