I have quite a bit of experience with warming up techniques to prevent aching muscles after digging. I hope you find this helpful.
Firstly, go for a walk. Start off slowly and gradually build up speed to a brisk pace and then slow down. This should last for about ten minutes.
Step 1....Now you might want to do the next step out of sight of anyone.
With your feet slightly apart and your arms to your side extend and raise your hands to shoulder height, forming a "T". Slowly rotate your hands in small circles, working up your arms to your shoulders, creating a "windmill" look. (Dont force anything)
Whilst doing this gently roll your head in a circle.You should do this for a couple of minutes.
Step 2... Lean against something sturdy and stand on one foot. Slowly form little circles with your foot gradually becoming bigger, repeat with the other foot. (again dont force anything). Do this for a couple of minutes also.
Step 3...With your feet together and your arms by your side, lean over to your left and bend until you have gone as far as you can. Hold this for 10 seconds. (dont bounce, just push it as far as you can). Repeat to the right. Do this 10 times on each side.
Step 4... With your arms straight up above your head, lean forward at the waist and stretch as far as you can, hold this for 10 seconds (DONT BOUNCE) just push it as far as you can. Straighten up and repeat 10 times.
You are now warmed up and your muscles have been "stretched out".
Digging....Remember... KINETICS...Let your body weight do the work.
Place your fork in the ground and jump up on it using your body weight to push it down. Lean back until the soil lifts. Then bending at the knees and keeping your back as straight as possible lift the soil. Turn it over using your shoulders, NOT YOUR WRISTS OR YOUR BACK.
When you have finished repeat steps 4 - 1, in that order.
Then home for a cool, and I repeat cool, bath. This will disperse the lactic acid in your muscles.
Remember DONT FORCE ANYTHING. Gardening should be enjoyable not painful.
HTH
Johnny