I have stomach pains when i excersise?

i do regular excersise including walking, weights, football and kickboxing but since i last went kickboxing on thursay i keep getting stomach pains when doing excersise. we did a thing called toning at kickboxing where you tense your stomach and get someone else to punch you in the stomach for 30 seconds. could the pains i am getting be related to having done toning.