In relatively untrained endurance athletes almost anything they do as far as strength training and endurance training will improve performance. The problem is what training techniques are best for the more highly trained elite athletes looking to incrementally improve their endurance performance.
Training for endurance sports is much like the power sports except in these cases body weight is important and needs to be the lowest possible with the maximum amount of strength and endurance. As such, training needs to be muscle specific, increasing strenght and invariably some size in the muscles involved in the endurance event, while decreasing weight in areas that are not. So while strength training using squats may be appropriate, exercises that work the upper body such as the bench press and arm exercises may not be. Regardless of the weight training done by endurance athletes, practicing their sport at various intensities is even more important. Endurance athletes should periodize their training with periods where they train at both low and high intensities specific for their event.
There are many training methods advocated to enhance endurance performance but in fact may not. for example, I don't believe that high intensity interval training is of much use for increasing endurance performance over the long term compared to consistent hard training with incremental increases in exercise intensity and duration. I'll be giving my reasons for this in an upcoming article as well as expounding on other training methods used to enhance endurance performance.