Between August 2012 and June 2013, all men and women born between years 1936 to 1942 (aged 70–77 years), with a permanent address in the municipality of Trondheim, Norway, were invited to participate in a randomized controlled trial, the Generation 100 study. The primary aim of Generation 100 is to determine the effect of five years of exercise training on morbidity and mortality. The Generation 100 study protocol and study sample characteristics have been published previously .
In total, 1567 participants (790 women) met the inclusion criteria, fulfilled baseline testing and were randomized 1:1 into an exercise training group or to a control group. The exercise training group was further randomized 1:1 to either MCT or HIIT. Participants in the exercise groups were instructed to fill in exercise logs after each exercise session they performed. Data in the present study is based on the exercise logs from the first year of the intervention. Therefore, only participants in the exercise groups were included in the present study (n = 787). Dropouts in the exercise groups during the first year (n = 123) and those with no exercise logs (n = 46) were excluded. A total of 618 participants (291 women) were included in the analyses (Fig. 1). The study was approved by the Regional Committee for Medical Research Ethics (REK sør-øst B: 2015/945) and all participants gave their written informed consent before participation.
The MCT group was prescribed two weekly exercise sessions of 50-min continuous activity at 70% of peak heart rate, or approximately 13 on the Borg 6–20 rating of perceived exertion (RPE) scale . The HIIT group was prescribed two exercise sessions a week with 10-min warm-up followed by 4 × 4 min intervals at 85–95% of peak heart rate, or approximately 16 on the Borg 6–20 RPE scale. The participants were given individual oral and written information about the training methods, including information about frequency, duration, intensity and examples of exercise sessions. The participants were free to exercise individually, with an exercise type and at a location of their own choosing. Every sixth week the participants met for a supervised spinning session where they exercised with a heart rate monitor. These exercise sessions gave the participants an opportunity to control their intensity during exercise. In addition, organized group exercise was offered twice per week for motivational purposes. Attendance to these exercises was voluntary and the activity performed varied between indoor and outdoor activities such as walking, jogging and aerobics . Besides the two prescribed exercise sessions, the participants were free to exercise as desired.
Assessment of exercise patterns
Exercise was defined as planned, structured activities, for instance going for walks, skiing, swimming and doing sports, but also as unplanned activities that the participants experienced as exercise. The participants were asked to fill in exercise logs immediately after each exercise session they performed throughout the year and send them to the research center either in prepaid envelopes monthly, or to use internet-based forms following each exercise session . Exercise frequency was calculated as the mean number of sessions reported per week during the year. To assess intensity of exercise the participants reported their subjective RPE on a Borg scale ranging from 6 to 20 . The participants were asked to report the mean intensity level during the exercise session. Ratings from 6 to 10 were classified as low intensity, 11 to 14 as moderate intensity, and 15 to 20 as high intensity. Duration of exercise was measured with a 4-point scale: less than 15 min, 15–29 min, 30 min to 1 h, and more than 1 h. Less than 15 min and 15–29 min was combined due to a low response rate on these response options (1.1 and 8.7% of the total number of exercise sessions, respectively).
To measure exercise type the participants were instructed to choose from the following response options: walking, jogging, cycling, dancing, cross-country skiing, swimming, golf, resistance training and an open-ended response option. Answers in the open-ended response option were categorized into: combined endurance and resistance training, other type of endurance training (e.g. treadmill, aerobic), domestic activities (e.g. housework, gardening), and other (e.g. bowling, horseback riding). Golf was categorized as “other” due to a low response rate (0.5% of the total number of exercise sessions).
The question used to assess location of exercise had the following response options: home, outdoor in nearby area, nature, gym, indoor- and outdoor sports facility. Indoor- and outdoor sports facility was categorized as “sports facility” due to a low response rate on the outdoor sports facility option (1%). For social setting of exercise, the response options were: exercised alone, exercised together with others, and organized by Generation 100.
Demographics and health characteristics
The baseline testing included clinical examinations, physical tests and questionnaires about health and lifestyle. Age and sex were obtained from the National Population Registry. A previously described questionnaire provided information on physical activity level and sedentary time at baseline . Detailed protocol for assessment of body weight (kg), body height (cm) and body mass index (BMI; kg/m2) is described elsewhere . Testing of peak oxygen uptake (VO2peak; mL/kg/min) was performed either as walking on a treadmill or cycling on a stationary bike. The test started with 10 min at a chosen warm-up speed. Approximately every two minutes, either the incline of the treadmill was increased by 2%, or the speed was increased by 1 km/h. The test protocol ended when participants were no longer able to carry a workload due to exhaustion or until all the criteria for a maximal oxygen uptake were reached .
Sample characteristics are presented as mean ± standard deviation for continuous variables and proportions for categorical variables. Pearson Chi-square test and independent samples t-test were used to assess potential sex differences. For BMI and weight, a non-parametric test (Mann-Whitney U) was conducted due to the lack of normal distribution. Data from the exercise logs are presented as proportions of the total number of exercise logs. Pearson Chi-square tests were run to assess the associations between frequency, intensity, type, location and social setting of exercise with sex and training group. The results were considered statistically significant if the p-value was less than 0.05. All statistical analyses were performed with SPSS 22 (Statistical Package for Social Science, Chicago, IL, USA).