This blog aims to go over what isometric (static) muscle contractions are and how they’re useful in the bodyweight training space. Also, there’s two types. And a summary at the bottom for key points.
A quick overview of main muscle contraction types:
Concentrics (positives): the muscles doing the work are getting shorter
Example: doing a pullup from a hanging position, the main workers (the lats and biceps) shorten as you reach the top of the movement
Eccentrics (negatives): the muscles doing the work are getting longer
Example: Starting from the top of a pullup and lowering with control back down to the hanging position (still the lats and biceps)
Isometrics (statics): the muscles doing the work are staying the same length
Example: holding a pullup at halfway (or anywhere part of the active range really) and not moving at all (still the lats and biceps)
Each have their place in training because each help in different(and overlapping) ways. Think most effective transference to the desired outcome. Parameters around isometric training are typically less understood than traditional strength training. How long should I hold it for, how many repetitions, how do I know what intensity I’m doing? Sets/reps/ time/ intensity/ total volume. All a big barrier if you want to add them with confidence to a routine. Note: hold out for part 2 for prescription principles, today’s about the what.
Isometric (static) muscle contractions are a staple in the rehab world, they’re a very controlled exercise in terms of body position, workload is relatively easy to control, and they’re low on fatigue demands. Great if you’re coming back from injury and we’re working on load introduction and building that up around a healing/ irritable area that we don’t want to piss off too much.
They are also used in the strength training and sporting worlds because of their ability to increase force output, rate of force development and work specific positions that might be points of weakness. In other words, how much, how fast, and where. Kind of useful! They are regularly used to prime athletes just before their performance to maximise output in that space as well as before specific exercises in the gym.
And there’s two main types.
A touch confusing considering the muscle’s not able to move to make it a static contraction, so how can it have further options beyond just working? Turns out it’s all about intent.
The two types of static muscle contractions
1) Pushing isometric muscle actions (PIMAs)/ aka Overcoming isometrics
2) Holding isometric muscle actions (HIMAs)/ aka Yielding isometrics
Overcoming isometrics/ PIMAs
Overcoming isometrics are when the body is at fixed position and pushing/ pulling into an immovable object. In other words there is zero chance that thing is budging. Think pulling a barbell up into the safety brackets. In other, other words an overcoming isometric is a failed/ blocked concentric (shortening) muscle contraction.
Typically fatigue on an overcoming isometric leads to diminishing force output into the immovable object with no change in joint position. Alternatively in the bodyweight set up where the immovable object is a joint range of motion that the body is unable to overcome in terms of a concentric (shortening) muscle contraction then once the intent and drive to overcome the movement is lost to fatigue then it is no longer an overcoming isometric. This works vs pushing into a literal immovable object because for the same relative workload we are strongest from eccentrics (lengthening), to isometrics (statics),to concentrics (shortening).
So there will be a range of motion that we can’t progress into, but we can sit on the threshold either trying to hold it there or overcome it. In this case the overcoming isometrics fails at the point we lose the ability to try to overcome the range, it moves to a yielding isometric when we are hanging on but not longer able to push it, and when that fails it turns into an eccentric (lengthening).
The key here with an overcoming isometric is the intention is to overcome that range of motion, rather than just trying to sustain the joint position.
Does this make yielding isometrics worse?
Nope, different strengths and weaknesses.
Yielding isometrics/ HIMAs
Yielding isometrics happen when the body is at a fixed position and applying force equal to that of the object/ force imposed on it. In this case we are resisting an eccentric (shortening) muscle contraction by maintaining but not overcoming the position. At fatigue a yielding isometric turns into an eccentric (lengthening) muscle contraction. At relative equal workloads an overcoming isometric can be held around 2x as long as a yielding isometric. It takes more effort to overcome something than to maintain its position.
In other/ shorter words:
Overcoming isometric: try to move it… but it’s not going to
Yielding isometric: stop it from moving, succeed.
How much do they help?
There is some evidence that isometric training improved muscle output most in the muscle mid-range>longer muscle lengths>shorter muscles lengths.
They’ve been shown to induce morphological and architectural changes in muscle and tendon- just like traditional strength training. They’re safe and have relatively lower fatigue demands vs traditional strength training.
