I like to spend a few hours most days reading ‘stuff’. This means I usually read a blog or two, half a dozen abstracts, and at least one research paper in full most evenings. Most of the stuff I read I would rate as ok, not bad, kinda meh, however once in a while something grabs my attention and gets me rather excited. Yesterday was one of those days!
As I was going through my daily email notifications of key word searches I have set up on various platforms, which I find an effective way to be alerted of new research I may be interested in, this paper here stood out. First due to it’s title but also when reading it in full it made me think more and more which is exactly what a good research paper should do.
As you can see its called ‘Are there two forms of isometric muscle action’ by Laura Schaefer and Frank Bittman from Potsdam, Germany. Now on first reaction you would think that’s stupid, isometrics are isometrics. But reading further they describe two ways in the literature that isometrics can be carried out, the first is where the forces are resisted against, the other is where the forces are pushed back against, both methods have no joint movement, hence both being isometric contractions.
These pushing and holding isometrics however appear to have different characteristics, with the pushing ones seeming to have more ‘endurance’ being able to sustain significantly longer duration times than the holding isometric contractions. The authors wanted to investigate this further and 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 pushing or holding isometrics, but they did find that pushing isometrics had significantly longer endurance times than holding isometrics
They go onto theorise why this maybe, possibly due to differences in metabolic fatigue and neural control strategies. This maybe due to holding isometrics being more akin to eccentric muscle actions and pushing isometrics more like concentric actions. This is also based on subjective feelings during the different isometrics and one I tend to agree with.
I don’t know about you but when I do maximum effort isometrics I feel much stronger/stable if I am pushing against something that I can’t move, rather than trying to hold a heavy force still. Think of trying to push a wall over v’s holding a wall up.
However, the BIG question I have 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 like bloody magic, with almost complete resolution of pain. However in the elbow we see the opposite with an increase in pain, and in the shoulder we see a kind of ‘meh’ response with cuff tendinopathy showing neither significantly good or bad effects.
Could this different response be due to how the isometrics are done, or is it more than that? Possibly, I also like my mate Erik Meira’s thoughts on why we see difference in isometrics between upper and lower limbs. He thinks that the margin for error in pushing beyond a pathological tendons threshold in the upper limb is less than in the lower limb and so upper limb tendinopathy’s are easier to piss off.
Think about how a lower limb can push 100s of Newtons of force, so a 5 Newton excess above this is nothing significant, however in the upper limb that can only push 10s of Newtons of force an excess of 5 Newtons is substantially more in percentage terms of over load. However, lets also not forget that Erik thinks Chimichangas are the height of fine dinning!
Anyway I found this paper really interesting and it got me thinking harder than anything I have read in the last few months. I am looking forward to see what the clever tendon nerds make of it and what other further research comes from it, but I am a bit of a sad geek who loves a bit of tendinopathy research. And talking of sad geeks, Erik and myself are doing a couple of combined courses next year, both UK and US based… so watch this space for further details.
As always thanks for reading