Wednesday, March 31, 2010

Training with Low Muscle Glycogen Enhances Fat Metabolism

This is a concept that hovers around a few training programmes and dietary approaches: training when you have low muscle glycogen either through prior intense exercise to deplete the glycogen (this is the approach Rusty takes in his Treadmill Ninja course) or via a low carb diet. Good to see a study to look at the concept.

Training in a state of glycogen depletion limited performance but increased fat burning. It would be interesting to see this compared with Phinney's work on low carb and endurance training.

Training with Low Muscle Glycogen Enhances Fat Metabolism in Well-Trained Cyclists.

PURPOSE:: To determine the effects of training with low muscle glycogen on exercise performance, substrate metabolism, and skeletal muscle adaptation. METHODS:: Fourteen well-trained cyclists were pair-matched and randomly assigned to HIGH or LOW-glycogen training groups. Subjects performed 9 aerobic training (AT; 90 min at 70% VO2max) and 9 high-intensity interval-training sessions (HIT; 8 x 5 min efforts, 1 min recovery) during a 3-wk period. HIGH trained once daily, alternating between AT on day 1 and HIT the following day, whereas LOW trained twice every second day, firstly performing AT and then 1 h later performing HIT. Pre and post-training measures were a resting muscle biopsy, metabolic measures during steady state cycling (SS), and a time trial (TT). RESULTS:: Power output during HIT was 297 +/- 8 W in LOW compared with 323 +/- 9 W in HIGH (P<0.05), however, TT performance improved by ~10% in both groups (P<0.05). Fat oxidation during SS increased after training in LOW (from 26+/-2 to 34+/-2 mumol/kg/min, P<0.01). Plasma FFA oxidation was similar before and after training in both groups but muscle-derived triacylglycerol oxidation increased after training in LOW (from 16+/-1 to 23+/-1 mumol/kg/min, P<0.05). Training with low muscle glycogen also increased beta-hydroxyacyl-CoA-dehydrogenase protein content (P<0.01).

CONCLUSION:: Training with low muscle glycogen reduced training intensity and, in terms of performance, was no more effective than training with high muscle glycogen. However, fat oxidation was increased after training with low muscle glycogen, which may have been due to enhanced metabolic adaptations in skeletal muscle.


Jamie Scott said...

A couple of things from that study;

Were the athletes adapted to low glycogen training? Taking athletes who are probably used to functioning on a high carb diet & then throwing them into this sort of study, you will see a drop in power unless they get a chance to adapt. I know when I shifted from a higher carb diet to a higher fat diet, my cycling went flat for 3-4 weeks. Power progressively came back after that point however.

The performance of the AT work in the morning and then HIT training in the afternoon is not a way in which I would advise to train. I would suggest that any power differences found might have been reduced or eliminated had teh HIT work been performed as the first session, followed by the steady state AT work in the glycogen depleted state. Thsi would have had the effect of allowing the athletes to maintain the training effect from the higher intensity work, plus gain the fat mobilisation benefits from the second session in a depleted state.

This is how I would use this sort of information in practice. And let's not forget that you would train low but race high. AFAIK, adapting over to higher fat mobilisation doesn't impair ones ability to carbo-load and maximise glycogen saturation (in fact, it may even enhance it).

Anonymous said...

I question your assumption that training with the HIT exercise before the AT would still create the fat mobilization benefits. Fat utilization is at its max around 60 to 70% of VO2max, depending on where you look.

By performing the AT first and depleting muscle glycogen you are forcing muscle to utilize fat during the HIT training at intensities where fat is usually not the key source. This is what I believe leads to the adaptation.

If you were to perform the HIT first you would preferentially use muscle glycogen as normal during HIT, then utilize predominantly more fat at 70% VO2 max where it is already more efficient to use fat.