Myths Under The Microscope: Fasted Cardio

Discussion & Afterthoughts

Not an “Either-Or” Issue

The current facts have been presented in parts 1 & 2, and the bases for conclusion should be self-evident. Let me clarify that HIIT and linear high-intensity cardio are not the best and only ways to go. Many folks have perfectly legitimate orthopedic, cardiac, and even psychological reasons to avoid them. Not only that, I sincerely believe that both low and high-intensity cardio have unique benefits unto themselves. Optimally, both types should be done, since each has specifically different effects. Saying that one is bottom-line superior to the other for improvement in body composition is as false as blanketly saying 5 reps per set is superior to 15. On the contrary, there is well-established benefit in periodizing training variables, including intensity of cardio.

Too Much of the Same?

I’ve heard it mentioned that high-intensity cardio shouldn’t be done concurrently with high-intensity weight training due to excessive stress on the central nervous system. Perfect excuse. My primary response is, there’s no solid proof of that danger. Certainly there’s no evidence of it in my observations as a professional in the field, working with bodybuilders, and all types of other competitive athletes such as gymnasts, sprinters, boxers, etc (you know, athletes whose incredible physiques have nothing to do with weights + high intensity cardio). It’s true that some folks regard a precociously low carb intake as a legit reason to keep intensity low. However, if your nutritional program doesn’t adequately support productive training, then you’ve designed it ass-backwards, painting yourself into a corner of compromised adaptation.

The Options

Options can be broken down in the following ways: If you’re pressed for time, and you can do HIIT without any delayed onset muscle soreness overlap (by virtue of doing a low frequency of HIIT), and you can tolerate it joint-wise & heart-wise, and you hate spending time doing cardio to begin with, then do HIIT. On the other hand, if you have the time to allot for low-intensity steady state (LISS), and you do a particularly high volume & magnitude of resistance training which raises potential recovery conflicts posed by a high frequency of HIIT, then do LISS. If you’re somewhere in between the aforementioned 2 camps and you don’t have a specific preference or tolerance limit, do both types on either a cyclical, rotational, or even combined basis. Also, it can’t be overstated that unless you undergo a very gradual progression towards the the musculoskeletal tolerance for something like sprinting, you can get hurt pretty bad & there goes your productive training for several weeks.

Fasted = Suboptimal

Fasted cardio is not optimal for reasons spanning beyond its questionable track record in research. There’s unavoidable positive metabolic synergy in fed (read: properly fueled) training, regardless of sport. This effect increases with intensity of training; even in untrained subjects, whatever fat oxidation is suppressed during training is compensated for in the recovery period by multiple mechanisms, many of which are not yet identified. Athletes are known for their gravitation towards self-sacrifice, but some rely on hearsay, while others rely on science. Did you know that way back in the 60’s, it wasn’t uncommon for coaches to tell athletes in various sports to avoid drinking water before and during training? No comment needed. Good thing researchers questioned it, and enough data surfaced to validate claims of the skeptics. Sometimes counterproductive dogma indeed dies, thank goodness. However, the myths addressed here are admittedly more subtle than the water example. Even on suboptimal protocols, athletes all over the world still inch along, although not at optimal rates, and not necessarily to optimal levels.

So…

I see the bottom line like this.. Do the type you have a personal preference for, and also respect your physical limits. HIIT is quicker but riskier. LISS is safer but takes twice as long to accomplish the same thing. Again, do what you prefer & can tolerate, but do NOT make the mistake of assuming that LISS burns more fat. That’s misunderstanding the physiology of the matter. I’ll end off by challenging you to diligently review the facts before blindly latching onto the myths.

References

1. Achten J, Jeukendrup AE. Relation between plasma lactate concentration and fat oxidation rates over a wide range of exercise intensities. Int J Sports Med. 2004 Jan;25(1):32-7.
2. Thompson DL, et al. Substrate use during and following moderate- and low-intensity exercise: implications for weight control. Eur J Appl Physiol Occup Physiol. 1998 Jun;78(1):43-9.
3. Phelain JF, et al. Postexercise energy expenditure and substrate oxidation in young women resulting from exercise bouts of different intensity.J Am Coll Nutr. 1997 Apr;16(2):140-6.
4. Lee YS. Et al. The effects of various intensities and durations of exercise with and without glucose in milk ingestion on postexercise oxygen consumption. J Sports Med Phys Fitness. 1999 Dec;39(4):341-7.
5. Melanson EL, et al. Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation. J Appl Physiol. 2002 Mar;92(3):1045-52.
6. Saris WH, Schrauwen P. Substrate oxidation differences between high- and low-intensity exercise are compensated over 24 hours in obese men.
7. Grediagin A, et al. Exercise intensity does not effect body composition change in untrained, moderately overfat women. J Am Diet Assoc. 1995 Jun;95(6):661-5.
8. Mougios V, et al. Does the intensity of an exercise programme modulate body composition changes? Int J Sports Med. 2006 Mar;27(3):178-81.
9. Okura T, et al. Effects of exercise intensity on physical fitness and risk factors for coronary heart disease. Obes Res. 2003 Sep;11(9):1131-9.
10. Tremblay, et al. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism. 1994 Jul;43(7):814-8.
11. Yoshioka M, et al. Impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness. Int J Obes Relat Metab Disord. 2001 Mar;25(3):332-9.
12. Broeder CE, et al. The effects of either high-intensity resistance or endurance training on resting metabolic rate. Am J Clin Nutr. 1992 Apr;55(4):802-10.
13. Gutin B, et al. Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents. Am J Clin Nutr. 2002 May;75(5):818-26.
14. Melanson EL, et al. Resistance and aerobic exercise have similar effects on 24-h nutrient oxidation.. Med Sci Sports Exerc. 2002 Nov;34(11):1793-800.
15. Ahlborg, G., and P. Felig. Influence of glucose ingestion on fuel-hormone response during prolonged exercise. J. Appl. Physiol. 1976;41:683-688.
16. De Glisezinski I, et al. Effect of carbohydrate ingestion on adipose tissue lipolysis during long-lasting exercise in trained men. J Appl Physiol. 1998 May;84(5):1627-32.
17. Coyle EF, et al. Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise. Am J Physiol. 1997 Aug;273(2 Pt 1):E268-75.
18. Civitarese AE, et al. Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes. Am J Physiol Endocrinol Metab. 2005 Dec;289(6):E1023-9.
19. Wallis GA, et al. Metabolic response to carbohydrate ingestion during exercise in males and females. Am J Physiol Endocrinol Metab. 2006 Apr;290(4):E708-15.
20. Coyle, et al. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J. Appl. Physiol. 1986;6:165-172.
21. Coyle, et al.. Carbohydrates during prolonged strenuous exercise can delay fatigue. J. Appl. Physiol. 59: 429-433, 1983.
22. Horowitz JF, et al. Substrate metabolism when subjects are fed carbohydrate during exercise. Am J Physiol. 1999 May;276(5 Pt 1):E828-35.
23. Febbraio MA, et al. Effects of carbohydrate ingestion before and during exercise on glucose kinetics and exercise performance. J Appl Physiol. 2000 Dec;89(6):2220-6.