Age-related differences in performance and fatigability during an isometric quadriceps intermittent fatigue test

The aim of the present study was to investigate age-related differences in fatigability induced by an isometric quadriceps intermittent fatiguing test in young (<35 years old), old (>60 years old) and very old (>80 years old) men and women. 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. Total work (absolute performance) was greater for young and old adults compared to very old adults (P < 0.001), without differences between young and old adults. At exhaustion, force loss was greater for young (-28 {+/-} 9%) compared to old adults (-19 {+/-} 8%), but not very old adults (-23 {+/-} 8%). The response to femoral nerve stimulation decreased similarly at exhaustion for the three age groups, indicating similar alteration in contractile function with age. No impairment in voluntary activation was observed. Impairments in neuromuscular parameters were similar for men and women. 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.