Rest Periods In Depth Part 2


By Rob Clarke Driven Sports

Part one introduced the metabolic pathways that fuel muscle under varying conditions. Today will continue will a discussion into what training these particular pathways can do for muscle growth.

Metabolic stress

No different to your car burning fuel to make it move, the metabolic pathways your muscle fibers can use create by-products. The metabolite build-up from oxidative phosphorylation in slow twitch fibers is largely a non-issue; like I said in part one, it is a comparatively slow process and with the presence of oxygen the body has the capacity to keep up with waste management. The anaerobic pathways – glycolysis and the phosphagen system – however, are a different story. Your body is only capable of anaerobic respiration for a fixed amount of time. The rapid build-up of metabolites alters the cellular environment so significantly that normal functioning becomes almost impossible. For anyone that can drive stick, it’s a bit like leaving the car in first gear and attempting to get up to 70mph. This metabolite build-up is known as metabolic stress.

The players that make up metabolic stress include lactate, hydrogen ions, phosphates, and even creatine to some degree. None of these should look foreign to you – at least they won’t if you’re a regular reader of the Driven Blog. Lactate is the salt of lactic acid. For a loooooong time lactic acid was wrongly accused of being the culprit behind “the burn” of training. In actual fact, the real culprit is the build-up of hydrogen ions. During aerobic respiration, the presence of oxygen acts as an electron acceptor, mopping up the hydrogen ion build-up. During anaerobic respiration, the lack of oxygen means that hydrogen ions accumulate, the cellular pH drops, and you feel that all too familiar sting. 

Hydrogen ions don’t appear to contribute directly to cellular messaging, nor do they trigger anabolic processes elsewhere – at least that I can see. Lactate, on the other hand, may play a very productive role. Powerlifters in their training design deplete PCr stores almost exclusively. During some preparation for competition they may create some lactic acid, but not a lot. They then rest an allotted time in order to replenish PCr stores. Bodybuilders most certainly do generate lactic acid when training in their traditional 6-12 glycolytic rep range, while also depleting PCr stores. They then attempt to stifle the complete replenishment of PCr by resting minimally. I will continue to look at this through the eyes of a bodybuilder and move on to the subsequent effects that this lactate creation exerts when in combination with mechanical tension and muscular damage. And more precisely what this all means for muscle growth.

Keeping oxygen out

The lack of oxygen in all this, officially called hypoxia, appears to be a contributing factor for muscle growth. This is one of the incentives to lift weights in a fashion of constant tension – by avoiding locking out on each rep. Locking out is literally the moment at the top of a rep where the load is transferred mostly off the muscular system and onto the skeletal system. For instance, when you bench press, if you straighten your arms completely, the “locking” of your elbows transfers the load more onto the bones. By avoiding the lock out – and I’m not on about half-reps here – it is believed that waste products are prevented from leaving the working muscle(s) akin to tying a tourniquet around the muscle. In fact, a Japanese bodybuilder has devised a training style specifically to take advantage of this. His name is Yoshiaki Sato, and he calls his program “Kaatsu”.

Kaatsu is occlusion training. The concept is to literally tie-off the target muscles to prevent fresh blood flow into a muscle, and maximize waste product build-up. The idea for Kaatsu came to Sato when he was kneeling while attending a Buddhist mass. His legs went numb from being in the same position for so long, and as he massaged his calves he associated the sensation with the sensation he felt during training. He then theorized that this was due to the blood flow restriction, so he put his idea into practice. Through a lot of trial and error – during which time he managed to hospitalize himself – he devised the ideal position for the tourniquets, and the ideal load to use. The latter is a key aspect of this, and something I feel too many Western weight lifters miss. The loads used for Kaatsu needs to be low. Kaatsu is the exception is alluded to in the “rep-centrics” article where I said you could initiate growth by using a load below 65% of your one-rep max. 

The premise of Kaatsu is to replicate the highly-anaerobic conditions of a heavy PCr/glycolytic set with a light set by amplifying metabolite build-up. In other words, don’t throw 405lbs on the bar and try and knock out six reps with belts around your quads. Ideally, you use around 30% of your one-rep max. In fact, one study found that Kaatsu could build muscle by simply walking. But it is not without dangers, as illustrated by the case study of the Norwegian hockey player that developed rhabdomyolysis after a single workout. 

Studies have also found that Kaatsu could have an anti-catabolic effect. One study found that leg size and strength could be maintained with periodical occlusion despite putting the ankle in a cast and preventing the participants from walking on it. Under usual circumstances muscle size and strength losses are evident. Another study displayed an anti-catabolic effect despite post-surgery bed-rest. Some brand new research suggests that myostatin restriction (dare I say inhibition?) may play a role in this but it is still early days to say for certain.

Hypoxic conditions may not need to be limited to the muscles themselves alone. Studies have looked into the concept of lowering the oxygen concentration of the atmosphere of the gym itself, recreating the conditions of altitude training – the so-called “train high, compete low”. Some of you may also recall that UFC athlete Wanderlei Silva also attempts to recreate this with his snorkel training. The results indicate a big increase in muscle growth. Another study of a similar setup has shown the same, along with large increases in hormones like growth hormone (GH). GH is believed to be stimulated due to the lactic acid, which has also been shown to increase testosterone levels. 

I should note here that increases in GH and testosterone have also been shown in normal atmospheres and without occlusion equipment. It appears to be a standard effect of lactic acid build-up from exercise. And this has another effect on the cell.

Swell the cell

Cellular swelling is an effect that activates hormones and enzymes involved in promoting glucose and amino acid uptake. The increase in water in the cell occurs by a process called osmosis. (Yep, this series is pitching throwbacks to high school science like Roy Halladay fastballs.) Combined with an increase in blood flow to the target muscle, largely under the direction of nitric oxide, you have what is affectionately known as “the pump”. The reason the body increases cellular swelling appears to be almost like a pre-emptive measure to help the muscle against overload. The swelling effect also signals for protein synthesis rates to increase and lower rates of protein degradation. Nitric oxide is also involved in satellite cell proliferation – which are heavily involved in muscle growth – and glucose uptake. In other words, providing you are challenging your muscles and not just inflating them for visual effect, the pump is not just cosmetic – it is functional. 

Cell osmosis is governed by a receptor called Aquaporin 4 (AQP4), which is found significantly on fast-twitch muscle fibers. Thus, the swelling is heavily influenced by lactate accumulation from glycolysis, demonstrating another benefit for higher rep training in the 6-12 rep region.

Hopefully all of this helps explain not just reasons for and again long and short rest intervals, but also the way in which muscles deal with stress. The final part for The hustle between sets will look more directly into studies involved in this topic.

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