** 1. if no systematic symptoms were there it could probably be due to overexertion, vitamin or mineral deficiency and/or dehydration, lack of fluids in system can lead to an electrolyte imbalance which in turn can cause the muscles to spasm or cramp. [check with potassium level]. 2. if rash and warmth are there and there is bruise like feeling, are you on any blood thinner medications, or it can be a blood clot, seek opinion of general/ orthopedic surgeon for Doppler study [if needed] 3. if soreness was sudden at calf region could be calf strain[gastronemius], following a direct impact to the calf resulting in damage to the muscle fibres, connective tissue and small blood vessels resulting in a bruise to the calf [calf contusion], a thorough subjective and objective examination from a physiotherapist is usually sufficient to diagnose a calf contusion who may order further investigations such as an MRI scan or ultrasound to confirm diagnosis. PS Investigations such as X-ray, ultrasound, MRI, CT scan, bone scan or compartment pressure testing are often required to confirm diagnosis and rule out other injuries.