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What is Muscular Failure: The Weight Room Part 1

Changes in Lever Arm During Biceps Curl

In the previous article I discussed the concept of muscular failure in a general sense.    This included a discussion of general muscular physiology and the definitions of muscular fatigue, muscular/task failure and exhaustion.    The one sentence summary of that article is as follows “Muscular/task failure occurs when the subject is unable to generate sufficient muscular force to meet or exceed the requirements of the task.”


Here’s the image from Part 1 again illustrating this.

Force Output vs. Force Requirements

So if a given task requires 100 units of force and you can generate 120 units of force, you can accomplish the task.  Once you can only generate 99 units of force, you cannot accomplish the task.  You have achieved momentary muscular failure. By which I mean that if you rested for some time so that muscular force could recover, you could once again achieve the task.  You have only failed at that moment.

In a lot of activities, determining when task failure has occurred is relatively simply.  If someone is on a bike and can’t generate the goal power output, or can’t turn the pedals above a certain cadence, they have reached task failure.  If someone is using their finger to generate 20% of maximum force against a push plate and can’t, that’s task failure.

But, as is almost universally the case with topics like this, muscular failure in the weight room is much more complicated and harder to define.    In fact, it’s so complex that it will take me two parts to address it as fully as I want to.

Muscular Failure in the Weight Room

In the weight room, defining task failure becomes more complicated for reasons I’ll shortly explain.  As importantly, multiple overlapping definitions of failure have been used in weight training literature and practice over the years.  Simply saying someone “Went to muscular failure” doesn’t mean very much without more details about how it was defined.

While this might seem like pedantic nitpicking, it’s not.  Because as I mentioned in Part 1, the specific definition of failure being used in any given paper or workout can drastically impact on what is actually being done.   If two research studies or workouts use different definitions of muscular failure, comparing them becomes problematic.  That’s in addition to all of the other variables that invariably vary between varying studies (i.e. intensity, sets, reps, rest intervals, exercise choice, frequency).

It’s even worse when people are talking with undefined terms.   Clarity matters and there tends to be a great lack thereof in exercise science.

Related: What Does Muscular Failure Mean?

That lack of clarity adds another level of complexity to an already complex topic.  So let’s uncomplexify it.  First some definitions.

Concentric, Isometric and Eccentric Muscle Actions

Ok, the first thing I need to talk about here is a little bit of detailed minutiae.   First you need to realize that there are three different types of muscle actions that can occur.

  1. Concentric muscle action: When a muscle generates force while shortening
  2. Isometric muscle action: When a muscle generates force with no change in length
  3. Eccentric muscle action: When a muscle generates force while lengthening

A couple of pedantic notes: First, an older terminology for the above were to refer to concentric, isometric and eccentric contractions.   Since contraction implies shortening and an eccentric contraction is an impossibility, these were abandoned for the more accurate muscle action.

Second, while an isometric muscle action is generally used to describe no change in the length of the muscle, this isn’t entirely entirely true.  Upon initial activation, a muscle will pull slack out of connective tissues and such so that there is some very slight shortening of the muscle.  At this point, the muscle does not change length due to the lack of movement around the joint.  And I only bring this up to head off the nitpickers who love to find the most minor fault with my articles.  Moving on.

Let me finally note that maximal eccentric strength is higher than maximal isometric strength which is higher than maximal concentric strength.  You can lower more weight than you can hold and hold more weight than you can lift.

Three Types of Movements in the Weight Room

In that there are three different types of muscle actions which can occur, there can be three different types of movements that occur during weight training.  They are:

  1. Concentric: Lifting the weight.  The muscle shortens under load.
  2. Isometric: Holding the weight.  The muscle does not change length under load.
  3. Eccentric: Lowering the weight.  The muscle lengthens under load.

So if you are doing a biceps curl, lifting it from the bottom of the movement to the top of the movement is the concentric phase. When you lower it back down under control, that is an eccentric phase.  If you were to hold it at some point in the range of motion, that would be an isometric phase.

As I talked about in Part 1, the majority of traditional weight training movements include a concentric and eccentric component.  There are exceptions, the Olympic lifts are generally dropped and some powerlifters drop rapidly from the top of the deadlift.  But for the most part, the movements we are talking about involve both concentric and eccentric phases.

Whether or not a true isometric is present depends.  In something like a leg extension or leg curl, a trainee might squeeze hard at the top, performing an isometric contraction there.  The same might be done at the top of a curl, bottom of a triceps pressdown or endpoint of a cable crossover.  Holding a row in the back position for a moment would be another example of an isometric.  But these are all situations where the isometric is held at peak contraction.

