Any acute injury that has swelling involved should be iced and elevated if possible for 48-72 hours. If it's a joint or sprain ice alone is fine. If the acute injury is being rested and stable ice will provide no improvement in pain or function past 48hrs. If you keep reaggravting the same injury then re icing can be beneficial.

Muscles in general need more heat to heal. Less fluid tends to pile up around a muscle like it does in joint spaces. Usually swelling around a muscle is a hematoma. Heat will improve circulation (increased blood flow heals) and also speed up the reabsorption of the hematoma. It can still be helpful to ice the muscle initially but usually 1-2 days of ice is sufficient for strains.

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