Very old adults show impaired fatigue resistance compared to old adults independently of sex during a knee-extensors isometric test.

The present study aimed to investigate age-related differences in fatigability induced by an isometric quadriceps intermittent fatiguing test in 30 young (<35 years old, 15 females), 19 old (>60 years old, 9 females) and 30 very old (>80 years old, 15 females) adults. Maximal force loss, contractile function and voluntary activation of the knee extensors were evaluated throughout an isometric fatiguing test using femoral nerve magnetic stimulations. Older adults performed more contractions (index of relative performance) than young (P = 0.046) and very old adults (P = 0.007), without differences between young and very old adults (P = 1.000). Force-time integral (absolute performance) was greater for young and old adults compared to very old adults (P < 0.001), without differences between young and old adults (P = 0.124). At exhaustion, force loss was greater for young (-28 ± 9%) compared to old adults (-19 ± 8%; P = 0.002), but not very old adults (-23 ± 8%; P = 0.106), and no difference between old and very old adults (P = 0.414). Data from the interpolated twitch technique suggested similar alteration in contractile function with age, with no impairments in voluntary activation. Impairments were similar across sexes. This study showed that older adults were less fatigable than young adults during an isometric intermittent fatiguing task of the knee extensors. This greater fatigue resistance was not maintained in very old adults independent of sex. Fatigability at exhaustion was likely due to impairments in contractile function for the three age groups.