There are cycles of recruitment and de-recruitment of motor units and, moreover, in different parts of a cycle, different motor unit types are activated (Barnes 1980, Milner-Brown et al. 1973a, Nardone et al. 1989). Having such variability can be important in some types of sEMG analyses (Klaver-Król et al. 2010a). This issue will be discussed in more detail in the chapters that follow. Refined features of sEMG analysis. The goal of the thesis Among the numerous studies on muscular functions using sEMG, little has been investigated under dynamic conditions. In particular, research is lacking that addresses continual and prolonged measurements of muscle fiber conduction velocities during dynamic processes. In this thesis, a method is presented for examining the biceps brachii muscle by Chapter 3