Physical activities can be classified into dynamic, static and postural transition. Activities that are characterized by large movements such as walking and running are classified as dynamic activity, while static activity is defined by activities that involve small movement such as sitting, lying down and standing. Postural transitions is the movements that change from one body posture to another body posture such as stand-to-sit and sit-to-stand. A few studies define classes such as small movement and unknown activity. They are defined as some random movements that do not fall under dynamic, static and postural transition [1-2].
 N. A. Capela, E. D. Lemaire, and N. Baddour, “Feature Selection for Wearable Smartphone-Based Human Activity Recognition with Able bodied, Elderly, and Stroke Patients,” PLOS ONE, vol. 10, no. 4, p. e0124414, Apr. 2015.
 J.-L. Reyes-Ortiz, L. Oneto, A. Samà, X. Parra, and D. Anguita, “Transition-Aware Human Activity Recognition Using Smartphones,” Neurocomputing, vol. 171, pp. 754–767, Jan. 2016.