Few concepts in the world of strength training have been more hotly debated than the
need (or not) to reach muscle failure during your sets. Is it necessary for muscle growth?
No. However, I feel it is necessary for optimal growth. Some argue that training to failure
is either dangerous or can lead to CNS fatigue. Others argue that training to failure too
often will cause too much muscle damage and can lead to localised overtraining. Some of
these misconceptions stem from the fact that muscle failure is not well understood.
The biggest proponents of training to failure have defined it as “creating a maximum
amount of inroads to the muscle on each set”. This is fine and well however am I the only
one who doesn’t understand what they mean by that? It is important to correctly describe
what muscle failure is and why it happens. This information will allow us to make an
objective assessment of the need (or not) of training to failure.
Failure is easy to understand. It’s simply the incapacity to maintain the required amount
of force output (Edwards 1981, Davis 1996). In other words, at some point during your
set, completing more repetitions will become more and more arduous until you are unable
to produce the required amount of force to complete a repetition. Failure isn’t the amount
of “inroad” to the muscle; it’s nothing esoteric as we just saw.
If the concept of training to failure is actually quite easy to grasp, the causes underlying
this occurrence are a bit more complex. There is no exclusive cause of training failure;
rather there are quite a few of them.
- Central/Neuromuscular factors: the nervous system is the boss! It’s the CNS that
recruits the motor-units involved in the movement, set their firing rate and ensure proper
intra and intermuscular coordination. Central fatigue can contribute to muscle failure,
especially the depletion of the neurotransmitters dopamine and acetylcholine. A decrease
in acetylcholine levels is associated with a decrease in the efficiency of the
neuromuscular transmission. In other words, when acetylcholine levels are low, it’s
harder for your CNS to recruit motor-units.
- Psychological factors: The perception of exhaustion or exercise discomfort can lead to
a premature ending of a set. This is especially true of beginners who are not accustomed
to the pain of training intensely. Subconsciously (or not) the individual will decrease his
force production as the set becomes uncomfortable. This is obviously not an “acceptable”
cause of failure in the intermediate or advanced trainees, but beginners who are not used
to intense training could slowly break into it by gradually increasing their pain tolerance.
- Metabolic and mechanical factors: It is well known that an increase in blood acidity
reduces the magnitude of the neural drive as well as the whole neuromuscular process.
Lactic acid and lactate are sometimes thought to be the cause of this acidification of the
blood, but this is actually not the case. The real culprit is hydrogen. Hydrogen ions can
increase blood acidity, inhibits the PFK enzyme (reducing the capacity to produce energy
from glucose), interferes 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 role in muscle fatigue during a set. Sejersted (2000)
has demonstrated that intense physical activity markedly increases extra-cellular levels of
potassium ions. Potassium accumulation outside the muscle cell leads to a dramatic loss
of force which obviously makes muscle action more difficult. Finally we can include
phosphate molecules into the equation. Phosphate is a by-product of the breadown of
ATP to produce energy. An accumulation of phosphate decreases the sensitivity of the
sarcoplasmic reticulum to calcium ions. Without going into excessive detail, this
desensitization reduces the capacity to produce a decent muscle contraction.
- Energetic factors: Muscle contraction requires energy. Strength training relies first
and foremost on the use of glucose/glucogen for fuel with the phophagen system (ATPCP)
also playing a role. Intramuscular glycogen levels (glucose reserve in the muscle) is
very limited and can become depleted as the training session progresses. The body can
compensate by mobilizing glucose stored elsewhere in the body (but this amount is also
finite), 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. The last two solutions cannot 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 is impossible to maintain the same level of intensity and force production.
So as you can see, it is impossible to attribute muscle failure to a single phenomenon.
Rather, it’s a mix of several factors that cause muscle failure. Contrary to popular beliefs,
reaching muscle failure in one set doesn’t ensure the complete fatigue and stimulation of
all the muscle fibers in a muscle. Far from it! Failure can occur way before full
contractile fatigue has been reached. This means that the “one set per exercise to failure”
method is not ideal for maximal growth. As a part of a more complex training system it
can be beneficial from time to time, but not as a discrete training system.
At some point it becomes necessary to increase training volume to fully stimulate a larger
pool of muscle fibers. Remember that simply recruiting a motor-unit doesn’t mean that
it’s been stimulated. To be stimulated a muscle fiber must be recruited and fatigued
(Zatsiorsky 1996).
If training to failure doesn’t ensure full motor-unit stimulation within a muscle, not taking
a set to positive muscle failure (the point where a technically correct full repetition cannot
be completed) is even less effective since it will not fatigue the HTMUs as much and
remember that a muscle fiber that isn’t fatigued isn’t fully stimulated! In other words
training to failure doesn’t guarantee maximal motor-unit stimulation but not taking a set
to failure drastically reduces the efficacy of a set. This indicates that high volume of work
without going to failure isn’t ideal for maximal muscle growth (but it’s okay for strength
and power oriented training). But the other end of the spectrum: low-volume training
taken to failure isn’t ideal either. Failure and volume are both needed for maximal motorunit
stimulation. That’s not to say that you should use a huge volume of work, but a
moderate volume of sets taken to failure is necessary for maximal muscle growth.
And what about the so-called CNS drain that can occur when you take your sets to
failure? While I do agree that for continuous improvements to occur one should avoid
CNS burnout/overtraining (also called the Central Fatigue Syndrome). I understand the
theory behind avoiding going to failure: going to failure increases the implication of the
nervous system because as fatigue sets in (accumulation of metabolites and energetic
depletion) it must work harder to recruit the last HTMUs. The argument is that we should
minimize training that has a high demand on the nervous system. However, most people
who espouse the “don’t go to failure” theory are generally proponents of heavy lifting
and/or explosive lifting. Both of which are just as demanding (if not more) on the nervous
system as training to failure.
Why are they against one neural intensive method but for another one? The fact is
that the nervous system is an adaptive system just like the rest of our body and it can
become more efficient at stimulating muscle contraction when it’s trained properly. And
while the CFS is a real problem, its occurrence in bodybuilders or individual training for
muscle mass gains is minimal, close to nil. Sure, we can suffer from CNS fatigue after a
training session (just like our muscles are fatigued too), but the body can recover from
that. Neurotransmitter depletion might be a concern, but rarely is a real problem. Using a
supplement like Biotest’s Power Drive can help in that regard by boosting acetylcholine
and dopamine levels.
