Always tired? Willpower isn't the problem.

The alarm goes off and you're already tired. By 3pm you've hit a wall and you're reading the same email for the third time. In the evening you collapse on the sofa, drained, yet in bed your mind won't switch off. And on paper, you should be fine.

So you tell yourself it's your age, or that you need more willpower. In more than twenty-five years of doing this work, I've found it's hardly ever either. You've got the strength. What's working against you is your day.

Tiredness is a signal

Rather than simply going flat like a battery, your body keeps to a timetable set by an internal clock: in the morning it pushes up cortisol, the hormone that gets you going, and in the evening it releases melatonin, which eases you towards sleep.

That clock sets itself by simple signals: light, mealtimes, movement, darkness. When they arrive muddled, with screens on until midnight and lunch at a different time every day, it falls out of step. You end up flat when you should be sharp, and wide awake when you should be asleep. That's why I say you're not tired. You're misaligned.

Your night starts in the morning

Light is the strongest signal your clock responds to. Sunlight first thing tells it the day has begun, gives you a lift and prepares the melatonin you'll need at night. In the evening, the reverse happens: screens and bright lights mimic dawn and push sleep back, even when you're shattered.

The 3pm slump isn't down to age

Some drowsiness after lunch is normal while you digest. The crash that sends you off for a third coffee, though, often starts on your plate. Pasta, bread and pudding send your blood sugar up fast, and the insulin that brings it back down overshoots. Within an hour and a half you're sleepy and reaching for something sweet. And round you go again.

Eat your usual lunch, just in a different order: vegetables and protein first, carbs last, so they reach your bloodstream more slowly. Then, if you can, walk for ten minutes. Working muscles use up the sugar that's just arrived.

You sleep, but you don't recharge

Plenty of people get their hours and still wake up wrecked. How you get to sleep matters more than how long you sleep. Get up at the same time at weekends too. Sleep doesn't work like a bank account: a Sunday lie-in shifts your body clock without paying off the debt. Keep your bedroom dark and cool, around 18°C.

Then there's coffee. All it does is switch off the fuel warning light for a few hours. And it lingers so long that an afternoon cup steals your deep sleep, the kind that repairs you.

And the mind that won't switch off? If stress keeps your cortisol high into the evening, your body stays on alert even in bed. Telling you to relax won't help. Breathe differently instead: when your out-breath is longer than your in-breath, your nervous system puts the brakes on.

Energy comes from moving

When you're tired, you wait until you've got the energy to move. Your body works the other way round: after every workout your brain gets a chemical boost that wakes you up and lifts your mood. And sitting all day takes its toll, even if you go to the gym. Get up every hour, and take calls standing.

Where do you start? With just one of these. Stick with it until it feels normal, then add the next. Clear signals, every day. That's how your clock gets back in step, and your energy with it.