Quadriceps function assessment using an incremental test and magnetic neurostimulation: A reliability study

We investigated the reliability of a test assessing quadriceps strength, endurance and fatigability in a single session. We used femoral nerve magnetic stimulation (FMNS) to distinguish central and peripheral factors of neuromuscular fatigue. We used a progressive incremental loading with multiple assessments to limit the influence of subject’s cooperation and motivation.Twenty healthy subjects (10 men and 10 women) performed the test on two different days. Maximal voluntary strength and evoked quadriceps responses via FMNS were measured before, after each set of 10 submaximal isometric contractions (5-s on/5-s off; starting at 10% of maximal voluntary strength with 10% increments), immediately and 30 min after task failure.The test induced progressive peripheral (41 ± 13% reduction in single twitch at task failure) and central fatigue (3 ± 7% reduction in voluntary activation at task failure). Good inter-day reliability was found for the total number of submaximal contractions achieved (i.e. endurance index: ICC = 0.83), for reductions in maximal voluntary strength (ICC > 0.81) and evoked muscular responses (i.e. fatigue index: ICC > 0.85). Significant sex-differences were also detected.This test shows good reliability for strength, endurance and fatigability assessments. Further studies should be conducted to evaluate its feasibility and reliability in patients.