It generally occurs after any exertion or after any kind of repeated movements 8f done for a long time. As the arms are not used to these kind of movements, so lead to fatigue and muscle soreness and therefore spasm.
Next Steps
Consult a physiotherapist.. Ultrasonic therapy +TENS +heat therapy will be helpful and will be ok within 3-4 days.
Health Tips
At home rest to the arm+ avoid exertion+hot water fomentation +pain killer gel is enough.