Assessment of ventilatory thresholds from heart rate variability in five incremental treadmill tests in cross country skiers

Abstract

Incremental treadmill tests are widely used in the field of exercise physiology for the assessment of Ventilatory Thresholds for clinical and sport oriented issues. The assessment of Ventilatory Thresholds (VTs) from Heart Rate Variability (HRV) is a relatively new approach with increasing popularity because it is a non-invasive and economical method. Nevertheless, this has not been used in Cross Country (XC) Skiing, an endurance sport where the knowledge of VTs holds special importance. The purpose of the study was to assess VTs using the data derived from HRV analysis in the five main XC skiing-related techniques, Double Poling (DP), Diagonal Striding (DS), Nordic Walking (NW), V1 Skating (V1), and V2 Skating (V2). V1 consists of an slightly off-set double poling action on every other skating glide, which is used for hill climbing, whereas the V2 technique uses a double poling action on every skating leg and is used on flat and on moderate uphills. Ten competitive national level skiers completed the five incremental treadmill tests until exhaustion with a minimum of one to two recovery days in between each test. Ventilatory gases, HRV and Poling Frequency (PF) were measured. Two methods (HRVT1-STD and HRVT1-MSD) derived from time-domain analyses of HRV were used for the assessment of the first VT (VT1), whereas the second VT (VT2) was assessed with two frequency analyses methods (HRVT2-HFP and HRVT2-HFP-RSA). The results showed that the only cases where the proposed HRVTs (i.e. Heart Rate Variability Thresholds) were good assessors of their respective VTs were the HRVT1-STD in the DS test, the HRVT1-MSD in the DS and V2 tests, and the HRVT2-HFP-RSA in the NW test. The lack of a wider success of the assessment of VTs from HRV was reasoned to be, among other things, due to the high entrainment between the Breathing Frequency (BF) and PF, where the rhythm of PF alters the usual ventilatory response in which the assessment of both VTs and HRVTs is based.