PURPOSE: To compare the effects of a standardized endurance-training program with individualized endurance training modified based on the cumulative training load provided by the Polar training-load feature. METHODS: After 12 wk of similar training, 24 recreationally endurance-trained men were matched to a training-load-guided (TL, n = 10) or standardized (ST, n = 14) group and continued training for 12 wk. In TL, training sessions were individually chosen daily based on an estimated cumulative training load, whereas in ST the training was standardized with 4-6 sessions/wk. Endurance performance (shortest 1000-m running time during an incremental field test of 6 x 1000 m) and heart-rate variability (HRV) were measured every 4 wk, and maximal oxygen consumption (VO(2)max) was measured during an incremental treadmill test every 12 wk. RESULTS: During weeks 1-12, similar changes in VO(2)max and 1000-m time were observed in TL (+7% +/- 4%, P = .004 and -6% +/- 4%, P = .069) and ST (+5% +/- 7%, P = .019 and -8% +/- 5%, P < .001). During wk 13-24, VO(2)max statistically increased in ST only (3% +/- 4%, P = .034). The 1000-m time decreased in TL during wk 13-24 (-9% +/- 5%, P = .011), but in ST only during wk 13-20 (-3% +/- 2%, P = .003). The overall changes in VO(2)max and 1000-m time during wk 0-24 were similar in TL (+7% +/- 4%, P = .001 and -9% +/- 5%, P = .011) and ST (+10% +/- 7%, P < .001 and -13% +/- 5%, P < .001). No between-groups differences in total training volume and frequency were observed. HRV remained statistically unaltered in both groups. CONCLUSIONS: The main finding was that training performed according to the cumulative training load led to improvements in endurance performance similar to those with standardized endurance training in recreational endurance runners.