I can’t put it any better myself so read this great article by Rich Willy http://semrc.blogs.latrobe.edu.au/5-myths-strength-training-endurance-running/
1. Resistance training reduces risk of overuse injuries by about 50% (Lauerson, Bertelsen and Anderson 2014)
2. It is a common misconception that resistance training will result in weight gain and reduce running performance – it does not. Total body mass does not increase when resistance training is added to an endurance programme.
3. And actually it improves running economy and increases speed (6 weeks heavy weight training 2xper week, 4 sets of 4 reps 80% 1RM lunges and heel raises improved 5km race time by nearly 4%…those who didn’t weight train didn’t improve – Karston et al 2016)
4. Light circuit type resistance training does not lead to improvements in endurance running, heavy strength training needs to be used, however runners should complete a preparatory phase of 2-4 weeks with 2-4 sets of 15 reps of lighter weight first.
5. The glut muscle are not the holy grail. The calf and thigh muscles are more responsible for supporting our bodies during running. In fact the calf musculature contributes about 50% of torque that supports our body during running (Willy et al 2017). Interestingly our ability to push off with our calf muscles declines about 31% between 20 and 60 years of age (Devita et al 2016). Train those calfs!!
6. Strength training cannot fix running mechanics. Common myth that weak gluts cause the inward collapse of the knee, however there isn’t even any good evidence to suggest that weak glut muscle are even associated with hip adduction (knee coming in) during running (Baggaley et al 2015).
7. Running exercises that are ‘functional’ do not transfer to running (Willy and Davis 2011). Don’t worry about trying to come up with funky exercises that mimic the running pattern, get the core exercise nailed – deadlifts, squats, lunges and calf raises.