Article
Objective. To determine the concordance between fractal heart rate variability analysis and established methods for identifying lactate and pulse thresholds during incremental step tests under laboratory and field conditions in adolescent cross-country skiers at the training-development stage.
Organization of research. During the preparatory period, adolescent cross-country skiers underwent incremental step tests in laboratory (n=20) and field (n=60) settings. Recorded variables included blood lactate, heart rate, and the detrended fluctuation analysis index DFA α1. Agreement between methods was assessed using Bland-Altman analysis.
Results. In the treadmill test, the highest agreement was found between the heart rate deflection point and the second lactate threshold. However, wide limits of agreement were observed across all studied variables, reaching up to 40 bpm for heart rate. Comparing DFA α1 = 0.75 with the first lactate threshold revealed a bias of –17.9 bpm (p < 0.01). Heart rate values at DFA α1 = 0.5, traditionally associated with the second lactate threshold in adult athletes, were statistically significantly overestimated in these adolescent skiers. The threshold hierarchy in the treadmill test followed: LT1 < DFA α1 = 0.75 < HRDP ≈ LT2 < DFA α1 = 0.5.
Agreement analysis in field tests revealed similar patterns, irrespective of the load regulation protocol. High concordance was observed between HRDP and DFA α1 = 0.75. The sequence under field conditions remained: DFA 0.75 ≈ HRDP → DFA 0.5.
Conclusion. The DFA α1 index, reflecting the transition from pronounced parasympathetic regulation to sympathetic-adrenal dominance, demonstrated concordance with the heart rate deflection point in adolescent cross-country skiers. In young athletes, DFA α1 = 0.75 characterizes the transitional zone between aerobic and anaerobic thresholds, whereas values at DFA α1 = 0.5 were higher than the anaerobic threshold. Thus, applying adult DFA α1 thresholds as criteria for regulating training load may inadvertently lead to significant intensification of the training process during adolescence.
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