Purpose : The aim of this study was to compare performance fatigability between young (n = 13; 18–35 yr.; 23.5 ± 3.3 yr.), old (n = 13; 60–79 yr.; 68.2 ± 4.3 yr.), and very old (n = 11; ≥ 80 yr.; 85.6 ± 1.8 yr.) females during single-limb isometric (ISO) vs. isokinetic concentric (CON) vs. cycling (BIKE) fatiguing tasks. Methods : Participants randomly performed three incremental fatiguing tasks where increments were set as percentage of body weight to better reflect the daily life: (1) ISO and (2) CON consisted of stages of 75 contractions (120 s, 0.8 s on/0.8 s off) on an isokinetic dynamometer and (3) BIKE consisted of stages of 120 s at 37.5 rpm with similar duty cycle. Knee extensors maximal force, voluntary activation and potentiated twitch amplitude were measured at baseline, after each stage and at exhaustion. Results : Compared to young, exercise performance was 20% and 53% lower in old and very old females in ISO, 46% and 76% lower in CON and 32% and 62% lower in BIKE (all p < 0.01). For a given workload (i.e. common stages), performance fatigability (i.e. force loss) was greater for very old compared to young females in CON only (p = 0.018). At exhaustion, performance fatigability was similar across groups and conditions (~ 30%; all p > 0.05), with similar impairments in both voluntary activation and twitch amplitude. Conclusion : These results emphasize the importance of the kind of fatiguing task and modalities of evaluation when investigating the effects of aging on performance fatigability.