Being Friends with Fatigue

Every runner knows the feeling. The heavy legs, the burning lungs, the internal negotiations that happen during the final few k's or miles of a long run or the last rep of a track session. We are often conditioned to view fatigue as the enemy, or a red light telling us to stop, slow down, or give up. But if we truly want to grow as runners, we need to fundamentally shift this mindset. As the renowned running coach and author Steve Magness so perfectly puts it: "The key is to change your relationship with fatigue… from something to be feared to something to be expected and tolerated." We need to become friends with fatigue.

Fatigue is a delicate balance, but fundamentally, it is the tangible proof that work is being done. It is the physiological receipt for the effort you have invested. By understanding how fatigue works, we can learn to work with it, rather than fighting against it.

The Science of Cumulative Fatigue: Rewiring the Body

In endurance running, there is a concept known as cumulative fatigue. This is the deliberate process of stringing together training days, so that you begin a run before you are fully recovered from the last one. While it sounds counterintuitive, this is where the magic of endurance training happens.

In the middle of April this year I recall one of my runners (let's call her Sarah), contacted me. She was in the peak phase of her training programme, about to approach a marathon taper and her legs felt like lead during a routine 10k easy run. "I feel like I'm losing my fitness," everything feels harder. I had to reassure her: "You aren't losing fitness. You are exactly where you are supposed to be." In the context of the week she just had, on top of the weeks she had just had, this peak training week, before the taper is where maximum fatigue will be felt. I had to reasure her that it is the weight of the hay in the barn. Sure enough over the coming weeks, she freshened up and smashed her marathon goal.

When you run on tired legs, your primary, go-to muscle fibres are often cooked. To maintain your pace and keep you moving forward, your central nervous system is forced into a corner. According to extensive research on motor unit recruitment and muscle fatigue (Enoka and Duchateau, 2008), as your primary muscle fibres exhaust, the brain must increase its neural drive. It begins to recruit new, secondary motor units, and muscle fibres and their attached neural pathways that usually lie dormant during shorter, fresher runs.

By training under a state of controlled fatigue, you are literally forcing your body to recruit new muscle and build new neural pathways. You are rewiring your nervous system to become a more resilient, efficient, and robust runner. Sarah's heavy Tuesday run wasn't a failure; it was the exact stimulus her body needed to help handle the final 10k of her upcoming marathon, when that very thing comes upon her.

Teaching the Mind to Push Through

This adaptation isn't purely physical. Becoming friends with fatigue is a psychological masterclass. Renowned sports scientist Tim Noakes famously proposed the 'Central Governor' model (1997). This model suggests that our brain creates the sensation of fatigue to protect our bodies long before our muscles actually reach their physical limits. The brain acts as a protective handbrake.

When we safely push through the discomfort of a heavy-legged run, we are teaching that central governor to relax the handbrake. We are proving to the mind that it is safe to keep going. As former marathon world-record setter, and widely considered GOAT of endurance running, Eliud Kipchoge often says, "Pain is everywhere... but if you accept it, you will be successful. Your mind must control your body."

Building this psychological resilience is what allows you to hold your pace on race day when everything hurts. You've been there before in training, you recognise the feeling, and you know you can survive it. I often have a mantra of my own when it gets tough. "Will I die? No. Then keep pushing."

The Fine Line: Healthy Fatigue vs. Overtraining

Here is where the balance comes in. Being friends with fatigue does not mean blindly running yourself into the ground. A good friend knows when to give you space. As a coach, one of my primary jobs is helping athletes recognise the difference between healthy, functional training fatigue and the slippery slope of overtraining.

The European College of Sport Science’s consensus statement on overtraining (Meeusen et al., 2013) highlights how easily athletes can slip from functional overreaching (where growth happens) into non-functional overreaching (where performance declines).

Healthy Training Fatigue looks like:

• Heavy or dull legs the day after a tough session.

• Mild Delayed Onset Muscle Soreness (DOMS).

• A feeling of physical tiredness that improves with a rest day, an easy recovery run, and proper fuelling.

• You still look forward to your training programme overall.

  
  

Overtraining (Non-Functional Overreaching) looks like:

• Persistent, heavy lethargy that doesn't resolve after a rest day.

• An elevated resting heart rate in the morning.

• Irritability, mood swings, and disrupted sleep patterns.

• A sudden and sustained loss of motivation to run.

• Going backwards in your training paces despite trying harder.

If you are experiencing the latter, you have tipped the balance. Fatigue is no longer your friend; it is a warning siren.

The General Fatigue of a Training Cycle: Managing Your Battery

As you move deep into a structured training cycle; especially during those peak weeks of marathon prep, you will inevitably encounter a pervasive, low-level tiredness. It’s the feeling of waking up in week ten and realising your legs haven't felt truly 'fresh' in a month. This general fatigue is entirely expected; it is the compounding effect of consistent, quality work.

However, to keep your relationship with this fatigue healthy, you have to become an expert at managing your energy reserves. I like to think of this as managing your internal battery. As I discussed in my recent article, Managing Your Battery: Why Energy Balance Matters for Progress, running isn’t just about ticking off miles on a plan; it’s really about managing the mental, physical, and emotional reserves that fuel both your running and your life.

Picture your body like a smartphone. If you start your day on low power mode with multiple apps running in the background, you are going to drain completely before the day is done. Training is a form of stress, the good kind that helps us adapt- but if you are constantly making withdrawals from your energy bank (like racing too often or pushing every session too hard) without taking the time to recharge, that expected training fatigue quickly turns into burnout.

The Invisible Backpack: Stress Outside of Running

When managing that battery, one of the most common pitfalls I see in my coaching practice is runners viewing their training in a vacuum. The human body does not compartmentalise stress. Your nervous system doesn't have a specific bucket for "Running Stress" and another for "Life Stress", it all draws from that exact same internal battery.

You must account for fatigue induced by factors outside of your running shoes. These include:

• Mental Energy: A demanding week at work, financial worries, or family challenges heavily tax the central nervous system.

• Diet and Fuelling: If you are under-fuelling, trying to lose weight too aggressively, or lacking essential micronutrients, your body cannot synthesise the energy required to repair muscle damage. You will fatigue much faster.

• Other Activities: A weekend of DIY, international travel, moving house, or playing a casual game of football all drain the battery.

I've worked and work with athletes who juggle demanding jobs, travel, and young families. Their challenge isn’t motivation; it’s bandwidth. If your life stress is exceptionally high, your training stress needs to drop to accommodate it. I frequently adjust my athletes' schedules mid-week, focusing on consistency over perfection, to ensure that running remains a supportive outlet rather than another stressor. Respect the total load on your body.

Embrace the Ache OF ENDURANCE

The legendary Emil Zátopek famously said, "We are different, in essence, from other men. If you want to win something, run 100 meters. If you want to experience some other experience, run a marathon." That "other experience" is the profound self-discovery that comes from navigating fatigue. The next time you are out on the roads and that familiar, heavy tiredness creeps into your quads, don't panic. Smile at it. Acknowledge it.

It’s proof that you are working. It’s proof that your brain is mapping new pathways and recruiting new muscle. Manage your battery, balance your training with proper fuelling, respect the stress of your daily life, and take your rest days seriously. Treat fatigue with respect, and it will turn you into the strongest runner you can be.