Estimation of anaerobic threshold by cardiac repolarization instability: a prospective validation study

BACKGROUND: Assessing lactate (LT) or anaerobic thresholds (AT) in athletes is an important tool to control training intensities and to estimate individual performance levels. Previously we demonstrated that ECG-based assessment of cardiac repolarization instability during exercise testing allows non-invasive estimation of AT in recreational athletes. Here, we validate this method in professional and amateur team sports athletes. METHODS: We included 65 team sports athletes (32 professionals and 33 amateur athletes; 51 men, 14 women, mean age 22.3 ± 5.2 years) undergoing a standardized incremental cycle exercise test. During exercise testing a high-resolution ECG (1000 Hz) was recorded in Frank-leads configuration and beat-to-beat vector changes of cardiac repolarization (dT°) were assessed by previously established technologies. Repolarization-based AT (AT(dT°)) was estimated by its typical dT°-signal pattern. Additionally, LT was detected in accordance to methods established by Mader (LT(Mader)) and Dickhuth (LT(Dickhuth)). RESULTS: All athletes performed exercise testing until exhaustion with a mean maximum workload of 262.3 ± 60.8 W (241.8 ± 64.4 W for amateur athletes and 283.4 ± 49.5 W for professional athletes). Athletes showed AT(dT°) at 187.6 ± 44.4 W, LT(Dickhuth) at 181.1 ± 45.6 W and LT(Mader) at 184.3 ± 52.4 W. AT(dT°) correlated highly significantly with LT(Dickhuth) (r = 0.96, p < 0.001) and LT(Mader) (r = 0.98, p < 0.001) in the entire cohort of athletes as well as in the subgroups of professional and amateur athletes (p < 0.001 for all). CONCLUSIONS: AT(dT°), defined by the maximal discordance between dT° and heart rate, can be assessed reliably and non-invasively via the use of a high-resolution ECG in professional and amateur athletes.