My son is a big runner and has run in several marathons. He has spent many weekends going to different cities to run in their races.
He learned the hard way how important it is to stretch before doing any running at all. In one of his first races, he was not warmed up enough and ended up with a soleus muscle strain.
He finished the race, but was sore for quite awhile after that race. Now he always makes sure his soleus muscles and legs are fully warmed up by doing stretches even before he takes off for a run in the morning.