Proteases accelerate recovery from muscle soreness

Delayed onset muscle soreness is caused by injury to the muscle cells. It is typically more painful one to two days after exercise due to secondary inflammation that is part of the healing process. Healing involves a release of chemicals called proteases that break down injured tissue so that it can be repaired.
Darryn Willoughby and colleagues from Baylor University showed that supplementation with proteases (fungal proteases, bromelain and papain) for 21 days resulted in greater force production during the days following intense eccentric training (45 minutes of downhill running on a treadmill). Scientists use eccentric exercise (lengthening muscle contractions) to induce muscle soreness because it involves greater force production and more cell damage than concentric (shortening) or static (isometric) muscle contractions. Protease supplements reduced muscle strength loss after eccentric exercise by promoting leukocyte activity (white blood cells involved in the healing process) and reducing inflammation.
Some inflammation after exercise is necessary for muscle hypertrophy and tissue repair, but excessive inflammation causes pain and reduces performance.
(Medicine Scence Sports Exercise, 41: 1908-1914, 2009)