Twenty-four healthy subjects (14 women and 10 men, ages 24-27) were recruited from a university setting in Norway to participate in the study. Blood levels were recorded 1 before and 4 days after the exercise component, so that the participants were acting as their own controls. Prior to the study, participants were instructed to refrain from any exercise for a week and to complete a questionnaire on how often they performed strength training.
For the study, the participants performed a high-intensity ‘Tabata’ type workout, lasting approximately 50 minutes. The program started with a generalised warm-up, then progressed to high intensity exercises for all major muscle groups over 8 different exercise stations, with short breaks (10 seconds of rest in between activity bursts of 20 seconds). Every exercise was repeated 6 times before a 1-minute break and change of exercise.
All participants had an elevation in CK levels, with 14 of the 24 participants having levels that qualified as 5 times the normal limits (>5000 IU/l). Of these, 4 participants had urine tests positive for blood on day 4 post-testing, and of these, 3 had muscle pain. Those who engaged in regular strength training had a smaller elevation of CK levels.