A caloric deficit doesn’t have to come entirely from the diet, and you probably guessed that adding some cardiovascular work to expend more energy rather than restricting your energy intake alone, could also be useful.
A simple way to estimate energy expenditure during cardio requires you to determine a rating of perceived exertion (RPE) during exercise. This can be simply done by considering how hard it feels on a scale from 1 to 10 (note, this is a different form of RPE from the repetitions in reserve-based RPE scale discussed in the Training Pyramid).
If you also track the time spent performing the cardio, and if you know your body weight, you can estimate caloric expenditure with reasonable accuracy. You burn approximately ~0.2, ~0.45 and ~0.7 kcal per 10 minutes per pound of bodyweight doing light (RPE 2 to 4 out of 10), moderate (RPE 5 to 7 out of 10) and vigorous (RPE 8 to 10 out of 10) cardio respectively, above what you would normally be burning doing everyday light activity in that same time period 1.
|How to Gauge the RPE of Cardio|
|RPE 1–2||Very light effort. You can talk with ease.|
|RPE 3–4||Light effort. You can talk with almost no difficulty.|
|RPE 5||Moderately light effort. You can talk comfortably with minor difficulty.|
|RPE 6||Moderate effort. You can talk with minor difficulty.|
|RPE 7||Moderately high effort. Talking is difficult.|
|RPE 8||High effort. Talking is very difficult.|
|RPE 9||Very high effort. Talking is maximally difficult.|
|RPE 10||Maximal effort. Talking is impossible.|
Cardio type, height, weight, and other variables affect these values, but these are decent values to use for estimation purposes. So for example, a 200 lb male performing moderate-intensity cardio would burn an additional 90 kcal in 10 minutes (0.45 x 200) over and above what they burn doing normal, day-to-day light activity for the same time period. In an hour, they would burn 540 kcal over what they would have burned had they been performing light everyday activity.
Below is a chart displaying the number of calories burned during 10 minutes of cardio activity at 3 different levels of intensity for individuals at 3 different body weights:
Cardio: Estimated Rates of Calorie Burn
|24 kcal||32 kcal||40 kcal|
|64 kcal||74 kcal||90 kcal|
|84 kcal||112 kcal||140 kcal|
Now if this hypothetical 200 lb (90 kg) male really enjoyed food he might think, “Hold on, if I did an hour of moderate-intensity cardio a day, that would put me slightly over a 3500 kcal deficit per week and I would be able to lose a pound weekly which is at a rate of ~0.5%. That’s what you prescribe and I wouldn’t have to restrict my food!” Well, he wouldn’t be wrong, but 7 hours of moderate-intensity cardio per week can cause problems for someone interested in muscle and strength.
Why the Type of Cardio You Do Matters
Doing cardiovascular exercise at moderate intensities is essentially endurance training. The adaptations and the work required to produce endurance adaptations can interfere with the training and adaptations required to generate muscular strength, hypertrophy, and power 2. Not to say that interference will prevent someone from getting bigger, stronger, or more powerful, but if excessive cardio is performed it can slow down the process of building muscle, strength, or power in a dose-dependent manner.
The Interference Effect in Low-intensity vs. Moderate-intensity Cardio
Glycogen depletion and the molecular signaling that comes from endurance training may play a role in interference 3. Additionally, interference might also be related to the extent of the impact and the contribution of eccentric actions from the modality of cardio, considering that cycling appears to interfere less with resistance training adaptations than incline walking 4.
Eccentric actions are essentially when your muscle lengthens while it contracts, often performed when guiding a load into place or decelerating a load; like what your bicep is doing when you set down a coffee mug. In endurance training, this is how your body brakes and controls your inertia and movement. High impact forces can create joint strain, and a high volume of high force eccentric actions can create a lot of muscle soreness. So, you can deplete the muscle of its energy and also go into training with sore joints and muscles if cardio training is excessive.
However, low-intensity cardio (if it doesn’t have an impact component, like cycling, or the elliptical) would be below the threshold of producing overload and therefore wouldn’t be an issue. For someone in decent shape who is lifting weights, casual cardio is not an adaptive stress, so it won’t cause endurance adaptations in the body. Thus, interference is not an issue with low-intensity cardio. However, the calorie burn is much lower when doing low-intensity cardio compared to higher intensities, and thus, you have to do a lot of it for it to add up.
