During the third week of the relentless mileage through Australia, something changed. The deep sleeps must have been working as I got my second wind. The fatigue, as expected, was still there but no longer at a prohibitive level.
It was still incredibly taxing and took huge resolve to fight my way out of the deep sleep, out of the tent and onto my feet each morning, but I felt stronger and knew I could handle it. The first two weeks of that mileage I was becoming increasingly fatigued with each passing day, and that scared me. That’s not something you can maintain for very long.
I was genuinely scared of not reaching Sydney on time, and the consequences this might incur.
Why all the fuss over an extra 5-10km a day, surely 10%-20% extra mileage is only 10%-20% tougher right? A resounding “NO” is the short answer there!
You see, humans aren’t robots, they can’t be understood with a calculus table. Unlike machines or mathematical equations, there’s nothing linear concerning the way the human body responds to changes in stimuli from the environment.
My body’s so conditioned to running that I only begin to feel some noticeable fatigue around the 35-40km mark, dependent upon the terrain, temperature and my recent quality of sleep. It’s a very mild fatigue and easily manageable. As the total number of kilometres increases however, so too does the intensity of the fatigue. Let’s take a look at a 50km, 60km and 70km example.
Let’s say I’m feeling good in general so I begin to fatigue at around the 40km mark, which equates to
10km run with some mild fatigue.
Now let’s compare that to running 60km and 70km distances which I often ran over the last month in Australia.
Obviously sleep wasn’t matching effort as I had to jack up on caffeine just to feel safe on the road because fatigue was beginning at around the 35km mark.
- Fatigue starts at around the 35km mark
- 25km run through moderate fatigue
Now your perception of fatigue and its debilitating effects on your progress is non-linear as well – it’s cumulative and grows rapidly.
For instance, running two hours in a fatigued state is a more than four times harder than running 30 mins in a fatigued state – it’s a completely different challenge! In fact, it’s around six times tougher. You’ll pass from mild fatigue, fatigued, highly fatigued to walking zombie in a very non-linear curve!
Now let’s see how the 70km day stacks up….
- The point at which fatigue is reached = 35km.
- Distance run whilst under moderate fatigue = 15km
- Distance run whilst highly fatigued = 20km.
Let’s compare the days:
A 50km day run while enjoying normal sleep means 10km of running with moderate fatigue versus a 60km day run following poor sleep,
The 60km day only represents 20% extra distance Perhaps it’d be 30% more difficult? Well let’s do the maths. It’s a whopping 250% tougher than the 50km day!
That equates to 25km run through fatigue versus 10km, a factor of 2.5.
Now let’s compare the 70km day.
It’s 40% further, so perhaps 50-60% tougher, after all humans aren’t robots right? Well the maths shows us it’s 15km of running through a moderate fatigue level versus 10km, so 150% tougher. However, we then reach the point where the highly fatigued state kicks in and this represents an extra 20km. Remember, a state of high fatigue is much tougher to overcome and run through than moderate fatigue – around 1.5 times tougher (and escalates exponentially).
So 20km run through high fatigue is equivalent to 30km of running with moderate fatigue 15+30 = 45km.
Comparing the 50km versus the 70km day we see a difference of 10km run under fatigue versus 45km under fatigue a difference of 450%!
Like I said humans aren’t robots and they aren’t linear!
The above maths gives you an insight into some of the thinking I do out on the road, when people ask me “what do you think about all day”, There are lots of things I think about, mainly trying to watch the traffic for idiots driving whilst texting on their phones and jumping out the way before they hit me!
However there’s also navigation, water, food, camping/accommodation to think of, and then I like to work out numbers such as this example.
I’ve thought about the same for steepness of hills and temperature and the environment, for instance running in 40 degree celsius heat should only feel 25% warmer than 30 degrees right?
Sure, if you’re dealing with a robot!
In reality it represents a ‘feeling of ‘ 300% warmer?! Why and how such a huge difference?
Well human beings feel comfortable between 18-25 degrees. Above 25 is experienced as warm/hot, so 30 degrees represents 5 degrees above baseline of ‘hot’ whereas 40 degrees is 15 degrees above baseline a factor of 3 times higher!
Of course we can reverse engineer these numbers, working backwards from the absolute limits for humans (furthest someone can run per day if running every day of the month for multi month effort max = approx 80-85km, highest temps can run in for 8-10 hours a day, back to back days = around 55 degrees) and we arrive at fairly similar numbers!