Variation in Heart Rate During Submaximal Exercise: Implications for Monitoring Training

Lamberts, R.P., K.A.P.M. Lemmink, J.J. Durandt, and M.I. Lambert. Variation in heart rate during submaximal exercise: implications for monitoring training. J. Strength Cond. Res. 18(3):641–645. 2004.—A change in heart rate at a controlled submaximal exercise intensity is used as a marker of training status. However, the standard error of measurement has not been studied systematically, and therefore a change in heart rate, which can be considered relevant, has not been determined. Forty-four subjects (26.5 ± 5.4 years; mean ± standard deviation) participated in a submaximal running test at the same time of day for 5 consecutive days. Heart rates were determined during each of the 4 exercise intensities (2 minutes each) of increasing intensity and during the 1-minute recovery period after each stage. The repeatability of the heart rate on a day-to-day basis during the stages and recovery periods were high (intraclass correlation coefficient: 95% confidence interval R = 0.94–0.99). The lowest variation in heart rate occurred in the fourth stage (≈90% maximum heart rate) with heart rate varying 5 ± 2 b·min-1 (95% confidence interval for coefficient of variation = 1.1–1.4%). In conclusion, the standard error of measurement of submaximal heart rate is 1.1–1.4%. This magnitude of measurement error needs to be considered when heart rate is used as a marker of training status.