The VO2 lull

I’m currently going through what I term a “VO2 lull”. It’s something I’ve encountered across my running years but taken a long time to understand, and even longer to recognise when it’s happening. Last Saturday I ran a good, hard parkrun at Upton House. Combining efforts up the hills with surges to try and catch runners ahead of me, as well as bursts to stay in front of those behind me, it was an all-out effort. With fresh legs going into it, from three days of easy running, I found an extra gear whenever I needed it. While I felt fairly good immediately afterwards, my legs have had nothing all week. I’ve lost a good minute off my easy run pace and this is what I’m calling the VO2 lull.

First off I need to explain the V02 part. Exercise physiologists like putting runners on treadmills and measuring the effects of running at ever-increasing speeds. One of the key measurements they take is the amount of oxygen breathed in, as well as carbon dioxide breathed out and heart-rate. When they measure the oxygen (O2) intake and utilisation it is correctly termed V̇O2 with a little dot over the V indicating it’s a rate but most people refer to it as VO2 partly because how do you pronounce a dot? It’s partly because it’s too onerous for them to figure out how to get the dotted V̇ on a word processor!

In chapter 8 of Build Your Running Body, Pete Magill details the growth cycle of mitochondria which are fundamental to producing aerobic energy. Mitochondria are often described as the powerhouses of the cell as they convert oxygen to energy which then powers your exercise. The importance of mitochondria to any distance runner cannot be overstated enough – they are the source of your aerobic ability which itself is key to distance running success.

Magill explains that it takes 4-5 weeks for mitochondria to fully grow but there’s a problem. “When mitochondria first begin adapting, they can’t contribute to aerobic energy production … this phase lasts from ten to thirteen days and creates an “oxygen utilistation problem” … you can expect to feel sluggish doing workouts that were easy the previous week” (p.142)

That’s exactly where I’ve been this week. Last week I was running a 20:55 parkrun at 6:45/mile pace; the next day my legs could barely achieve eight minute miles on my long run. This might have been due to recovery factors but it’s continued on through the week. My Tuesday Steady run which I was running at an average of 7:20/mile last week came in at 8:10/mile this week. Wednesday’s recovery run averaged 9:10/mile; today’s, five days after parkrun, came in at 8:44/mile. My legs have got nothing – no bounce, oomph or power. I’m barely getting out of the fat-burning zone on these runs.

So I now just have to wait for the mitochondrial adaptation to take place and in the meantime, plod along. This isn’t the first time I’ve been here but this phenomena is so poorly known that, in the past, I would start to take action to try and get back ontrack. I might rest (not a bad option if it’s only a day or two), do some strides (poor option as legs are already tired), do less mileage (not great as you won’t necessarily reinforce the growth), or try to continue doing what I usually do at the usual paces (effectively overtraining which usually led to injury). When it happened to me after marathons, it usually led me to quit running for six months or more. It’s only now I realise you just have to jog until the legs splutter back into life as they eventually will. It’s quite a remarkable experience because one day running feels awful, the next it’s like you’re running on bedsprings as the adaptations finally kick in.