If you’re a typical gym buff working with weights, you want to lose weight, gain some muscle, and become stronger. You usually target your biceps, pecs, and quads to look bulkier. These muscles are skeletal because they attach to the skeleton to produce motion. Skeletal muscles are cells needed for general functions and muscle proteins, such as the contractile proteins actin and myosin. When a muscle cell is stimulated by a nerve cell, actin and myosin interact to produce force through what are known as "power strokes." The sum of all the power strokes produced by the muscle cells determines the total force.
The energy source adenosine triphosphate (ATP) binds with myosin to create a high-energy state. A cross-bridge begins when the myosin head attaches to an actin filament. Next, the myosin heads bend and move through a power stroke, pulling the actin filaments inward to the sarcomere, the smallest functional subunit of muscle tissue. Next, ADP and inorganic phosphate are released, and the myosin heads reach a low-energy state as the sarcomere shortens and the muscle contracts. Finally, the ATP binds to myosin to break the cross-bridge, and the cycle begins for the next muscle contraction. The whole process describes the sliding-filament theory.
Generally, two processes are involved in strength training: hypertrophy and neural adaptations.
Muscular hypertrophy is the increase in muscle mass and the cross-sectional diameter of the muscle fibres. Working out a muscle causes muscle damage, which the body eventually repairs, resulting in increased muscle fibres and greater strength and muscle size. In addition, appropriate training load with adequate rest periods and nutrition enhance muscle protein synthesis.
Strength training causes adaptive changes within the nervous system that allow the recruitment of specific muscles with coordinated activation of relevant muscles to achieve the desired motion, resulting in a greater net force. The brain can recruit more muscle cells and thus more power strokes — synchronous activation. The neural adaptation generates significant gains in strength with less obvious hypertrophy. In addition, neural adaptation pushes the muscles to work harder and regain strength more quickly after long periods of inactivity.
Hypertrophy and neural adaptations can affect strength training progress:
You can get stronger over the first few weeks of exercise without apparent muscle size changes. It’s because neural adaptations initially take effect when you’re new to or returning to training. Over time, hypertrophy adaptations will have a more significant impact on training while neural adaptations stabilize.
Powerlifters can lift a tremendous amount of weight without looking very muscular because they can activate many motor neurons and contract their muscles better (neural adaptation). On the other hand, bodybuilders may look bulkier but may be less strong than powerlifters (hypertrophy adaptation) because they build their muscles to grow more muscle fibres.
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