muscle cell activation
Actin and Myosin are the contractile proteins of the muscle. Their connection is the only way for a muscle cell to generate force (Powers & Howley, 2004).
As seen in the illustration above, there exist different stages in the bonding of the contractile proteins. Because of this, there exists a physiologically optimal level of contraction to generate optimal force (Powers & Howley, 2004).
This crossbridge activation takes place only in the presence of adenosine tri-phosphate (ATP) and Calcium (Powers & Howley, 2004). The rates of ATP availability and calcium uptake can therefore guide several components of muscular contraction, including rate of activation and force production (Kraemer, Fleck & Evans, 1996).
Graphic by Alberts, Bray, Johnson, Lewis, Raff, Roberts & Walter. (2004).