[Is there a disassociation of ventilatory and electromyographic thresholds in patients with heart disease during a graded cycling exercise?].

UNLABELLED

Exercise prescription was generally based on the determination of ventilatory thresholds (VT, VT) during cardiopulmonary exercise testing (CPX). Changes in surface electromyographic activity (EMG, EMG) were also related to VT and VT in healthy subjects.

OBJECTIVE

To observe the occurrence of EMGt and EMG and whether these events accompany VT and VT during CPX in cardiac patients (CP).

METHOD

Thirty-four CP (62.1±7.3years, 172.1±6.3cm, 81.3±15.3kg, BMI: 27.3±4.1) performed a cycle CPX at a 60-rpm cadence. VT was determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (V-slope method). VT was defined as the point at which the ratio of minute ventilation to carbon dioxide output starts to increase. The root mean square of electromyogram (rms-EMG) was on-line calculated from the real time bipolar surface electromyographic signals recorded from the vastus lateralis. EMG and EMG were defined as the first and the second breakpoints in the rms-EMG-power output relationship.

RESULTS

Peak values of oxygen uptake (16.3±4.6mL·min·kg) and heart rate (106.7±13.8bpm) were reached at 112.9±38.5w (PMT). VT and VT occurred at 71.1±25.9w (62.5±5.5% PMT) and 87.9±28.6w (78.0±5.1% PMT). All subjects presented two breakpoints in the rms-EMG curve, EMG at 68.0±24.7w and EMG at 88.5±30.1w, i.e. 60.0±7.6 and 78.6±5.0% of PMT. EMG occurred significantly before VT (P=0.004, small effect size). No significant difference was observed between EMG and VT (P=0.13, small effect size).

CONCLUSION

The EMG occurrence before VT suggested a role of skeletal muscle conditioning on ventilatory responses, which should be taken into account in cardiac rehabilitation program prescription.