Summary

• Muscle injuries occur from either direct or indirect trauma.
• Predisposing factors include type of muscle architecture (i.e., pennate muscle, type II fast twitch muscle fibres, and muscle-tendon units that span 2 joints), previous injury, and inadequate warm-up before exercise.
• Eccentric contraction (i.e., muscle contraction associated with forcible lengthening of the contracting muscle, such as when lowering a weight or pitching a ball) causes more frequent injury.
• History and physical examination are key in diagnosis and grading of the injury as grade 1 (mild), 2 (moderate), or 3 (severe with complete rupture).
• Conservative treatment is all that is required for most patients with grade 1 or 2 injuries.
• Imaging studies are usually not necessary but can be obtained if grade 3 rupture is suspected, or to confirm or determine associated injuries.