In contrast, it is far more rare to do a true isometric in the middle of a movement, at least among bodybuilders.

Powerlifters and OL’ers sometimes do this, though.  So a powerlifter might do the first part of a deadlift to below the knee and hold it there for several seconds before putting it down or pulling to the top.  Ol’ers may do the same, lifting the bar to below the knee, holding it there for 1-2 seconds before finishing the rep.

But for hypertrophy training, this type of thing is very rare.

Three Types of Muscular Failure

Inasmuch as there are three different types of muscle actions which lead to three different “phases” of weight training, you can therefore have three types of muscular or task failure during weight training.

Concentric failure would mean an inability to lift the weight.  While I’ll get deeper into the definitions of failure below, I will qualify this now as “through a full range of motion.”  So you start a biceps curl with 100 lbs and can’t get past the middle of the movement to reach the top.  You have reached momentary concentric muscular failure.

Note: Let me reiterate from Part 1 that this isn’t muscular exhaustion.  If you put down the 100 lb weight and picked up a 90 lb weight you could continue.  When you could no longer lift that, you could move to 80 lbs.  You wouldn’t reach muscular exhaustion until you could literally not curl just the arm with no weight.

Related: What is Muscular Failure?

Let me also reiterate that this failure is only momentary.  If you rested 15 seconds you might do another 2-3 repetitions with the 100 lbs before reaching muscular failure a second time.

Isometric failure would mean an inability to hold a weight without moving.  So imagine that you hit concentric failure in the middle of the biceps curl above and then just held the weight at the same position.  When you couldn’t hold that position anymore and the bar gradually descended, that would be isometric muscular failure.

If a powerlifter squatted halfway down and then held that position until he started to sink to the safeties, that would also be isometric failure.

It’s a rare trainee who goes to isometric failure although some of the HIT and Superslow camp might since they are big on maximal fatigue/”inroad” and pushing and pulling for 5-10 seconds into an isometric after concentric failure is something they sometimes do.   Then they wonder why they are exhausted for a week.  I wouldn’t generally recommend this although, as I’ll show in Part 4, it can be a useful teaching tool.

Eccentric failure describes an inability to lower a weight under control.  Usually this is qualified with a specific lowering speed.  So if the goal is to lower a weight over 4 seconds and you can’t lower it any more slowly than in 2 seconds, that’s eccentric failure.  True eccentric failure might be defined as the total inability to control the weight on the way down.

And inasmuch as few go to isometric failure, fewer still go to eccentric failure except maybe the dipshit gym bros who live for forced reps and other dumb shit like that on bench press.   I certainly wouldn’t recommend training to the point of eccentric failure under most situations.  It’s incredibly stressful, can get dangerous fast and either requires specific equipment or spotters willing to put up with this bullshit by repeatedly lifting the weight to the top so you can lower it repeatedly until they get bored and just let it crush your sternum.

Make no mistake, supra-maximal eccentrics have their place in some strength sports like PL’ing but they are only sporadically used.  When I them with my athlete Sumi Singh it’s once per week for about 4 weeks total and she does a single rep at 105-110% above her best single.

You can hear me counting time on this in the background, aiming for a 4 second lowering which she invariably stretches out to 5 seconds.

The Focus is on Concentric Failure

Since training to the point of deliberate isometric or eccentric failure is relatively rare in practice, I will be talking about momentary muscular failure only in terms of concentric failure.  Yes, there are  studies examining isometric or eccentric training in terms of hypertrophy.  But in terms of the volume wars studies they were all using some definition of concentric failure so that will be my only focus.  That’s also how the majority of people train the majority of the time.

Related: How Many Sets Should I Do for Maximum Muscle Growth?

So for all practical purposes, we’re only talking about concentric failure: the momentary inability to lift a weight through the full range of motion.   Once again, I’ll qualify this definition more below.   And while this seems pretty simply, it’s not when you start talking about the weight room.

Because now we have to consider the biomechanics of lifting a bit.  Specifically we need to talk about the sticking point.

The Sticking Point

In a conceptual sense, the sticking point of any exercise represents the position in that movement where the force requirements of the activity are highest relative to muscular force output.  As the paper linked above states:

In the context of resistance training the so-called “sticking point” is commonly understood as the position in a lift in which a disproportionately large increase in the difficulty to continue the lift is experienced.

Without getting too deeply into the physics of it this generally represents the point in the movement where the perpendicular distance between the weight and the axis of rotation (i.e. the lever arm) is at its greatest point.  This is where the greatest force (strictly speaking torque) will be required to continue moving the weight.

