Introduction. It has been well established that performance fatigability depends on the kind of task performed, sex, and the method of evaluation (maximal isometric vs. concentric torque loss). However, only a limited number of studies evaluated performance fatigability following isometric vs. dynamic fatiguing tasks in the same participants, and none of those studies reported changes in both maximal isometric and concentric (isokinetic) torque. Fatigability of men and women was also seldom compared in these conditions. The aim of this study was to compare performance fatigability of the knee extensors, assessed as isometric and concentric torque loss, between isometric and concentric fatiguing tasks in men and women. Methods. Twenty healthy participants (25 ± 4 yr, 10 women) randomly performed the isometric and dynamic (isokinetic) quadriceps-intermittent-fatigue (QIF) tests with similar duty-cycles. The isometric QIF test consisted of 10-contractions (5-s on/ 5-s off) incremental stages, starting at 10% of maximal isometric torque with 10% increments for each stage. The dynamic QIF test consisted of 100-contractions (120°.s-1 for 60° range-of-motion, 0.5-s on/0.5s off) incremental stages, starting at 10% of maximal concentric torque with 10% increments for each stage. Maximal isometric and concentric torque, voluntary activation and contractile function were quantified before, at the end of each stage and at exhaustion. Fatigue aetiology was investigated using peripheral nerve electrical stimulation during maximal voluntary isometric contractions and at rest. All the procedures were approved by the institutional ethics committee and performed in accordance with the Declaration of Helsinki (except for registration in a database). Results. Greater number of stages (6.2 ± 0.7 vs. 4.9 ± 0.8; P < 0.001) and torque-time integral (TTI; 20,166 ± 7,821 vs. 11,285 ± 4,933 Nm.s; P < 0.001) were performed for the isometric compared to the dynamic QIF test. Maximal isometric and concentric torque, as well as voluntary activation, decreased along the tasks (P < 0.001) without differences between sessions. However, impairments in resting twitch amplitude were greater for the dynamic than the isometric QIF test (P < 0.001). Men were stronger and performed higher TTI than women (P < 0.001), but no sex differences were observed in the number of performed contractions (isometric: 62 ± 8 vs. 61 ± 5 contractions; dynamic: 521 ± 67 vs. 458 ± 76 contractions for men and women, respectively; P < 0.05). Women showed greater loss in maximal concentric torque independent of the session, while maximal isometric torque loss was similar between men and women. Conclusions. These results indicated that, despite greater TTI after the isometric fatiguing task, no differences between sessions was noticed for performance fatigability quantified as both isometric and concentric maximal torque loss. Contractile function was more reduced in the dynamic QIF test, suggesting that those impairments manifest earlier during dynamic than isometric fatiguing tasks. Moreover, sex-related differences in fatigability depend on the contraction mode used to assess performance fatigability during and / or after the test.