How to Prepare to Run 100km (And NOT Die)

Have you signed up for a half-marathon this year? Who am I kidding, of course you have. Whether your goal is to run 21km, 42km or 100km, Giles has done it all and then some and is sharing what he knows about how to get it done.

Back in 2014, my wide-eyed 18-year-old self took on his first ultra-marathon. It absolutely broke me, but I craved more. Since then, I’ve become hooked on trail running, completing seven 100km runs whilst dodging the DNF (did not finish) curse. So after a decade of running long distance, here’s my two cents on how to successfully prepare for and complete one hundred clicks.

1. How You Move Matters

The human body is highly adaptable. You can get away with poor running technique for a while, but the fact remains that compromised running mechanics will eventually bite you in the ass. Heavy heel striking and maintaining a low cadence are the most common mistakes new runners fall victim to.

Coaches and running-specific physios can help analyse and improve your form. This has the potential to:

• Distribute impact effectively across the body
• Reduce energy expenditure
• Reduce the likelihood of injury
• Boost confidence

Maintaining a high cadence at Kosci 100 | Photo by UTMB

2. Build a Solid Foundation

Gradually increase your weekly mileage until you can comfortably run 90-110km in total, spread across seven days of training. Yes, this takes time, devotion, and consistency.

A general rule is to progressively increase your weekly distance by around 10%. For example, if you already have a decent running base, you could spread your weekly mileage in the following manner:

• Week 1: 60km
• Week 2: 66km
• Week 3: 73km
• Week 4: 37km (down week: 50-70% of your biggest week thus far)
• Week 5: 73km
• Week 6: 77km
• Week 7: 85km
• Week 8: 45km (down week)
• Week 9: 85km
• Week 10: 94km

You get the drill.

New runners often unknowingly play Russian roulette with their weekly distances, heavily changing them and then acting surprised when an injury shows up.

Don’t be a guinea pig if you’re serious about showing up at that start line.

3. Know Your Heart (Rate Zones)

As the engine and control centre of your body, the heart plays a crucial role in running.

There are five heart rate zones, each corresponding to different intensities and serving different purposes.

To build a strong aerobic base, experts recommend spending 70-85% of your running time in Zone 2. This is the zone that improves your general endurance, helping your body to more efficiently oxidise fat and build your capacity to comfortably run for hours.

The five heart rate zones | Photo via sundried.com

4. Have a Fuel and Hydration Plan

Calories – to train for and race long distances, you generally need a lot of them. Experiment during training and figure out what works best for you.

Here’s the kicker though: you can rarely prepare for or know what you’ll feel like eating or drinking when you’re ten hours deep into a race. Expect the unexpected.

A general nutrition rule is to aim for 50g of carbs per hour of running.

I’m a big fan of Spring Energy gels which are made from wholefoods and differ from other industry players whose products are often highly processed and maltodextrin-based.

It’s also important to replenish the electrolytes you lose. Supplement with salt pills and/or electrolyte powders before dehydration gets you in trouble.

If you’re a heavy sweater, train in hot conditions or struggle to stay hydrated during exercise, I recommend doing a sweat test. This analyses your sweat content and gives you specific numbers about your physiology.

I did one a while back and it turns out on average, I lose 1.4L of sweat per hour of running, and 3.4g of sodium per hour. Since learning this, I heavily supplement with electrolytes and have seen a significant boost in performance.

Gels all round | Photo by Steven Mortinson

5. Surround Yourself with Other Weirdos

Finding people that have common or similar goals to you is a game changer. You’ll enjoy yourself miles more, learn a thing or two, and likely end up jogging and chatting in that golden Zone 2.

Back in 2019, I moved to Costa Rica, trained alone for months, and signed up for a 50km trail race. The course proceeded to chew me up and spit me out in a feral manner. Luckily, I was able to meet another participant who invited me to join a local trail running group, coordinated by two experienced coaches. I accepted the invitation, showed up week after week, and made some epic friends in the process. My running knowledge went from zero to something more, and I successfully ran an 80km ultramarathon a few months later.

Moral of the story: Don’t do it alone when undertaking challenging ventures.

My running family ‘30 Grados’ in Costa Rica | Photo via The Trail Challenge

6. Get a Coach and Training Plan

Unless you’ve been running for a long time and seriously know your stuff, you’ll benefit from having a coach guide you and write up a training plan based on your experience and goals.

Sticking to a clear-cut system designed by a professional trumps your own ability to organise sessions. Depending on your experience, training plans for 100km typically range from 16 to 24 weeks.

To find a coach, a quick Google or social media search for running coaches in your area should help. Alternatively, there are plenty of remote coaches to pick from. Greg Pearson is one that gets a lot of praise.

7. Play the Long Game

If you want to complete a seriously long distance with zero to minimal training, by all means, run the damn thing, callous your mind, and wreck your body. I’ve fallen into this trap more than once. It’s humbling.

Taking shortcuts might seem insignificant in the moment. However, when accumulated, you pay the price.

Go hard but play smart and respect your body.

8. Strength Train

Ditch static stretching and prioritise strength training instead. The benefits are widely researched and proven to make you a better and more resilient runner.

The minimum effective dose is two sessions a week. Start with basic movements like the squat, hinge, jump, and calf raises.

Add load over time and your body will thank you during and after your races.

Bonus points if you strengthen your feet as well. Wearing barefoot or minimalist shoes is an underrated tool that can help minimise common injuries like plantar fasciitis and lead to fewer blisters.

Getting those single leg Romanian deadlifts in

9. Recover, Recover, Recover!

Picture this: you do a great speed session, have a few beers later that night, and end up sleeping for five hours. You go for a slow trot the next day and feel atrocious. This shouldn’t sound surprising.

Here’s the thing though. The progress, also known as adaptation, from each training session, isn’t produced by the work itself. It’s shaped by what you do in the next 24-72 hours. Reread that if you have to.

To recover adequately, the non-negotiables are eating and hydrating well, as well as getting quality sleep.

Great recovery diagram | Photo by Dr Peter Tierney

10. Mindset is Everything

Building a strong mindset is the single most important factor in completing a difficult task. The mind calls the shots, the body follows suit.

One way to do this is to put yourself through stressful scenarios, time and time again. These don’t need to be masochistic soul-sucking challenges. Rather, they can be small tangible tasks such as doing a class of HIIT or hot yoga, practising intermittent fasting, taking a cold shower, or staying in the sauna for a little bit longer.

Each time you override that voice in your head telling you to jump ship, you prove to yourself that you’re capable of more. Less power is given to the reactive mind craving comfort.

Friction is the critical ingredient. Leverage it enough and you can build an indestructible mindset.

The bottom line is this: if your life depended on running 100km tomorrow, you’d do it.

If you’re serious about something, don’t just hope, give yourself no other choice but to finish the damn thing.

Mind over matter | Photo by Alina Grubnyak via Unsplash