GUEST POST: Can CrossFit improve aerobic fitness and body composition?

This is a guest post from Bret Contreras. He is drawn to the controversial studies…

Although many people in the mainstream fitness industry are very critical of CrossFit because of the perceived higher injury risk, this research study demonstrates that there are positive aspects of that kind of training, including improvements in both maximum aerobic capacity and body composition.

The study: Crossfit-based high intensity power training improves maximal aerobic fitness and body composition, by Smith, Sommer, Starkoff, and Devor, in Journal of Strength and Conditioning Research, Published Ahead of Print


What is the background?

Many researchers have previously investigated high-intensity interval training (HIIT). HIIT is used as an alternative to traditional steady-state endurance training for improving aerobic fitness with minimal time commitment. However, a new form of HIIT has emerged which incorporates high-intensity resistance training using a variety of multiple joint movements.

This type of training can be referred to as high-intensity power training (HIPT) and it differs from traditional HIIT since it lacks prescribed rest periods, focuses on sustained high power outputs and relies upon compound movements that are traditionally found in heavy resistance training or Olympic weightlifting.

CrossFit training utilizes HIPT and makes extensive use of functional exercises such as the squat, deadlift, clean, snatch, overhead press, Olympic lifts, gymnastics ring exercises, hand-stands and parallel bars. Workouts can be performed for time, or for “as  many rounds as possible” using varying time domains ranging from 10-20 minutes.

Since CrossFit is a relatively new phenomenon it has not been extensively studied by sports scientists. It is therefore currently unknown whether HIPT offers the same benefits as HIIT since no studies exist for this style of training on aerobic fitness and body composition.


What did the researchers do?

The researchers recruited 54 subjects but only 43 of these (43 males and 20 females) completed the study. Two dropped out because of time-constraints and 9 dropped out because they experienced overuse injuries. All of the subjects followed a Paleo diet prior to and during the study, which lasted for 10 weeks.

Before and after the 10-week intervention, the researchers measured the body composition of all subjects using Bod Pod air displacement plethysmography and they also measured maximal aerobic capacity (VO2-max) using an incremental treadmill test.

During the 10-week intervention, the subjects performed CrossFit-style workouts. All of the workouts were performed at a CrossFit affiliate under the supervision of a fellow of the American College of Sports Medicine (ACSM) and an ACSM certified registered clinical exercise physiologist.

The researchers noted that the strength/skill portions of the session did not have prescribed recovery periods but the Workout of the Day (WOD) portions of the workout were completed as quickly as possible with no rest periods. They noted that some exercises were performed for a best time and others for as many rounds as possible in a 10 to 20 minute time frame while little or no traditional aerobic training was performed.

The researchers referred to a table in which full details of the workouts were provided but this table was unfortunately not available in the version of the study that was obtained for this review. Moreover, no details were provided regarding the frequency of training, the length of the workouts or the loads lifted or their proportion of one repetition maximum (1RM).


What happened?

Maximum aerobic capacity

The researchers reported that significant increases occurred for both males and females in respect of VO2-max, as shown in the chart below:

CrossFit VO2-max

The table shows that VO2-max improved by 13.6% in males and 11.8% in females. Moreover, these improvements were not simply because of weight loss. They were in fact genuine gains in aerobic fitness. Also, when broken down into 5 quintiles of well below average, below average, average, above average and well-above average, it was shown that every single group increased their VO2-max.

The researchers commented that prior research has struggled to show improvements in VO2-max with well-above average subjects. However, this CrossFit-based HIPT program was in fact able show improvements with this population. This may indicate that HIPT is superior for maximal aerobic capacity improvements in well-trained subjects. This is clearly an avenue worth pursuing in future research.


Body composition changes

The researchers also reported that there were significant decreases in body fat percentage for both males and females, as shown in the chart below:

CrossFit body fat

Although the chart only shows results for males and females separately, the researchers noted that body fat across the board dropped around 3.7% over the 10-week period. Males lost 3.46 kgs in bodyweight (from 90.71 to 87.25kg), which corresponded to 4.2% body fat (from 22.2 to 18.0kg). Males also gained 0.98kg of muscle (from 70.25 to 71.23kg).

Females lost 1.79kgs of bodyweight (from 68.02 to 66.23kg), dropped 3.4% body fat (from 26.6 to 23.2kg) and gained 1.06kg of muscle (from 49.0 to 50.06kg). Also, when broken down into 5 quintiles of well below average, below average, average, above average and well-above average, it was shown that every single group reduced their body fat percentage.


What were the limitations to the study?

The researchers noted that although the 10-week programs were periodized and that ACSM certified fitness professionals supervised the training, an alarming 16% of the subjects dropped out due to overuse injuries, indicating that CrossFit training involves a high risk-reward ratio. While it appears to be able to produce very beneficial results in both aerobic fitness and body composition, it does also appear to involve a high risk of injury.

Also, the study was limited as all of the subjects also adhered to the Paleo Diet. It is therefore impossible to know how much of the results could be attributed to the training and how much could be attributable to the diet.


What did the researchers conclude?

The researchers concluded that CrossFit-based high-intensity power training (HIPT) programs combined with the Paleo Diet produced meaningful improvements in both body composition and VO2-max in both men and women of all levels of fitness. However, they also noted that all good things come at a price, as the risk of overuse injury with CrossFit-based HIPT training is very high.


What are the practical implications?

For experienced trainees:

CrossFit-style training can significantly improve maximal aerobic fitness and body composition even in trainees with above average aerobic fitness. However, there is a risk that this type of training could lead to overuse injury and therefore care should be taken to vary loads and exercises and to monitor any signs of muscle or soft tissue damage carefully.


About the author

Bret Contreras is a Certified Strength and Conditioning Specialist (CSCS) and is currently seeking his PhD in Sports Science. Many people consider him to be the world’s foremost expert on glute training. You can read more from Bret at his blog.

Chris Beardsley

Chris Beardsley is a sports scientist specialising in lower body biomechanics. He writes the monthly Strength and Conditioning Research Review service.

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