A global analysis has delved into helicity-dependent parton distribution functions (PDFs), key elements for understanding how the spin of a polarized nucleon is shared among its constituents: quarks, antiquarks, and gluons. These functions are fundamental in Quantum Chromodynamics (QCD) to describe the internal spin structure of fast-moving protons and neutrons. The study reviews the definition and physical interpretation of these polarized PDFs, as well as the perturbative QCD framework used for their determination.