Homeopathic arnica is a wonderful treatment for sore muscles with the feeling of being bruised. It's great for sports injuries, to reduce swelling after surgery or dental work and is used by cosmetic surgeons with great success.
Although topical creams and gels may be most well known to the general public, using arnica internally produces spectacular results. It can be purchased (Boiron is one well known manufacturer) in pellets. The pellets can be dissolved under the tongue or, for people who know how to mix them with water it can be ingested that way.
If you know the potency which is correct for yourself, you can put some pellets in a bottle of spring water and sip it before doing things like playing tennis or other sports to stop any strains or sprains before they start.
Homeopathics do not cause side effects of any type.