Heavy legs is one of the most common complaints from new runners. You head out feeling fine, but within five minutes your legs feel like they belong to someone else. Lead-filled, sluggish, slow.

The good news: this is fixable, and it's almost never a fitness problem. Here are the real culprits, and what to do about each.

1. You ran too hard the last time

The most common cause is simple under-recovery. Beginners often run their second session before the legs have recovered from the first. Your muscles need 24 to 48 hours to repair after a new stimulus. If you're running on legs that haven't bounced back, they'll feel heavy.

Fix: leave at least one full rest day between runs in your first month. Three runs a week, not four or five.

2. You're dehydrated without realising

Even mild dehydration makes muscles feel sluggish. Most people running in the morning are starting in a slightly dehydrated state from sleep. By the afternoon, if you've only had coffee, you're worse off.

Fix: aim for a glass of water on waking and another 30 minutes before you run. Pale yellow urine is your benchmark.

3. You ate the wrong thing, or nothing at all

Running on completely empty legs can feel rough, especially if you slept lightly. So can running an hour after a heavy meal. Your body is either short of fuel or busy digesting.

Fix: a small carb-based snack 60 to 90 minutes before, like a banana or a slice of toast with honey. For very early morning runs, a few sips of squash or a date can be enough.

4. You're not warming up

Cold muscles don't move well. If you walk out the door and immediately start running, your first few minutes will always feel grim.

Fix: walk briskly for three to five minutes, add some leg swings, ankle circles and a few easy strides. Then start running. The whole warm-up takes seven minutes and changes how the run feels.

5. Your strength work is missing

This one sneaks up. If you only run, the small stabilising muscles in your hips, glutes and core get neglected, and your legs end up doing all the work. They feel heavy because they are working harder than they should.

Fix: two short strength sessions a week. 20 minutes is enough. Squats, glute bridges, calf raises, single-leg deadlifts and a plank. That's the full menu.

The hidden one: shoes past their date

If your trainers have done 500 to 800km, the foam is dead, even if they look fine. Dead foam means more impact, more fatigue, heavier legs. If your runs have suddenly started to feel hard and nothing else has changed, check the mileage on your shoes.