Cortisol release during training is largely triggered by depletion of glycogen from muscles and liver! (Also from stimulants, and adrenaline released from over-psyching up).
Cortisol goes up after about 1 hour of activity, even walking as the percentage of calories burned from carbs goes up due to the fact that intra and extra muscular fatty acids gets depleted and can’t provide enough energy for higher work output anymore.
Basically, cortisol release during training is tied DIRECTLY to how fast your body is running out of glycogen. The purpose of the cortisol is to break down protein to produce supplemental glucose so the way to block it is to avoid getting into a glycogen deficient state again related to intensity and volume of training.
At about +3 mets (300-450 cals an hour for 200 pound man) you only burn about 30% carbs and 70% fat because fat can replenish ATP fast enough to keep going. You will burn up about 30 grams of glycogen an hour, but eventually your body will have to release cortisol to turn protein into glucose. A 200 pound man will have about 500 grams of stored glycogen.
At about 6-7 mets which would be a pretty intense weight training routine, you burn about 50% fat and 50% glucose at around 700-900 calories an hour (200 pound male). Now instead of burning up about 25 grams of glucose an hour you are burning bout 100 grams of glucose an hour because fatty acids can only provide a baseline of about 300 calories an hour of energy continuously. So doubling your intensity will increase glucose depletion 300-400%
At 9-10 mets you now burn maybe 1000-1200 cals an hour, but pretty much ALL of the extra energy is coming from glucose now, about 200 grams an hour.
The only way to provide more glucose besides eating it is to break down muscle with cortisol.
The only way to provide more glucose besides eating it is to break down muscle with cortisol.
(or circulating amino acids which won’t last long).
So the key is to eat enough carbs to prevent glycogen depletion.
Note that low intensity activity like walking will burn 70% fat and so is much likely to deplete glycogen and turn on cortisol.
So is shorter training at moderate levels.
One critical issue with drug free lifters is that cortisol, adrenaline, glucagon, testosterone and growth hormone (the counter insulin hormones) all rise during training, but testosterone and GH peter out at about 1 hour of hard training, at that point, cortisol (and to a lesser extent adrenaline) rise even higher.
By the way, all of those counter-regulatory hormones, but particularly cortisol and adrenaline make you more insulin resistant, so letting your cortisol go high because you get glycogen depleted will make your body release MORE insulin to manage your basal insulin needs as well as carbs consumed in a high cortisol state.
Training makes you more insulin sensitive unless you get to that point where cortisol and or adrenaline have to spike to keep you going. Again, this typically happens when you start to outrun your glycogen reserves. Also lifts over 90%, stimulants, and overpsyching for sets. It is a main reason why the russians beleived in staying under 90% of competition maxes in training, and also why Louie Simmons claims that you should not psych up for max effort lifts, because the adrenaline release is catabolic.