What is CrossFit?
CrossFit is a popular generalist training program that includes exercises for strength, power, speed, agility, and endurance, often in the same workout. The CrossFit.com website describes the approach and concludes, “In sum, our specialty is not specializing.”
Supporters of CrossFit value this balanced approach. They cite improvements in different aspects of fitness as evidence to support its effectiveness.
Critics of CrossFit argue that the effects of resistance training in these workouts are not as large as they would be with more traditional programs. They also believe the greatest benefits are seen in those who are new to training, and that early and noticeable improvements are unlikely to continue.
Who’s right? It depends.
Concurrent Training
Although research on the effectiveness of CrossFit is limited, there’s a body of related research on “concurrent training” that’s relevant here.
Concurrent training combines resistance and endurance training in the same workout, same day, or on alternating days. Some studies find that resistance training is superior to concurrent training for promoting muscle mass, strength, and power; others find no difference.
The variability across studies may be due to a variety of factors, such as the frequency, duration, or type (running or cycling) of endurance training.
Recently, Wilson et al. (2012) examined data from 21 studies to determine whether these aspects of endurance training explained differences between resistance training and concurrent training programs.
The researchers used a statistical procedure called a meta-analysis, which involves finding the strength of an effect across multiple studies. The advantage of this method is that it allows us to draw a conclusion about the body of research as a whole.
Results
General Findings
There were no reliable differences between resistance training and concurrent training in upper body muscle mass, strength, or power. There were also no differences for lower body muscle mass and strength. Resistance training was, however, superior to concurrent training for promoting lower body power (such as vertical jump height and exercise bicycle output over 30 seconds).
These results appear to suggest that the endurance component of CrossFit and other concurrent programs are unlikely to reduce muscle and strength gains. The impact on lower body power may be meaningful to some, but for others who value endurance, this is an acceptable trade-off.
What we don’t learn from these findings is whether the frequency, duration, and type of endurance training matter if you’re looking for big changes in muscle mass, strength, and power. If these are your goals, you’ll want to know what happens if
- you devote too many days each week to endurance work
- your endurance workouts are too long
- you’re running rather than cycling
Frequency and Duration
As you can see in the following graphs, more is not better when it comes to endurance workouts in concurrent training programs.
Frequency: As frequency (number of days) increased, lower body muscle mass, strength, and power decreased.
Duration: As duration (length of each workout in minutes) increased, lower body muscle mass, strength, and power decreased.
Conclusion: Effects of resistance training on lower body development are reduced with frequent and long endurance workouts.
Type of Training (Running or Cycling)
- Type of training was unrelated to upper body muscle mass, strength, and power
- For lower body muscle mass and strength, resistance training was superior to concurrent training with running but not concurrent training with cycling.
- Lower body power was unrelated to type of training
Conclusion: Effects of resistance training on lower body development are generally reduced when endurance workouts use running but not cycling.
Summary
- Concurrent training in general does not seem to have a negative impact on upper body muscle mass, strength, or power
- Resistance training is superior to concurrent training for developing lower body power
- The effects of concurrent training on lower body muscle mass, strength, and power are reduced if endurance workouts are too frequent, too long, or running-focused
Application
Have you experienced a plateau in your training? Practitioners of CrossFit or other concurrent programs who find their resistance workouts are not delivering mass, strength, or power can use this information to modify their training strategies.
Suggestions based on concurrent training research:
- Reduce the frequency of endurance training to 1-2 days a week
- Limit endurance training to 20-30 minutes
- Replace running with cycling
Additional suggestions for improvement:
- Engage in resistance training and endurance training on different days
- Program goal-directed resistance training workouts that target muscle mass, strength, OR power, rather than all three
- Evaluate and modify your diet if necessary (e.g., increase carbohydrate intake to support intense training, replenish glycogen, and prevent muscle breakdown)
What Do You Think?
Have you noticed plateaus in your training? How do you prevent or eliminate them? I welcome your comments below.
Source: Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M. C., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: A meta-analysis examining interference of aerobic and resistance exercise. Journal of Strength and Conditioning Research, 26, 2293-2307.
(Note: Although this study considered other outcomes (i.e., aerobic capacity and body fat %) and also compared the training methods to endurance training only, I chose to focus exclusively on muscle mass, strength, and power here. Interested readers should refer to the original publication for more detailed results.)
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I'm Joel Minden, PhD, licensed clinical psychologist, cognitive behavior therapist, sport psychology consultant, and strength and conditioning specialist.