November 23, 2014

Everything You Need To Know About Training To Failure

Is it necessary to train to failure for optimal growth?
While training to failure can be dangerous (especially with heavy weights), as well as lead to neural fatigue, cause an excessive amount of muscle damage, and contribute to localized overtraining, there are significant benefits as well, but it really depends on what it is that caused failure in the first place.

What is ‘muscle’ failure?
Failure in this context refers to the incapacity to sustain the required amount of force output for a specific task. In other words, the task of performing more and more repetitions will become more daunting until it’s no longer physically possible to continue to produce the required amount of force to complete a repetition – this is failure.

What causes failure?
The concept of training to failure is easy to understand, but the reasons underlying its occurrence are more complex because there's not always a single isolated cause of failure – they are (but are not limited to):

1.    Neurotransmitter levels: The central nervous system (CNS) recruits the motor-units involved in movement, sets their firing rate, and optimizes proper intra-/inter-muscular coordination. Neural fatigue, especially the depletion of the neurotransmitters dopamine and acetylcholine, can contribute to failure. A reduction in acetylcholine levels is associated with a decrease in the efficiency of the neuromuscular transmission meaning, when acetylcholine levels are low, it's harder for the nervous system to recruit motor-units, and thus limiting your ability to generate a high level of force output. Therefore, in some instances it’s probable that the muscles are fully capable of handling the load, but the nervous system can’t keep up with the current demand.

2.    Fatigue and/or lack of oxygen - hypoxia: Failure can also be the result of the recruited fibers being too fatigued to continue producing enough force, and the remaining fibers (fatigue resistant slow-twitch fibers) not having the capacity to produce the required amount of force to enable you to keep going. Oxygen debt can also become too high, thus impairing recruitment (and energy production, which is also limited without oxygen).

3.    Accumulation of metabolites: Increased blood acidity reduces the magnitude of the neural drive and also the whole neuromuscular process. When lactate and hydrogen ions accumulate in the muscle as a result of a series of intense contractions, the muscle becomes acidic which makes it harder for the nervous system to recruit motor units to perform the task.

On top of increasing blood acidity, hydrogen ions also inhibit the PFK enzyme (reducing the capacity to produce energy from glucose), interfere with the formation of the actin-myosin cross bridges (necessary for muscle contraction to occur), and decrease the sensitivity of the troponin to calcium ions.

Potassium ions can also play a part in muscle fatigue during a set, since intense physical activity markedly increases extra-cellular levels of potassium ions. Potassium accumulation outside the muscle cell leads to a dramatic loss of force, thus making muscle action more difficult.

Phosphate molecules can play a part as well, as phosphate is a by-product of the breakdown of ATP to produce energy, and an accumulation of phosphate decreases the sensitivity of the sarcoplasmic reticulum to calcium ions. This desensitization reduces the capacity to produce a decent muscle contraction.

4.    Depletion of energy substrates: Muscle contraction requires energy, and strength training first and foremost relies on the use of glucose/glycogen for fuel, along with the phosphagen system (ATP-CP).

Intramuscular glycogen levels (glucose reserves in the muscle) are very limited and can become depleted the longer a training session progresses. While the body can compensate by mobilizing glucose stored elsewhere in the body by transforming amino acids into glucose (which is a less powerful way of producing energy for intense muscle contractions) or turn to free fatty acids and ketone bodies, these amounts are also finite, and in either case they still can't provide energy as fast as intramuscular glycogen can. As a result, even though it will be possible to continue exercising with a depleted muscle, it's not possible to maintain the same level of intensity and force production.

These reasons alone make it readily apparent that muscle failure cannot be narrowed down to a single phenomenon, but that it’s a combination of several factors which can be responsible for its onset.

All for 1, or 1 for all?

The wide range of factors contributing to failure make it so that failure can occur long before full contractile fatigue has been reached. Training to failure does not guarantee full motor-unit stimulation, it just means that full motor-unit recruitment took place. Therefore, to fully stimulate a larger pool of muscle fibers, it’s necessary to repeat efforts because simply recruiting a motor-unit doesn't mean that it's been stimulated, because to be stimulated, a muscle fiber must be recruited and then exhausted.

If training to failure doesn't guarantee full motor-unit stimulation within a muscle, then not taking a set to positive muscle failure (the point where a technically correct full repetition can't be completed) must be even less effective. Think about it like this – if training to failure doesn't guarantee maximal motor-unit stimulation, then not taking a set to failure definitely does not. Because both failure and volume is needed for maximal motor-unit stimulation a moderate volume of sets taken to failure is necessary – but does this mean that training to failure is necessary for growth? Saying yes implies that full contractile fatigue is necessary for growth, but is it? (We’ll get back to that later)

Training to failure comes with its own specific drawbacks, among them is the drainage that can occur to the CNS, as it is very demanding to have to recruit the maximal amount of muscle fibers possible, just to perform the task. For this reason, should one wish for progress to be sustainable, they may want to avoid burning out/overtraining their CNS by continuously pushing the envelope (also called the Central Fatigue Syndrome – CFS). Failure increases the demand of the nervous system because as fatigue sets in (accumulation of metabolites and energetic depletion), it must work harder to recruit the last high threshold motor units. This is why in theory it may be advisable to avoid going to failure – to minimize training that has a high demand on the nervous system (heavy and/or explosive lifting are both just as, if not more, demanding on the nervous system as training to failure).

