It coulde be minor strain to your bicpes. Try cold pack and volini or voveran gel. If it does not subside kindly visit a physiotherapist for ultrasound therapy for healing the strain.

That is perfectly normal as per your given description. no need to worry, You have mentioned about an aggressive workout i.e curl ups straightaway. Which is rightfully a WRONG method. Workout etiquettes should always be followed i.e warm up and cool down along with PROGRESSIVE WORKOUT instead of AGGRESSIVE one likd you mentiond