Strength and the training of strength is still a bit of a misnomer in endurance sports. It is relevant to swiming, cycling and running? Why? Strength training build postural balance and also aims to build efficent movement in the body. 
There are different facets of strength. Strength endurance is the one most commonly associated with endurance sports however it is greatly misunderstood. Doing 50 squats and 100 lunges is not really relevant in theis case. The need to feel the burn seems to be a pre-requisite for most endurance trainers however this is not an efficent way of training and may be harming your progress.
Strength endurance is the ability to hold and move to correct body position. A lot of your postural muscles need strength endurance to continue to hold correct position allowing your other larger muscles to generate force. A lot of endurance athletes will fundamentally have great endurance capabilities in their major muscle groups- however posturally they wil not necessarily have strength in the right areas. What is the product of this? Poor posture equals poor form and limits good technique. Maximal Strength is the ability of the muscles to move a maximal weight. Commonly this area of training is not utilised because of the perception that it is not relative to the sport trained for. However you could not be more wrong. Maximal strength trains the nervous system and the bodys ability to recruit as much muscle mass as possible. While not feeling the burn of a hill climb training in this way reminds the body where it’s leverages need to be. Weight training in itself is often corrective in nature- the goal is to build muscular balance facilitating better technique. Individual’s can have great strength endurance but poor maximal strength. As strength endurance is often a product of maximal strength then developing strength levels should be a primary method of training.
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