Some info and a view for those that like the morning cardio workout:
The Truth About Fasted Cardio,
by Christian Thibaudeau
Is fasted morning cardio good or bad? First, let's look at the pros:
Pro #1: Morning cardio could potentially increase the amount of free fatty acids (FFA) used up as fuel. This is not due to performing cardio in a glycogen depleted state though, since this isn't happening here. Unless you go to sleep in an already depleted state, you won't wake up in such a state.
During sleep almost 100% of the energy expended comes from fatty acids because of the extremely low intensity of the activity and because of the natural hGH burst which occurs 30 minutes or so after you enter the deep sleep phase (hGH increases fatty acid mobilization).
So you really aren't depleting your intramuscular glycogen stores during the night. You might be tapping your hepatic glycogen stores slightly, but even then that can't account for much since at best this contains maybe 200-300kcals of stored energy. So it's a fallacy to believe that when you wake up your muscles are emptied of their glycogen.
However, since fat is the primary energy source during your sleeping period, chances are that upon waking you have a greater amount of free fatty acids available. Since you don't have to mobilize them (they're already freed up) they become easier to oxidize for fuel and are thus more readily used up during morning cardio.
Pro #2: Fasted morning cardio could also potentially be glycogen-sparing for the same reason as stated above: the greater availability of FFAs reduces the reliance of glycogen for fuel during low-intensity energy systems work.
Pro #3: Fasted morning cardio could lead to an improved fatty acid mobilization during exercise and increase insulin sensitivity afterwards. This might be true of exercise at a low level of intensity (50-75% of max VO2) since this decreases insulin levels via the stimulation of adrenergic receptors. A lower insulin level can increase fatty acid mobilization.
However, a higher intensity of work (above 75% of max VO2) can actually have the opposite effect. So in that regard a moderate or even low intensity of work would seem to be superior in the morning as far as fat mobilization goes. (Galbo, 1983, Poortmans et Boiseau, 2003)
To counterbalance the reduction in insulin production during exercise at a moderate intensity, insulin sensitivity is increased, especially in the muscle. Since insulin sensitivity is already high in the fasted state, morning cardio could allow you to significantly increase glycogen storage and reduce the storage of carbohydrates as body fat.
So in that regard, morning cardio in a fasted state could increase fat loss during a cutting period and allow a bodybuilder in a bulking phase to significantly increase his carb intake without gaining more fat.
If fasted state cardio could potentially increase fat mobilization, it's also potentially more catabolic to muscle tissue. This is due to an increase in cortisol production during fasted exercise. Since cortisol levels are already high in the morning, this could lead to more muscle wasting than during non-fasted cardio.
In fact, cortisol levels could increase muscle breakdown and the use of amino acids as an energy source. This is especially true if high-intensity energy systems work is performed. If an individual uses lower intensity (around 60-65% of maximum heart rate), the need for glucose and cortisol release are both reduced and thus the situation becomes less catabolic.
I personally do believe in the efficacy of morning cardio, but not in a completely fasted state. For optimal results I prefer to ingest a small amount of amino acids approximately 15-30 minutes before the cardio session. A mix of 5g of BCAA, 5g of glutamine (yeah, I know that Dave Barr won't agree with me on this!), and 5g of essential amino acids would do the trick in preventing any unwanted muscle breakdown.
However, I'll also play devil's advocate and say that morning cardio won't be drastically more effective than post-workout or afternoon cardio work when it comes to fat loss. Personally, I prefer to split up my cardio into two shorter sessions (morning and post-workout).
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Originally Posted by Vash
