Strength endurance training always includes a drop off in performance. This is important for you as the coach. When defining a set of interval runs you can get a feeling about the players by measuring this drop off. On the Interval page you see how I combine ball and support running skill drills from Pierre Villepreux with the interval requirements as defined by David McLean. This is the ability to overcome a resistance or hold against a force.
Strength can be very static, like scrumming, or very dynamic like breaking out of a tackle.
Therefore strength training can take various forms. This is why I have made plyometrics an integral part of training programs. Plyometrics is based on the principle that a contracted muscle can deal with more weight. It also uses the body as the weight in the exercises. Read more under Power for strength training programs and plyometrics.