What actually happens when I use and train my muscles…
As we age a person loses metabolically active muscle tissue, Factors that contribute to the devel- opment of sarcopenia include muscle disuse, age-related decreases in several hormones, training can help to prevent this and keep our muscles and bones healthy for longer.
Different movements and different contractions effect the body differently. A popular comparison highlighting these differences compare both concentric (a concentric contraction causes muscles to shorten) and an eccentric (eccentric contractions cause muscles to elongate(lengthen)).
All of our muscular cells are designed with the ability to generate force and movement. Skeletal muscles do this due to the fact they are attached to bones and move. Skeletal muscles are striated (striped in appearance) due to actin and myosin filaments (that power their contraction) . They are arranged on the muscle in a relative way and are known as a whole sarcomeres(Sweeney & Hammers, 2018). During a muscle contraction , a muscle is stimulated to contract and actin and myosin filaments slide other one another.
After strength training your body must repair. It does this by replacing any damaged fibers to create new muscle protein and new myofibrils. Muscle growth and strength occurs when the rate of this protein synthesis is larger than the breakdown of the muscle.(Loenneke et al., 2019).
Click here for more detail on the sliding filament theory.
Physiology and Nutrition 