Hi everyone, and welcome to week six. When people hear seven marathons in seven days, they assume we're running. We're not. We're walking, and that's a deliberate decision built on what low-intensity work actually does to your physiology. This week I explain what happens inside your muscles when you go easy for a long time, why it's healing both of us rather than wearing us down, and why the most useful thing you do today might be the least impressive.
Watch time = 5 minutes. This week's prompt is below the video.
These videos were filmed over the summer, so the countdowns you hear won't match today's date.
Why We're Walking
When people hear that Ingrid and I are doing seven marathons on seven continents in a week, they assume we're running. We're not. We're walking the whole thing.
Part of it is impact. Walking loads your body far more gently than running, which matters when you're covering 295 kilometres in seven days on two bodies with injury histories. But the bigger reason is what low-intensity work does to your physiology, which is far greater than what most people assume.
Here's what happens when you go easy for a long time. Your muscles sense the sustained energy demand and activate an enzyme called AMP kinase, which is essentially your cell's fuel gauge. AMPK switches on a signalling protein called PGC-1α, and PGC-1α is the master regulator of mitochondrial biogenesis. So your cells build more mitochondria, which are where you turn the food you eat into usable energy. At the same time you grow new capillaries through the muscle, which means you deliver more oxygen and clear more waste at every level of effort.
The part worth understanding is that this response is driven by accumulated time under load, not by how hard it feels. A long easy walk and a hard interval session both reach the same signalling machinery by different routes. Walking works because you can do a great deal of it, day after day, without needing to recover from it (or get injured again!). Easy is repeatable, and consistency is what builds capacity.
Exercise also raises BDNF, brain-derived neurotrophic factor. BDNF supports the survival of your existing neurons and it drives synaptic plasticity, meaning the strengthening and growth of connections between the neurons you already have. That's the mechanism most closely tied to learning and to mood. You'll often hear that exercise grows new brain cells. Whether adult humans generate meaningful numbers of new neurons at all is disputed, with major papers landing on both sides since 2018, and the conservative reading is that if it happens it's modest. The plasticity effect is, however, well established.
When we started this, I had plantar fasciitis from too many hours in dress shoes, and Ingrid's ankle was still sore after two years of failed comebacks. All this walking has been repairing us. My feet work better. My hips have opened up, which has taken the load off my lower back. I broke my neck as a kid, and learning to carry my head properly over my shoulders across long distances has strengthened it and settled my traps.
Consistent, gentle, repeated loading changes what your tissues can tolerate and gradually changes how you move.
Most of you are watching this sitting down. Tight hips, sore lower back, whatever your desk has done to you. Breaking up long periods of sitting with brief bouts of light movement measurably improves how your body handles glucose and insulin after meals, which is a real effect from a few minutes at a time.
You don't need to run. You don't need to sweat. You don't need a gym.
Your 1% this week: go for a walk today, and leave the phone behind. No music, no podcast, no photographs, no checking anything. Make it an if-then so it actually happens: when I finish lunch, I walk for fifteen minutes. The walk does the physiology. Leaving the phone does something else, and you'll notice it by the end of the first one.
