For decades, long-distance runners avoided strength training over the fear that it would make a runner bulky, muscle-bound, and slow. Over the past 20 years, coaches and runners have been more open-minded to the inclusion of strength training as a part of a comprehensive marathon training program. However, the focus continued to be on lifting lighter weights for higher repetition ranges. The thought was that doing 15-20 reps with a lighter weight would preferentially improve muscle endurance and aid in creating a toned physique (versus a more muscular physique thought to be caused by heavier weights).
The last 20 years of research have conclusively debunked the notion that the amount of weight and the number of reps performed preferentially improves endurance or strength (or muscle tone or muscle size).
Authors of a brand-new research study published in the Brazilian scientific journal, Revista Brasileira de Medicina do Esporte specifically studied the impacts of heavyweight versus lightweight strength training on marathon running performance. Their conclusion: strength training with light, moderate, or heavy loads can help improve the performance of long-distance runners.
Take home message: Strength training should be included in a comprehensive training program for a 5K, half marathon, or marathon, and the amount of weight and number of reps performed seems to be unimportant. Rather, the runner should focus on performing each exercise to the point of momentary muscle failure (or very near).
Note: Encouragingly, the strength training practices of the most elite distance runners worldwide are starting to reflect this current research. Elite men and women now include lifting heavier weights to the point of muscle failure and attributing their success (and injury prevention) to this type of training.