Schaefer LV, Bittmann FN. Are there two forms of isometric muscle action? Results of the experimental study support a distinction between a holding and a pushing isometric muscle function.BMC Sports Sci Med Rehabil. 2017;9:11. PubMed #28503309
This paper describe two ways that isometric exercises can be carried out. The first way isometrics can be done is pushing against an immovable object or surface. The other is holding a fixed resistance or load still. Holding isometrics are where the forces are resisted against, pushing isometrics is where the forces are pushed back against, both methods have no joint movement, hence both being isometric contractions.
Although both isometric exercises these pushing and holding differences appear to have different characteristics. Pushing isometrics, for example, have more ‘endurance’ being able to sustain significantly longer times under tension than the holding isometrics.
The authors wanted to investigate this further to see if there were any other objective differences such as peak forces, EMG amplitudes, and oscillations that could also distinguish pushing isometrics (PIMA) from holding isometrics (HIMA).
What they found was peak forces, EMG profiles and oscillations had no significant difference between either pushing or holding isometrics, but they did find again that pushing isometrics had significantly longer endurance times than holding isometrics
They theorise this may be due to differences in metabolic fatigue and neural control strategies, and holding isometrics being more akin to eccentric muscle actions and pushing isometrics more like concentric actions. This was also based on the subject’s feelings during the different isometrics
However, the question is, do these differences in pushing v holding isometrics help explain why we see such a wide and varied response with pain modulation when using isometrics for tendinopathy.
For example, in some lower limb tendinopathy research such as the patella we see isometrics work, with complete resolution of pain in some cases. However in the elbow we see the opposite with an increase in pain, and in the shoulder we see a kind of confusing ‘meh’ response showing neither significantly good nor bad effects.
Could this different response be due to how the isometrics are done? Or could it also be that the margin for error in pushing a body parts capacity beyond its threshold in the upper limb is much less than in the lower limb? Meaning upper limbs are much easier to anger if they have pain or pathology with isometrics or any other exercise for that matter.
Think about how a lower limb often has to do things that require 100s if not 1000s of Newtons of force daily in tasks and functions. A little 50 or 75 Newton isometric exercise is there nothing significant to it
However, the upper limb often experiences far less force in tasks and activities, meaning that the same extra 50 or 75 Newton isometric exercises have a much greater chance of anger it off, especially if it has pain or pathology.
this paper is really interesting and make you thinking about how there is no such thing as a standard isometric exercise. And there is most certainly no such thing as a standard response to any exercise.