HIGH-INTENSITY INTERVAL EXERCISE IN CHRONIC HEART FAILURE: COMPARISON OF CARBOHYDRATE AND LIPID OXIDATION

BACKGROUND: high-intensity interval exercise has been extensively used with athletes and healthy subjects. There are a few evidences that it could improves physiology and functional capacity in heart failure patients, but still some answers about muscle metabolism need to be addressed. METHODS: substrate oxidation was compared during 4 different high intensity intermittent exercise (HIIE) protocols in patients with heart failure and reduced ejection fraction (HFREF). Eighteen males (56 17 years, LVEF: 28 7%) randomly performed 4 HIIE with measurement of gas exchange. Exercise intensity protocols were set at 100% of peak power output (PPO). Interval duration was 30 seconds (A and B) or 90 seconds (C and D), and recovery was passive (A and C) or active (50% of PPO in B and D). Energy expenditure was calculated using Weir equation and substrate oxidation (glucose: CHO, and lipid) was calculated by the Frayn equation (for quantitative measure) and from a table of non-protein respiratory quotient (qualitative measure) using gas exchange analysis. RESULTS: mean O2peak was 17.8 4.6 ml/min/kg (or 1.54 4.6 L/min) and peak power output was 109 31 Watts. At rest, fat oxidation averaged 0.13 0.04 g/min, representing 68 22 % of total substrate utilisation. CHO oxidation averaged 0.16 0.1 g/min representing 31 22% of total. During exercise, absolute CHO oxidation significantly decreased and absolute lipid oxidation significantly increased in each HIIE protocol (P<0.0001). Protocol B induced higher energy expenditure after 8-10 minutes of exercise compare to passive recovery modes (A and C) (P<0.0001). Short duration intervals with passive recovery (mode A) resulted in significantly lower CHO oxidation in absolute terms compare to modes with active recovery (B and D) (P<0.0001). In relative terms (%), CHO oxidation in mode A was significantly lower than mode C only, after 8-10 minutes of exercise. Lipid oxidation in absolute terms was significantly lower in mode C compare to the other 3 modes of HIIE at time 8-10 min whereas in relative terms it was significantly lower than mode A only (P<0.0001). All together, these 4 HIIE protocols showed increased lipid oxidation over time, and short interval duration with passive recovery showed higher lipid oxidation compared to the others. CONCLUSION: the choice of an active mode during HIIE may favors glucose oxidation during exercise in patients with HFREF, if the improvement of glucose metabolism is targeted.