For those of you that don’t know me, I am not a big advocate of aerobic (cardio) exercise. Why do so many doctors and health professionals recommend it for fat loss and health gains then? Whilst for certain populations – such as the obese, sedentary, those with high blood pressure and high visceral fat, and of course athletes or those training for a specific event – aerobic exercise is beneficial, it carries with it several negatives for those of us that don’t fall in to these categories. For example, those people slogging away for 45 minutes on the cross-trainer every day of the week to lose the fat around their stomach are actually doing something that is counter-productive. I would love to walk into the gym and (nicely) grab each and every one of these individuals and give them some dumbbells or a kettlebell and (nicely) inform them that with half the time, they could burn double the fat.

Before I get too carried away, I would like to clarify the major difference between aerobic and anaerobic (often in interval format) exercise. There are two methods of cardio (cardiovascular) training. Aerobic and anaerobic exercise utilise different metabolic processes and energy pathways in the body and accomplish different goals. The main difference is the presence of oxygen. Aerobic exercise requires the presence of oxygen constantly to generate energy. When you jog or walk for example at a low to medium intensity your body uses oxygen to burn carbohydrates and fats to produce energy.  This can be performed for long periods of time due to it’s constant energy supply. Anaerobic exercise involves working your muscles at a higher intensity, whereby the need for oxygen exceeds available supply. When we lift weights or sprint for example, because the intensity is very high, you can not sustain it for very long. This type of exercise burns only carbohydrates for energy. This last fact alone is the reason many of us have been mis-informed as to the ‘benefits’ of aerobic exercise (“cardio”) by the talk of fat-burning heart-rate zones and burning more fat at lower intensities. This is true. Anaerobic exercise doesn’t burn as many calories from fat, as an equivalent bout of aerobic work. However, it is not this that truly counts.

Anaerobic exercise in the form of intervals (whereby we schedule rest with high-intensity bouts), is critical and far more beneficial for fat-burning purposes for the following three reasons:

  1. It encourages the development of lean muscle mass, by creating a favourable hormone environment of increased testosterone levels, helping to increase lean muscle mass.
  2. It causes an increase in lactic acid levels, by signaling the release of growth hormone, which in turn signals to the body to release fatty acids in to the blood stream, which can then be utilised or ‘burned off’. If you are not feeling a touch dizzy or sick from an interval workout at least once or twice a week, you will not be triggering that release of lactic acid required for optimal fat-burning.
  3. It raises resting metabolism. For up to 24-48 hours after exercise, the effects of a tough interval workout can still be benefited from. Therefore, rather than just burning calories during a cardio workout and then literally stopping once you jump off the exercise bike, you will be burning calories at rest, long after you have finished an anaerobic interval session (King, 2001).


After we have considered the basic above advantages of anaerobic versus aerobic exercise, there are other downsides to aerobic exercise, many of which are reasons why I will very rarely advocate it’s use in a training programme. Whilst the potential for tonight’s blog is colossal, I will stick to the top three negatives of aerobic-training that I deem to be the most important.

  1. push upsAerobic exercise causes androgen levels (namely testosterone) to drop. Relative to anaerobic exercise, aerobic exercise does not cause testosterone levels to increase. For many females reading this who think “so what”; testosterone is essential for fat loss whether you are a man or a woman. Whenever I have performed a Biosignature on a lean female client (let’s say sub-14% body fat), I have never seen a tricep caliper reading (the androgen site) of more than 10mm. Whether male or female you will struggle to become truly lean, unless your androgen levels (testosterone and DHEA-sulphate) are adequate. This can only be achieved through resistance-based exercise (i.e. weight training) and anaerobic sprint work. The more you train aerobically, the more your androgen levels will plummet and your relative ratio of oestrogens to testosterone will increase (causing fat to accumulate in the upper thigh and bum region as well as the tricep, or ‘bingo wing’ site).
    Worryingly for the men, studies (although limited in this area and almost exclusively performed on animals) have pointed to a significant relationship between aerobic exercise and reproductive dysfunction and decreased size of reproductive organs (Manna et al., 2004). Scary huh?!
  2. Aerobic exercise elevates cortisol levels acutely (in the short-term), which can lead to fat gain. A recent study by Shojaei et al., (2011) in the International Journal of General Medicine, which tested a group on a 45-minute aerobic cycle session, saw significant rises in cortisol (amongst other inflammatory markers, such as lecuocyte, C-reactive protein and epinepherine) in the short-term, post-exercise. These levels of cortisol can lead to an increase in fat storage rather than fat loss. Often referred to as the ‘hibernation effect’, when the body is stressed (for example through lack of frequent feeding, that is for another day!), it reacts by switching to a fat accumulation mode.
  3. Aerobic increases oxidative stress and accelerates aging. A useful review article by Packer (1997) in the Journal of Sports Science, documents abundant evidence that associates aerobic exercise with an increase in free radicals (that is the opposing force to the antioxidants that we seek in ‘superfoods’ such as blueberries and raspberries), and damage to lipids, damage to DNA and lowering of natural antioxidatns such as glutathione. Alongside the aforementioned acute (short-term) rise in cortisol, chronic (long-term) cortisol levels are also elevated in those who engage in regular aerobic exercise (Skoluda et al., 2011). If you have high chronic levels of cortisol, your body will store fat instead of burning it. Moreover, this fat wil be specifically gained in the belly area. This high level of chronic cortisol results in a quicker aging process as it increases inflammation all over the body, including the brain, GI tract, reproductive organs and the heart. Interestingly, the athlete population (when compared with other sports, not the general population) with the lowest life-expectancy is triathletes. This sport is very much aerobic (often lasting for over 2 hours).

