The aim of this study is to examine acute affective responses during and after a series of exercise sessions with different intensities in young healthy adults. The study is a randomized controlled trial with three different groups (A: moderate continuous training (MIT), B: high-intensity aerobe interval training (HAIT), C: high-intensity sprint interval training (HIIT)). Healthy adults aged 18-40 years (n=30) will be invited to participate. Each participant will perform a VO2max test followed by five session of the randomized type of training. The sessions will be completed within two weeks. The participants will complete questionnaires regarding exercise motivation (Behavioral Regulation of Exercise Questionnaire), mood (Positive and Negative Affect Scale, Profile of Mood States, Visual Analogue scale, Self-assessment Manikin Rating Scale) and perceived exhaustion (Borg Ratings of Perceived Exertion scale). In addition, blood lactate and heart rate will be obtained during and after each session.

Physical activity has is considered as one of the most important health related aspects of the 21st century. In Norway, large epidemiological studies show that only about 30% of the adult population meet the physical activity recommendations of 150 minutes per week with moderate-to-vigorous intensity physical activity. Also, studies show that there are large dropout rates from lifestyle interventions, and that approximately 50% drop out from physical activity interventions within 6 months after start. One explanation for the dropout is performance of exercise with too vigorous intensities.

Very vigorous intensity physical activity can be experienced as unpleasant. According to the dual-mode theory there are positive affective responses after low-to-moderate intensity physical activity, whereas vigorous intensity physical activity trigger negative affective responses which again can lead to reduced motivation for the exercise. Unfortunately, many of the studies performed on affective responses to exercise have used one session only. The studies who have examined changes in affective responses after series of exercise have used vigorous intensities above the anaerobic threshold, and it is therefore unknown whether similar affective responses occur in vigorous intensity aerobe exercise.

The aim of this study is to examine acute affective responses during and after a series of exercise sessions with different intensities in young healthy adults.

To examine this, a randomized controlled clinical trial with three different groups (moderate intensity training (MIT), high-intensity aerobic interval training (HAIT) and high-intensity sprint interval training (HIIT)) will be conducted. A power calculation showed need for recruitment of 30 participants. The sample will consist of healthy young adults. All participants will perform one VO2max test, and five sessions with the intensity they are randomized to. All six sessions (test + exercise sessions) will be conducted within two weeks.

Inclusion Criteria:

• Healthy
• No high intensity interval training during the past three months prior to participation
• Regular exercise up to two sessions per week
• 18-40 years of age
• BMI <30 kg/m2

Exclusion Criteria:

• Competing athlete
• Smoker
• Injury not compatible with performing the exercises
• BMI <16 kg/m2
• Pregnant