You can see this in the following image, demonstrating the changes in the lever arm, the red line, throughout the biceps curl.  When the lever arm is the longest, the force/torque requirement at the elbow is highest.

Changes in Lever Arm During Biceps Curl

What you see is that the lever arm (red line) is short at the bottom, gets longer as the arm bends, reaches a maximum when the forearm is perpendicular to the floor before getting shorter again to the top.

Note: Although I left it out of the graphic for clarity, the lever arm of the biceps is changing throughout the movement as well.  And, as it turns out, is also longest when the forearm is perpendicular to the floor. This means that the force/torque output of the biceps is highest when the force/torque requirement of the biceps curl is highest.

I’d add that a further factor in all of this is something called the length- tension curve.  This describes the fact that a muscle/muscle fiber generates less force at maximal stretch or contraction compared to in the middle.  The reasons aren’t relevant, that’s just how it works.

What this ultimately means is that the muscles force (really torque) requirements will be highest when the forearm is perpendicular to the floor.   That’s the sticking point.  And this is why curls are easy to start, get a little bit harder, are hardest in the middle and then gets easier again with little to no effort being required at the top as the lever arm approaches almost nothing (which I really didn’t show well in the graphics).

And the consequence of this is that the only place that the biceps is maximally taxed is in the middle of the movement.    If the muscles cannot generate sufficient force at this point, the rep cannot be completed.  As the same paper linked above puts it:

If the lift is taken to the point of momentary muscular failure, the sticking point is usually where the failure occurs.

Well that’s not true, of course since you can always do goofy stuff to get the rep.  Curling at the wrist shortens the lever arm slightly which may get the weight through the sticking point.   Or folks will just lean back and cheat it up.

As well sometimes failure happens after the sticking point before the movement is completed but this is due to accumulating fatigue lowering force output to such a low level that even the relatively “easier” part of the movement can’t be accomplished.

The same concept above holds for something like triceps pushdowns as well.  It’s easiest at the start, gets hardest, is hardest when the forearm is perpendicular to the floor and then gets easier again. And usually failure will happen in the middle if you keep it strict.  Of course, people will cheat by flaring their elbows to let their pecs help more or lean into it or whatever.

Let me note that not all movements work this way, with the sticking point occurring in the middle.  Consider a leg extension for example, shown below.Changes in Lever Arm During Leg Extension

Here, the lever arm is shortest at the bottom of the movement, increasing in length and reaching a maximum level, the distance from the knee to where the pad hits the leg at the top.   So it starts easy, gets harder and harder with the most difficult bit being at the very top.

In contrast to the biceps curl, the peak force/torque requirements occurs at the very top, when the muscle is in its most contracted position.  Hence why movements like this are often called a “peak contraction” movement.

Now Let’s Not Talk About Compound Movements

This gets way more complicated for compound/multi-joint movements, however.  Now you’re dealing with multiple muscles changing length and changing lever arms at multiple joints throughout the movement.

The principle is the same, of course: the sticking point will occur when the force requirements of the movement are highest relative to muscular force output.  But for any given muscle at any given joint, this may occur at a different point in the movement.

And here you often see a situation where failure doesn’t occur at the sticking point but elsewhere in the movement.  So think about someone benching who fights the bar through the sticking point (when their upper arm is perpendicular to their torso and the lever arm is the longest) but doesn’t make it to lock out.

In this situation there is not only the accumulating fatigue but differences in muscular involvement throughout the movement.  Specifically pecs tend to work “more” out of the bottom with shoulders and then triceps taking more of the load.  Lockout is usually related to triceps strength such that even if the pecs can get through the sticking point, the triceps may be too fatigued to lock it out.  And this is true even though the lever arms at the shoulder and elbow are getting shorter and shorter.

But the physics is a lot harder to work out or even demonstrate and none of us are in the mood.  Well I’m not.

An Important Consequence of the Above

The above has an important consequence for weight training.  That is that the only portion of the movement that a muscle or muscles will be maximally taxed is at the sticking point.   In a barbell curl, the force requirements of the biceps will be lower at every other part of the movement than in the middle.  Only at/near the sticking point will maximal force output be required.

At least that is true for free weight movements.  The development of the machine cam with Nautilus and Cybex was an attempt to remedy this.     In this case, the shape of the cam was altering the load requirements in an attempt to match them better with the mechanics of the movement.  At least that was the goal.

Rubber tubing is different as well.  Here force increases exponentially with the degree of stretch of the tubing (and what is called the modulus of elasticity).   Which means that the start of every movement is fairly trivial, the middle gets hard and the tubing provides the most resistance at the end of the movement.  So even if the lever arm is longest in the middle in the movement being done, the force requirements might be higher at the end because of how tubing resistance works.

