Fitness evaluation is indispensable for elite sporthorses. This requires the use of protocols and equipment adapted to equine practice able to give useful, reliable and quantifiable results. This study evaluates the utility of a maximal incremental test (MIT) in the recognition of the adaptations induced by an aerobic-training. 12 nontrained Arabian horses were studied (3-10 years/340-460kg). The training was performed in a treadmill, during 8 weeks, 6 days/week, 30' trotting at 80% of the aerobic threshold (AeT). Before and after the training a MIT was performed. The MIT was a treadmill test where O₂ consumption (VO₂), CO₂ production and RER were measured continuously by an ergoespirometry and gas-meter. Heart rate (FC) was also registered. The anaerobic threshold (AnT) was calculated on RER basis. Oxygen pulse was obtained at three intensities: AeT (PO₂Ae), AnT (PO₂An) and maximum (PO₂Max). The MIT started with a warm-up, then at 3%slope, the horse performed an incremental exercise beginning with 5m/s increasing 1m/s each 3' until the fatigue upset. Training induced a significant increase in AeT (5.4±0.7 vs 6.7±1.1m/s), AnT (7.8±0.9 vs 8.6±0.7m/s), VO₂Max (95.4±3 Vs 109.6±3.6ml.min-1.kg-1), time of fatigue (755±38 vs 910±43sec), V160 (6.8±0.9 vs 7.7±1m/s), PO₂Ae (0.42±0.04 vs 0.53±0.06ml.min-1kg.-1lpm-1), PO₂An (0.59±0.07 vs 0.67±0.07ml.min-1.kg-1.lpm-1), and PO₂Max (0.51±0.1 vs 0.57±0.08ml.min-1.kg-1.lpm-1); and a significant decrease in RER at 1.7m/s (0.79 vs 0.74), and FCAeT (141±13 vs 126±7lpm). The greater increments were in PO₂Ae (+26%), AeT (+24%) and time of fatigue (+20%). A MIT is useful for the detection of the physiological adaptation induced by an aerobic-training.