Submuscular breast implants are the best location for long term results.
After you have healed from your surgery (4-6 weeks), I have my patients begin their normal exercise routine as well as massage and pectoralis muscle contraction to help keep the implants soft and avoid capsules.
Of course, you must ask your surgeon for advice and if he/she agrees with this course of action.
If you are unhappy with the appearance of your breasts during active contraction of your pectoralis muscle, then perhaps you might consider changing the implant to a submammary location.
However, if you are happy with the appearance during muscle contraction, long term, I believe your results will be better if the implant is under the muscle.
If when you contract your pectoralis muscle, the implant is pushed out from beneath the pectoralis muscle and creates a funny bulge under the skin, below the muscle, then repeated vigorous pectoralis muscle exercise may cause the implant to bottom out.
Discuss this with your plastic surgeon.
See before and after photos of breast augmentation.