When you’re doing a run training program and have several runs per week, some of which will be long and take hours out of your day, you will have less time to dedicate to strengthening. However, you need to be strong to be able to withstand the increasing demand of upping your mileage. Using your time wisely and getting into a strengthening program before you need to start thinking about how you are going to get the miles in is your safest bet.
The repetitive load of running and the increasing demand on your musculoskeletal system requires you to be nice and strong. It is not enough to think you can rely on gradually getting stronger as your miles rack up. A marathon program will push anyone to their limits and should be respected. It is specifically designed to challenge your stamina and endurance, because that is what most people will need to work on to get round. However it is not designed to build strength or power.
These are different, and require different types of training. Not many peoples’ bodies, or diaries, will be able to tolerate the demand of introducing both at the same time. That would be a prime recipe for injury. As is not doing strength training at all. The stronger the muscles are the better they are able to withstand the forces the body is put under when running. Sub optimal strength of the muscles will lead to excess stress on the joints and other soft tissues. These other tissues do not tolerate new stresses well and can quickly become painful when overloaded. They are also slower to recover and regenerate and can cause a considerable set back to your training if injured.
Getting a decent strength training program underway now will help to ensure you are up to the task of getting through your marathon training program. It gives the body a gradual ramp up of loading and a chance to get used to being under more physical stress. If you are a seasoned marathon runner who knows they have the miles in them then strength training will likely be the thing between you and a new PB for next season.