High Intensity Interval Training in a Real World Setting: A Randomized Controlled Feasibility Study in Overweight Inactive Adults, Measuring Change in Maximal Oxygen Uptake

Background: In research clinic settings, overweight adults undertaking HIIT (high intensity interval training) improve their fitness as effectively as those undertaking conventional walking programs but can do so within a shorter time spent exercising. We undertook a randomized controlled feasibility (pilot) study aimed at extending HIIT into a real world setting by recruiting overweight/obese, inactive adults into a group based activity program, held in a community park. Methods: Participants were allocated into one of three groups. The two interventions, aerobic interval training and maximal volitional interval training, were compared with an active control group undertaking walking based exercise. Supervised group sessions (36 per intervention) were held outdoors. Cardiorespiratory fitness was measured using VO(2)max (maximal oxygen uptake, results expressed in ml/min/kg), before and after the 12 week interventions. Results: On ITT (intention to treat) analyses, baseline (N = 49) and exit (N = 39) VO2 was 25.3+/-4.5 and 25.3+/-3.9, respectively. Participant allocation and baseline/exit VO(2)max by group was as follows: Aerobic interval training N = 16, 24.2+/-4.8/ 25.6+/-4.8; maximal volitional interval training N = 16, 25.0+/-2.8/25.2+/-3.4; walking N = 17, 26.5+/-5.3/25.2+/-3.6. The post intervention change in VO(2)max was +1.01 in the aerobic interval training, 20.06 in the maximal volitional interval training and 21.03 in the walking subgroups. The aerobic interval training subgroup increased VO(2)max compared to walking (p = 0.03). The actual (observed, rather than prescribed) time spent exercising (minutes per week, ITT analysis) was 74 for aerobic interval training, 45 for maximal volitional interval training and 116 for walking (p = 0.001). On descriptive analysis, the walking subgroup had the fewest adverse events. Conclusions: In contrast to earlier studies, the improvement in cardiorespiratory fitness in a cohort of overweight/obese participants undertaking aerobic interval training in a real world setting was modest. The most likely reason for this finding relates to reduced adherence to the exercise program, when moving beyond the research clinic setting.