Isometric versus Dynamic Measurements of Fatigue: Does Age Matter? A Meta-analysis

Purpose The assessment of power changes after fatiguing exercise provides important additional information about neuromuscular function compared with traditional isometric measurements, especially when exploring age-related changes in fatigability. Therefore, the aim of this review was to explore the effects of age on neuromuscular fatigue (NMF) when measured in isometric compared with dynamic contractions. The importance of central and peripheral mechanisms contributing to age-related NMF was discussed. Methods Medline, EMBASE, Cochrane Central Register of Controlled Trials, and SPORT Discus databases were searched. The combination of terms related to the intervention (fatiguing exercise), population (old people) and outcomes (isometric force and power) were used. This meta-analysis was registered on PROSPERO (CRD42016048389). Results Thirty-one studies were included. The meta-analyses revealed that force decrease was greater (there was more NMF) in young subjects than their older counterparts when fatigue was induced by isometric tasks (effect size [ES], 0.913; confidence interval [CI], 0.435-1.391; P < 0.001), but not when the fatiguing exercise was performed in dynamic mode (ES, 0.322; CI, -0.039 to 0.682; P = 0.08). Older individuals demonstrated a greater reduction in power after fatigue induced by either dynamic or isometric tasks (ES, -0.891; CI, -1.657 to -0.125; P = 0.023). Conclusions There is no difference in the isometric force loss between young and old people when fatigue is induced by dynamic tasks. However, maximal power is more decreased after fatigue tasks in older adults. Thus, the assessment of fatigue (isometric force vs power) must be considered in identifying age-related NMF mechanisms.