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 ben@paramounttraining.ca. 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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