Stiff Tendons = Free Speed: Why Heavy Lifting Beats More Miles
Estimated read time: 3.4 minutes (about as long as it takes to find a matching pair of running socks). 😉
Hey Performance Nerds! Jonah here. 🤓
Your tendons aren't too tight. They're too weak.
Too weak to handle each footstrike efficiently. Too weak to return energy as free speed.
Today we're breaking down:
🏎 Why stiffer tendons = free speed
🛡 Why stiffer tendons can reduce injury risk
🏃♂️ Why mileage alone won’t stiffen them (and what will)
🏋️ The lifting plan behind a ~39% stiffness increase
Study spotlight: In well trained endurance athletes, a 12 week heavy strength block increased Achilles tendon stiffness by 39%. Endurance only training showed no meaningful change.
🚨 Quick heads up:
The strength bundle we've been developing with 10+ PhDs is almost ready—and you'll want to get on the waitlist for early access pricing.
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Stryd — the running power meter trusted by serious athletes — is now an official performance sponsor of Marathon Science, delivering real-time pacing precision so you can train smarter and race faster.
💡 See this week’s full 300-word Stryd training tip at the end of this newsletter.
The Science - Your Tendons Are Energy-Saving Machines 🧬
Stiff tendons don't just store energy, they let your muscles cheat.
Research shows runners who increased Achilles stiffness by 39% improved their running economy by 4%. That's similar to strapping on carbon-plated super shoes.
Here's why:
Your Achilles acts like a spring. It stretches on landing, stores energy, and snaps back at push off. A stiffer spring snaps back faster and wastes less.
This means your calf muscles produce the same force while burning less oxygen.
Stiffer tendons = less oxygen needed = faster pace at the same effort.
Stronger Tendons, Fewer Injuries 🛡️
Here's what most runners miss: Stiffer tendons experience less strain, not more.
When your Achilles is stiffer, it deforms less under load. Less stretch means less mechanical stress on its fibers.
Think of it like upgrading from a rubber band to a steel cable.
The rubber band stretches to its limit every rep. The steel cable barely moves under the same load.
The result? Your tendons can handle higher training volumes without hitting the danger zone of overuse.
More miles without breaking down? That's how PRs are built.
Why Your Miles Aren't Enough ⚠️
You'd think running more would strengthen your tendons.
It doesn't.
In fact, the running-only group in the study saw stiffness decrease over 12 weeks.
Why? Running gives you thousands of reps at moderate load.
Tendons remodel under big, slow loads — 80–90% of your max — the kind you only get in the weight room.
The Protocol That Built 39% Stiffer Tendons 🔧
Here's exactly what the intervention group did. Screenshot this and take it to the gym.
Exercise | Sets x Reps | Tempo |
|---|---|---|
Single-Leg Calf Raise | 3 x 5 | 2-4 sec down, 1 up |
Seated Calf Raise | 3 x 8 | 2-4 sec down, 1 up |
Back Squat | 3 x 8 | 2-4 sec down, 1 up |
Leg Press | 3 x 8 | 2-4 sec down, 1 up |
Split Squats | 3 x 5 each | 2-4 sec down, 1 up |
Calf Iso Holds | 4 x 4-5 sec | Hold for 4 seconds, rest for 2, then repeat x4 for 1 set |
The Non-Negotiables:
Load: Weight that forces failure at 5-8 reps
Frequency: 3x/week in base, 2x/week at peak mileage
Rest: 3 full minutes between sets (no shortcuts)
Pick: 4 exercises per session
Progress: Add 2-5% weight every 2 weeks
Safety check: Soreness should fade within 48 hours. If not, back off.
🎯 TL;DR — How to Build Tendons for Speed & Durability
✅ 39% stiffer tendons = 4% economy boost (like wearing super shoes)
✅ Mileage alone won’t get you there — you need heavy loads
✅ 12 weeks, 2-3x/week, 4 exercises per session
✅ Stiffer tendons = less strain = more miles without breaking
💬 One last thing before you go.
After the NFL, I wasn't sure if obsessing over performance science still mattered—until I started helping this community.
Your training goals? They brought that fire back.
If you're 3 weeks into heavy lifting and your calves hate you—hit reply. I read every message and I'm here to help however I can.
Keep chasing those PRs, Jonah
🚨 #1 Muscle to Train for Fast Marathons.
Did you miss my post about #1 Muscle to Train for Fast Marathons? You can find it below!
I won’t lie. These posts take me a while to make. If you find it helpful, share it on your story or with a friend. It helps me a ton!
Are You a True Running Nerd? Prove it.. 🧐
Welcome to the prove you’re a nerd section. Each week, I ask a question about a common running science myth.
Answer correctly, and you’ll be entered into a weekly raffle to win a package of Jonah’s favorite supplements.
What weekly training structure reflects how most elite marathoners organize intensity—allowing for 2–3 big sessions without wrecking recovery?
Last Week’s Results: HRV on the Edge ⚠️📉
Most of you spotted the warning sign, but there’s still some debate on what a low and jumpy HRV really means in the middle of a hard training block.
The correct answer?
B. You’re on the edge — training stress is starting to outweigh recovery ⚠️ ✅
When HRV trends lower and becomes more volatile, it usually means you’re teetering on the line between productive training and overreaching. Your body is struggling to bounce back before the next session.
Here’s how the votes shook out:
🟩 B. On the edge — stress outweighing recovery: 195 ✅
🟨 A. Adapting well — bouncing back stronger: 11
🟨 C. Good thing — nervous system adapting: 21
🟨 D. Doesn’t matter — HRV too noisy: 19
What about other interpretations?
A short-term HRV dip after a single hard session can be normal — it’s the persistent drop + bigger day-to-day swings that flag trouble.
“Adapting well” (A) shows up when HRV rebounds quickly and trends upward week-to-week, not down.
HRV is variable, but consistent downward trends paired with fatigue symptoms are reliable red flags.
Bottom line?
If HRV is low and jumpy during a block (and you feel off), it’s time to adjust: keep the key sessions, but back off intensity or volume elsewhere, double down on sleep and carbs, and watch for HRV to stabilize. 📈
🏃♂️ Stryd Training Tip — Master Your Marathon Pacing with Power
GPS pace lags on hills or in poor signal, and heart rate drifts with heat, stress, or fatigue. Stryd’s running power meter measures your real-time effort in watts — giving you an instant, accurate read on how hard you’re actually working.
Why power works:
Terrain: Power shows the true effort cost of every hill, so you don’t burn out early.
Wind: Headwinds and tailwinds change pace, but power keeps your effort steady.
Surges: React quickly to mid-race moves without spiking your energy cost.
Control: One number that reflects your total effort, helping you pace evenly from start to finish.
Don’t forget: You + Science = AWESOMENESS 😎
Yours in science,
Jonah
P.S. - We have a crew of 17,450+ nerds here who are running FAST using science.
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