Ever get into that state in heavy marathon training where you're reduced to an incredibly slow pace, even though your legs aren't stiff, but your breathing is quite fast? For ages I couldn't figure it out, and then had an idea about what was going on. As posted here on the RW Sub 3 forum:
6.5M steady this morning at a reasonable 7:25/M or so. But excitingly, my legs were fine, felt pretty fresh after my 3hr marathon on Sun including 10x km reps. Whereas last week I wasn't up to running again until the Weds after XC on the Sat and a super-slow marathon plod on the Sunday. This time, I had a bunch of antioxidant vitamins before my big run.
So for the public record, here is my cellular hypothesis to explain "the plods". Don't worry if you don't follow -- just remember you read it here first when the Nobel committee make their award later. During sustained intense exercise, fuel is oxidised OK in the mitochondria, but some bits and pieces escape (free radicals or ROS). They get hoovered up pretty well but not completely. Dosing with antioxidants may help stop them building up so badly (I hope). Now the ROS attack the fatty cell membranes, including the internal membranes round mitochondria ("lipid peroxidation"), making them leaky. I guess a lot of that damage actually happens after the exercise bout while the ROS are still floating around (that explains why studies have not found antioxidants to boost performance directly). And this will happen even if the exercise wasn't bad enough to cause structural damage (DOMS). Mitochondria are like little batteries -- they got that right in The Matrix -- but having their membranes attacked makes them leak some protons (electric charge) without doing useful work, just like a shorted battery. So next time you run, part of the energy released from the fuel you burn will be lost as heat instead of doing useful work, because of the partial short circuit. And that explains why I experience the plods as having very low power output (very slow pace) and yet with relatively high breathing rate -- lots of fuel is still being burnt, but it is just being wasted. After a couple of days, the membranes are restored, and my legs feel fresh again, and breathing rate goes way down even as pace goes up.
This thing with the loss of energy, fast breathing, and yet no real leg stiffness, was what I never understood previously, and which I hope this is a workable explanation for; at least one worth basing experiments on. If I can crack it, I can train better. Ta-da!
So now I plan to have a dose of antioxidants before long/tough sessions. But not otherwise -- because adjusting to the ROS load is one of the training adaptations we need. All inspired by the RW The Runner's Body book BTW, which I really enjoyed recently.
Train hard -> free radical production
...they attack the mitochondrial membranes for some while
...which then leak more electric charge (protons)
...so you burn plenty of energy, but waste a bigger proportion of it
...leaving you slow but breathing fast;
...but after a day or two, the membranes recover, you get faster, and breathe easy again.