Why do ultrarunners do back-to-backs, anyways?

What’s up with the back-to-back long runs, you ask?

If you’re new to trail running and ultrarunning training plans, you may notice something weird: back-to-back long runs on the weekends. This is something you don’t see in marathon training plans, so you’re probably wondering why you need them at all. Let’s start with some theory on how we gain fitness to start.

You need GAS! (General Adaptation Syndrome)

To understand how you gain fitness and get stronger/faster, you need to know you the body adapts to stress after a workout. This was first uncovered by an endocrinologist named Hans Selye, who conducted an experiment and found how adaptations (fitness increases) occur following exposure to resistance (or, “pushing yourself”). A visual of this from Jason Koop’s Training Essentials for Ultrarunning book is below:

GAS has 3 stages:

1. Alarm: The body has an immediate response and shifts its resources to muscular needs (like on a normal run)

2. Resistance (also called adaptation): The body is able to adapt to stressful situations and become stronger.

3. Exhaustion: If stressed for too long, the body will begin to break down.

Why is this important?

This means that unless you push yourself into resistance, you body isn’t adapting to new stressors. Running your first 50k or 50M is definitely a stressor! When marathon training, you’re able to expose your body to enough stress in a single 20-mile run to induce the adaptations needed to finish that 26.2 miles, but when the distance increases, the races take longer to complete, and your body is exposed to more stress, you need more adaptation to prepare! Enter, the back-to-back. By running on “tired legs” (and more importantly a tired body), you’re pushing yourself into that “resistance” zone.

Recovery is key

It can’t be stated enough that true training adaptations occur during recovery, not during the activity itself. Skipping the recovery day is a very bad idea, and will put you into that nasty “exhaustion” category, also known as Overtraing Syndrom. We don’t want to touch that! Every person’s ability to recover varies based on their fitness level, so when we first attempt a back-to-back, we’ll be very careful to monitor how you’re feeling 1-2 days after the activity to see if it’s well-tolerated.

Why can’t I just do one big training run and make it longer?

Well, if you’re training for a 50 or 100M, that would be quite a training run! Research on mechanical stress has shown that running anything over 20 miles can actually be detrimental to the body, and is generally unsafe, particularly for your bones. There’s a great article about elite ultrarunner Camille Herron which further proves this point. Camille still destroys races in her 40’s: she won the Jackpot Ultra Festival’s 100-mile race in 2022 and only ran one 20-miler in her training. What gives?! Camille does back-to-backs, and because she’s an elite athlete, she frequently does two runs in one day. Since most of us are not (1) elite athletes or (2) full-time athletes with time for this, we tend to split it into two days. What this looks like practically is: Saturday will be your big effort (the hard effort comes first), say 18 miles, and the second day will be an easier effort, say 8-10 miles. Even 100M training plans follow a 20-mile big day/something shorter format. Perhaps this brings you a sigh of relief that you don’t have to be spending 6+ hours out on the trails every weekend to finish your event. :)

I feel like crap on day 2: is that normal?

Absolutely! One big thing you might notice on day 2 is Cardiac Drift - which means your heart rate may be depressed on your 2nd run.

• Cardiac drift up is due to an increase in body temperature - you might experience later in a long run on a hot summer day.

• Cardiac drift down is due to fatigue related to muscular efficiency.

Know that cardiac drift is normal occurrence in your training, and an indication your are getting into that “resistance” area of your training.

I’m running a 50M or greater distance, I see some people do 50ks to train for this - is that safe?

Yes! Even though generally it’s a bad idea to go out and run a 50k every weekend, integrating one 50k (or 50M if you’re training for a 100M) training race is standard practice for your peak training week. This is a great time to see how your body responds to that level of stress. Just keep in mind that proper recovery after your training race is key to those adaptations!

To sum it up

If you’re training for 50k or longer, we’ll definitely be discussing back-to-backs for your plan. If you’re new to this, be sure to listen to your body and make sure you’re recovering properly after these efforts. Celebrate that 20 miles is the longest you have to go - you got this!

Camille Herron’s Advice for Ultra Athletes: Skip the Long Run!

Back-to-Back long runs and workouts: Next-level training, if done right