The CNS, just like the rest of the body, is an adaptive system, and it can become more efficient at stimulating muscle contraction over time. And while CFS is a real problem, its occurrence in bodybuilders or individuals training for muscle mass gains is minimal, at best.

It is possible to suffer from CNS fatigue after a training session (much the way our muscles become fatigued as well), but the body can recover from that, although neurotransmitter depletion might be a real concern, but even that is rarely a problem.

To recap:

·         Failure DOES NOT MEAN that every muscle fiber within a muscle has been fully stimulated, although going to failure will at least ensure maximal motor-unit stimulation occurred during that set

For a muscle to contract:

·         The nervous system must first send the message for it to contract

·         The muscle must receive the signal – metabolic waste accumulation from previous contractions may prevent the signal from being received

·         It must not be too fatigued to perform the work

·         It must have the energy available to perform the work

So, if the question was – Is it necessary to recruit and fatigue as many muscle fibers as possible for optimal growth? – Then training to failure would be absolutely necessary, since a moderate amount of work to failure is required for full motor-unit stimulation.

But, failure itself doesn’t produce a growth stimulus, it only ensures that a set produced as much motor-unit recruitment as possible. The act of reaching failure however, does produce a growth stimulus – depending how you got there.

The production of metabolites and hypoxic state that comes with training to muscle failure have both been linked to an increase in the production of local growth factors, as well as the ERK pathway, which can have a positive impact on muscle growth, is highly dependent on the time under tension – which is generally associated with training to muscle failure.

The only real drawback with training to failure is that it’s harder to modulate volume and frequency, as it’s much easier to overdo it which can limit gains as a result, and strength gains may be suboptimal. So a better, more ‘out of the box’ question, may be:

Is it possible to produce enough time under tension/metabolites and create a hypoxic state, to increase local growth factors, and the ERK pathway, WITHOUT training to failure?

An ‘out of the box’ question like this provides the kind of ‘out of the box’ answer which explains why it is NOT necessary to train to failure for optimal growth, because if the reps are high enough and/or time under tension is great enough, you will accomplish:

1.    An accumulation of metabolites (lactate and hydrogen ions) – which lead to the release of local growth factors

2.    Oxygen deprivation – which also leads to the release of local growth factors, and does occur with occlusion, but occlusion doesn’t really occur when performing regular reps, but after enough reps the oxygen debt has the same occlusion effect

3.    Increased blood flow to the muscles – this is especially beneficial if the blood is full of nutrients  to be transported to the muscles (which it will be with proper pre-/intra-workout nutrition)

4.    Finally, some cell signaling responsible for initiating protein synthesis is activated with longer times under tension, provided by high repetitions

All of this will contribute to optimal growth, and training to failure is not necessary for any of this to happen – although going to failure may once again help ensure it. However, briefly discontinuing the set by stopping shy of failure, only to restart again after a few seconds, may allow you to keep going beyond the point in which you would have had to stop, possibly facilitating even greater accumulation of metabolites, lengthening the duration of oxygen deprivation, while also allow the nutrient rich blood to briefly enter the muscle.

Practical Application – Using Low Reps To Accumulate High Reps

One of the major knocks against performing high reps for prolonged times under tension is that form/technique almost inevitably breaks down, thus reducing the quality of the exercise, while at the same time reinforcing poor motor pattern habits. Since the benefits of performing high reps for prolonged times under tension are undeniable when it comes to muscle growth, the most practical solution would be to perform multiple low rep ‘mini’ sets back to back to back, with minimal rest.

For example, perform mini-sets of 2-3 reps at a time, with 10 seconds rest in between, aiming for 8-12 reps performed without any deviation in form. Perform as many mini-sets as possible per set until at least 2 reps cannot be performed consecutively, and until 8 total reps per set can be accomplished. Start conservatively with 65-70% of max, and go from there. These numbers and rep brackets are based on using compound free weight movements – if using machines or cables, slightly higher rep brackets are advised:

2-4 for compound free weight exercises
4-6 for compound machine exercises
6-8 for isolation free weight exercises
8-10 for isolation machine exercises

Essentially you’re looking for at least 4 mini-sets per set, going until you fail to complete the amount of reps on the low end of the bracket, or can’t get to that 4th mini-set – yes this does require going to failure, but the amount of times reaching failure is limited, and the training effect comes from the high reps/prolonged time under tension combined with very short rest intervals.

What about going past failure?

Aside from ensuring full motor-unit recruitment, and even greater motor-unit stimulation than just training to failure, going beyond failure (rest-pause, drop-/supersets, etc) really stresses the adrenals, leading to water retention, softer feeling muscles, and just a negative overall feeling. It’s for this reason that training to failure, and especially beyond, should be used periodically, and never as an absolute part of your training – after all, it’s not necessary to do so to stimulate growth anyway.

If you have any questions about any of the strategies presented in this article, feel free to contact me at I'm available for online consulting and personalized program design, as well as one on one training if you are located in the Greater Toronto Area (GTA).

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