Understanding Muscle Failure — Is it a Good or Bad Thing?

Two people performing dumbbell exercises in a gym.

The other day, someone asked me, “Isn’t muscle failure a bad thing? After all, failure means that you can’t do something, so muscle failure means that your muscles are unable to work any longer, right?”

Interestingly enough, the term “muscle failure” is actually a good thing, and it’s what many resistance trainers will have you work towards. If you’re working your muscles to 100% intensity – which you should be if you’re trying to bulk up – you’ll find that muscle failure is guaranteed.

Basically, if you do the workout right, your muscles will fail. This is, of course, something you want.

Remember: Never lock out your joints, especially when you’re doing heavy weight lifting. You can damage your ligaments, cartilage, tendons, and joints, so avoid full extension of your arms when curling, pressing, or lifting.

Types of Muscle Failure

The term “muscle failure” describes the conditions under which the muscle fibers stop contracting.

There are a few types of muscle failure, because there are a few types of muscle fiber:

Myofibril Failure

Naked upper body of a muscular man perofrming an exercise with an EZ Curl bar.

Myofibrils are the cells that make up the muscle, and they contract when you lift weights or exercise the muscles.

See For Yourself: Do a bicep curl, and you’ll see that the bicep muscle looks shorter but bigger. That is thanks to the myofibrils, which shorten but increase in circumference when they are used.

Myofibril failure occurs if the weight and resistance of your exercise is so great that the muscle can’t contract anymore, during exercises to build power and size. The muscle hasn’t yet burned up all of the energy (glycogen) it has stored, but it fails because the exercise is just too intense.

This is something that you want if you’re trying to build strength, as it will recruit the maximum number of myofibrils, damage them (once again, a good thing), and repair them – which results in slightly larger muscles. The white fast twitch motor units are especially exercised when you do intense exercise, using heavy weight and low repetitions.

For those that want to see the best results using this muscle failure, you should do 4 to 6 repetitions per set. This is the optimum number for high weight, low rep exercise, and studies have shown that it will yield the best results.

Note: Some people do sets of 1 to 3 reps, but this is a mistake if you’re working for strength and size. Your muscles will develop tiny tears that your body won’t be able to heal fast enough, and there is a very real risk of damaging the muscle fibers. Only use sets of 1 to 3 reps when competing or trying to measure progress.

Intermediate Failure

Naked upper body of a muscular man performing exercises with two dumbbells.

Intermediate failure occurs when the muscles tire out at roughly the same time as the energy (glycogen) stored in the muscles run out. The muscles can store some energy to use quickly, but it doesn’t take much to drain them. When you do the right number of reps with the right amount of weight, the energy is depleted and the muscle fiber is damaged the right way.

When this happens, both myofibrils and mitochondria are built, as the muscle needs to adapt to the expenditure of the energy. The red fast twitch motor units get a lot of new muscle fibers, and your muscles develop a lot more stamina.

Usually, this type of muscle failure occurs when you are doing exercises using 12 to 15 reps. This is ideal for those that want to increase strength, size, and stamina, and it is the ideal rep range for anyone working out for general fitness.

Note: Many prefer to do sets of 7 to 11 reps for this muscle stamina increase, but that is wrong. If you do fewer than 12 sets, you will be using both the white and red fast twitch muscle fibers – and neither will receive the stress they need to be damaged properly. The white fast twitch muscle fibers are needed for high weight, low rep exercises, while the red fast twitch muscle fibers are needed for the medium weight, medium rep exercises that build muscle stamina.

Mitochondrial Failure

A woman performing exercises with two dumbbells

The mitochondria are attached to the myofibrils, and they are the part of the muscles that provides the power. When the myofibrils contract, the mitochondria produce ATP — which the muscle uses as energy for its contractions, repair, and use.

Mitochondrial failure occurs when you use up all of the energy in your muscles, but without damaging your muscles (still a good thing) completely. When the energy is depleted, lactic acid begins to form in the muscle – effectively stopping it from contraction.

When this happens, not enough of the muscle is damaged to increase the size of the muscle fibers. However, it will cause the muscle to store a lot more energy for further use, which is why your muscles have more endurance when you train it to mitochondrial failure.

Your muscles will have to increase the number of mitochondria along the myofibrils, as that will give them more energy when you do more of the endurance exercises later. Most of the mitochondria are built in the red slow twitch motor units, which have a lot more power than the other two motor units (white and red fast twich).

If you want to work to mitochondrial failure – and thus build more muscle endurance – your optimum set is in the 20 to 25 rep range. You will be using very light weight, but the high number of reps will drain the muscles of energy without damaging them too much.

Note: Don’t make the mistake of doing 16 to 19 reps. This will use the red fast twitch muscle fibers along with the red slow twitch fibers, which means that neither will be stressed optimally. You’ll be doing too many reps to build the red fast twitch fibers, but too few to build the slow fast twitch fibers.

Sources: National Federation of Professional Trainers Resistance Training Specialist Manual

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