What is the mechanism of muscles in the human body?

The mechanism of muscles in the human body involves a highly complex and coordinated process that allows muscles to contract, generate force, and perform various functions. 

The sliding filament concept is the most widely accepted theory of muscle mechanism in the human body. According to this theory, muscle contractions are caused when the thin filaments slide over the thick filaments, shortening the myofibril.  

The sarcomere, which is the fundamental unit of muscle contraction, is composed of two main types of protein filaments – actin and myosin. 

• Actin, a thin contractile protein, is concentrated in the light band or the I-band. The thin filament composed of actin is firmly anchored to the Z line, a type of elastic fiber that bisects each I-band. 
• Myosin, a thick contractile protein, is concentrated in the dark band or the A-band. The central region of the thick filament, where thin filament does not overlap, is referred to as the H-zone. The process of muscle contraction involves the dynamic interaction of these components.

During muscle contraction, myosin heads bind to exposed actin binding sites, forming cross-bridges. ATP (adenosine triphosphate) provides the myosin heads with the energy they need to undergo a power stroke, which alters the conformation of the myosin heads. This change causes the actin filaments to slide past the myosin filaments, shortening the sarcomere. The myosin head then binds to ATP and detaches from actin, following which the ATP is broken down or hydrolyzed, releasing energy which is used by myosin heads for another power stroke. This process continues until the muscle contraction is complete.