The aim of the current investigation was to quantify the training intensity distribution of hurling players and their association to changes in aerobic fitness measures within hurling players. Thirty hurling players (n = 30; age 25.5 ± 3.2 years; height 178.9 ± 3.2 cm; body mass 78.5 30 ± 4.5 kg) were observed during the pre-championship training period (12 weeks). Aerobic fitness measures (VO2max), peak treadmill velocity (PVT; km·h-1) and heart rates (HR) at 2 and 4 mmol·L-1 blood-lactate concentrations, Yo-Yo intermittent recovery test performance (Yo-YoIR1) were assessed pre and post the training period. Training intensities were categorized using 3 individualised HR zones based on the following criteria: low intensity (≤ HR 2 mmol·L-1), moderate intensity (between HR 2 and 4 mmol·L-1), and high intensity (≥HR 4 mmol·L-1). Analysis of 1025 individual training sessions showed that players spent 58.1 ± 2.5%, 24.3 ± 2.9% and 17.6 ± 1.3% of time in the low, moderate and high intensity zones. The training time spent at high intensity (Zone 3) showed moderate to large associations with improvements in S2 (r = 0.80; p = 0.04) and S4 (r = 0.58; p = 0.03). Similar trends were observed for time spent in high intensity and improvements in VO2max (r = 0.77; p = 0.001) and Yo-YoIR1 performance (r = 0.65; p = 0.05). Hurling players have been shown to spend the majority of training time in low (≤ HR 2 mmol·L-1) to moderate intensity (between HR 2 and 4 mmol·L-1) training. However, only the time spent at high intensity (≥ 90% of maximal HR) was related to changes in aerobic fitness. These results support the usefulness of the quantification of aerobic training load using HR. The study also supports the efficacy of spending elements of training time within the high intensity zone in order to increase hurling player’s aerobic fitness characteristics.