Fit, But Still Falling

A few years ago, a friend of mine, mid-50s, active, walked most days, stepped off a curb wrong. Nothing dramatic. Just a slightly uneven step. But her body couldn't catch itself fast enough, and she went down. Broke her wrist.

She wasn't unfit. She wasn't inactive. So what happened?

That split second where your body either catches you or it doesn't comes down to one specific type of muscle fibre. And it happens to be the one we lose first as we age.

What even are muscle fibres?

Your muscles aren't one uniform tissue. They're made up of different fibre types, each built for a different job.

Slow-twitch fibres (Type 1) are your endurance workers. They're packed with mitochondria, run on oxygen, and can go for hours without tiring. They're what keep you standing at the kitchen bench, walking the dog, holding good posture through a long day. Gentle, steady movement, walking, swimming, easy yoga, keeps these fibres ticking along nicely well into old age.

Fast-twitch fibres (Type 2) are built for something else entirely: speed and power. They fire hard and fast, but tire quickly.

There are actually two sub-types here. Type 2a fibres are a bit of a hybrid, fast but with some endurance. Type 2x fibres are pure power, the ones that fire when you need to react instantly, catch yourself from a stumble, or push hard to stand up quickly.

Here's something most people don't know. Your body recruits these fibres in a set order. Slow-twitch first, for everyday gentle movement. Fast-twitch only gets called in when the demand is sudden or heavy. Which means if your exercise never asks for speed or power, your fast-twitch fibres barely get used at all.

Why do we lose fast-twitch fibres first?

Starting in our 30s, we begin losing muscle mass generally. But it isn't even. Fast-twitch fibres shrink and disappear faster than slow-twitch ones, and the pace picks up noticeably after 50.

By our 70s, some people have lost a significant share of their fast-twitch capacity, while their slow-twitch fibres are still relatively intact.

This is why someone can walk for miles and still lose their balance stepping off a curb. Walking trains slow-twitch. It does very little for the fibres that catch you when things go wrong.

What does this have to do with osteoporosis?

More than you'd think.

Bone doesn't stay strong on its own. It needs load, specifically the kind of strong, forceful pull that comes from powerful muscle contraction. That pull is one of the main signals telling your body "keep building bone here."

Fast-twitch fibres are the ones capable of generating that kind of force. So when they fade, the signal to maintain bone density fades with them. Weaker fast-twitch muscle and thinning bone tend to arrive together, quietly, over the same years. Right when a fall matters most.

Muscle is the organ of longevity

There's a bigger picture here too. We tend to think of muscle as something cosmetic, something for the mirror, not the doctor's chart. But researchers who study ageing have started calling muscle an organ in its own right, one that actively shapes how long and how well we live.

Muscle doesn't just move you. It regulates blood sugar, influences hormone levels, and is one of the strongest predictors of independence in later life.

Low muscle mass in older adults is linked to higher risk of hospitalisation, slower recovery from illness, and loss of independence. Grip strength alone, believe it or not, is used in research as a marker of how long someone is likely to live.

So the fall, the balance, the osteoporosis risk, they're all part of one story. Fast-twitch fibres aren't just protecting you from a stumble. They're part of the organ that keeps the rest of you working.

Are you training the right fibre?

Which brings up the real question, the one worth sitting with.

Most people over 40 who exercise regularly are, without realising it, only training Type 1. Walking. Swimming. Steady-state cardio or lifting too light. All genuinely good for the heart. None of it asks the fast-twitch fibres to do their job.

So the question isn't "are you active?" It's "are you training for how you feel now, or for who you want to still be at 75?" Independent. Steady on your feet. Able to get up off the floor without a second thought.

So what actually helps?

Here's the good news. Fast-twitch fibres respond to one thing: force, delivered with intent. Not more time exercising, but a different quality of movement within the time you already have.

The right kind of strength and power training, done safely and progressively, is one of the few things proven to bring these fibres back into play. It's not about lifting the heaviest thing in the room. It's about training with enough resistance, and enough intent behind the movement, that your body has no choice but to recruit those fast-twitch fibres again.

That might look like a fast, controlled sit-to-stand. A heavy carry. A push or lift done with purpose rather than on autopilot, and progressed over time as you get stronger. It doesn't need to be extreme, and it definitely doesn't need to be a boot camp. It needs to be specific, and it needs to load the muscle with real resistance, not just repetition.

Muscle isn't just about how you look. It's an organ that's working for you every day, and for a lot of us, it's quietly the thing standing between an ordinary stumble and a hospital visit. Worth training like it matters.

If this got you thinking, about your own training, or about someone you know who's had a fall or a bone health scare, I'm always happy to have a chat. No pressure either way.

Shikha Founder & Head Coach, LifeForce Strength & Conditioning, Newlands, Wellington