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Yes, no doubt in general.....and I'm not arguing that at all, of course BUT.....high intensity or HIGH intensity.....for how long.....how frequent?someone who trains 3-5x per week, even if it's HIIT or other high intensity stuff, is still better off than someone who's not exercising at all.
As said there is a tipping point....an individual's response, is, er, individual, isn't it? Otherwise the 100m final will be a close call between 7.1 billion people. Bit of a photo finish.
While exercise-induced addition of new mitochondria is of extreme importance, the maintenance of a healthy population of mitochondria may be of equal or greater value. Mitochondrial damage induced by reactive oxygen species (ROS) (2) can lead to the accumulation of metabolic intermediates (19), which in turn further impair mitochondrial function and trigger a vicious cycle. These pathological changes ultimately hinder the ability of mitochondria to function properly. It is conceivable that efficient removal of damaged mitochondria is critical in maintaining overall mitochondrial function in a tissue/organ like skeletal muscle. Furthermore, an accumulation of damaged mitochondria, associated with sedentary lifestyle and/or high-fat diets, may impair skeletal muscle contractile and metabolic functions.
from: Exercise training-induced Regulation of Mitochondrial Quality
Exercise training-induced Regulation of Mitochondrial Quality
Zhen Yan, Ph.D., Vitor A. Lira, Ph.D., and Nicholas P. Greene, Ph.D.
.....which kind of backs up both arguments for exercise as a positive adaptation and too little/too much exercise being maladaptive due to oxidative stress. Hopefully, maybe not, supports what I'm badly trying to say...
Cells are damaged and replaced/renewed....well they do, otherwise we wouldn't be here, exercise or not.....I'm not backing that up, please, give me that one! But those beastly little mitochondria are delicate things....
from the appropriately titled:
Mitochondrial Death Channels
Mitochondrial Death Channels
Related to cardiac mitochondria during a heart attack....not that swinging a kettlebell induces a heart attack but nonetheless explains what happens to a cell in extreme oxygen debt, like none....
there is no oxygen available to accept electrons from the electron-transport chain. Electron transport backs up, proton translocation stops, and ATP production by ATP synthase ceases. An alternative ATP-producing pathway, glycolysis, meets the energy needs of the cell temporarily until glycolysis is halted by the exhaustion of glucose and the buildup of acidic end products. Cell death follows unless the oxygen supply is restored.
....so extreme glycolysis and acidity causes cell death in the absence of oxygen.....That isn't your normal swing session, well hopefully not anyway....
The article describes 2 forms of mitochondrial suicide, the death channels. One of which is when the ph of the cell is acidic/oxidative stress, the other by disruption of calcium.
You can read up on stress and disease at your leisure suffice to say that there are numerous articles related to oxidative stress.
The earlier comment.....the poison is in the dose.....it really is and it really depends on the individual from a coach potato to elite athletes and the cumulative effects of stress overtime. One session can give you a heart attack? Sure, in untrained, or genetic predisposed cardiac issues, it could and s*it does unfortunately happen.
Excessive thrashing in the glycolytic pathway? Good for some, bad for others....no? Recovery, stress, all very important variables that affect positive or negative outcomes...no?
Very hard thrashing requires greater recovery costs....what you've just built needs to be re-built, including but not limited to....mitochondria.
I freely admit that doesn't give a definitive account of the mystery of life, forgive me. And mitochondrial cell death isn't stopping me from doing what I do but what is an absolute truth that I hope you do not want to give a peer reviewed study....no atp, we dead. And on that note mitochondria are important things to have around. Sure, blow them out from time to time in competition, an event, an escape for your life, a test....and recover. But for training? Do we really need to thrash ourselves to death, all the time? Some people do, I know. Fair enough, each to their own.