In each case above, the number of repetitions and the distance of each repetition are reduced, but the pace is the same. After one to two weeks, you can gradually increase the distance and the number of reps.
The goal of any mini-workout is to mimic the longer version of the workout. As you get in better shape (which will happen quickly), the workouts will start to get longer to more closely mimic the demands of your goal race.
This strategy can be used for beginner runners, or those coming back to training after an injury or a long layoff. It's best to err on the side of caution and do a little bit less than what you think is possible to prevent an overuse injury.
More: Prevent Running Overuse Injuries in 6 Steps
Start with one workout per week. Once that's comfortable for you, instead of adding another workout, add a mini-workout. It's a better strategy for the injury-prone or beginner runner who shouldn't run too much, too fast, too soon.
Before you know it, you'll be racing faster than you ever thought possible.
More: 9 Race-Day Tips for First Timers
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