In the article Designing an Effective Circuit there is a statement that in a fat loss program lactic acid build up inhibits lypolosis. Can you explain this? I have been trained to do high reps on legs 'to go for the burn',when trying to lose body fat.
Good, but complex, Question.
From the question I will attempt to cover three areas briefly (hopefully covering the entire scope of the question): 1. Lactic Acid and fat burning, 2. Effect of Lactic Acid as a training stimulus ('the burn'); 3. Training to lose body fat.
Part 1. Lactic Acid and fat burning:
Lactic Acid is created when the Oxidative system can no longer produce ATP, thus the mechanism for ATP production becomes Anaerobic whereby Glucose/ Glycogen, once converted to Pyruvic Acid, cannot enter the Kreb's (Citric Acid / TCA) cycle and Lactic Acid is produced. Thus the development of Lactic Acid shows a 'breakdown' in the effectivity of Oxidative ATP production. So what?
The breakdown of fats requires a large amount of Oxygen - far larger than the amount required for the breakdown of Glucose/Glycogen. Therefore if there is not enough Oxygen to complete the oxidization of the more malleable Glucose/Glycogen (and lactic acid is produced), there would not be enough oxygen for the oxidization of fat. Furthermore, the carrier of lipolysed fat to the Kreb's cycle, Oxaloacitic acid, is converted to glucose thus no longer carrying out its transport function - thus 'backing up' the system
Some research and trains of thought have linked the development of Lactic Acid to a breakdown in the delivery process of Hydrogen (by the Hydrogen shuttles FAD and NAD),from the Kreb's Cycle to the Electron Transport Chain (where most of oxidative ATP is produced - This is why fat, with a high Hydrogen content, is such a good fuel source). The impairment of this transport mechanism means that the ETC is disabled and the production of Oxidative ATP is halted. In this train of though Lactic Acid may not be the cause of muscle fatigue and oxidative impairment, but rather the response to a Hydrogen shuttle problem. (There is also some research being looked at that discusses the acidity of Lactic Acid and Lactate (Salt of Lactic Acid) and the negative effect on oxidative enzymes)
In summary when developing Lactic Acid you are training Anaerobically and the Aerobic fat burning process is impaired. This is not to say however that training at a level that develops Lactic Acid will does not help in fat loss AFTER the training session (I'll discuss this in part 3). (There are several key areas that lead to the statement that fat burning is inhibited by Lactic Acid. For greater detail look at Respiratory Exchange Ratios, Effect of Oxaloacitic acid on Acetyl Co-A - especially during glycogen fatigue, Effect of Lactic Acid on Mitochondrial function - where Beta Oxidization of fat occurs, Diversion of oxygen for reconversion of Lactic Acid back to Acetyl Co - A and glycogen (Kori cycle) and the Effect of acidosis on Lipolysis and Lipogenesis.)
Part 2: Effect of Lactic Acid as a training effect.
The primary responses developed by high levels of lactic work (ie 'burning') is the improvement of Lactic Acid tolerance or 'buffering'; this being the ability to convert Lactic Acid to a weaker acid (carbonic Acid) and to physiologically and psychologically handle the high levels of acidosis. For Anaerobic / Aerobic Conditioning (Eg Intervals) this also improves Anaerobic biochemical characteristics (like increasing Glycolytic enzymes).
In summary high levels of lactic work develop local muscular ability to continue doing more of the same repetitions (muscular endurance as opposed to Aerobic endurance) and / or utilize Glucose/Glycogen more effectively anaerobically.
Part 3: Fat Burning Stages
When talking of Fat burning there are three stages / areas that I recommend a training program consider: A. Fat utilization during training: B. Fat utilization after training (recovery), and; C. Lifestyle fat utilization.
- For the best means of utilizing fat during exercise, moderate intensity Aerobic activity must be used; thus ensuring that ATP is produced from Oxidization of Fat - This is not necessarily the most effective way of burning fat long term as total calories consumed play by far the more important role. (See my Fat Burning Zone Article)
- This involves the training used to ensure greater fat utilization post activity. This is where High Intensity Training, like lactic work, is best suited. During recovery from a training session, which could last for several hours after an intense session, the ATP used for recovery is predominantly derived from fat oxidization, which means you are utilizing a greater amount of fat to assist in your recovery. (Be aware however that doing an exercise like Side Leg Lifts or Crunches to exhaustion, not only utilize few calories during training but also after training for recovery; thus the TOTAL amount of calories used is relatively small. This is due to the small volume of muscle involved - you would be better suited to doing high levels of Compound Complex movements than Isolated ones).
- This involves using more fat in everyday life and would involve not only being more active during the day (eg Walking instead of driving / bussing) but also increasing muscle size, as the more muscle you have the more energy you utilize during the day to keep the muscle active and repair the muscle (Eg bigger engine in the car means more fuel needed to run it.)
I have attempt to cover three complex issues in under a thousand words but I hope this helps cover the scope of the question...if you would like to go further and more detailed please give me a mail.