Why High-intensity Interval Training (HIIT) Should Be Used Sparingly
The final option is high-intensity cardio. High-intensity cardio is very taxing, and unlike lower-intensity cardio cannot be done continuously for very long unless you are a well-trained anaerobic athlete. This is one of the reasons you often hear people talk about high-intensity interval training or HIIT. HIIT is when you do a burst of maximal-intensity cardio, followed by a rest period and then repeat.
Similar metabolic adaptations can come from either HIIT or lower-intensity cardio performed for longer periods, but in less total time 5. Also, the risk of interference seems to be reduced when HIIT is utilized because the high-intensity nature of the cardio is more similar to resistance training 6. Lastly, the higher the intensity, the greater the increase in metabolic rate in the short time period afterward. High-intensity exercise provides a short-term, small, but significant increase in metabolic rate 7 while low-intensity does not.
So does that mean HIIT is a home run and that our 200 lb (90 kg) male who loves to eat can do a bunch of HIIT and some low-intensity cardio and keep all his food? Well, unfortunately, some of the same issues that come with moderate-intensity cardio come with high-intensity cardio.
If there is a significant eccentric component or a high level of impact, it can cause problems. In fact, sprinters suffer more than twice the number of hamstring injuries that long-distance runners suffer on average, despite running only a fraction of the distance or time 8.
While a larger risk of injury (with certain modalities) and a greater need for recovery are the only risks of HIIT, these are significant risks. It’s hard to make the argument that you are avoiding interference and retaining more muscle by avoiding moderate-intensity cardio and doing high-intensity cardio when you have a hamstring tear.
What Is the Appropriate Cardio Prescription?
Okay, so then what is appropriate for a cardio prescription?
Because of interference, cardio should not be the primary vehicle for fat loss, regardless of whether you perform low or high-intensity cardio. The majority of fat loss should come from the diet.
Secondly, resistance training performance is the most critical aspect of muscle maintenance. The diet supports the training as best as possible while creating fat loss and the training supports muscle retention. Don’t put this paradigm at risk. Remember you are a strength athlete or a bodybuilder, not an endurance athlete.
As a rule of thumb, your total cardio for the week should take no more than half the time you spend lifting weights. So if you spend 90 minutes 4 times per week lifting weights (6 hours), that means you should do no more than 3 total hours of cardio per week. As an aside, smaller women may find that they reach a point where food cannot be realistically further reduced to continue losing weight; in these cases, it may sometimes be needed to max out the amount of cardio performed or even to go slightly above this amount.
Choose cardio that is easy on the joints (low impact) and easy on the muscles in subsequent days (won’t make you sore). Rowing, cycling, swimming, elliptical trainers, or even lightweight barbell or kettlebell complexes could all be used.
Cap the number of HIIT sessions at one to two sessions per week that last no more than 30 minutes. Do no more than an hour per week in total of moderate-intensity cardio as this intensity causes the most interference. For the rest of your cardio, keep it at a low intensity. Also, choose the modalities you like. When the goal is just to expend calories the modality is not that important, why not enjoy it?
So what might this look like?
In the example of lifting 6 hours per week and doing 3 hours of cardio, you could perform two 30 minute HIIT sessions, 1 hour of moderate-intensity cardio, and 1 hour of low-intensity cardio as one way of doing the absolute maximum amount that should be performed.
If you have found this helpful, you might be pleased to know it is just a small section taken from our Muscle and Strength Nutrition Pyramid book. The second edition, along with the Training companion book, was released this January 3rd, 2019.
Join 16,000+ other readers, get your copies here.
Thank you for reading. Questions welcomed in the comments.
– Eric, Andy, and Andrea
» Reference List
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- Wilson, J.M., et al., Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res, 2012. 26(8): p. 2293–307.
- Hawley, J.A., Molecular responses to strength and endurance training: are they incompatible? Appl Physiol Nutr Metab, 2009. 34(3): p. 355–61.
- Gergley, J.C., Comparison of two lower-body modes of endurance training on lower-body strength development while concurrently training. JJ Strength Cond Res, 2009. 23(3): p. 979–87.
- Burgomaster, K.A., et al., Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. Journal of Physiology, 2008. 586(1): p. 151–60.
- Balabinis, C.P., et al., Early phase changes by concurrent endurance and strength training. J Strength Cond Res, 2003. 17(2): p. 393–401.
- Borsheim, E. and R. Bahr, Effect of exercise intensity, duration, and mode on post-exercise oxygen consumption. Sports Med, 2003. 33(14): p. 1037–60.
- Lysholm, J. and J. Wiklander, Injuries in runners. Am J Sports Med, 1987. 15(2): p. 168–171.