posterior chain spasm/dynamic flexibility

mon the day after my day off is when i do speed & weights.

I do a dynamic flexibility routine consisting of 5 moves. After this routine I do a hip bridge/1 legged to fire up the posterior chain b4 doing my sprint warmups. while lying there whith my legs bent an feet close to my but (beg position of a hip bridge) my hams were in slight spasm. When i did the bridge there were no cramps. when i ran there were no pulls. whats with the spasming??? too high of muscle tonus? i wasnt recovered? a sign of the muscles not ready to be hit again?