Heart failure (HF) is currently considered a common pathology, with 15 million adults in Europe and 26 million worldwide. The American Heart Association (AHA) estimates that their number will increase by 25% by 2030. In France, HF affects more than one million people. Because of the repeated hospitalizations of this disease, it is considered a costly pathology and with a high mortality rate (23.000 deaths per year in France). Moreover, HF is a severe pathology that affects the quality of life of patients and their families. Treatment and medical follow-up are required.

A cardiac rehabilitation program is also a primary indication according to the latest recommendations and repositories in Cardiology. Various studies show that "Interval Training" exercise program improves VO2 peak compared to a "continuous" program, which constitutes a major prognostic factor in the population of heart failure. However, it is sometimes a difficult program to offer to more deconditioned patients as it requires reaching powers around 80% - 95% of its maximum exertion capacity. So, a variant of the interval training is offered, called Progressive Interval Training (PIT), based on the same model as the conventional interval training (CIT), but with an increasing power and breathing threshold, so that the patient can adapt gradually.

The hypothesis is that PIT could improve VO2 peak better than CIT in cardiac rehabilitation program. Therefore, study the benefits of PIT training to improve the conditioning and quality of life of patients with chronic heart failure will be studied.

Chronic Heart Failure (CHF) is due to structural or functional cardiac anomalies which causes a lack of oxygen perfusion to various organs provoking symptoms as dyspnea, fatigue, palpitation at rest or during efforts. International prevalence is 1-2% in adult population, wich represents 15 million people in Europe and 26 millions in the world. In France, CHF represents the first cause of hospitalization. The rate of intra-hospital mortality is 8.2 % and the mortality in 1 year is 26 % according to the study OFICA in 2013. Its treatment is first medication.

Cardiac rehabilitation programs are also proposed. According to the latest recommendations of the European Society of Cardiology in 2016, patient education on diet, medical treatment observance and facilitation of psychosocial assistance with access to a multidisciplinary team, will reduce the rate of hospitalization and mortality (level of evidence IA). Similarly, the regular practice of an aerobic-type activity will increase the patient's functional capacity and improve the symptoms related to the disease. In the same way, the risk of re-hospitalization will be reduced (level of evidence IA). Cardiac rehabilitation of CHF patients includes a so-called "segmentary analytics" rehabilitation based on strength exercises and aerobic-type endurance work. This classical program is called "continuous" training in which the patient must exert on a cycloergometer or walking on a treadmill between 60% and 70% of his maximum exertion capacity, evaluated with initial VO2 max exercise test, before cardiac rehabilation. More recently, a new form of rehabilation mode appeared: "Interval Training" (IT) inspired by high level athletes training. It is a training model that alternates periods of intensity between 60%-95% of maximum effort (depending on the modality) and periods of passive or active rest between 20-30% of maximum effort. IT is more suitable for endurance work in CHF patients than continuous training. Indeed, this type of exercise has a muscular impact, in terms of strength, superior to that brought by continuous training without significantly increasing cardiac work or hemodynamic and metabolic parameters. Some studies show the effectiveness of both types of programms (continuous or IT) on improving the 6 minute walk test distance (6MWD) and displacing the first ventilatory threshold (VT1) for higher intensities. However, the interval training has a better effect than continuous program: 19.4% versus 8.3% for 6MWD improvement and 95% versus 75% for heart peak rate gain.

Nevertheless, it have been observed in daily practice that classical conventional IT (CIT) program could be difficult to perform in most of CHF patients, due to the severity of their pathology, poor physical condition and especially muscle deconditioning. Indeed, this deconditioning is linked to the sedentary behaviour of this type of patient because of the specific symptoms of his cardiac pathology, which will result in severe intolerance to effort. In Cardiac rehabilitation department of Montpellier University Hospital, a new type of IT program for severe CHF patients have been tested, with progressive intervals of maximum effort and active rest periods, called the Progressive Interval Training (PIT) program. After 6 months of applying this training model to our patients, it seems to be effective in endurance gain in final exercise test and without side-effects in terms of safety. The objective is to compare the 2 types of IT workouts (CIT and PIT) in 2 different randomized groups, on the improvement of VO2 peak in patients with severe CHF. Secondary ojectives are the imporvemnt on 6MWD, life quality and ventilatory threshold at the end of rehabilitation (VT1).

A typical session for a patient takes place in two parts: the first one with analytical segmentary rehabilitation exercises identical in terms of the muscular group worked and the number of series and repetitions and adapted (charge in kg) to each patient, and a second one of endurance aerobic work with conventional interval training (CIT) program or progressive interval training (PIT) program according to the randomized groups.

• CIT intervention consists in: warming 7 minutes at 15 watts, then alternating exercices phases at 30% of maximum power (reached by patient at initial VO2 maximal exercise test realized before cardiac rehabilation) during 3 minutes and peak at 60% of maximum watts during 1 minute, then return to calm 3 minutes at 15 watts. Total duration of the endurance session is 30 minutes. The power in watts of the peak work will be shaped according to the Borg (if 6, increase of 5 watt the value of each peak at the next session).
• PIT intervention consists in: warming 7 minutes at 15 watts, then alternating exercices phases at 30% watts of maximum power (reached by patient at initial VO2 maximal exercise test realized before cardiac rehabilation) during 3 minutes, a first peak work at 40% of maximum power, a second at 45%, a third at 50%, a fourth at 55% and a fifth at 60%, then return to calm 3 minutes at 15 watts. Total duration of this endurance session is also 30 minutes. The peak powers will be shaped according to the Borg (if 6, increase of 5 watt the value of each peak to the next session).

Each patient conducts a total of 20 sessions at a rate of 2 sessions per week. It is a monocentric, controlled, randomized, prospective study with two parallel groups (open except for the evaluation which will be blind). The sample size is estimated at 50 subjects. Inclusion criteria are patients with CHF (left ventricular ejection fraction <40%), men or women over 60 years of age, admitted on a cardiac rehabilation medical, with a functional capacity of less than 5 Mets, all of whom have their free and informed consent for the study.

The benefits to the patient are those related to Cardiovascular Rehabilitation that increase its functional capacity while improving its quality of life.

If the effectiveness of PIT program on improving aerobic capacity (VO2 max), functional abilities (VT1, TDM6 ') and/or quality of life is demonstrated, this program could be recommended for cardiac rehabilitation in patients with severe CHF. A larger number of patients could benefit from this program which takes into account the muscular deconditioning related to their pathology.

Inclusion Criteria:

• Patients with chronic systolic heart failure (LVEF <40%)
• men or women
• 40 years patients or older
• Patients admitted on cardiac rehabilitative medical prescription
• Patients with a functional capacity of 6 Mets or less
• Patients having given their free and informed consent to the study.

Exclusion Criteria:

• Contraindication to rehabilitation,
• Refusal of the patient to participation in the study
• impaired comprehension
• inability to perform the cyclometer
• participation in another therapeutic protocol simultaneously