Should I apply heat or ice to an injury? 

Q31:

After an injury you should always follow the RICER and No HARM principle for a minimum of 48 hours or as long as inflammation is present (redness, warmth, pain hypersensitivity, bruising and swelling). That is R - rest, I - Ice, C - Compression, E - Elevation, R - Referral to a physiotherapist or other healthcare provider. Always avoid H- Heat, A - Alcohol, R - Running/Exercise to the area, M - Massage. Following these simple rules will prevent secondary damage to the injured tissues and will reduce healing times. Icing should be done for 20 minutes every 2 hours and can be applied as a bag of ice or frozen peas, frozen gel packs, breakable icepacks (chemical kind) or ice-water emersion. Always wrap ice in a towel and check skin regularly. Application of ice directly to your skin can result in an ice burn which will look like white blotches that turn red and may blister.

For non-acute and chronic conditions such as muscle pain and tightness, or joint stiffness heat can be applied. Heat helps to relax muscle and joint tissues by increasing blood flow to the area and improving extensibility of tissues. Heat can be applied for as long as needed and in the form of wheat bags, warm baths/whirlpools, heat packs/stick on pads, or electric heating pads. Never apply heat to areas where your sensation or circulation is compromised. 

If swelling is a problem you can combine heat and ice after 48 hours post injury. By alternating the two temperature you encourage blood vessels to dilate and constrict. This combined with elevation of the swollen part will encourage fluid movement out of the damaged tissues and will in turn improve pain and movement of the affected area. Alternate hot and cold by applying each modality for 5-10 minutes for a total of 30-40 minutes