Injury Risk and the 'Cascade of Failure'

What is the ‘cascade’ of failure during an exercise?

When someone is lifting weights their muscles don’t just give up suddenly, what happens first is a battle between their brain and the discomfort they are feeling.

So, failure comes in different forms and really occurs as a cascade of events as follows:

1. Tempo failure - the speed of different parts of the exercise change
2. Technique failure – the alignment of the body parts change
3. Supported muscular failure – two causes; energy system / neuromuscular / voluntary cessation (stopping) by the client

Let’s take a look at each of these ‘failures’ and see why they occur.

Tempo failure

Tempo failure is something you’ll see when a person does not lift at the same speed/timing as they did when they started because they are becoming tired. 

The brain does this quite naturally as it detects things are getting hard and makes them easier by accelerating through the easy parts of a movement using the momentum gained to get through the harder parts of the movement.  The brain essentially modifies tempo to achieve the easiest force profile required to get the bar from point A to point B as per the aim of the exercise.  This change in tempo can be seen as bouncing, slinging, swinging or any other ‘segmenting’ of the tempo across the movement.  Basically if the tempo the client is following isn’t the one prescribed by you and achieved within the first repetitions of the set – tempo failure has occurred.

It’s important to start spotting – if you’re going to push the client to energy system or neuromuscular failure – at this point.  It allows you to maintain the correct tempo, work muscles through tough parts of the exercise properly and be right there if your client’s brain decides to change technique!

Technique failure

Technique failure is something you’ll see all the time.  It’s where the brain has said “this is hard, these muscles are tired, but these ones over here can help”.  The brain then rearranges the body to involve the fresh muscle mass and give the tired muscles a break. 

The problem with technique failure is that the brain has no understanding of the risks it’s running until it’s too late.  An example is when a person completing the standing shoulder press leans back to open the chest to the exercise so that the pectorals can add force and the deltoids can get some rest. 

In order to do this the lumbar spine has to be put too far into extension jamming facet joints together and putting uneven compressive loads through intervertebral discs.  If the person has a ‘kyphotic’ or rounded upper back posture and poor abdominal control this further raises the risk of injury.  In fact, in order to adopt this posture the abdominals need to be released so the spine can extend therefore by default you now end up with a weight up to a metre or more away from the joint around which it’s pivoting – usually the L3/L4 vertebra in the lumbar spine.  Technique failure like this should not be allowed amongst your clients.

Further, what the brain begins to record is that under duress, when these muscles are failing, this is the posture to adopt to help out.  Nothing could be further from the truth.  What you really want is the brain to be saying, if I can’t lift it in this position, I won’t lift it at all!  You want your body to learn that in all circumstances for safe lifting this is the posture I should adopt.

As suggested above the fatigue being experienced in most agonist muscle groups involved in an exercise will cause the brain to look for options.  Most of those options involve a change in limb and trunk position of some kind.  That means the brain must relinquish control of some of the joint positions it has originally adopted, essentially meaning the synergists and fixators of the movement will modify their actions, allowing movement in planes and around joints that are unplanned.  This is not what we want.  We don’t want the stabilizers of a joint taking a little holiday when the going gets tough. 

Fundamentally technical failure requires a relinquishing of joint stability and soon afterward the adoption of a higher risk position.  So, if your client is changing their technique during a push up it’s likely their abdominal group has let go of their trunk, their lumbar is in extension, their upper back is rounded and they are trying to add deltoids into the exercise or shorten the path of the exercise by shooting the head forward toward the ground. 

Good trainers know what changes will occur during technical failure and will already be spotting (as tempo failure becomes evident) and will add to that clever cues to remind the client to hold their technique even before their technique starts to waiver.

Supported muscular failure

This is where either the energy systems can’t provide enough ATP or the nervous system can’t continue to stimulate a contraction due to fatigue.

Supported muscular failure refers to a situation where the client is receiving spotting support and is maintaining technique.  The spotting will be helping maintain tempo while the client is being cued on technique.

This allows the muscles to be worked beyond where they could be by the client independently.  It allows this to be achieved with no relinquishing of technique or tempo.  Typically this involves only one to three more repetitions in a given set. 

Remember that tempo failure may occur, and the trainer starts spotting/assisting.  Then the technique cues start – most exercises have only one or two areas where stability will be lost first – so it’s a matter of concentrating on those areas.  Then the encouragement of the client to finish the last rep begins.  Usually you’ll get one or two good reps after tempo failure and one or two good reps after technique is starting to become a real challenge.

The nice thing about supporting someone to lift properly and extend their lifting is that they learn to maintain technique under duress and they quite quickly develop strength in the difficult parts of an exercise.

Every exercise has a point at which it is hardest.  This is because of the biomechanics in play.  This point is sometimes called the ‘sticking point’ of an exercise.  Many exercisers ‘cheat’ at the sticking point either by modifying tempo and/or technique.  They essentially train their bodies to avoid the hard part and as a result never develop strength in that range.  So, it becomes a self perpetuating cycle.  It’s hard here so I cheat here so I don’t get strong here but I do everywhere else, so next time I do this exercise it’s even harder here by comparison.

