The CrossFit craze has now hit the mainstream with more than 10,000 gyms (or “boxes”), 35,000 accredited trainers, and 10 million participants worldwide.
The increased popularity of CrossFit prompted the American Council on Exercise (ACE) to commission an independent study to evaluate the effectiveness of two popular CrossFit workouts.
The workout study
“Fitness seekers are often enticed by the results touted by popular workout programs, and the results demonstrated by dedicated ‘CrossFitters’ often present such results,” said ACE Chief Science Officer Cedric Bryant, PhD. “Based on the study results, there’s no doubt that CrossFit can offer an effective workout option that burns calories at a high rate.”
In the study, researchers from the University of Wisconsin, LaCrosse began by selecting 16 healthy, moderately to very fit female and male volunteers between the ages of 20 and 47.
The subjects were asked to familiarize themselves with two popular Workouts of the Day (WODs). The “Donkey Kong” incorporates burpees, kettlebell swings and box jumps, while the popular “Fran” consists of thrusters (a front squat into a push press with a barbell) and assisted pull-ups. For both, the goal is to complete all repetitions in the shortest amount of time possible.
All subjects first underwent a treadmill test to determine maximal heart rate (HR) and maximal aerobic capacity (VO2 max), with ratings of perceived exertion (RPE) assessed at the end of each stage.
Exercises were then performed three times, with the number of repetitions decreasing each time. During the first round, each exercise was performed 21 times, the second round 15 times, and the final round nine times.
HR was monitored throughout and RPE assessed after each round. Additionally, an overall RPE was taken at the end of the workout session, while blood lactate concentration was tested at the beginning and end of each CrossFit workout.
Researchers found that males burned an average of 20.5 calories per minute while females averaged 12.5 calories per minute.
Heart-rate responses were an average of 90 percent of maximum heart rate (HRmax) throughout the workout. Given that fitness industry guidelines suggest a training range of 64-94 percent of HR max to improve cardio endurance, both CrossFit workouts met the mark.
VO2 also increased immediately and slightly with subsequent rounds averaging at 80 percent of VO2max, indicating the subjects were exercising well above their anaerobic thresholds and at the higher end of industry recommendations.
“Like any type of high-intensity physical exertion, CrossFit workouts place high demands on the cardiovascular and musculoskeletal systems and present a risk of injury,” Bryant said.
“One type of exercise programming will never be appropriate for all individuals. Participants who have the desire, skill set, and physical capacity to engage in CrossFit workouts can expect improved fitness and performance levels while engaging in a relatively safe and effective training method if proper exercise principles and techniques are followed.”