Movements are typically atomic, with no distinct parts. To recognize movements one only needs a description of the appearance of the motion. Time can typically be handled by only linear scaling. Sitting down or swinging a bat are good examples.
Activity is a sequence of either movements or of static configurations.
Time is manipulated by some form of dynamic warping. The gesture literature exploiting HMMs is a good example. Still only the object or objects in motion needs to be considered, not the surrounding context. Action are the high-level entities that people typically use to describe what is happening. Representing and recognizing actions requires qualitative descriptions of time, such as intervals.