Swelling or bruising in the calf muscle will be apparent in severe calf muscle tears. What Causes a Calf Muscle Tear? Calf muscle tears usually occur during acceleration or changes in direction eg a change of running speed. However, there is a small percentage of the populations who can tear their calf muscle by simply walking. The most common calf muscle that is torn is your medial gastrocnemius. Shields et al (1985).