Experiencing Aerobic Limitation

I spent a rainy bank holiday morning sprinting up a nearby hill repeatedly. It’s a key part of getting faster and one that I’ve not done since last summer. Having woken at 6am, I grabbed a bowl of cereal then did the crossword while breakfast digested. About 8:15am, I headed out the door and there was light rain falling. The session I had in mind is not big – a 15 minute warm-up run, 5 mins of drills to help the mobility, the main session of 10 hill sprints and then a ten minute warmdown. But it is time-consuming because each sprint is followed by three minutes of recovery. In the end, it took over an hour to complete. What interested me is what the session told me about how to train for distance running.

Setting off on my warm-up it took three minutes for my body to crank the pace up and reach eight minute miling. My route is a mixture of ups and downs such that, by the end of the first mile, I’d been hitting sub-6 pace on a steeper downhill stretch – 7min38 popped up on my watch. The second mile came in at 7min04 and then I tacked on another thirty seconds back to home. What surprised me was how relatively hard I was finding it. My breathing was beginning to huff and puff like I was running a parkrun and my heart-rate reached 160bpm at the end. All in all, I was glad when I finished my warm-up and could walk back round the corner to do drills.

With the rain falling steadily and knowing I’d be standing around between the hill efforts, I elected to keep the drills short. Just one repetition of each drill taking 15 seconds and then a stride back to my start position with around 30s time to recover before the next. The stride reinforces what I’m programming as well as warming the legs up for the quicker, more violent efforts up the hill. Once again, by the end of these I was puffing and my heart-rate had steadily increased to 155bpm; each subsequent effort building the heart-rate higher than the one before.

Finally I was ready. I walked to the base of the hill and then spent a few minutes chatting with an old chap about goings on. The important thing about hill sprints is to attempt them with fresh legs so I didn’t mind an extra few minutes spent conversing. Hills sprints want to get maximum effort from the muscles which is why they only last seconds and then you get a nice long recovery. The short timeframe allows your ATP-PC energy system to be the key producer of energy while the long recovery ensures it has recharged.

The first effort I sprinted up the hill and my legs were turning over so smoothly. I was barely breathing, it was how I’d feel if I was out for a jog. Then I started to walk back down the hill and the oxygen debt kicked in and within fifteen seconds my heart-rate had reached 139bpm having started down at 90bpm. The second effort felt a little harder on the breathing especially afterwards and my heart-rate reached 143bpm. By the time I’d ambled back downhill to my starting place, it was back to 114bpm and I was feeling okay. After that my heart-rate never got out into the 140s again. Sometimes the oxygen debt after each effort resulted in very quick gasps for breath yet it didn’t take long to be back to normal. As the sprints went on they got a little slower, this is unsurprising because the muscles are beginning to fatigue and they can’t power getting as far up the hill.

After my 10th and final effort, I walked down until one minute had elapsed then began a warmdown run. My legs felt like they were springing along yet the pace was barely quicker than nine minute miling.

What intrigued me about this session was how two such different ways of training – the warm-up and sprints both taxed me in different ways. The warm-up pace picked up gradually to be a little quicker than seven minute miling where I still had room to run faster. Yet it would have been hard to stay running like this for an extended period of time. By contrast the hill sprints which are an absolute blast of maximal energy felt so much easier.

According to the wisdom of heart-rate training I could have done sprints all day long as I maxed out at whereas my warm-up reached 160bpm. Yet I know that wouldn’t be a good idea – no-one would do that, neither a sprinter or distance runner.  It highlights one of the problems of heart-rate training.

What really came home to me from the warm-up is that the thing limiting my distance running is not speed related. This is what I experienced when I first began parkrunning a decade and more ago. Every week I would run and feel there was more available in the tank yet not understand what was stopping me.

The limitation was not one of being able to run very fast for a short time as it is with anaerobic limitation, it was one of being able to run fast for a relatively long time. That’s where aerobic development is required. It took me the next five years to really begin unravelling this conundrum in detail. I read many books which talk about it needing to be done yet it’s not until you viscerally experience it that it becomes clear what is going on.

I meet many runners who haven’t yet had this realisation that being able to run fast 200s, 300s, 400s is not necessarily going to turn them into a faster distance runner. Sometimes it does but more often than not it’s about building speed through good distance training.

Maybe this is something I can help you with? Not everybody wants to be coached for a race, sometimes they simply need a training review. Understanding what they need to do next to get to the next level – is it speed or endurance they should work on. Just head over to the Contact page and give me some basic details and we can arrange a 1 hour consultation.