Originally posted by: KoolDrew
Originally posted by: EvilYoda
I'm not exactly worried about anything and that was just an example anyway...sorry all-mighty and all-knowing KoolDrew. Thanks for the great answer though 😛
Fair enough. To answer your question, the calorie burn during weight training isn't likely to be much (sorry, I don't have a number, too many variables), and the energy used is pretty much completely by carbohydrates, not fatty acids. However, resistance training (mainly higher rep work) still does have an effect on fat loss by depleting muscle glycogen. In order for FFA's to burned for energy it has to be transported into the tissue by an enzyme called CPT (look up the full name if you wish). CPT activity is directly correlated with muscle glycogen (as well as liver glycogen). When muscle glycogen is depleted, CPT activity rises, as well as fat oxidation. This is one advantage of higher-rep metabolic type training as well as lowered carbohydrates. So while the calories burned during weight lifting is completely by carbohydrates (which is why calorie burn isn't likely to be high during the activity), it does result in increased fat oxidation .
Weight training has an added effect on fat mobilization as well. The primary hormones which activate HSL (the enzyme that controls how quickly fat is mobilized) are the catecholamines: adrenaline and noradrenaline. Both of which are released during high intensity training and continue to rise as intensity rises, helping fatty acids get mobilized out of the fat cells, resulting in a large amount of FFA's floating around in the bloodstream. However, since higher intensity exercise does not burn fatty acids for fuel, instead using glucose, the FFA's have to be burned through other means. So while the weight training does nice things as far as mobilization goes, it should be followed with lower intensity work in order to take advantage of that and burn the FFA's. This is one of the reasons low-moderate cardio is recommended after weight training.
So weight training may not burn many calories while doing the activity, but it will have an effect on both fat mobilization and oxidation which is definitely helpful if your goal is fat loss.
EDIT - I'd also like to mention that while higher rep weight training will create such responses that do help fat loss, it doesn't do much as far as maintaining muscle mass goes. So if you only chose one type of weight training, it should be heavy weights with low reps. However, using both methods can have great metabolic and hormonal effects while still maintaining lean body mass.