The following is an exclusive excerpt from the book Developing Speed, part of the NSCA’s Science of Strength and Conditioning Series with Human Kinetics.

Endurance athletes who are stronger can generally perform at a much higher level.

This suggests that training modalities that stimulate increases in muscular strength without compromising endurance capacity may be beneficial for the endurance athlete. Support for this contention can be found in the scientific literature; research shows that the appropriate integration of resistance training into the endurance athlete’s training plan can result in significantly better performance when compared to classic endurance training plans that focus only on aerobic endurance training.

When looking closely at endurance performance, several key factors—including the athlete’s maximal aerobic power (V˙ O2max), lactate threshold, and movement efficiency—contribute to performance (see figure 7.1). The training modality selected influences these factors by inducing changes to the athlete’s aerobic power and capacity, anaerobic capabilities, and neuromuscular function.

Aerobic training exerts a strong influence on both aerobic power and capacity, but it does not exert a great impact on the athlete’s anaerobic or neuromuscular abilities.

Conversely, resistance training exerts a strong influence on the athlete’s neuromuscular function and a moderate influence on anaerobic power and capacity, while offering only a minimal influence on aerobic power and capacity. By influencing the athlete’s anaerobic abilities as well as neuromuscular function, resistance training can elevate the athlete’s lactate threshold, movement efficiency, and ability to engage in high-intensity activities.

The ability of resistance training to improve endurance performance is likely related to several key factors, including the specific physiological and mechanical adaptations that are stimulated by the resistance training regimen. The integration of resistance training into the overall training plan appears to be central to creating these specific performance-enhancing adaptations.

Traditionally, endurance athletes and coaches have believed that resistance training either does not affect or negatively affects endurance performance. However, this view may be partially explained by a design flaw in many of the training programs that include both resistance and endurance training. The flaw is that resistance training is simply added to the endurance training plan. Athletes who undertake this approach often experience excessively high levels of fatigue that can negatively affect overall performance.

If athletes reduce their endurance training load to account for the addition of resistance training, then resistance training has a positive effect on the athletes’ endurance performance. The athlete who performs both resistance and endurance training in an integrated and appropriately planned fashion will perform at a higher level than the athlete who performs only classic endurance training.