Strength training and endurance training: two completely different training strategies, resulting in two different training adaptations. Performances in endurance events are often determined by energy costs and the possibility to sustain a certain force over a longer time or distance. In contrast, strength training often aims to increase muscle mass and maximal strength. Nevertheless, there seems to be a common interest between both. Strength training may in fact improve endurance performance and its determinants. A combination between both training schedules, called a concurrent training program, may yield beneficial results!

What are the benefits of concurrent training?

Exercise economy, which is defined as the oxygen uptake during a certain sub-maximal exercise intensity, can be improved with strength training. In other words: you can get more efficient by inserting strength training into your program! After all, you use less oxygen. Though, in this reasoning a difference should be made between heavy and explosive strength training. Running economy might be improved by both. Cycling economy only seems to improve after heavy strength training. The theory behind this difference? Explosive strength training aims to increase energy storage and reuse during movements. While this is effective in running, it’s less useful in cycling.



”You can get more efficient by inserting strength training into your program!”



An endurance performance determinant, related to movement economy, is the lactate threshold. Some studies suggest that the lactate threshold (the point after which lactate levels will increase drastically and cannot be removed at the same rate as its production) will be improved after strength training as well. Other studies suggest that the lactate threshold is unaffected. Nonetheless, no negative outcomes have been reported. Whether strength training is truly beneficial for the lactate threshold, remains to be subject for scientific research.
Of course, not all endurance performance determinants will be influenced by strength training. For instance, maximal oxygen uptake (VO2max), one of the most important determinants of an endurance performance, doesn’t seem to be affected by strength training. So, while you use less oxygen during sub-maximal exercises, your maximal oxygen uptake doesn’t improve.

“VO2max, lactate threshold and economy together comprise over 70% of the between-person variance in endurance performance.”



VO2max, lactate threshold and economy together comprise over 70% of the between-person variance in endurance performance. But maximal velocity and power output at VO2max are important factors as well. These factors are dependent on exercise economy, but also on anaerobic capacity and neuromuscular characteristics (muscle control). Heavy strength training may improve those contributors, and therefore endurance performance.



How can concurrent training improve endurance performance?

One thing we may state for sure: (heavy) strength training and endurance training can be combined to improve endurance performance. But how? One possibility is that the maximum force and the time to exhaustion of the slower (endurance) muscle fibres will be improved. This will postpone the activation of the less efficient fast muscle fibres. Another possibility is that the fast muscle fibres are transformed into a less uneconomical form, which might result in a better endurance performance. Yet another possible mechanism is one of mechanical nature. An increased maximal force and force development, will result in less blood restriction and therefore a better blood flow during sub-maximal exercises. Which mechanism is actually true, is still subject of debate.



Conclusion

What the exact mechanisms are behind a successful concurrent training, is still subject of debate. However, there are certainly positive effects, while there seem to be no negative outcomes at all! Therefore, concurrent training seems to be capable of improving endurance performance by improving economy, delaying fatigue, improving anaerobic capacity and enhancing maximal speed.

Some practical tips:
• To improve running economy, explosive and heavy strength training will suffice.
• To improve cycling economy, only heavy strength training will suffice.
• Always train the muscle groups you will use during the actual performance.
• Strength training movements should be sport-specific.
• Heavy strength training should be optimized by pursuing maximal velocity during the concentric phase of the movements.
• Strength training should be performed 2 times a week for at least 12 weeks.
• Start at a low level, emphasizing the correct technique!

More about concurrent training?
Read our blog, or read our full article about running! (Dutch Only)

Rønnestad BR, Mujika I. Optimizing strength training for running and cycling endurance performance: A review. Scandinavian journal of medicine & science in sports. 2014;24(4):603-12.