Laurentia<span> (</span>North American Craton<span>) is a large continental </span>craton<span> that forms the ancient geological core of the </span>North American<span> continent. Many times in its past, Laurentia has been a separate </span>continent<span> as it is now in the form of North America, although originally it also included the cratonic areas of </span>Greenland<span> and also the northwestern part of </span>Scotland, known as theHebridean Terrane<span>. During other times in its past, Laurentia has been part of larger continents and </span>supercontinents<span> and itself consists of many smaller </span>terranes<span> assembled on a network of Early </span>Proterozoic orogenic<span> belts. Small </span>microcontinents<span> and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable </span>Precambriancraton seen today.
During the course of a continuous isometric contraction of given strength, the electrical activity progressively increases. This is due to recruitment of motor units taking place to compensate the decrease in force of contraction occurring in the fatigued muscle fibres.
