Sisu Endurance Lab

Endurance performance is often talked about as one thing, aerobic fitness, but underneath that phrase are two distinct physiological systems doing very different jobs: capillaries, which deliver oxygen to muscle, and mitochondria, which use it. They adapt to training differently, on different timelines, and in response to different stimuli. Understanding the difference changes how you think about training design. Two Separate Systems, One Shared Goal Capillaries are the deliv

A dive into the biology of stress, hormones, and why more is not better. There's a stubborn myth in endurance training: that the workout is where fitness is built. It isn't. The workout is where fitness is broken down. Adaptation, the actual improvement in your aerobic capacity, muscle strength, and metabolic efficiency, happens afterward, when you're not training at all. Training load is the stimulus. Recovery is the response. Confuse the two, and you end up chasing fatigue

Endurance isn't just about distance, speed, or personal records. It's about how we navigate effort, discomfort, and time, the same things we face in life. Every long run, every grueling ride, every race isn't just a test of fitness. It's a mirror. It shows us how we handle struggle, patience, and the small, repetitive steps that add up to progress. The Mile You Don't Want to Run There's always a moment, mile 14, hour three, the last set when your legs are begging you to stop,

The fittest person on the start line doesn't automatically win. The person who can sit in severe discomfort the longest does. Here's why that's a trainable skill, and how to develop it. Your body lies to you. Constantly. At some point in every hard race, your body sends a very clear message: slow down. It feels urgent. It feels like a warning. And for most athletes, that message ends the race, not a collapse, not a bonk, just a negotiation they lose. The problem is that your

Molveno World Championships. Lessons learned. The 2022 World Championship race in Molveno, Italy, was one of those experiences that stays with you, not because everything went perfectly, but because of what it taught me about preparation, balance, and the fine line between peak fitness and burnout. Looking back, there were a lot of things that went right in the months leading up to the race. The biggest one was consistency. Day after day, week after week, the work just got do

The Weight of Being Weightless: Why Endurance Athletes Get Obsessed, and Why It Never Pays Off There’s a strange seduction that floats around endurance sports, a whispered promise that just a little lighter will make you faster, smoother, more efficient, and perhaps spiritually enlightened (?) in the process. Most of us who’ve spent years in triathlon, distance running, or cycling have brushed up against it. I had a chapter of my life, stretching across a few years, where the

At some point, every serious athlete crosses a line: the moment when the sport stops being something you do and quietly becomes who you are. You stop saying I run and start saying I’m a runner. It’s a subtle shift, but it changes everything. That identity can be powerful fuel. It keeps you accountable when motivation fades, and it provides a sense of belonging in a world that doesn’t always understand why you’re up at 5:00 a.m. chasing watts or pace or heart rate zones. But w

ELITE WINTER BASE WEEK (81 MILES) This is my personal week of running from the winter of 2022-2023, not including my swim (20km) and bike (7 hours) training. For those interested. MON – AM: 8 miles easy / PM: 4 miles easy Mobility + band activation (5–8 min) TUE – 10 miles easy + 6 x 10-sec hill sprints Strength Session (30 min): split squats, single-leg RDLs, calf raises WED – 12 miles aerobic + light mobility/band work THU – Light Tempo Session (11 miles total)

Runners love to talk about strength. Quads of steel, core stability, glute activation, the language of performance often sounds like a weight room. But the best runners in the world aren’t just strong. They’re elastic. Running isn’t a display of muscular force, it’s a symphony of stored energy. Every stride is a cycle of tension and release, a conversation between gravity and the body’s connective web. When your foot hits the ground, your tendons, fascia, and ligaments stretc

If you talk to world-class endurance athletes, especially those coming out of Scandinavia or the Alps, you’ll notice a pattern: a lot of them Nordic ski. Not casually. They grew up logging serious hours on skis before ever specializing in running, cycling, or triathlon. That’s not a coincidence. Even American elites like Ben True, a 13:02 5K guy and one of the most aerobically durable runners in U.S. history, spent his winters Nordic skiing. He was a national-level skier befo