FALSE HOPES FOR FASTED CARDIO
The bandwagon is lead by blind horses
Many trainees pigeonhole weight training as an activity exclusively for building muscle, and cardio exclusively for burning fat. On the contrary, weight training can yield very similar results to cardio of similar intensity when 24-hr energy expenditure and macronutrient oxidation is measured [14]. The obvious advantage of weight training is the higher potential for lean mass and strength gains. In the bodybuilding context, cardio should be viewed as merely an adjunctive training mode to further energy expenditure and cross-complement the adaptations specific to weight training. As far as cardio being absolutely necessary for cardiovascular health, well, that depends upon the overall volume and magnitude of your weight training - another topic for another time.
Chaos theory strikes again
On the surface, it seems logical to separate carbs from cardio if you want a maximal degree of fat oxidation to occur during training. But, there’s the underlying mistake - focusing on stored fuel usage during training instead of focusing on optimally partitioning exogenous fuel for maximal lipolytic effect around the clock. Put another way, it’s a better objective to coincide your carb intake with your day’s thermic peaks, where insulin sensitivity & lean tissue reception to carbs is highest. For some reason, this logic is not easily accepted, nor understood. As we know, human physiology doesn’t always cooperate with logic or popular opinion, so let’s scrutinize the science behind the claims.
LET THE RESEARCH SPEAK
Carbohydrate ingestion during low-intensity exercise reduces fat oxidation
As far as 3 decades back, Ahlborg’s team observed that carb ingestion during low-intensity exercise (25-45% VO2 max) reduced fat oxidation compared to fasted levels [15]. More recently, De Glisezinski’s team observed similar results in trained men at 50% VO2 max [16]. Efforts to determine the mechanism behind this phenomenon have been made. Coyle’s team observed that at 50% VO2 max, carbohydrate availability can directly regulate fat oxidation by coordinating hyperinsulinemia to inhibit long-chain fatty acid transport into mitochondria [17].
Carbohydrate’s effect on fat oxidation during moderate-intensity exercise depends on conditioning level
Civitarese’s team found glucose ingestion during exercise to blunt lipolysis via decreasing the gene expression involved in fat oxidation in untrained men [18]. Wallis’ team saw suppressed fat oxidation in moderately trained men & women when glucose was ingested during exercise [19].
In contrast to the above trials on beginning and intermediate trainees, Coyle’s team repeatedly showed that carb ingestion during moderate-intensity (65-75% VO2 max) does not reduce fat oxidation during the first 120 min of exercise in trained men [20,21]. Interestingly, the intensity margin proximal to where fat oxidation is highest was unaffected by carb ingestion, and remained so for the first 2 hours of exercise.
Horowitz’ team examined the effect of a during-training solution of high-glycemic carbs on moderately trained men undergoing either low intensity exercise (25% VO2 max) or high-moderate intensity (68% VO2 max) [22]. Similar results to Coyle’s work were seen. Subjects completed a 2-hr cycling bout, and ingested the carb solution at 30, 60, and 90 minutes in. In the low-intensity treatment, fat oxidation was not reduced below fasted-state control group’s levels until 80-90 min of exercise. In the 68% group, no difference in fat oxidation was seen whether subjects were fasted or fed throughout the trial.
Further supporting the evidence in favor of fed cardio in trained men, Febbraio’s team investigated the effects of carb ingestion pre & during training in easily one of the best-designed trials on this topic [23]. Subjects exercised for 2 hrs at an intensity level of 63% VO2 max, which is now known as the point of maximal fat oxidation during exercise [1]. Result? Pre & during-training carbs increased performance - and there was no difference in total fat oxidation between the fasted and fed subjects. Despite the elevated insulin levels in the carb-fueled groups, there was no difference in fat availability or fat utilization.
Summing up the research findings
• At low intensities (25-50% VO2 max), carbs during exercise reduce fat oxidation compared to fasted trainees.
• At moderate intensities (63-68% VO2 max) carbs during exercise may reduce fat oxidation in untrained subjects, but do not reduce fat oxidation in trained subjects for at least the first 80-120 minutes of exercise.
• Carbohydrate during exercise spares liver glycogen, which is among the most critical factors for anticatabolism during hypocaloric & other conditions of metabolic stress. This protective hepatic effect is absent in fasted cardio.
• At the established intensity level of peak fat oxidation (~63% VO2 max), carbohydrate increases performance without any suppression of fat oxidation in trained subjects.
DISCUSSION
The current facts have been presented, 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 on either a phasic or rotational basis. 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, or as they say in the trenches, “mixing it up�.
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.
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.
Bodybuilders 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 sub-optimal protocols, bodybuilders all over the world still inch along, although not at optimal rates, and not necessarily to optimal levels.
I’ll end off by challenging you to diligently review the facts before blindly latching onto the myths… Maybe someday in the near future, natural bodybuilding contests won’t look like they’re missing a pool.
REFERENCES
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