Fitness fanatics with their bulging biceps may be the envy of the gym, but there’s more to muscle-making than dumbbells and protein shakes. Muscles are made up of fibres, which form when cells called myoblasts fuse together. Myoblasts contain strands of two proteins – called actin and myosin – which slide past each other to cause muscular contraction. These developing zebrafish muscle fibres have been magnified over a thousand times using a technique called confocal microscopy. Strands of actin have been stained blue to outline the fibres, each of which contains several nuclei (stained red) that once belonged to individual myoblasts. The extra nuclei allow fibres to rapidly synthesise actin, myosin and other vital proteins. The muscle-making process occurs continuously to replace and repair damaged fibres – so even the laziest of couch potatoes are body builders on the inside.
Written by Emma Stoye