Abstract
AIMS: The clinical syndrome of heart failure includes exercise limitation that is not directly linked to measures of cardiac function. Quadriceps fatigability may be an important component of this and this may arise from peripheral or central factors. METHODS AND RESULTS: We studied 10 men with CHF and 10 healthy age-matched controls. Compared with a rest condition, 10 min after incremental maximal cycle exercise, twitch quadriceps force in response to supramaximal magnetic femoral nerve stimulation fell in both groups (CHF 14.1% ± 18.1%, p=0.037; CONTROL: 20.8 ± 11.0%, p<0.001; no significant difference between groups). There was no significant change in quadriceps maximum voluntary contraction voluntary force. The difference in the motor evoked potential (MEP) response to transcranial magnetic stimulation of the motor cortex between rest and exercise conditions at 10 min, normalised to the peripheral action potential, also fell significantly in both groups (CHF: 27.3 ± 38.7%, p=0.037; CONTROL: 41.1 ± 47.7%, p=0.024). However, the fall in MEP was sustained for a longer period in controls than in patients (p=0.048). CONCLUSIONS: The quadriceps is more susceptible to fatigue, with a similar fall in TwQ occurring in CHF patients at lower levels of exercise. This is associated with no change in voluntary activation but a lesser degree of depression of quadriceps motor evoked potential.