I did a pubmed search for creatine phosphate depletion and limited the search to just the entries with the terms in the title. Three papers came up and none of them included anything about eccentric muscle actions. The research to answer the question “Does doing negatives with the load that concentric failure was attained with immediately after con failure cause microtrauma and how and why?” simply has not been done. I can only piece things together from various seemingly unrelated articles. I’ll see what I can do.
In spite of the dearth of research, I think it is reasonable to hypothesize that if you cannot lift the weight after each negative rep and if you cannot stop the weight from descending through the dropping zone then the amount of ATP is inadequate at that moment for the task at hand. The demand for ATP is greater than the supply at that precise moment.
ATP is required for the detachment of the cross bridges. If there is not enough ATP to enable the detachment of all of the cross bridges then something has to give such as actin getting torn from the z line and causing z line streaming.
I am currently in the midst of a cycle in which I am doing one set of continuous tension reps per exercise to concentric failure and then doing negatives immediately after with the same weight. My body weight at the beginning of the cycle was 210lbs and now it is at 220. My concentric work power product has been steadily increasing throughout. I continually increase the amount of negative work done after con failure too. I’ll share more about the hows and whys of my training if anyone is interested.
This style of training seems to be effective for me without endangering my 46 year old joints.