INTRODUCTION. Cognitive efficiency during cognitive-motor dual-task (CMDT) varies with exercise intensity, with low-to-moderate intensities supposed to enhance performance according to an inverted-U theory. This effect remains unexplored in trained individuals, who may better preserve cognitive function at high intensities due to improved prefrontal cortex (PFC) homeostasis. Additionally, neuromuscular fatigue from high-effort exercise is influenced by sustained attention tasks, but its development during whole-body CMDT remains unclear. This study aimed to explore sustained attention and neuromuscular fatigue simultaneously during incremental cycling in trained individuals using an innovative ergometer. METHODS. Forty well-trained adults performed an incremental cycling test combined with a sustained attention Mackworth task. The test involved 3-min ramp stages starting at 1 W·kg -1, increasing by 0.4 W·kg -1 per stage, until achieving “extremely strong” perceived effort (CR 100 Borg scale, task-failure TF). At each stage, concurrent psycho-physiological assessments included Mackworth score, quadriceps isometric maximum voluntary contraction (IMVC), neuromuscular fatigue indices (peripheral: twitch force, Pt; central: voluntary activation, VA), PFC oxygenation via near-infrared spectroscopy, and mental effort. Data were interpolated at 20, 40, 60, and 80% of TF. RESULTS. Pt decreased linearly throughout the test (Baseline-TF= –40.7±15.1%, Ptextless0.001). VA started to decrease at 40%TF (–1.5±0.9%, P=0.003), with an exacerbated decline from 80%TF (Baseline-TF= –6.9±2.4%, Ptextless0.001), concomitant to IMVC exacerbated declines (Baseline-TF= –20.9±8.9%, Ptextless0.001). PFC oxygenation declined from 60%TF up to TF (–7.9±2.2%, Ptextless0.001). The Mackworth score was not significantly affected during the test until 80%TF (–11.0±6.7% at TF, Ptextless0.001), associated to ≥84±7% of maximal heart rate. CONCLUSION. Sustained attention did not follow the inverted-U theory during incremental cycling in trained adults. Cognitive impairments were observed at very strong intensities, in correlation with PFC deoxygenation. Central fatigue emerged early, itself correlated with increased mental effort and cerebral deoxygenation, questioning the relevance of dedicated CMDT training in sports and occupational settings.