Jerry Telle (who most of you have never heard of) tried to accomplish the same thing by changing body position.

Other devices such as those shitty pneumatic machines or even computerized machines have attempted to do the same where the resistance is changed through the movement in an attempt to maximum force requirements all the way through.  Using chains and bands is another way of altering the resistance throughout the movement.  In both cases they increase resistance at the top of the movement when shortening lever arms are making it easier to complete the movement.

The point being that, by definition, fatigue/failure in a weight training sense will occur when the muscle is unable to generate sufficient force to move the resistance through the sticking point.  And it is only at that point that maximum muscular force will be required.

And while this is pretty simple to understand in isolation/single joint movements, well…..

Again With the Compound Movements

In compound movement it’s far more complex.   Now we have multiple muscles working across multiple joints with changing lever arms, force outputs and force requirements.  Factors such as limb lengths, biomechanics and relative muscular strength all go into determining when and how someone might fatigue or fail.

So if someone has their bench press stall right off the chest, that has implications for how hard their pecs, delts, serratus, or triceps are working.   It also impacts which of those muscles hit muscular failure or whether they even got close.

If someone has a particular weak point in their bench that means that failure may occur due to the triceps being unable to meet force requirements.    That doesn’t mean that the other muscles such as the pecs got anywhere close to fatigue.

So let’s say someone has very weak triceps relative to their pecs.  In a bench press movement, either the amount of weight that can be lifted or the number of reps that can be done will be limited by the tricep’s strength and/or endurance.  When the trainee fails in the movement and it’s due to the triceps, that doesn’t remotely mean that the pecs were (or were not) anywhere close to failure.

Or consider someone power squatting who has their low back give out during the movement.  By definition only the low back hit failure.  But that doesn’t tell us anything about the quads. Did they get a training effect?  Didn’t they?   We can’t really say.  If the differential between the quads and low back is small, both might get a training effect.  If the low back is really limiting, the trainee might fail in the squat long before their quads have gotten a training stimulus.

But despite what the Internet thinks about the issue, the fact is that people with shitty mechanics usually get poor quad growth out of squats for this reason: it’s not their quads that are limiting the movement.  How could their quads possibly get an optimal training stimulus under those conditions?

For that reason, many find that a leg press, where the low back is taken out of the movement is superior for quad growth.     Because now a muscle unrelated to what’s primarily being trained is no longer limiting the trainee’s performance.

Related: Are Squats or Leg Presses Better for Leg Growth?

The same holds true for other movements.  Hell, consider the idea of whether or not to wear lifting straps, another topic about which there is much macho posturing.  If someone is performing rows or lat pulldowns and their grip gives out first, there’s no way to say that their midback or lats got a sufficient training effect.    The same would hold for an RDL or deadlift.

And in the sense that some threshold of intensity (whether load or fatigue) is required to stimulate growth in the target muscle, this matters.

In a practical training sense, it matters because it will determine whether or not a given exercise is good for any given individual to train a specific muscle group.   If someone isn’t built to back squat due to their mechanics or their upper or lower back giving out, then it will not be a good exercise for them to build their quads.

In contrast, a movement that removes that limiter such as split squat/lunge or leg press may very well be superior.  Only those trainees for whom mechanics and relative muscle strengths allow their quads to be the limiting muscle will find squats to be a particularly good movement.

But it matters in a research sense due to the fact that all too frequently studies use exclusively compound exercises but measure smaller muscle groups.    If you’re talking about volumes of training and all someone does is  ton of sets of barbell bench press “to failure” during the study, do we even know what muscle failed?  Or what muscle might or might have not received a training stimulus?

Especially if you insist on measuring only a peripheral muscle such as the triceps which be getting a hugely variable training stimulus for any given trainee.  Even if you measured pec growth, something no study seems capable of doing for some reason, it wouldn’t tell you if the trainee were actually failing at the pecs during their bench.

This is less of an issue in studies that use an isolation movement like leg extensions (or studies that include isolation work with the compound work).  But for any study using mostly or even exclusively compound exercises, the above is a consideration.  Even without completely defining muscular failure, we have to ask what muscle is actually failing during the movement.  Or even getting close enough to failure for the set to be worth counting.

And all of the above can and will eventually be the topic of another article.

And that is actually where I am going to cut it today.  In the next part of this series, I’ll actually look at the different definitions of failure that have been or are still used.   I’ll start out that discussion by first looking at the concept of the repetition maximum (RM).

Read What is Muscular Failure: The Weight Room Part 2

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