Take time to care for it! Muscles, especially, need extra attention to keep working properly.
Tense muscles are more prone to injury than those that are relaxed. Muscles, like many other parts of ourselves, need opposites. Action and relaxation. Movement and rest. If you give them one, they're more likely to give you the other. Try this:
Turn your head gently from side to side for a while, maybe 10 or 20 seconds, no pushing past comfort, even if you can only turn it a few inches. Stop, go limp for a slow count of ten. Turn your head again. And then again. Your head will naturally turn a bit farther, the muscles less tight. Even the muscles of your upper back will loosen.
This is a bit easier if you're lying down, but works even standing up.
Now try this with other muscles, moving them without effort, then stopping for a while. Then try a bit of fun. Dancing, making rude gestures, marching or doing a strip tease. Anything your body would have fun doing. Then relax completely. Repeat.
What does this have to do with gardening? Your body is your most essential piece of equipment. And the only reason I'm still gardening four or five hours a day when I'm close to seventy is this simple and useful way of keeping my body in good working order.