Acute muscle injury occurs when a muscle is torn or overstretched. It can occur as a result of overuse, fatigue or improper use of muscles. Strenuous activities that can increase the risk of a muscle injury include sports like tennis, soccer, rugby, rowing or baseball. Holding the neck in awkward position for long a time, heavy lifting, and poor posture can also cause a macro-trauma to your muscles. Acute muscle injury can also happen when performing irregular work tasks.