A 100 miler is a big day out, but it is not a mystical distance reserved for genetically gifted lunatics. For most athletes it is a project, not a miracle, and the best results come from simple training done consistently and aimed at the right things. This blog is your 100 mile warrant of fitness, a checklist of the fundamentals that make you ready to toe the line with confidence, without needing to double your life’s training volume to get there.
The first misconception to bin is the idea that because the race is longer, training has to scale up in a straight line. That’s not how humans work. If marathon training included 30 km long runs, it does not follow that a 100 mile plan needs 120 km long runs. That is not bravery, it is just maths cosplay, and it usually ends with an injury, a fatigue hole, or a training plan that collapses under the weight of its own ambition. The job of training is to prepare the limiting factors of the event, inside the time you actually have available, without wrecking your ability to train next week.
Most people considering 100 miles have already done ultras. That matters. They probably already have a decent aerobic base, some connective tissue toughness, and at least one vivid memory of a stomach mutiny or a blister that could have its own postcode. So the goal is not to reinvent you, it is to optimise you. A 100 miler is less about becoming wildly fitter and more about becoming better at moving for a long time, managing damage, managing energy, and keeping your brain from writing cheques your legs cannot cash at hour sixteen.
The biggest lever is workload distribution. You can prepare for 100 miles without dramatically increasing weekly training time by shifting more of the meaningful load onto the weekend. Weekdays are there to maintain fitness and durability, build frequency, and keep your mechanics honest. Then the weekend becomes your rehearsal space for long duration movement, time on feet, hiking, technical terrain, and fuelling practice. You stop treating weekdays like the main event. You make them repeatable. Most athletes do better running most days, even if some runs are short, than they do chasing one or two massive weekday sessions that make the rest of the week fall apart.
Weekend specificity is where the magic lives, because a 100 miler is rarely a “run” in the way a half marathon is a run. For most athletes it is a moving event. You run the runnable bits, you hike the climbs, you manage effort, and you keep forward momentum. That is why long adventures matter. A long trail outing where you are moving steadily for hours is a better fitness deposit than a single heroic pace session that leaves you trashed for three days. Back to back weekend sessions are often the closest safe simulation you can get, because they teach you to perform with residual fatigue, which is basically the whole sport.
Specificity also means respecting the course. Not all 100 milers are the same beast. Tarawera is relatively runnable, so economy at steady running pace, long runnable trails, and pacing discipline matter. UTMB is obviously mountainous, so climbing strength, descending resilience, poles skills, and hiking efficiency matter a lot more. If your training is all flat bike path and your race is a ladder made of rocks, you are bringing a butter knife to a sword fight. The best training often looks like the race, even if it is shorter. Get on similar surfaces. Practice the gradients. Learn what your “all day” hiking rhythm is. Learn what your “runnable” pace feels like when you are deliberately undercooking it.
This is where eccentric strength deserves a proper mention, because it is one of the boring things that quietly decides outcomes. A lot of fatigue in the primary driving muscles, quads, calves, glutes, comes from small damage accumulating over time, especially on downhills and technical terrain where you are constantly braking, stabilising, and catching yourself. That micro damage is like tiny dents in a car panel. One dent is nothing, but after ten thousand of them the door stops closing properly. Eccentric strength work helps because it improves your ability to tolerate braking forces and absorb load without the same level of tissue disruption. That can mean less soreness, better control late in the race, and fewer moments where your quads feel like wet cardboard on every downhill.
You do not need a fancy program. You need consistent exposure. Downhill running in sensible doses. Step downs, split squats, lunges, calf raises done slowly, and some work that loads the posterior chain. Keep it simple and keep it regular. The goal is resilience, not a gym PB that makes walking down stairs a horror film for three days.
A few special modalities are worth adding if they are relevant to your event. Night running is one. If you will be out there overnight, or even if you might finish late enough that your brain is operating on low battery, you want night to feel familiar, not spooky. You do not need to live like a vampire. A handful of sessions finishing in the dark, or a late start long run, or the occasional evening plus early morning combo can reduce novelty. Novelty is stress, and stress is fatigue.
Practice events are also useful when they are used as rehearsals, not as ego projects. A 100 km race can be an excellent lead in if you treat it like a 100 mile execution drill. Start easier than you want to, fuel early, walk climbs, and finish feeling like you could keep moving. You are training patience and durability, not chasing a time. A backyard ultra can also be a good lab for fuelling and mental rhythm, and it is one of the more practical ways to experience moving at night without turning your weekend into a solo bush survival documentary. None of this is mandatory, but the right rehearsal can remove a lot of uncertainty.
Fuel and gut training are non negotiable. In a 100 miler your stomach is not a passenger, it is on the steering wheel. If you stop absorbing energy, the wheels come off even if your fitness is fine. Your plan does not need to be complicated, it needs to be practised. Eat early. Eat consistently. Learn what works at low intensity and what still works when it is hot, cold, wet, or you are sick of sweet things. Practice drinking without overdrinking. “Drink to thirst” is a useful anchor for most athletes, then adjust based on conditions and sweat rate rather than forcing a fixed number.
Foot care is the other predictable failure point. Over long durations, small problems become big ones. Shoe choice, socks, lacing, swelling, grit, hot spots, it all matters. Use long weekend outings to test systems and note what fails. A 100 miler is not the day to discover your shoes eat your arch after eight hours, or that your socks turn into sandpaper when wet. Dial the simple stuff in early and it pays you back late.
The final part of the warrant of fitness is mindset. A 100 miler is achievable for a lot of athletes because cut offs are often generous and a run hike strategy can get you home. That does not mean it is easy, it means the barrier is not raw speed, it is preparation and execution. The biggest mistake is trying to race it like a shorter ultra. The early hours should feel almost boring. If you are breathing hard early, you are writing a debt your legs will repay with interest later. Keep effort under control, keep eating, keep moving, and stay emotionally neutral when the inevitable rough patches arrive. They do not mean you are failing, they mean you are doing a long event.
If you are considering a 100 miler, the best first step is not asking how many kilometres you should run. It is working out what time you realistically have, what the course demands, what your injury history looks like, and what you already tolerate well. From there, build frequency, shift load toward long weekend specificity, include a bit of night or terrain rehearsal if needed, and add eccentric strength so your legs can handle the slow grind of accumulated damage.
If you want help turning that into a plan that fits your actual life, get in touch with me at SQUADRUN. We can look at your event, your schedule, and your training history, then map out a build that makes sense and gets you to the start line ready to do the job.
