HIIT, Complexes, the Lactate System, and Fat Loss

Quite a few people swear by using complexes for weight loss, ie series of – generally compound – movements, executed in an anaerobic manner but with pauses in between. Now admittedly, choose any exercise routine, and any goal, and you’ll find people on the Internet advocating it. However, one of the proponents of the above is Dan John, and if Dan says something I listen.

I have been putting together a few things that I learned of the bodies energy systems, and in the light of this, the above statement actually makes sense. It also allows us to optimise this kind of training for the fat-loss goal, which is of course a plus if this is what we want to do…

Before I go to the meat I need to present a collection of factoids that I will need when describing how complexes impact fat loss. So please stay with me

Important Factoids

  1. The body has two primary energy sources, carbohydrates (“carbs”) and fat. Those are used to “charge” the ATP/CP system that ultimately provides the energy for all cells that need it
  2. There are aerobic and anaerobic pathways, the former being relient on blood oxygen, the latter aren’t. ATP/CP is anaerobic, fat is aerobic, and carbs are either or. The anaerobic pathway for carbs goes via lactates
  3. Carbs are in the body stored as glycogen (there is also some sugar in the blood, but this is de-minimis). The glycogen stores are in the liver (~80g glucose equivalent) and in the muscles (~300g, but obviously highly dependent on muscle mass and training)
  4. Liver glycogen can be released into the bloodstream in the form of glucose (that’s the whole purpose of it). Muscle glycogen sits there until it gets used – so eg glycogen in the glutes is used for contracting the glutes, and contracting the glutes only
  5. The body can convert proteins into glucose if need be (ie no glucose from the digestive tract, and empty liver glycogen stores; note that muscle glycogen stores are irrelevant due to factoid #4). There is no significant pathway to convert fat into glucose
  6. The brain uses about 150g of glucose per day if available; if need be this can be reduced to about 75g/day – but not below that – in a state called “ketosis”. The brain takes what it needs, first from whatever is currently being supplied from the digestive tract, then from the liver (not muscle) glycogen stores, and then by breaking down proteins, first from the digestive tract, and then from the muscles
  7. After 12h of fast, the liver glycogen is pretty much depleted (see factoids #3, #6)
  8. Lactate produced on the anaerobic pathway (see #2) is recycled into glucose in the liver. This process uses ATP, and the ATP is produced in the liver by aerobic oxidation of either carbs or fat.
  9. The glucose produced in #8 can either be stored in the liver in the form of glycogen, or it is release in the bloodstream, where – inter alia – it can be used to refill the muscle glycogen stores
  10. Fat oxidation uses more blood oxygen than glucose oxidation for any given level of ATP obtained
  11. Aerobic exercise uses a mix of carbs and fat for fuel. The closer the body gets to the anaerobic threshold, or rather the VO2 max, the more the ratio is geared towards carbs (because of #10)
  12. HIIT brings the body into an mixed anaerobic/aerobic state. What this means is that over the long term the workout is aerobic (there is no other way as the anaerobic system have very limited capacity and need to be recharged) but there are “sprint” periods where anaerobic energy systems are used

How Complexes Impact Fat Loss

Congratulations! You have made it through all those random factoids above (or did you skip them?!?) and now it is time to put them all together. I’ll start with the big picture process that I want to lay out, and after that I will go a bit more into the details:

Complexes bring the body into the mixed anaerobic/aerobic state according to #12. What this means is that the muscles do use muscle glycogen to perform the task (ie 100% carbs). However, those carbs are recycled in the liver and can in principle be returned into the glycogen stores where they came from. The liver takes the energy from aerobic oxidation of either carbs or fat (#8), and the mix will be determined by how close the average effort is to the VO2max (#11). The average effort in turn will be determined by the effort put into the exercises (eg weight, speed) and the Recovery Load Ratio (“RLR“) ie the ratio between the recovery time between the sets, and the time taken for performing the sets.

By now you have probably seen the magic of this: if the average effort is far away from the VO2 max then the effective fuel mix for the exercise will be geared towards fat, even though the primary fuel was 100% carbs. This will be even more so the case if the liver does not have ready access to glucose because (a) there is none coming from the digestive tract, and (b) its glycogen stores are empty (it can still metabolise muscle protein though…).

So what are the implications of this, ie how to optimise the training for fat loss? The following rules should do the trick:

  1. Ensure that muscle glycogen stores are full, liver glycogen stores are empty, and there is no glucose coming from the digestive tract. This is carb cycling in conjunction with intermittent fasting: first eat enough carbs that all stores are refilled, then let the liver stores run down due to the demands of the brain by fasting for 12 hours (#7)
  2. Some BCAA pre workout (10g?) in line with to Martin Berkhan’s LeanGains could be a good idea to protect muscle. Assuming I got the pecking order right in #6 fat should be used ahead of proteins, but better safe than sorry…
  3. Choose “big” exercises, ie those that use many and/or big muscles to maximise energy expenditure. Biceps curls wont do I am afraid. Also mix exercises working different muscle groups so that the overall exposure is maximised (ie do complexes)
  4. Perform the exercise to maximise the build of lactate. According to Roman’s Lactic Acid Protocol this means medium weights (50% of 1RM), high reps (10-15x), slow concentrics (3s), fast eccentrics (“negatives”; <1s). Or just “feel the burn baby” – sets should finish when the lactate becomes unbearable, but one should be still safely away from muscle failure (after all, we want to do it again, and again, and again, …)
  5. Leave enough recovery time between sets so that the average effort stays far away from the VO2max. For many people this will mean an RLR of 3:1 or more. I often use a heart-rate-monitor for that, and wait until my HR goes down to about 100-110.
  6. Total sets a volonte, but the whole thing should probably finish within 1/2h, 1h max

Have fun!


One thought on “HIIT, Complexes, the Lactate System, and Fat Loss

  1. Pingback: Anaerobic training / HIIT | Thor Falk

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