To get the best results for clients you don’t need to jeopardise their safety, just guide them through tempo failure, get one more rep with good technique when they would prefer not to, and hey presto, your clients strength will progress nicely.

Why is the injury rate quite high in gyms?

There are a lot of little lifting errors that can be masked if the brain has enough time to deal with them.  Two things shorten the time the brain has to deal with an error

1. Load – because the rate at which a muscle produces force is dictated by the resistance it is under, higher loads mean higher rates of firing.  Load also creates momentum which means the reflexes and connective tissues of the body are more challenged.
2. Speed – because the rate at which a muscle produces force is also dictated by the intended speed of the movement, higher speed movements mean higher rates of firing.  Speed also creates momentum which means the reflexes and connective tissues within the body are more challenged.

So, new members turn up to the gym to get results and are willing to push themselves along a bit initially.  However, their systems (nervous, energy, musculoskeletal) may be in the worst condition at this time and their movements may be ‘rusty’ to say the least.

This is one reason why the injury rate in gyms is actually quite high; because in our profession you do push people along, load them up and encourage them to extend themselves.  Gym members and personal training clients do get injured and part of the reason for that is we’re not as thorough as we should be in the area of movement analysis and prescribing exercises that will not harm or put our clients at risk.  We also don’t always seek perfect movement but accept ‘good enough’ and concentrate more on load.  Our supervision, teaching and monitoring of exercise technique generally needs work!

Being ineffective in this area leads to two things.  Firstly we create a lot of ‘false gains’ with clients.  Secondly we stimulate a lot of latent problems into becoming ‘active injuries’.

False gains is a term we use to describe progress that is essentially unsustainable or can not be built on.  An example would be a personal best lift completed by an athlete with poor technique.  They won’t be able to progress the load much more without eventually being injured and they will unlikely be able to use the load lifted as a personal best to prescribe their training from as lifting at or around those loads consistently will lead to injury.

Latent problems are simply movement errors (software) or musculoskeletal restrictions (hardware) that are not attended to and become aggravated by excessive overload.  It can be as simple as prescribing the wrong shoulder press exercise to someone who is at risk of shoulder impingement because of their posture, job, warm up practices, sequencing of exercises, the plane of movement of the exercise and their willingness to push hard despite all of this. 

In order to progress our clients we must first protect them.  The only way to protect something is to understand the state of it and the risks involved in what you are about to do.  To this end all fitness professionals must improve their ability to understand how movement is created, what errors look like, identify the likely causes, and either refer out or if the issue can be fixed by regressing and coaching the client, deliver on that need.

In another folder here at ptdirect we look at movement analysis, common issues and some basic ways of assessing movement.  Couple that with careful exercise selection based on your clients’ capabilities and you will be well equipped to deal with most of the people you will train.  You should realise though that continual study in this area is required to enable you to deliver more and more value to your clients.

How does stability affect the primary movements?

When a movement occurs the brain is co-ordinating a lot of parts of the body at once.  Around some joints it will produce movement in some planes whilst stopping movement in others.  For example during a lunge the knee, hip and ankle complete flexion and extension and at the same time the brain will be stopping rotation (stabilizing the transverse plane) and forward tilting (stabilizing the frontal plane).  So, these primary patterns are complex and triplanar (involve activity in the three movement planes).

Any movement that occurs in one plane alone is completed whilst the other two planes are stabilized.  Our example of the lunge, which most frequently occurs in the sagittal plane, involves frontal and transverse plane stability also. 

Instability in the other planes will cause problems with the movement.  You can see this when children learn to walk.  Human gait is a sagittal plane affair.  But because the brain of a child still has to learn to move each of the body segments in sequence, and get the timing right, and control the internal (muscle) and external (ground reaction) forces, and create stability in the remaining two planes, they will sometimes fall or teeter or wobble.  This is quite handy as it makes them slow enough to catch...but not for long!

Another interesting point is that once the brain learns a primary movement any errors in the movement (be it instability, pain, an erroneous initial pattern etc) can cause a cascade of errors throughout the movement.  This is because the movement uses kinetic chains, that is the brain links the body through the pattern and a problem in one area flows over to the next.

A common example is hip instability during lunging.  With hip instability you may see some change in movement at the hip but much more pronounced is the error seen at the knee.  This is caused as the problem within the kinetic chain at the hip is transferred to the movement at the knee and the brain then makes compensatory movements to sort out the mess.  An experienced trainer will work on the stability at the hip by regressing the lunge exercise and emphasizing control in the hip region.  Someone without proper training may think the problem is simply weakness around the knee and they might try to strengthen the knee joint in isolation doing very little to deal with the real issue.

So, understanding what the primary movements should look like and the progressions and regressions of those movement patterns is a key factor for all personal trainers.