Thanks to Andrew Fox from Aim Workout for this post about strength training:
Most runners tend to ditch their weight training sessions and opt for running an extra mile. There is no doubt that running an extra mile can increase your endurance but it can also lead to injury. Running puts a huge strain on the body. If the working muscles are not strong enough to bear the load then the bones or connective tissues absorb the stresses. Over time, the body becomes more susceptible to injuries. Therefore, it is important to maintain a strength training program.
A well designed strength training program is essential in order to improve the efficiency of running as well as your finishing times during competition. During long distance running, muscle gets broken down which can result in a loss of strength which in turn can slow down your pace. However, with a proper strength training program, the muscle breakdown can be facilitated and the strength can be sustained without any significant loss. 
Helps to Maintain Weight
With strength training, you can gain more lean muscle mass which in turn helps to increase metabolism. A high metabolic rate means that you can burn more calories during a workout or even at rest. The majority of runners who add strength training to their training sessions find that it makes losing weight easier and that they are better able to maintain a healthy weight even in the off season. This is because muscle burns more calories than fat, so it helps to add some lean muscle to your body.
Decreases the Risk of Injuries
It is important to keep the lower body strong in order to lower the risk of injury. Running may lead to knee, back or hip injuries that could result from a poor balance of muscles. Strength training is important to build strong leg and core muscles. This will help to maintain proper running form for longer periods of time and make the body less prone to common running injuries, including runner’s knee, achilles tendonitis, hamstring issues as well as other related injuries.
It’ll Make You a more Competent Runner
Most runners experience fatigue sooner or later. How well you perform and how quickly you finish are a function of your endurance and strength. Strength training help runners to build strong core muscles that helps to improve their performance in competitions. Strength training is also important to those who run long distance races or marathons since it helps to increase endurance levels. 
By improving running form and endurance, strength training also contributes to faster running times. It is a great way to improve the running speed. Most athletes and runners have seen improvement in their speed after they started doing some strength training. There is no need to spend hours in the gym in doing strength training, 30-40 minute session of strength training 2-3 times a week are enough to build lean muscle.
Improved Body Composition
With strength training, you can improve the composition of your body. Having an excess of fat in the body can be a hurdle. To improve your running for longer time periods, it is essential to eliminate excess body fat . This will improve your speed by keeping all factors equal. With strength training, you can increase the level of metabolism in your body thus your body will burn more fat and store less fat. You will become a stronger runner with solid lean muscles.
Strength training is a great way to maintain weight, strengthen muscles and bone health. It not only make you fitter but also improves heart rate. A better heart rate means you greater endurance and a better overall performer. To improve your strength includes Goblet squat, push up, dumbbell row, etc in your workout routine and see their positive effects on your running.
Author Bio: Andrew is the founder and CEO at Aim Workout. He is passionate fitness professional and triathlete, with years of experience teaching spin bike workout routines. He has also been an avid mountain biker, deep sea diver, rock climbing guide and has spent considerable time learning and practising mixed martial arts. In short, Andrew has a penchant for the wild and extreme.