Central and peripheral quadriceps fatigue in congestive heart failure

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.

Keywords: Brain; Exercise; Muscles; Transcranial magnetic stimulation.

Fig. 1

Schematic of the protocol that all subjects underwent. The rest period lasted 30 min. Assessments were made at baseline and at 10, 30, 60 and 90 min after the intervention (either rest or exercise). TMS transcranial magnetic stimulation; TwQu Quadriceps twitch in response to femoral nerve stimulation; MVC quadriceps maximum voluntary contraction.

Fig. 2

Change in force of peripheral quadriceps twitches over time in control subjects (A) and patients (B) relative to baseline expressed as a percentage. There was a significant difference in the pattern of the response between the two interventions in both groups (Controls: p = 0.002, CHF: p = 0.019). Difference between interventions at 10 min: *p < 0.001, **p = 0.037.

Fig. 3

Change in magnitude of the force of maximal voluntary contractions (MVC) over time in control subjects (A) and patients (B) (n = 9 in both groups) relative to baseline expressed as a percentage. There was no significant difference in the pattern of the response between the two interventions in both groups (Controls p = 0.44, CHF p = 0.084).

Fig. 4

Change in motor evoked potential (MEP) over time in control subjects (A) and patients (B), corrected for changes in the compound muscle action potential (CMAP) relative to baseline expressed as a percentage. There was a significant difference in the pattern of the response between the control subjects and patients (p = 0.048). Difference between interventions at 10 min: *p = 0.024, **p = 0.037.

Fig. 5

Changes in the compound muscle action potential (CMAP) over time in control subjects (A) and patients (B) expressed as a percentage. There was no significant change in the electrical response to peripheral stimulation in either group in either condition.

Fig. 6

Changes in the latency in milliseconds (ms) of the motor evoked potential (MEP) over time in control subjects (A) and patients (B). There was no significant change in the latency in either group in either condition.