A day in the garden can be very rewarding but going 'whole hog' to get a bed planted up or to bend over pricking out hundreds of seedlings can casue us to have stiffeness in the low back when we come to stand up.
One-sided activaties such as digging or sweeping leaves can cause us to use our bodies asymetrically and thereby cause us to twist ourselves. Over-use of muscles on one side of the body can lead to a postural imbalance resulting in pain and discomfort.
Lifting of heavy objects such as rocks or garden ornaments should be approached with caution and it is always best to get help.