Could someone help explain to me why have researchers mostly focus on the GSP muscles ( gastrocnemius, soleus and plantaris) , but not the tibialis anterior (TA) in the hindlimb suspension model?
The tibialis anterior muscle is not a weight-bearing muscle as compared to the gastrocnemius, soleus, and plantaris muscles. Thus, hindlimb unloading has less effect on the TA as compared to the others. The amount of chronic load imposed on a muscle has a direct effect on the muscle's size and strength.
As Gordon Warren mentioned, the triceps surae includes postural muscles while TA is not one. While it does atrophy during unloading, it is not the most responsive muscle in terms of mass, fiber size, and fiber type switch. However, force production can be affected relatively quickly.
Thank you Marie Mortreux and Gordon L Warren . I did a pilot study looking at force recovery, fiber size and mass recovery of the the TA using HU and it seems the TA force recover very slowly comparing to fiber size and mass. I am just curious if not due to fiber size and mass then what cause such slow recovery in force.
Ta Hu it is actually fairly easy even for humans to show decreased force during dorsi flexion even when the muscles are not directly affected. However it's an interesting finding, usually (for gastroc and soleus) function recovers firs, and CSA/mass take longer.
Ta Hu, how did you measure TA muscle force production? It cannot be assessed ex vivo (in vitro) like smaller muscles can. It has to be assessed in situ or in vivo and that requires direct stimulation of the common peroneal nerve.
@Gordon L Warren, we assessed the TA muscle force in vivo using the Aurora system. I have a followed up question. I am also trying to measure the force of the gastro in vivo but seem like most people has to engineer their own device. I did not find any commercial system for gastro invivo except for the in situ one from Aurora. Do you know of any commercial system or an easy modification to measure gastro force invivo, it could be the whole hindlimb muscle as well ( soleus, plantaris and gastro)?
Ta Hu I use the Aurora system as well to study both dorsi and plantar flexion. We do the study in vivo using the foot plate so we can assess it weekly. If you want gastrocnemius specific force then you will have to do a non survival surgery where you cut off the tendon and attach solely the gastrocnemius to the lever arm. That will provide more information such as optimal length. When I use the foot plate i don't measure solely gastrocnemius, since it is plantar flexion,, both gastroc and soleus are involved.
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