The goal of this clinical trial is to learn if pleasure-oriented exercise intensity manipulation increases physical activity (PA) behavior in patients who have suffered acute coronary syndrome during a cardiac rehabilitation program. The main question it aims to answer is:

• the manipulation of exercise intensity performed to produce more pleasure and arousal will impact the PA behavior? Researchers will compare the PA levels and affective responses to see if the manipulation of exercise intensity guided to pleasure and arousal works to increase PA behavior compared to the control group who will follow a conventional exercise program.

Participants will do:

• sixteen individualized hospital exercise sessions (two per week) and complementary physical activity program integrated into their daily life
• be evaluated before and at the end of the exercise sessions and after 3 months

Ischaemic heart disease remains the top global cause of death, with cases rising by 2.7 million to 9.0 million deaths over the past two decades and between 1990-2019 the percentage of years of life lived with disability increased 83%.

Ischaemic heart disease includes acute coronary syndromes (ACS) that consist of acute myocardial infarction (AMI) and unstable angina. After ACS there is a greater risk of recurrence of the event, arrhythmias, heart failure and sudden death. These patients also have a lower quality of life which impacts their physical function and psychological well-being. ACS represent a substantial direct cost and economic burden for national health systems. Prevention must be prioritized and the emphasis on encouraging physical activity (PA) and routine exercise has become more vital than ever.

The 2023 European Society of Cardiology Guidelines for the management of ACS recommend that all patients participate in a medically supervised, structured, comprehensive cardiac rehabilitation (CR) program with a multidisciplinary team. Its core components are patient assessment, management and control of cardiovascular risk factors, PA counselling, prescription of exercise training, dietary advice, tobacco counselling, patient education, psychosocial management, and vocational support. Exercise plays a key role having a Class I, Level A evidence supporting its benefits, while specific components such as aerobic PA and muscle-strengthening exercises are supported by Class I, Level B evidence. CR plays a crucial role in lowering rates of hospitalization, fatal and non-fatal myocardial infartion, while improving exercise capacity and quality of life. There is also a reduction in healthcare costs for participants in a CR program compared with nonparticipants.

CR typically consists of three phases: phase 1 (in-hospital), phase 2 (mostly in an outpatient setting: centre-based or home-based) and phase 3 (maintenance phase in outpatient or community settings, aimed at sustaining lifestyle changes). Phase 2 CR is typically provided as an outpatient program, lasting between 8 to 24 weeks, with sessions offered 3 to 7 days per week.

A progressive program of structured exercise and PA are a fundamental part of a CR program. Exercise training should be tailored to the individual, following a thorough clinical assessment that includes risk stratification, behavioral traits, personal objectives, and exercise preferences. Exercise should be prescribed based on FITT-VP (frequency, intensity, time, type of exercise, volume, and progression) model. It is recommended to do aerobic training at a frequency of at least 3 days per week, with a preference for 6-7 days per week, at a moderate or moderate-to-high intensity. It is also advised to do resistance training, 2 days per week, at 30-70% of one-repetition maximum (1RM) for the upper body and 40-80% of 1RM for the lower body, with 12-15 repetitions/set. After the end of the CR program (i.e., beginning of phase 3), ACS patients should accumulate at least 30 minutes per day, 5 days per week of moderate intensity PA (equating to 150 minutes per week) or 15 minutes per day, 5 days per week of vigorous intensity PA (equating to 75 minutes per week), or a combination of both. These PA levels are needed for reducing disease progression and increasing quality of life.

Despite being aware of the benefits of regular PA and intending to stay active, many patients struggle to adopt or maintain these behaviors in the long-term. One-third of their sample did not reach the recommended PA levels in the first weeks after discharge from CR. Moreover, in long-term approximately 66% of patients failed to meet the established PA goal.

The central problem is the sustainability of PA after phase 2 CR. Therefore, strategies aimed at improving patients' attitudes toward and adherence to exercise are warranted.

Patient should be actively participating in their exercise program, tailoring it to their needs and preferences, as personalized care increases the likelihood of improved adherence to an exercise routine during and after CR. Knowing that adherence is influenced by complex psychological factors, exploring them should be a crucial effort in such programs. As such, exploring the individual motivation may be a relevant consideration for such effort.

Patient should be actively participating in their exercise program, tailoring it to their needs and preferences, as personalized care increases the likelihood of improved adherence to an exercise routine during and after CR. Knowing that adherence is influenced by complex psychological factors, exploring them should be a crucial effort in such programs. As such, exploring the individual motivation may be a relevant consideration for such effort.

Improving adherence to phase 3 CR recommendations The success of a CR program could be measured by the extent of the individual recovery process and the ability to introduce sustainable, long-lasting behavioral changes capable of preventing relapse, where PA is a crucial component. In apparently healthy individuals, several theories and approaches have been used for adherence support and healthy habits adoption. These are often grounded in motivational aspects, where several prominent theories have been used.

