The assessment of heart rate variability (HRV) thresholds (HRVTs) as an alternative of Ventilatorythresholds (VTs) is a relatively new approach with increasing popularity which has notbeen conducted in cross-country (XC) skiing yet. The main purpose of the present study wasto assess HRVTs in the five main XC skiing-related techniques, double poling (DP), diagonalstriding (DS), Nordic walking (NW), V1 skating (V1), and V2 skating (V2).Ten competitive skierscompleted these incremental treadmill tests until exhaustion with a minimum of one to tworecovery days in between each test. Ventilatory gases, HRV and poling frequencies weremeasured. The first HRV threshold (HRVT1) was assessed using two time-domain analysismethods, and the second HRV threshold (HRVT2) was assessed using two non-time varyingfrequency-domain analysis methods. HRVT1 was assessed by plotting the mean successivedifference (MSD) and standard deviation (SD) of normalized R-R intervals to workload.HRVT1 was assessed by plotting high frequency power (HFP) and the HFP relative to respiratorysinus arrhythmia (HFPRSA) with workload. HRVTs were named after their methods(HRVT1-SD; HRVT1-MSD; HRVT2-HFP; HRVT2-HFP-RSA). The results showed that the onlycases where the proposed HRVTs were good assessors of VTs were the HRVT1-SD of theDS test, the HRVT1-MSD of the DS and V2 tests, and the HRVT2-HFP-RSA of the NW test. Thelack of a wider success of the assessment of HRVTs was reasoned to be mostly due to thehigh entrainment between the breathing and poling frequencies. As secondary finding, anovel Cardiolocomotor coupling mode was observed in the NW test. This new Cardiolocoomtorcoupling mode corresponded to the whole bilateral poling cycle instead of correspondingto each poling action as it was reported to the date by the existing literature.
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