The New York Times recently (Nov 7, 2015) tackled the question of whether to use Ice or Heat for sore muscles.
Cold therapy, or cryotherapy, is usually recommended immediately after an acute injury, like a severe bruise or sprain. The familiar RICE protocol (Rest - Ice - Compression - Elevation) helps reduce the pain and inflammation these injuries. However, cold therapy loses efficacy after a couple of days. At this point in recovery, applying heat to the area may provide additional relief and recovery.
Delayed Muscle Onset
In contrast to an injury, the lingering muscle pain that emerges some time after vigorous exercise, both heat and cold have been used with significant success in individual cases, but scientific studies comparing the efficacy of treatments have been sparse and inconclusive.
According to the New York Times, a new comparison, published this year in The Journal of Strength and Conditioning Research, looked at muscle damage and pain in 100 people of comparable fitness. After 15 minutes of leg squats, half of the test subjects received either cold OR heat treatment, while half received no treatment at all. The study concluded that both heat and cold appear to be effective in reducing muscle damage, but cold used immediately after exercise or 24 hours later was superior in reducing pain.
The good news, with FrozenPeaz - you don't have to choose. FrozenPeaz is just as effective for heat therapy as it is for cold therapy.