When you start out on a running schedule you will see your fitness will improve week after week. You will improve just because of the consistency of training. For example Forerunners primary schedule has you run 3 to 4 times per week. Eventually you will reach a fitness plateau where your rate of improvement has leveled off. You can increase your paces across the board and you will continue to improve. If you want to improve more, then you can work on improving your aerobic fitness.
Adding more miles
The most common and simple way to improve your fitness is to increase weekly mileage at an easy pace. A basic schedule will have you run 5 to 7 times per week, and the additional miles are run at an easy pace (which is usually marathon race pace plus 20 seconds to 60 seconds per km.) There will be improvement and the temptation is to continue to increase weekly mileage. The downside is that there is a far greater risk of injury and burnout with increased mileage. You only have so much time and energy. Is there a more efficient way to get fitter and faster?
Another way is to spend more percentage of your running time at the aerobic threshold. Running at, or, just below the aerobic threshold is more effective at improving aerobic fitness than running high mileage at a slow pace. Coincidentally the aerobic threshold is very near your marathon race pace.
Aerobic Threshold Repeats
You have the option of running at marathon pace during your weekly long runs. Most of our long runs are at an easy pace but we frequently add in 2km to 3km repeats at marathon pace. Why repeats of 2km to 3km? Because repeats of 10 to 15 minutes are the most efficient way of improving aerobic fitness over several months. My clinic schedule usually has 3x2km pace pick-ups at marathon pace which is a total of 6km at marathon pace. If you are looking to improve you can add additional pace pick-ups to your long run up to a maximum of 15km (such as 6x2km or 5x3km.) You should take a 3 to 6 minute easy pace break between each repeat. The key to success of this approach is not to run faster than marathon pace during the pace pick-ups and you will see your fitness improve week after week.
Continuous Aerobic Threshold Runs
Some runners opt for long continuous runs at aerobic threshold (12km to 15km at marathon pace). Weekly long continuous runs at marathon pace are not as effective as repeats: a) lower quality- it is not as easy to maintain the goal marathon pace for 12km to 15km; and, b) greater fatigue – continuous runs can lead to muscle fatigue and long term race performance deterioration. It takes more effort to run continuously at marathon pace for an hour or longer and can add to excess fatigue. Repeats of 2km to 3km allow for improvement without the fatigue.
Simply, Aerobic Threshold repeats of 10min to 15min during long runs lead to faster marathon and half marathon race times.