The likely mechanism for improved strength/ force output and speed of that output in the immediate short term is increased neural drive (think better body-brain connection). If the signal between body and brain is clearer then the brain/ central nervous system can recruit more muscle fibres (more force) and the speed at which you can recruit and coordinate muscle fibres (reactivity).We can therefore improve strength at fairly specific positions of a movement as well as enhance certain training types by performing isometrics as a priming exercise before this training.
It's worth noting that this increased strength is fairly specific to the ranges the isometrics are performed in.
Now here’s the thing… are isometrics really static positions?
Technically not really, but they’re as close as we’re likely to get.
Instead of thinking of isometrics as purely static positions at an exact given point of a movement, think of them as rapidly fluctuating muscle shortening/ lengthening around a very specific point.
In order to regulate force output our sensorimotor system is in a constant state of revision/update. Rapid adaption to external forces for movement/ positional control (while it’s happening) by the neuromuscular system is coined adaptive force. If a position is more demanding (think greater balance requirements or more joints the body has to control) then there is increased demand on our sensorimotor system. Yielding isometrics, where there is potential to move in both directions (up/down or forward/ back etc) will have greater adaptive force requirements and therefore increased demands on our sensorimotor system. This increased kinaesthesia demand can be why fatigue occurs earlier.
One more thing here: as the position of an isometric is held we get what is called tendon creep. Essentially the tendon itself slightly lengthens which means to maintain the same static position then the muscle have either lengthened or shortened slightly. This tendon elongation is short term- think of it like an elastic band, but another reason why isometrics aren’t truly static.
So which one should I use?
Well, what’s the goal? The overarching principle here is the SAID principle: specific adaptions to imposed demands (and due to emerging research in this space much of this is principle driven while the research catches up).
Because overcoming isometrics have the intent to move the object there is a concentric (shortening) bias. This is most likely to assist in the development of concentric based strength and power movements and acceleration. Holding isometrics are a resisted eccentric and probably lead to improvements in eccentric strength and control, deceleration, and circumstances where muscles are typically used in an isometric stabilising roles (e.g. the side butt in a single leg squat).
Again, still emerging in the research but it would also make sense that increased kinaesthesia and somatosensory demands (higher balance or degrees of freedom to control) would transfer well to end range flexibility holds where more information for the body can increase it’s perception of safety/ control and help reduce muscle tension opposing the movement deeper in range as a safety precaution (topic for another time!).
An example for each in the bodyweight training arena:
Example 1: a bodyweight skill someone can’t perform to full range, such as a pullup to ¾ range.
Isometric choice: Overcoming isometric at ¾ range of motion held for 3-10s
Reason: there’s a concentric bias to the exercise and a weak point in the range of the movement. By priming that point of the range we can hope to increase strength there so when followed up with normal pullups to maximise range we can hopefully get a little higher in the range (or all the way!)
Example 2: A back lever on the rings
Isometric choice: Yielding isometric at maximum hold height OR a little deeper with assistance (someone supporting weight of the legs). Note here: I would recommend working very close to maximum independent range in that case, rather than the hardest point with a lot of external help.
Reason: there is an eccentric (shortening) bias to the exercise- the skill is entered typically through a lower down and the aim is to achieve maximum lowest position (not to return to the start point in this case).
Isometrics are static muscle contractions and there are two main types: pushing isometric muscle actions (PIMAs) aka overcoming isometrics & holding isometric muscle actions (HIMAs) aka yielding isometrics
The main difference between overcoming and yielding isometrics is intent- move it vs hold it (respectively)
Overcoming isometrics are probably better for concentric based movements and yielding isometrics for eccentric and stabilising isometric movements.
Oscillations in rapid concentric/ eccentric (shortening/ lengthening) muscle activity occur in isometrics- meaning the muscle fibres do shorten and lengthen but in a very specific joint range.
We can these to prime performance in the short term and build strength like traditional strength training in the longer term
For skill movements we can only perform partial ranges for these isometrics can be a good way of increasing force where we are weakest and increase our range of movement or increase how long we can hold at set positions
Hold out for part 2 which will be a touch more practical on how they might look exactly in a bodyweight training program!
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