Every now and then a runner asks me if he or she should do P90X or CrossFit. If you've been living under a rock, both P90X and CrossFit are very intense and challenging fitness programs that emphasize strength building.
http://running.competitor.com/2013/10/training/how-hard-should-strength-training-be-for-runners_54746
http://running.competitor.com/2013/10/training/how-hard-should-strength-training-be-for-runners_54746
