Strength training is now becoming widely accepted as a way to improve sports performance in sports that require high levels of speed and power but is still only just making its way into endurance sports.
Many people have studied the effects of concurrent strength training and endurance training programs and the results are quite beneficial in terms of endurance. Basically strength training can help improve endurance by preventing injuries, reducing the amount of time the athlete spends on the ground during running (ground contact time), and increasing the lactate threshold. Increasing the lactate threshold is of importance in my opinion as I find too many people are overly concerned with Vo2 max when it comes to endurance. Having a superior Vo2 max doesn’t mean that athlete will win come competition. If you have a high lactate threshold you can still outperform someone with a better Vo2 max than you. Obviously there are many other factors that come in to play such as mental toughness and will power etc.
Strength training can also help endurance athletes during certain parts of their race whether it’s at the start to get into a good position, during the race to “kick” away from the pack, or for a sprint finish.
Endurance training on the other hand does have a negative effect on strength and it seems to affect power output even more. High-intensity endurance training can also reduce short term anaerobic performance. Now this doesn’t mean you won’t make any gains if you perform endurance work and strength training simultaneously it just means that you may not get the same increases in strength as you would if you trained primarily for strength. In one study a difference of 15% was seen, so you have to prioritize the amount of time you spend on each component of training depending on the demands of your sport.