Endurance 101 - Edition 11 - Rest, Fuel & Adaptation

The Endurance Athlete’s Guide to Actually Getting Fitter

We’re officially in the last week of November—unbelievable, right? So let take a sit down and chat about the road ahead. Some of you are easing into the final taper before the last marathon on the Cape Town calendar for 2025. Others are quietly shifting your mindset toward 2026: the big ones like Two Oceans, Comrades, the Cape Town Marathon, early-season triathlons, 70.3 races, road cycling tours, open-water swims… all the events that make the endurance world come alive.

And no matter what discipline you’re in—running, cycling, swimming, triathlon, ultra—your body operates on the exact same biological foundations.

Two of the most misunderstood components of endurance training are:

🟡 Rest (especially de-loads) 🟡 Fuel (total calories + carbs during training/racing)

Athletes often obsess over mileage, pace, power, bike sessions, intervals, heart rate zones… yet the REAL gains come from the things most athletes undervalue.

Let’s dive deeper—scientifically, conversationally, and with a practical slant.

1. REST: The Most Underrated “Training Tool” in Endurance Sports

If you zoom out and look at how the human body works, training is basically controlled stress. Every session is micro-damage. Every week adds load. Every block adds cumulative fatigue.

But here’s what many athletes forget:

You don’t become stronger during training. You become stronger during recovery.

That’s not motivational fluff—that’s hard physiology.

The Stress → Recovery → Adaptation Cycle

➡ Training is Stress

Here’s what actually happens during endurance sessions:

Muscles:

• develop micro-tears

• accumulate oxidative stress

• deplete glycogen

• trigger inflammatory responses
  

Tendons & Bones:

• experience repetitive strain

• undergo micro-damage

• need time for re-modelling
  

Cardiovascular System:

• temporarily drops stroke volume

• increases heart strain

• shifts autonomic balance (sympathetic stimulation)
  

Nervous System:

• “slows down” to conserve energy

• decreases neuromuscular recruitment efficiency

• fatigues mentally and physically
  

Brain:

• experiences mental fatigue

• increases perceived exertion

• reduces motivation
  

So yes—training stresses EVERYTHING: muscles, connective tissues, hormones, nervous system, gut, immune system.

➡ Recovery Repairs and Rebuilds

During rest:

• mitochondria repair and multiply

• muscle fibers rebuild thicker

• capillaries expand

• glycogen stores refill

• hormones (cortisol, testosterone, leptin) rebalance

• immune system strengthens

• neuromuscular firing improves

• metabolic flexibility increases

All the “magic” happens when you're not training.

➡ Adaptation Makes You Fitter

This is when:

• LT (lactate threshold) improves

• VO₂ max climbs

• FTP (cycling) rises

• Endurance increases

• You hold pace or power longer

• You burn carbs and fats more efficiently

• You recover faster

Rest isn’t a break from training. It IS training.

2. WHY DELOAD WEEKS ARE NOT OPTIONAL

Most endurance athletes ignore de-loads… until they get injured, burnt out, or chronically fatigued.

A de-load week is simply a planned reduction in load every 4–6 weeks to allow full-system recovery.

This does not mean no training, it simply is a week where the intensity load gets lowered either by effort, time or impact. So you coach might swop a run session for a extra swim session or you will still do the interval run but for a shorter time.

Why your body needs de-loads:

🟣 A. To Prevent Accumulated Fatigue (AF)

AF builds up silently over weeks:

• heart rate drifts higher

• power/pace feel harder

• legs feel heavy

• mood drops

• sleep worsens

• stress increases

• motivation fades

Your nervous system and endocrine system show strain long before your mind admits it.

🟣 B. To Prevent Overuse Injuries

This applies across endurance sports:

Cyclists:

knee pain, Achilles pain, lower back strain, saddle numbness

Runners:

shin splints, tendinopathy, stress fractures, plantar fasciitis

Swimmers:

rotator cuff irritation, shoulder impingement

Triathletes:

a combination of all three

Most injuries happen because load outruns tissue adaptation.

De-load weeks stop this from happening.

🟣 C. To Supercharge Performance

After a de-load:

• your legs feel fresher

• power is more responsive

• pace feels easier

• HR is lower at same output

• neuromuscular firing is sharper

• mental focus improves

Your body LOVES a reset.

