I had a tough workout yesterday that left me asking this question. I mean, all my workouts are tough, but this one was exceptional. I hadn't eaten well all day (two cookies and two cups of coffee prior to my 4:00 pm effort) but was determined to squeeze the workout in. Going in I suspected that my performance wouldn't be stellar but was hell bent on at least matching my performance from the previous week where I'd done the same workout. I'd actually commented in my training journal that I thought I'd be able to 'move up' the next time I tackled it, so just matching it felt like I was giving myself an 'easy day' pass.
I fought tooth and nail to keep my RPM's above 80 during the final interval. It was as close as I think I've come to truly finding the 'gun to your head' level of determination. And as that last interval ended and I struggled to keep the cadence during the 20 second 'warm down' I knew I was in trouble. When the pain I knew was coming started I tried to spin through it. It got worse and worse until I had to try another tactic. Hobbling straight legged to the corner I collapsed and put my legs up the wall, hoping the pain would drain from my legs with the blood. My heart rate, which had come down a bit from its peak of somewhere above 205 (the machine's sensors stop reading above this number) was still in the neighborhood of 130 or so, ensuring both the pain and blood remained where they were.
Eventually, of course, the pain subsided and my ability to walk normally returned. But it had me wondering how much is too much.
So today I spent a few minutes trying to answer the question. In particular I was concerned with the condition called exertional rhabdomyolysis, which is essentially a degeneration of your muscles' cell membranes, leading to release of cell contents into surrounding tissues. Blood potassium levels skyrocket (not a good thing apparently) and if the condition is pervasive enough the kidneys become unable to restore the balance (they get clogged with myoglobin, another content of the muscle cells) and bad things happen.
Although Rhabdo (as it is called for short) is widely known about in CrossFit and similar extreme training circles, I'd been worried that my own brand of 'extreme' training might also be flirting it. I'm not sure I've found any definitive answers, but I did find a pretty soothing article from Women's Health Magazine, which is probably about as close as one can come to definitive without actually arriving there.
It mentions five signs that you might be going too hard--cheating on form (hard to do with cardio - bad form usually means less efficiency); sore joints (I'm never sore, muscularly or joint-wise, from short high intensity efforts--races of course are a whole other ball of wax); increasing intensity too fast (no danger there, it's been high intensity for years!); training every day (even at only seven minutes I couldn't imagine doing this, not with adequate intensity); and pushing past pain. This last point gave me pause. I routinely push past pain--in my legs and arms and lungs--in fact a workout without some facet of pain seems a foreign concept. And sometimes, like yesterday, it is temporarily debilitating. But even that effort only left me crippled for ten minutes and left no other lasting effects, either later in the day or in days following. So this leaves me hopeful that my radical attention to intensity over very brief intervals is safe given my history with it and the absence of other warning signs.
In thinking further, I believe that there is a level of protection against something like rhabdo in my systematic, machine driven approach. My intervals and intensity is very calculated--prescribed as part of a computer program--and are the same (or nearly so) every time I repeat a workout. Although the intensity is very high, the duration is short and the movements are such that bad form lessens my ability to make the intervals. Typically I stop right after my 'peak' interval--the goal of stimulating growth and causing supercompensation having been accomplished. I seek to approach maximum effort during this last interval, carry it out briefly, and then am done.
So my fingers are crossed that my system of training, despite the pain it creates, isn't too much at all. In fact, for me anyway, it seems to be just right.