In the CR context, some efforts have been made for this purpose. Some studies used Self-Determination Theory assumptions to explore its potential role in supporting PA in these patients. Results indicated that promoting basic psychological needs satisfaction and supporting autonomy predicted PA/exercise behavior. In other studies, the Theory of Planned Behavior was used as the theoretical background for the same exploration, and once again, evidence was found to the theory underpinnings, mainly for intention, and their positive relation to PA. These are just a few examples of how the study of motivation has been used in the past in CR programmes to try to improve patient adherence in later phases and to support lifestyle changes. However, these are also examples that mimic several of the current issues in translating motivational and behavioral theories into practice, not only in these programmes, but also for general PA promotion. For once, these suggestions emerge from cross-sectional and longitudinal studies, thus evidencing the struggle that translating and operationalization the distinct theories' assumptions brings, given the absence in the last decades of experimental efforts in the most of contexts. Then, it is also possible to easily verify that CR programmes still struggle to improve PA adherence in later stages of the recovery process, even though the unquestionable, evidence-based indication of its worthiness, and the ever-growing support emerging from psychological theories of motivation.

Given that this is not an exclusive problem in this context and patients, researchers concerned with the motivational aspects of PA have been exploring other possibilities and approaches. One that will be used to support the current study's experimental approach is grounded on the emerging line of the psychological study of affectivism. This line of thought assumes that non-rational aspects of behavior, as is the case with core affect, can influence individual motivational development through a hedonistic lens (i.e., tendency to approach activities that promote pleasurable sensations, and to avoid those experienced as unpleasant ones). Core affect is posited to be a neurophysiological state that is consciously accessible as a simple, nonreflective feeling that is an integral blend of hedonic (pleasure-displeasure) and arousal (sleepy-activated) values. Some recent efforts grounded on dual-process theories, where core affect is an integral component of implicit and, indirectly, reflective pathways, have been made in similar CR programmes. That showed support for the role of affective attitudes in supporting PA, thus evidencing the emerging concern and focus of potential affective constructs in this matter.

Current study In PA settings, several conditions can manifest in these feelings (i.e., core affect) and thus impact motivation, but one stands as the one more directly responsible - exercise intensity. As posited by the Affect and Health Behavior Framework (AHBF) and the Dual Mode Theory (DMT), intensity is closely related to core affect manifestations. Generally, the exposure to higher intensities is tendentially experienced as unpleasant, and lower intensities as pleasant. Often, a pleasurable heterogeneity zone emerges between some metabolic (e,g., ventilatory threshold) or load (~75% RM) thresholds that anticipate the decrease and often emergence of unpleasant responses . A successful and individual experience of pleasurable responses is posited to support motivation development and subsequently align with being physically active and supporting lifestyle changes, but experimental efforts to test these theoretical assumptions are lacking.

There is a study where it was manipulated the exercise intensity to promote pleasurable experiences in individualized exercise sessions in fitness centers. An 8-week follow-up showed that the experimental group had a 77% higher session attendance when compared to the control group (14.35 vs. 8.13). This was achieved using the ACSM exercise guidelines for healthy adults, were the exercise intensity, in the experimental group, was adjusted to support pleasurable affective responses and align with individual intensity preference and tolerance, in an autonomy supportive manner.

The current study will be developed in an ongoing CR program aligned with the European Association of Preventive Cardiology (EAPC) guidelines, which presents its own specification of the FITT-VP principles. As such, the general conditions to allow the manipulation of exercise intensity and the replication of the motivational approach are present and are inherently of relevance for increasing phase 2 and 3 CR physical activity levels.

Selection criteria include:

• patients older than 18 years
• diagnosis of ACS within the past 12 months who have not previously participated in a CR program
• patients classified as low-risk (Class B) according to the American Heart Association: (a) New York Heart Association (NYHA) class I or II, (b) exercise capacity greater than 6 METs, (c) no evidence of heart failure, (d) no signs of myocardial ischemia or angina at rest or during exercise testing at or below 6 METs, (e) appropriate systolic blood pressure response during exercise, and (f) absence of sustained or non-sustained ventricular tachycardia at rest or during exercise.

Standard exclusion criteria include:

• left ventricular ejection fraction (LVEF) < 40% at rest
• uncontrolled arrythmias (e.g., complex ventricular arrhythmias, atrial fibrillation or flutter with rapid ventricular response, second-degree atrioventricular block Mobitz type II, or third-degree atrioventricular block)
• presence of an implantable cardiac device
• symptomatic peripheral arterial disease
• comorbidities that may interfere with the ability to perform the exercise program safely.