Variations in Heart Rate at Blood Lactate Threshold Due to Exercise Mode in Elite Cross-Country Skiers

This study attempted to quantify the difference in heart rate and exercise stage at which blood lactate threshold (T sub(bla)) occurs using 3 different modes of exercise: running, double poling (DP) on roller skis, and skating (SK) on roller skis. Nine elite collegiate cross-country ski racers (4 men, 5 women) served as test subjects. Testing was conducted on a motorized FitNex treadmill, specially designed for roller skiing. Heart rate was monitored via telemetry with values averaged over the last 30 seconds of each stage. A 40- mu l blood sample was obtained at the fingertip at the end of each 4-minute stage, and 25 mu l was analyzed for whole blood lactate concentration. The T sub(bla) was determined by the first exercise stage that elicited a concentration over 4.0 mmol.L super(-1). The same test protocol was used for all 3 exercise modes. Mean heart rate, in beats per minute (b.min super(-1)), at T sub(bla) was not significantly different (P < 0.05) for SK (mean 187 +/- 14 b.min super(- 1) SD) vs. running (mean 187 +/- 12 b.min super(-1) SD); however, heart rate was significantly lower at T sub(bla) for DP (mean 161 +/- 17 b.min super(-1) SD) vs. running and DP vs. SK. The mean exercise protocol stage that induced a blood lactate value which exceeded T sub(bla) was significantly different (P < 0.05) for running (5.22 +/- 1.20 mmol.L super(-1) SD) vs. DP (1.89 +/- 0.78 mmol.L super(- 1) SD), running vs. SK (3.67 +/- 0.71 mmol.L super(-1) SD), and SK vs. DP. It was concluded that T sub(bla) occurs at a lower heart rate and exercise stage during DP as compared with SK or running. Therefore, it stands to reason that the heart rate at T sub(bla) may vary based on mode of exercise, and when using heart rate to estimate blood lactate concentration, coaches and athletes should be aware that different modes of exercise elicit a different blood lactate concentration at a given heart rate depending on exercise mode used.