The Effect of Cigarette Smoking on Heart Rate and Oxygen Consumption During Submaximal Exercise

The YMCA cycle ergometry protocol is a submaximal exercise test to predict maximal oxygen consumption (VO₂max). Our purpose was to determine whether smoking altered the relationship between VO₂ and heart rate during this cycle ergometer test. Twenty-three male and 11 female college-aged students (ages 18-27 yrs), who were current cigarette smokers, participated in the study. The YMCA cycle test is a multistage, incremental test beginning at 150 kg•m/min. Stages 2, 3, and 4 are dependent on heart rate during stage one. Subjects were required to complete a minimum of 2 stages that elicited heart rates between 110 and 160 bpm. Subjects completed two exercise tests following the YMCA protocol: 1.) after abstaining from smoking for three hours prior to exercise; and, 2.) after smoking two cigarettes within 20 minutes of the test. Subjects were randomized as to the order in which they completed the trials. Workloads during the second trial were matched to the first trial. Subjects performed the trials with at least 48 hours between tests. Heart rate was measured prior to exercise and every minute during exercise. Heart rate values were calculated as the mean of the heart rates during the last two minutes of each stage. VO₂ was measured continuously using a SensorMedics 2900c gas analyzer and averaged for each minute. Data for the smoking and non-smoking trials for pre-exercise and for the two stages during which heart rate was between 110-160 bpm were analyzed with paired t-tests. An alpha level of 0.05 was set as statistically significant. Cigarette smoking prior to the exercise test elevated heart rate 15% compared to no smoking (Non-smoking vs. smoking: 83.8 + 11.7 bpm vs. 96.5 + 13.7; mean + SD). Heart rate remained 6 - 10% greater in the smoking condition throughout the exercise test (Stage 2: 116.1 + 13.2 vs. 128.1 + 13.7; Stage 3: 137.6 + 17.7 vs. 146.2 + 17.2). VO₂ was unaffected by smoking prior to exercise (0.26 + 0.09 L/min vs. 0.29 + 0.11). VO₂ increased with each exercise stage, but was not different between smoking and non-smoking trials (Stage 2: 0.94 + 0.33 L/min vs. 0.98 + 35; stage 3: 1.28 + 0.38 vs. 1.29 + 0.44). These data show that cigarette smoking prior to submaximal aerobic exercise disproportionately increases heart rate relative to VO_2; therefore, smoking 20 minutes prior to a cycle test used to estimate cardiorespiratory fitness will underestimate maximal VO₂.