A friendly single leg wall sit competition among conditioned individuals (with no contraindications) took place the other day“ and lasted no longer than a 1 minute 15 sec.

I have to wonder, what causes the failure first? Engergy system-mostly ATP/PC & Glycolosis, Lactate threshold or something else? I’ve read research indicating that the myosin heads decrease their movement almost 3-fold during isometric exercise which I supposed has to do with a more static sarcomere. This leads me to believe they are using less ATP and that it is the lactate threshold. What do you think? Anyone know of research on LT and isometrics?