To wrap-up
Although there are other downsides to regular aerobic exercise (such as compromised immunity to illness), I hope that you get the idea. When compared with anaerobic exercise the advantages and disadvantages in terms of fat loss and even fitness gains are comprehensively weighed against aerobic training.

woman kettlebell trainingTo summarise, I would like to use a famous study by Izumi Tabata et al. (1996). In this study, two groups were compared over six weeks with 2 very different training protocols. The first group trained aerobically on a stationary bike for 60 minutes, five times per week. The second group trained on a stationary bike for high-intensity anaerobic intervals of 20 seconds of work and 10 seconds of rest (seven to eight times). After the six weeks training period the first (aerobic) group whilst improving their VO2max (aerobic capacity), did not improve their anaerobic capacity. The second (anaerobic interval) group improved their VO2 max by more than first group and what’s more interesting, they increased their anaerobic capacity by 28%! That’s O% versus 28%.

Being that an improvement in anaerobic capacity and not aerobic capacity is more fundamental for increased fat loss (through increased lactic acid, testosterone, growth hormone and metabolic levels), the proof is irrefutable. This is a dramatic example of how 4 minutes of high intensity intervals is more beneficial than 45 minutes of steady-state aerobic work. Of course, there is a catch. In order to reap the rewards of this high intensity interval training, you need to be training at 100%. That is all very well in theory, but a concept which is tough to keep up when training on your own.

There are many ways in which anaerobic intervals can be performed – many of which, my ‘Campers’ (at Bootcamp) and one-to-one clients experience on a daily basis. Through the use of free weights (kettlebells, dumbbells, barbells) to perform whole-body compound movements or sprint-type activities, ‘tabata protocols’ can be put to great effect at the end of, or during any session. The bottom line is – you don’t have to put in the time on a piece of cardio-equipment in the gym to burn fat and improve fitness levels, you just have to put in a little bit of hard work and train intelligently.

I hope you enjoyed this post and look forward to the next time… Have a great training week 🙂

King, J., Panton, L., et al. A Comparison of High Intensity vs. Low Intensity Exercise on Body Composition in Overweight Women. Medicine & Science in Sports and Exercise. 2001. 33, 228.
Manna, I., Jana, K., Samanta, P. Intensive Swimming Exercise-Induced Oxidative Stress and Reproductive Dysfunction in Male Wistar Rats: Protective Role of Alpha-Tocopherol Succinate. Canadian Journal of Applied Physiology. April 2004. 29(2), 172-185.
Packer, L. Oxidants, Antioxidant Nutrients, and the Athlete. Journal of Sports Science. June 1997. 15(3), 353-363.
Shojaei, E., Farajoy, A., et al. Effect of Moderate Aerobic Cycling on Some Systemic Inflammatory Markers in Healthy Active Collegiate Men. International Journal of General Medicine. January 2011. 24(2), 79-84.
Skoluda, N., Dettenborn, L., et al. Elevated Hair Cortisol Concentrations in Endurance Athletes. Psychoneuroendocrinology. September 2011. Published Ahead of Print.
Tabata, I., Nishimura, K., et al. Effects of Moderate-intensity Endurance and High-intensity Intermittent Training on Anaerobic Capacity and VO2max. Medicine & Science in Sports and Exercise. 1996. 28 (10), 1327-1330.

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