Increasing the Reinforcing Value of Exercise in Overweight Adults

Altered motivation states for physical activity and 'appetite' for movement as compensatory mechanisms limiting the efficacy of exercise training for weight loss

Weight loss is a major motive for engaging in exercise, despite substantial evidence that exercise training results in compensatory responses that inhibit significant weight loss. According to the Laws of Thermodynamics and the CICO (Calories in, Calories out) model, increased exercise-induced energy expenditure (EE), in the absence of any compensatory increase in energy intake, should result in an energy deficit leading to reductions of body mass. However, the expected negative energy balance is met with both volitional and non-volitional (metabolic and behavioral) compensatory responses. A commonly reported compensatory response to exercise is increased food intake (i.e., Calories in) due to increased hunger, increased desire for certain foods, and/or changes in health beliefs. On the other side of the CICO model, exercise training can instigate compensatory reductions in EE that resist the maintenance of an energy deficit. This may be due to decreases in non-exercise activity thermogenesis (NEAT), increases in sedentary behavior, or alterations in sleep. Related to this EE compensation, the motivational states associated with the desire to be active tend to be overlooked when considering compensatory changes in non-exercise activity. For example, exercise-induced alterations in the wanting of physical activity could be a mechanism promoting compensatory reductions in EE. Thus, one's desires, urges or cravings for movement-also known as "motivation states" or "appetence for activity"-are thought to be proximal instigators of movement. Motivation states for activity may be influenced by genetic, metabolic, and psychological drives for activity (and inactivity), and such states are susceptible to fatigue-or reward-induced responses, which may account for reductions in NEAT in response to exercise training. Further, although the current data are limited, recent investigations have demonstrated that motivation states for physical activity are dampened by exercise and increase after periods of sedentarism. Collectively, this evidence points to additional compensatory mechanisms, associated with motivational states, by which impositions in exercise-induced changes in energy balance may be met with resistance, thus resulting in attenuated weight loss.

Comparing the reinforcing value of high intensity interval training versus moderate intensity aerobic exercise in sedentary adults

Exercise is a reinforcer for both animals and humans, as they will work progressively harder to gain access for the opportunity to exercise. Exercise activates brain reward pathways similar to drugs of abuse, and the magnitude of the reinforcing value of exercise is a predictor of exercise behavior. The majority of research on exercise reinforcement has studied moderate intensity aerobic exercise (MIAE) or resistance training. There is limited research on the relative reinforcing value (RRV) of high intensity interval training (HIIT), which is often reported to be a preferred form of exercise in comparison to MIAE. Experiment 1 was a pilot study of 20 sedentary females designed to compare the reliability of differences in RRV_HIIT vs RRV_MIAE over two sessions, assess protocols comparing different volumes of HIIT in comparison to MIAE, and estimate sample sizes needed for a fully powered study to assess which type of exercise protocol was a better substitute for a highly liked sedentary activity. Experiment 2 studied 44 participants to assess whether HIIT or MIAE would be better substitutes for highly liked sedentary activities. Experiment 1 showed that measures of RRV_HIIT or RRV_MIAE were reliable, and that volume of HIIT did not influence RRV_HIIT, even if it was of equal amount or duration to MIAE. Experiment 2 showed that HIIT was a more preferred substitute for sedentary behaviors than MIAE. Predictors of RRV_MIAE were liking of MIAE and pleasantness of affect post MIAE. These results suggest inactive people may find interval training to be more reinforcing than MIAE, and may be more likely to adopt and maintain an exercise program involving HIIT rather than MIAE. The next stage of research should be to understand how to sensitize the RRV of exercise to motivate sedentary people to be more active.

