How to Return to Endurance Training After Illness

Whether it’s the flu, a nasty cold, or just life handing you a timeout, getting back into training isn’t as simple as pressing play on your pre-sick self. Athletes—especially us Type A’s—are notorious for trying to make up for lost time. That’s where this guide comes in.

I tried finding a stock photo with "Mom sick". This is the best I found. Because we don't get sick?!

Let’s face it: returning to training after being sick, or injured is like trying to jump on a treadmill that’s already moving. Whether it was the flu, injury, or a mystery virus gifted to you by a child with a runny nose, the comeback demands patience, strategy, and a good dose of humility.

You’re not weak. You’re rebuilding. And rebuilding takes brains, not just brawn.

The Emotional Whiplash of Forced Rest

For high-performing, goal-driven athletes, being sick, or injured can feel like identity theft. You go from feeling invincible to being winded walking up the stairs. Whether you had mild symptoms or something that knocked you flat, the psychological toll is real.

But instead of fighting your body, start working with it. This is not a detour. It’s part of the journey. Life's ebbs and flows are all part of it. You can't truly enjoy the highs without the lows.

How to train after illness?

The following advice is based on my "pro-level" experience after many, many illnesses. You should always consult a medical professional when symptoms persist or you are severely ill. Note I'm not a medical professional, and don't offer medical advice. Proceed at your own risk only. I will get back to you about returning after injury, but for now, let's focus on illness.

Step One: The Symptom-Free Start Line

Before lacing up again, wait at least 1-2 days symptom-free. No sniffles. No brain fog. No wishful thinking. THIS is the hard part. Your devil on your right shoulder is calling you lazy.. am I right?

Once you've given yourself a go-ahead, follow a protocol similar to the one laid out by Elliot et al. (2020):

Phase 1: Daily Activities Only (Days 1-3 post-symptom-free)

• Light walking, stretching, or mobility.

• Gauge your energy. You should feel better after movement, not worse.

Phase 2: Low-Intensity Training (Days 3-5)

• Short walks, gentle cycling, drills.

• Heart rate stays low zone 1-2. RPE stays below 3/10.

Phase 3: Build the Base (Day 5-7)

• Reintroduce resistance training with bodyweight only.

• Low volume runs or bikes. Think 20-45 minutes.

• Avoid any interval work.

Phase 4: Return to Load (Week 2)

• Slowly increase training duration.

• Add light resistance, agility, and some sport-specific movement.

• Intensity stays low. You're still building tolerance.

Enter the 50-30-20-10 Rule

This was a game changer for me: once you’re through the initial phase, use this percentage approach to reintroduce training volume.

Let’s say your regular training load is 15 hours/week.

• Week 1: 50% = 7.5 hrs. Including mobility, stretching, walking.

• Week 2: 30% = 10.5 hrs

• Week 3: 20% = 12 hrs

• Week 4: 10% = 13.5 hrs

Then... big recovery week.

I know, you are shocked. "What is MJ saying?! I need to take a month easy after being ill?" you gasp. How can I return to training after illness - without losing all my fitness?

Ok, so I'm no medical expert. But, believe me, I've done the yo-yo back to training, oops, no I started too early, so many times I've learned it can take a full month to fully recover WHEN I do the whole back to training thing all wrong. In fact, I'd say my entire 2022was like that, see here:

See all those dips in fitness? Recurring illness. I could never really build fitness because I was constantly hopping on to the training wagon too early.

What to Watch For

You may think you're "back," but your body might have other plans. Warning signs to slow down:

• Elevated resting or training heart rate. HRV that keeps declining below your 7 day average. See the photo below from Athletica.ai.

• Feeling worse after training (not better)

• Headaches, fatigue, brain fog. My standard warning bell is headache.

• Needing naps after easy sessions

• 
  

This isn’t just about surviving. It’s about thriving again. This is where most people do the biggest mistakes. They have one good morning and they overdo their training, only to find out that they are back on the recovery train. I know - because I've been there too many times.

Athletica's recovery chart showing HRV. Check out the measurements inside the pink rectangle. Constantly below my normal range. I got sick at the end of the February, my dog was sick all March, and woke me up every night. It was a stressful month, and it showed.

Hidden Gold: Focus on What You Neglected

This forced pause? It’s your golden window for:

• Strength training: start with mobility and move on to more demanding workouts patiently.

• Core and mobility: great time to build those beach abs. Nah, just kidding: focus on funtional core and mobility work. Time to get those hips open again.

• Nervous system regulation: meditation, yoga, floating tanks. Sleep, anyone?

• Breathing work: box breathing to nervous system rescue.

• Drills and proprioception. Once up and "running", focus on running drills like ABCs and the way you run.

You’re not just coming back. You’re coming back better.

Mindset: Reframe the Return

You are not starting over. You are rewiring your foundation. And this time, you’re doing it with knowledge you didn’t have before.

Rewiring my own mindset when I was napping twice a day on the coach due to overtraining was a total game-changer for me. From doubting I'd ever go back to training to actually being able to absorb high volume training was because of that rewire. I found that not only do I thrive when I attempt to tackle big challenges, but I glow when I balance being tough with gentleness and joy.

My Story, Briefly

Many times after illness or injury, I've tried to jump back in too fast. A 60-min ride could turn to a three-day energy crash. Lesson learned. Now, I pivot to strength, movement quality, and training frequency at low over high intensity. Finding feeling good first before attempting to knock the socks off.

Result? A stronger, healthier more resilient version of me came back — one that now respects recovery as much as hard intervals.

A note worth mentioning here is that of course prevention is the key. Since I cut processed foods off my plate and in general live a pretty low-carb lifestyle, I haven't been sick more than once a year. Prior this diet change, it was not unheard of me being sick every 2-3 months. Consequence? Possible.

The Takeaway

Coming back from illness/injury isn’t about toughness. It’s about strategy.

• Use science-backed phasing (Elliot et al. 2020, Caterisano et al. 2019.)

• Butter yourself with patience

• Respect your body’s signals

• Build gradually (50-30-20-10 rule)

• Prioritize strength and quality of movement

Days off don’t erase your fitness. They reveal what still needs building.

So take the long way back. You’ll thank yourself on race day.

XO, MJ

PS. Follow me on Strava

Resources:

Elliott N, Martin R, Heron N, et al.Br J Sports Med Epub ahead of print: [please include Day Month Year]. doi:10.1136/bjsports-2020-102637

Accepted 31 May 2020

Br J Sports Med 2020;0:1–2. doi:10.1136/bjsports-2020-102637

Caterisano, Anthony Co-Chair1; Decker, Donald Co-Chair2; Snyder, Ben Co-Chair1; Feigenbaum, Matt1; Glass, Rob3; House, Paul4; Sharp, Carwyn5; Waller, Michael6; Witherspoon, Zach2. CSCCa and NSCA Joint Consensus Guidelines for Transition Periods: Safe Return to Training Following Inactivity. Strength and Conditioning Journal 41(3):p 1-23, June 2019. | DOI: 10.1519/SSC.0000000000000477