Dashing around makes your muscles tense. If you are in a hurry, try to move smoothly and build up to full speed, remembering to breathe at the same time!
At the yard, start off with tasks that are easier on your back such as feeding horses, and leading them to the field.Then you can proceed with the heavier work such as mucking out and carrying water buckets about. As you work be aware of your breathing and the way you move around- for example do you stoop forwards when you walk or carry things more in one hand than the other? Grooming your horse can be a good workout in itself. Applying pressure as you brush him is good for toning your arms, bending down to pick his feet out and to brush his legs is good for your leg and back strength. Relax and breather as you groom- you will enjoy the experience as much as your horse!