A call for an exercise prescription aiming at pleasure promotion has been proposed by several authors. This entails that current exercise prescription guidelines are heavily focused on a dose-response relation derived from an effectiveness (e.g., fitness gains) and safety of the prescription (e.g., reduced risk of injury for the general population) standpoint. Despite its relevance, this bipartite or biomedical approach (e.g., rationale for a given dose of a drug and expected outcome) tends to overlook other relevant variables that are needed for, for example, behavior maintenance, or individual preferences. Although some flexibility of this rationale may account for personal differences, how to adequately adjust the training variables to individual characteristics is still poorly explored or even expressed.

The call for a tripartite exercise prescription reflects the bout of evidence that supports the relevance of pleasurable experiences in exercise and their impact on adherence. Thus, besides an effective and safe program, contemplating how to assess and promote exercise-related pleasurable experiences are paramount. As stated in 2011 on the ACSM position stand, affect-regulation did not behold the necessary evidence to be a primary method of exercise prescription, although affect assessment (e.g., through the feeling scale) was proposed to be relevant for exercise intensity self-regulation. A decennial look at the ACSM exercise guidelines shows that although presenting an advancement in affect-related behavioral strategies and theories, no clear indications on operational instruments for assessment and admeasurement of affect are presented depicts a barrier to an adequate advancement in this matter. This can be seen, for example, in ACSM principles for exercise prescription (Frequency, Intensity, Time, and Type; FITT). Although supporting the use of affect regulation for exercise promotion and maintenance, the FITT is not based on a previous (e.g., preexercise evaluation) or in-session affective assessment, and more importantly, does not address how to adjust exercise prescription/supervision aiming to improve the pleasure/displeasure relation.

Background and rationale From a public health standpoint, gyms and health clubs are one of the most relevant contexts of supervised exercise practice, targeting millions of individuals worldwide. However, exercise adherence has proven to be a challenge in the last 20 years. Several indicators show high attrition rates (i.e., clients' dropout in a given period) in these contexts, particularly in the first 6 months.

Individual physical activity promotion can be challenging as it reflects several aspects of a complex human behavior. Many psychological theories and strategies have been used to address this issue, albeit with differentiated results. These are usually based on cognitivist assumptions and have shown small to moderate effects on exercise adherence. However, in recent years, exercise psychology started to shift attention to other constructs that can help expand the predictive value of current theoretical models. Particularly, affective processes (e.g., emotions, mood) have been highlighted as relevant when trying to understand or predict behavior, and a call for a new era - the affectivism - is emerging. This reflects a new parading resulting from decades of evidence in which affective processes can be seen as outcomes, but also as relevant constructs that can expand the understanding of current behavioral strategies and theories.

For example, the latest edition of the American College of Sports Medicine (ACSM) guidelines presented an expanded chapter addressing behavioral theories for increasing physical activity, which, besides the most commonly used (e.g., self-efficacy, self-determination theory, theory of planned behavior), now explores affect regulation as a product of non-conscious motivational processes (e.g., dual-process theories), and the automatic associations between behavior and previous affective response (i.e., remembered affect).

Affective determinants in exercise and the role of exercise intensity

Affect can be understood as an umbrella term that encompasses (1) the most general valenced experiential responses (e.g., pleasure/displeasure; good/bad), termed basic affect or core affect, and (2) emotion and mood, which reflects appraisal processes of basic affect, and are usually called distinct affective states. Several theories and models have been developed in recent years that reflect this conceptualization and the evidence of affect-related constructs, as is the case, for example, of the Affective-Reflective Theory of physical inactivity and exercise (ART); the Physical Activity Adoption and Maintenance (PAAM) model; the Theory of Effort Minimization in Physical Activity (TEMPA), and the Affect and Health Behavior Framework (AHBF).

In the broader look given by the AHBF, the affective response (i.e., how one feels while performing an activity or immediately after completing the activity; core affect), triggers a set of influences that can, via an automatic or reflective affect processing, influence motivation, goals, behavioral intentions and, ultimately, the exercise behavior. As shown in some research, the affective response during exercise has demonstrated to be a determinant of future behavior, and core affective valence and activation the most relevant aspects in this matter. This seems to be grounded in hedonic assumptions (i.e., pursuing pleasure and avoiding displeasure or pain), in which positive (and regular) shifts in affective valence and/or activation tend to increase the likelihood of future exercise behavior, and a negative shift may have an opposite influence.

Regarding exercise characteristics that may influence the affective response, exercise intensity stand out as the most relevant. Current evidence suggests that people present distinct responses as intensity increases. Generally, aerobic activities intensities below the ventilator threshold depict similar patterns among exercisers, given that an increase in intensity usually corresponds to an increase in the pleasurable response. After the ventilator threshold, inter-individual variability marks how soon or accentuated the pleasure decline will be manifested. For resistance training, some evidence also indicates that increases in intensity (e.g., Repetition Maximum (RM) %) are positively associated with pleasure until the 70-80 RM% interval, a moment from which individual characteristics will reflect, albeit unclear at this point at which rate or magnitude, an inverted association with pleasure. Thus, targeting the intensity-pleasure/displeasure relation individually may be of particular relevance for the exercise domain when aiming to promote adherence.

Exercise prescription - a tripartite approach

A call for an exercise prescription aiming pleasure promotion has been proposed by several authors. This entails that current exercise prescription guidelines are heavily focused on a dose-response relation derived from an effectiveness (e.g., fitness gains) and safety of the prescription (e.g., reduced risk of injury for the general population) standpoint. Despite its relevance, this bipartite or biomedical approach (e.g., rationale for a given dose of a drug and expected outcome) tends to overlook other relevant variables needed for, for example, behavior maintenance or individual preferences. Although some flexibility of this rationale may account for personal differences, how to adequately adjust the training variables to individual characteristics is still poorly explored or even expressed.

The call for a tripartite exercise prescription reflects the bout of evidence that supports the relevance of pleasurable experiences in exercise and their impact on adherence. Thus, besides an effective and safe program, contemplating how to assess and promote exercise-related pleasurable experiences are paramount. As stated in 2011 on the ACSM position stand, affect-regulation did not behold the necessary evidence to be a primary method of exercise prescription, although affect assessment (e.g., through the feeling scale) was proposed to be relevant for exercise intensity self-regulation. A decennial look at the ACSM exercise guidelines shows, and although presenting an advancement in affect-related behavioral strategies and theories, that no clear indications on operational instruments for assessment and admeasurement of affect are presented, which depicts a barrier to an adequate advancement in this matter. This can be seen, for example, in ACSM principles for exercise prescription (Frequency, Intensity, Time, and Type; FITT). Although supporting the use of affect regulation for exercise promotion and maintenance, the FITT is not based on a previous (e.g., preexercise evaluation) or in-session affective assessment, and more importantly, does not address how to adjust exercise prescription/supervision aiming to improve the pleasure/displeasure relation.

Inclusion Criteria:

• Between 18 and 45 years old,
• Apparently healthy and without contraindications to exercise,
• Normal weight (BMI ≥18.5 <29.9 Kg/m2);
• To have previous experience in a gym or health club
• To be at least 6 months without any type of regular strength, cardiovascular, or flexibility workouts (< 5 workouts/month) in a health club or any kind of structured sports activity).

Exclusion Criteria:

Before enrollment

• High in the risk stratification for cardiovascular disease (ACSM, 2021)
• High blood pressure (≥ 130/80mmHg) in the initial preexercise evaluation

During the intervention

• Acquired injury
• The inability to perform 2 exercise sessions (48h to 96h apart) in two consecutive weeks