Circuit vs. Classic Strength Training, Which System is More Metabolically Demanding? What are the Energetic Costs and Where Does the Energy Come From, Fat or Glucose?

When you build a circuit training routine, don't forget: There are lot's of metabolically demanding kettle- bell exercises to spice things up.
There are probably a dozen of reasons why people train. Many of them are really good: Wanting to stay healthy, to live longer, or to excel in your sports. Of others, however, I am not so sure whether they are actually worth pursuing, or do you think training to look like a walking stick to make it to the catwalk was a "good" motivation to go to the gym? Personally I don't think so and that's partly why I am hesitant to judge a workout by the amount of energy it may burn. So, before I get to the results of a recently conducted study from the University of Pernambuco/Federal University of Paraíba, the , University of Pernambuco, Recife and the University of Southern Maine (Aniceto. 2013), I short word of caution: NEVER let burning energy (let alone "calories") become the main goal of your workouts... well, unless you are one of those wanna-be-sticks and supplement cotton balls pre- and post-workout, obviously.

Classic or circuit training - does it even make a difference?

The experiment Aniceto et al. conducted was a randomized, controlled, cross-over trial. After having evaluated the body composition and strength the 10 normal-weight previously trained subjects (at least 6 months training experience with weights under their belt), the scientists assigned the subjects to perform two test workouts,  both workouts...
  • Suggested read: "Cardio & Weights - Mutual Exclusives or Synergists? Cardio "Before" and After Workouts Offers More Benefits Than Downsides for Strength & Mass" | read more
    were performed with a relatively light weight of 60% of the subjects individual 1-RM (=the maximal amount of weight the subjects could lift for one picture-perfect rep)
  • lasted rougly 34 min.
  • had a total of 24 working sets with 10 reps per set and 60s recovery in-between the sets
  • all repetitions were performed with a TUT of 101, which means that both the con- and eccentric phase of the lift lasted for 1 second (the two "1"s) and there was no rest or stretch (the "0") in-between, and
  • were performed in in the morning after a standardized breakfast consisting ofa bun of 50 g with a slice of cheese of 30 g and a glass of fruit juice of 200 ml (350 kcal; carbohydrates: 61.7%; proteins: 13.44% and lipids: 24.86%)
The only difference between the workouts was that in one session the subjects walked from one exercise, i.e. bench press, leg press (45º), seated row, leg curl, triceps pulley, leg extension, biceps curl, and adductor chair, to the other and performed only one set each (3x CIRCUITS total), while in the other, the CLASSIC condition subjects were advised to perform all three sets of an exercise subsequently before they switched over to the next one.
Suggested read: "Triple Your Energy Expenditure During Shuttle Runs + Learn Why Intensity and not Just Weight x Distance Counts" | read more
"The resting metabolic rate (RMR) has been calculated using the equation by Weir, being obtained by indirect calorimetry with the individual at rest after night fasting of 10-12 hours. The VO2 and the VCO2 were collected for 30 minutes; however, only the 10 final minutes were considered as measurement or the RMR. Estimation of aerobic energy expenditure (AEE, kj) and the rest interval (RIEE) the indirect calorimetry method was acquired through the VO2, being the caloric values of 21.1 kj and 19.6 kj, respectively." (Aniceto. 2013)
Using the lactate levels the scientists were also able to quantify the contribution of aerobic vs. anaerobic work and when they plugged all the data in the corresponding equations their result looked like this:
Figure 1: Anaerobic, Aerobic and Rest Interval total energy expenditure (EE in kcal; left) and lactate levels during the CIRCUIT and CLASSIC training regimen (Aniceto. 2013)
Now, if you look at the data and do the math, you will probably realize that the absolute energy expenditure was almost identical with a non-significant 4% = 5kcal advantage for the CIRCUIT group (185 vs. 180kcal). You may also realize that 5kcal/min is not exactly an earth-shatteringly high energy expenditure and this is not merely due to the relatively low workout intensity. And even with heavier weights, strength training is not best-suited to burn excess energy.

Strength training is not meant to "burn calories": Getting back to the point I made in the introduction, the findings of the study at hand confirm that weight training is not the ideal mean to become a scrawny. That does yet not mean that it cannot be the ideal complement to a calorically reduced (~20%) diet. On the contrary, unless you have to prepare for a show and got a deadline to meet, both CIRCUIT and CLASSIC resistance training regimen are equally suited to gear the weight loss you will be experiencing away from your precious muscle and towards those nasty fat stores you want to burn.

Outline of a powerful high resistance circuit training program (learn more)
If we also take into consideration that previous longer-term studies such as Alcarez et al. (2011) observed significant greater fat loss and muscle gains in likewise previously trained subjects  with an allegedly more intense (6 reps at 80-90% 1RM) CIRCUIT workout compared to its CLASSIC counterpart, it would thus be worth a try to go for the intense CIRCUIT on your next cut, although it may burn only 50% of the energy of a classic light intensity cardio or HIIT workout and have your diet take care of the rest. Everything else is only suitable for short term interventions and a recipe for overtraining and exercise dependence.

  • Alcaraz PE, Perez-Gomez J, Chavarrias M, Blazevich AJ. Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men. J Strength Cond Res. 2011 Sep;25(9):2519-27.
  • Aniceto RR, Ritti-Dias RM, Scott CB, de Lima FFM, Pessôa dos Prazeres TM, do Prado WL. Acute Effects Of Different Weight Training Methods On Energy Expenditure In Trained Men. Rev Bras Med Esporte. 2013; 19(5/6): 181-185.
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