Crossfit, circuit training, metabolic conditioning, GPP. Call it what you will it has become popular in recent years. Scott (The Modern Forager) had an excellent post on this a few days ago: Picking the Right Tool for the Job, Part 1: GPP vs SPP
I think there is something of a backlash against crossfit at the moment and it is worth reading all of Scott's post and the comments.
It does all depend on what you are training for. Crossfit is about being an all-rounder - and probably fitter than 95% of the population - which is fine. Some of the criticism I think is coming from those who are trying to excel in a specialism while using a generalist programme.
For example Mark Twight - the guy who trained the actors for 300 - has moderated his training away from pure crossfit stuff and added in a lot more endurance work. But this makes sense because he is an endurance athlete - doing bike racing. He explains here
January 2008: Every now and then someone posts an old quote of mine about Crossfit and using short-duration, high-intensity effort to improve endurance, referring to my initial experience. Those who imagine I still believe what I did then, or train the way I did when testing the validity of the method should re-read the following paragraphs:
“... it must be understood that these workouts were not undertaken in a vacuum; they were used to sharpen a 20-year endurance base gained by training and climbing at intensities specific to long endurance effort. The same results would not be produced in the athlete without a similar aerobic base ...”
Surely the meaning of “20-year endurance base” is clear.
“During the two years since that race I have learned – through personal experimentation and experience and discussion with coaches and scientists smarter than me – that recovery must be trained, and recovery adaptations occur just like the compensatory reaction to imposed athletic demands. Similarly, it is now absolutely clear that there is no such thing as a free lunch and there never was: to go long you have to go long, if you want genuine endurance and/or multi-day endurance you have to train it. Period.
A few have asked me to update my thesis on the subject and I’ll do so eventually. For now, the link below should clear up any misconceptions regarding how I think about endurance and what I am doing to train it. Endurance Revisited
Anyway......Here is a study just published. You get what you train for of course, but this is interesting in that the subjects were doing a "heavy circuit" - rather than the sort of metcon stuff on which crossfit is built - and they built and some degree of "cardio" as well as strength.
Physical Performance and Cardiovascular Responses to an Acute Bout of Heavy Resistance Circuit Training versus Traditional Strength Training.
Circuit training effectively reduces the time devoted to strength training while allowing an adequate training volume to be achieved. Nonetheless, circuit training has traditionally been performed using relatively low loads for a relatively high number of repetitions, which is not conducive to maximal muscle size and strength gain. This investigation compared physical performance parameters and cardiovascular load during heavy-resistance circuit (HRC) training to the responses during a traditional, passive rest strength training set (TS). Ten healthy subjects (age, 26 +/- 1.6 years; weight, 80.2 +/- 8.78 kg) with strength training experience volunteered for the study. Testing was performed once weekly for 3 weeks. On day 1, subjects were familiarized with the test and training exercises. On the subsequent 2 test days, subjects performed 1 of 2 strength training programs: HRC (5 sets x (bench press + leg extensions + ankle extensions); 35-second interset rest; 6 repetition maximum [6RM] loads) or TS (5 sets x bench press; 3-minute interset rest, 6RM loads). The data confirm that the maximum and average bar velocity and power and the number of repetitions performed of the bench press in the 2 conditions was the same; however, the average heart rate was significantly greater in the HRC compared to the TS condition (HRC = 129 +/- 15.6 beats.min, approximately 71% maximum heart rate (HRmax), TS = 113 +/- 13.1 beats.min, approximately 62% HRmax; P < 0.05). Thus, HRC sets are quantitatively similar to traditional strength training sets, but the cardiovascular load is substantially greater. HRC may be an effective training strategy for the promotion of both strength and cardiovascular adaptations.