The polarization index for the five-zone training load intensity model: theoretical justification

Abstract

The three-zone intensity model and the polarization index are widely used to quantify the structure of the training load. However, in modern sports physiology, a five-zone classification is becoming increasingly widespread, allowing for a more subtle differentiation of metabolic and neuromuscular adaptation mechanisms, for which there is no adapted polarization index. The purpose of the study is to develop and justify a modification of the polarization index for a five–zone training load intensity model. Materials and methods. A narrative review of the literature in the PubMed, Google Scholar, and eLibrary databases (2006-2026) has been performed. Based on the analysis of the physiological characteristics of the intensity zones and mathematical modeling, a modification of the polarization index is proposed. Results. The proposed index PI₅ = log₁₀ (((Z₁ + Z₂) / (Z₃ × (Z₄ + Z₅))) × 100), where Z₁–Z₅ time percentage in the corresponding zones of intensity. The combination of Z₁+z₂ (low intensity) and z₄+z₅ (high intensity) is based on the physiological similarity of metabolic mechanisms (mainly aerobic and anaerobic-alactate, respectively). Mathematical modeling has confirmed that Pi₅ > 2 corresponds to a polarized load distribution, and pi₅ < 2 corresponds to unpolarized structures. Modifications are proposed for boundary cases (zero time values in certain zones). The developed index makes it possible to quantify the degree of polarization of the training process within the framework of the five-zone model, while maintaining the interpretative logic of the original index.