A my friend told me that I will burn the most fat by doing cardio at the end of the workout because my muscles are “glycogen depleted” from my strength training exercises. What does that mean and is it true?
Actually it’s your liver that is glycogen depleted - it would take several days of eating near zero carbohydrates to deplete all the muscle glycogen. The liver provides a constant flow of glucose to the brain and body for use as energy. As liver glycogen becomes depleted SNS activity is increased and cortisol increases, which increases utilization of fat for fuel. That makes performing cardio after your weight training sessions good for fat loss, but equally bad if you’re trying to gain muscle.
Not even close.
An endurance athlete can deplete muscle glycogen in 40-120 minutes depending on intensity. Why do you think marathoners bonk at the 20 mile mark?
how much glycogen a weight training workout will depend on set length and total number of sets. Full muscle glycogen depletion would take a pile of volume but could be done in a single (~2 hour or so) workout. From normal muscle glycogen, I have estimated that it takes ~12-16 sets (average set time 45 seconds) to deplete a muscle of glycogen. T his is based on average starting muscle glycogen and what little data is out there on rates of glycogen depletion during weight training.
Lyle
When muscle glycogen is depleted, teh muscle will rely more on circulating fatty acids for fuel, this is what your friend means.
Whether or not actually burning fat has any real impact on fat loss is up to debate and, in general, it doesn’t matter that much: daily caloric balance has the greatest impact on fat loss. There are a couple of possible weird exceptions, involving extremes of bodyfat (high and low) but beyond that, it doesn’t really matter what you burn during your cardio: create a deficit and you’ll lose fat.
Lyle
520 grams of carbs in 40 minutes? What event and intensity?
40 minutes at lactate threshold or slightly above (which is sustsainable for that time period) could easily burn that many carbohydrate calories.
Lyle