3. FUEL: The Other Half of the Adaptation Equation

Now let’s talk about fuel—because this is where most endurance athletes make their biggest mistake.

And it’s often not intentional. It’s because the endurance world culturally glorifies “less”—lighter, leaner, lower intake, fasted sessions…

But your body doesn’t care about trends; it cares about physiology.

ENERGY AVAILABILITY (EA): Your Body’s “Operating Budget”

Energy Availability = Calories eaten – Calories burned in training

Then divided by lean body mass.

Low Energy Availability is extremely common in endurance sports—especially in runners, cyclists, and triathletes.

Low EA leads to:

• hormonal dysfunction

• poor recovery

• increased cortisol

• weakened bones

• low iron

• chronic fatigue

• immune suppression

• frequent illness

• poor performance

• RED-S (Relative Energy Deficiency in Sport)

The body CANNOT adapt to training without adequate energy.

It’s like trying to build a house with no bricks.

4. WHY ENDURANCE ATHLETES ABSOLUTELY NEED CARBS

Carbs are your body’s preferred high-intensity fuel. Period.

At race intensity:

• 65–85% of your energy comes from carbohydrates

• Fat alone cannot fuel endurance races—it’s too slow

• Glycogen stores are limited (90–120 minutes max at tempo effort)

This is across disciplines:

Running:

marathons, ultras, tempos

Cycling:

long rides, climbs, surges, time trials

Swimming:

intense pool sessions, open-water races

Triathlon:

every single discipline + transitions + cumulative fatigue

Your body is not built to race without carbs.

5. WHY YOU MUST FUEL DURING LONG TRAINING

Here’s where people underestimate training:

If you're doing 2–4 hour rides, 90-minute runs, long swims, brick sessions—you are depleting glycogen rapidly.

Fuelling during these sessions:

• reduces muscle breakdown

• lowers cortisol

• improves session quality

• increases mitochondrial adaptation

• reduces injury risk

• accelerates recovery

• helps your metabolism stay efficient

• improves your ability to tolerate carbs on race day

Fueling during training is not "extra calories."It’s the cost of doing endurance work.

6. RACE FUELING: WHAT YOUR BODY ACTUALLY NEEDS

General Guideline:

40–90g of carbs per hour depending on the event.

For ultra endurance events:

60–120g/hour using glucose + fructose blends.

Why this works:

• stabilizes blood sugar

• delays fatigue

• spares muscle glycogen

• sharpens cognitive function

• maintains neuromuscular coordination

• prevents the “bonk”

• keeps pace/power consistent

You cannot race your best on fumes.

7. WHY YOU SHOULD NOT FEAR FUEL CALORIES

1. Calories eaten during endurance exercise are burned immediately.

They don’t “stick.”

2. Under-fuelling increases cortisol and slows metabolism.

This often leads to weight gain.

3. Fuel supports hormonal health.

Especially for female endurance athletes.

4. Better fuelling = better training = better performance.

5. You’ll recover faster and train better the next day.

Food is not the enemy. Food is part of your training plan.

8. HOW TO APPLY ALL THIS IN REAL TRAINING

Here’s how to put the science into practice.

During Training Blocks:

• Eat enough overall calories (don’t undereat during big weeks!)

• Prioritize carbs around workouts

• Fuel every session >45–90 minutes

• Plan a de-load every 4–6 weeks

• Listen to fatigue markers

• Emphasize post-training carb + protein within 1 hour

• Don’t skip rest days
  

During Taper:

• Keep carbs high (fuel tanks full)

• No diet-style “cutting”

• Reduce training load—not calories

• Sleep more

• Stay hydrated

Your goal in taper is supercompensation, not restriction.

During Races:

• Start fuelling early

• Fuel consistently

• Stick with practiced products

• Avoid “winging it”

• Drink before you feel thirsty

• Don’t be afraid of calories—they’re your superpower

FINALLY

Endurance athletes often celebrate suffering, grinding, pushing harder…But the real game-changers are the things done quietly:

Rest, recovery, de-loads, fuelling, and trusting the physiology.

Those who understand this don’t just perform better—they last longer, stay healthier, and actually enjoy the sport more.

The strongest endurance athletes aren’t the ones who train the most. They’re the ones who train smartest.