Efficiency and my postman

I often say “Hello” to my postman, if he doesn’t look too busy I’ll engage him in conversation or give him a wave as I zoom by in the car. Before Christmas there were a couple of days where I received post at around 4pm. This being later than usual, I chased after him with a couple of mince pies and commiserated about the long hours he was doing and asked what time he’d started and finished. He said he was arriving at the sorting office just after 6am; doing a couple of trips back there pushing his trolley up the hill and on the longest day had delivered his last letter at 4:45pm, arriving back in the office at 5:07pm. He delivers six days per week.

I once did a spot of leaflet delivering to local houses and was tired after two hours of it. On paper, it doesn’t seem much, walking around, occasionally climbing two or three steps to a door, and sometimes bending down to a low letterbox. By the time I finished I was tired and hungry and I’d only done my local roads. I’d estimate my postman’s route is three times bigger than what I’d done.

So you’d think he’s superfit from all that walking and to an extent, he is. You rarely see an overweight postman or woman. It’s an active job. Yet when I looking at that fitness from a running perspective, he’s not going to go out and run a sub-3 marathon without some other training. What’s he’s got is functional fitness for a specific task – walking at low speeds, pushing a trolley with letters and parcels and the ability to do some step-ups. He could probably go out and do a charity walk or ultra with ease.

This is the mistake many people make as they get older. They think that if they do lots of walking or playing golf, it’s keeping them fit but it’s really not doing that much because there’s very little exertion taking place. Same with people cycling bikes along the promenade or cycle paths. If you don’t push yourself, the body becomes efficient at what it does.


We can begin to get an idea of how efficiency works by looking at things through a biological / chemical perspective. For muscles to contract they need to be fuelled by a substance called ATP which the body sources or creates from its fuel stores using one of four energy pathways. I’ll give an overview of the four here but if you want to jump past the details, the info relevant to the remainder of this post is in the summary lower down.

ATP-PC or Alactic Anaerobic energy system

A small amount of ATP is stored and readily available for fuelling high intensity activity. Energy is created very fast, so the muscles are able to work fast. But there’s a limited quantity of the substances used in the ATP breakdown and rebuilding process so it’s exhausted after around ten seconds. This is why it’s sometimes referred to as the sprinter’s system. Those guys and gals are quick but they can’t last even one lap of the track. For distance runners, this energy pathway isn’t very useful other than for a quick start off the line, or a kick at the end of a race.

Anaerobic Glycolysis or Fast Glycolysis

Carbohydrates stored (as glycogen) in the muscles and liver can be broken down to release glucose. Each molecule of glucose, when broken down by Anaerobic or Fast Glycolysis, creates 2 ATP. When we talk of anaerobic exercise, it’s usually this system we’re talking about (although the ATP-PC system is also covered, but as I wrote it’s mostly irrelevant to distance runners).

Aerobic Glycolysis or Slow Glycolysis

Usually referred to as the aerobic system, this takes a molecule of glucose and breaks it down to create 36-38 ATP. To create this quantity (much higher than the Anaerobic version) it uses oxygen in the breakdown and goes through more steps hence it powers muscles slightly slower. This is why a marathon, which is run almost purely using this pathway, is never going to be as fast as the runner’s 5K.

Lipolysis or fat-burning

The other part of the aerobic system is fat-burning. Depending on the type of fat and how long its molecular chain is, a molecule of fat breaks down to produce 120-140 ATP. Again it needs oxygen but the reason why it produces so much ATP is because it goes through even more steps and chemical reactions to achieve it. This is why ultra-running is even slow than marathon running!

Summary

ATP-PCInstant energy for 10 seconds
Anaerobic / fast glycolysis2 ATP
Aerobic / slow glycolysis36 – 38 ATP
Lipolysis / fat-burning120 – 140 ATP

Enough jargon, let’s get back to postal deliveries …

What I’m about to describe is more of an analogy than physically possible. Firstly the numbers are wrong in magnitude – there are billions of ATP being processed in each muscle cell to keep the body alive. Secondly the body doesn’t use one energy system exclusively at any one moment, it’s often a mixture of them all. Putting the technicalities aside, let’s use those ATP numbers to begin to get an idea about efficiency.

When I went delivering leaflets as an untrained delivery worker, let’s say I was only using the Anaerobic / Fast glycolysis system. After two minutes I’d used up the fuel I’d created and was having to break down more. It’s no wonder then that, after two hours of delivering leaflets, I arrived home feeling tired and hungry – I’d used up my fuel stores and exhausted the muscles sixty times over. Such a big effort probably triggered a stimulus to adapt to a more efficient, aerobic pathway.

If I’d stuck at the delivering for a few weeks, my body would have adapted aerobically and I’d have found myself able to last over thirty-five minutes, almost forty minutes, using the same quantity of fuel I’d previously used anaerobically in two minutes. So now if I was out for two hours – what had previously required sixty refills would only need three to fourr. The job would feel much easier and I’d likely arrive home feeling less hungry.

If like my postman, I was doing this job six times per week for months on end my body would go a step further and begin to get efficient at fat-burning. Suddenly all the energy which had been used up in two minutes on my first day out would now be more than enough to last for over two hours (120 – 140 minutes). Or to put it the other way around. When my postman was delivering for over ten hours at Christmas time, he was able to fuel it with the same level of food that I would use up in ten minutes of delivering leaflets.

And in a nutshell that is efficiency and why, as runners we get faster at running if we train effectively. We go from sweating, gasping and wanting to stop while running at ten minute mile pace to being able to jog aerobically at that pace.  We arrive home feeling fresher, less tired and without so much hunger. Suddenly on our runs we have more energy available to run further and push harder. But if, like my postman, all you ever do is go at one speed then you won’t get any faster, only more efficient. It’s why once the body has adapted from running anaerobically at one pace to running it aerobically, doing some speedwork recruits the next level and begins the process all over again.

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