Motivation States for Physical Activity and Sedentary Behavior: Desire, Urge, Wanting, and Craving

To better explain daily fluctuations in physical activity and sedentary behavior, investigations of motivation are turning from social cognitive frameworks to those centered on affect, emotion and automaticity, such as the Affect and Health Behavior Framework (AHBF), Integrated Framework and Affective-Reflective Theory (ART). This shift has necessitated: (a) re-examination of older theories and their constructs, such as drives, needs and tensions and (b) an inspection of competing theories from other fields that also attempt to explain dynamic changes in health behaviors. The Dynamical Model of Desire, Elaborated Intrusion Theory and others commonly share with AHBF the idea that human behavior is driven strongly by desires and/or the similar concepts of wants, urges, and cravings. These affectively-charged motivation states (ACMS) change quickly and may better explain physical activity behavior from one moment to the next. Desires for movement predominantly derive from negative but also positive reinforcement. Data from clinical populations with movement dysfunction or psychiatric disorders provides further evidence of these drivers of movement. Those with Restless Legs Syndrome, akathisia, tic disorders and exercise dependence all report strong urges to move and relief when it is accomplished. Motor control research has identified centers of the brain responsible for wants and urges for muscular movement. Models elaborated herein differentiate between wants, desires, urges and cravings. The WANT model (Wants and Aversions for Neuromuscular Tasks) conceptualizes desires for movement and rest as varying by magnitude, approach or avoidance-orientation (wants versus aversions) and as occupying independent dimensions instead of opposite ends of the same axis. For instance, one hypothetically might be in a state of both high desire for movement and rest simultaneously. Variations in motivation states to move and rest may also be associated with various stress states, like freezing or fight and flight. The first validated instrument to measure feelings of desire/want for movement and rest, the CRAVE Scale (Cravings for Rest and Volitional Energy Expenditure) is already shedding light on the nature of these states. With these advances in theory, conceptual modeling and instrumentation, future investigations may explore the effects of desires and urges for movement and sedentary behavior in earnest.

The consequences of exercise-induced weight loss on food reinforcement. A randomized controlled trial

BACKGROUND

Obesity remains a primary threat to the health of most Americans, with over 66% considered overweight or obese with a body mass index (BMI) of 25 kg/m2 or greater. A common treatment option many believe to be effective, and therefore turn to, is exercise. However, the amount of weight loss from exercise training is often disappointingly less than expected with greater amounts of exercise not always promoting greater weight loss. Increases in energy intake have been prescribed as the primary reason for this lack of weight loss success with exercise. Research has mostly focused on alterations in hormonal mediators of appetite (e.g.: ghrelin, peptide YY, GLP-1, pancreatic polypeptide, and leptin) that may increase hunger and/or reduce satiety to promote greater energy intake with exercise training. A less understood mechanism that may be working to increase energy intake with exercise is reward-driven feeding, a strong predictor of energy intake and weight status but rarely analyzed in the context of exercise.

DESIGN

Sedentary men and women (BMI: 25-35 kg/m2, N = 52) were randomized into parallel aerobic exercise training groups partaking in either two or six exercise sessions/week, or sedentary control for 12 weeks.

METHODS

The reinforcing value of food was measured by an operant responding progressive ratio schedule task (the behavioral choice task) to determine how much work participants were willing to perform for access to a healthy food option relative to a less healthy food option before and after the exercise intervention. Body composition and resting energy expenditure were assessed via DXA and indirect calorimetry, respectively, at baseline and post testing.

RESULTS

Changes in fat-free mass predicted the change in total amount of operant responding for food (healthy and unhealthy). There were no correlations between changes in the reinforcing value of one type of food (healthy vs unhealthy) to changes in body composition.

CONCLUSION

In support of previous work, reductions in fat-free mass resulting from an aerobic exercise intervention aimed at weight loss plays an important role in energy balance regulation by increasing operant responding for food.

Incentive sensitization for exercise reinforcement to increase exercise behaviors

Individuals can be sensitized to the reinforcing effects of exercise, although it is unknown if this process increases habitual exercise behavior. Sedentary men and women (body mass index: 25-35 kg/m², N = 52) participated in a 12-week aerobic exercise intervention. Exercise reinforcement was determined by how much work was performed for exercise relative to a sedentary alternative in a progressive ratio schedule task. Habitual physical activity was assessed via accelerometry. Post-intervention increases in exercise reinforcement predicted increases in physical activity bouts among those who expended over 2000 kcal per week in exercise and who compensated for less than 50 percent of their exercise energy expenditure.