Many reasons:
Putting too much exertions on weak muscles
working out or lifting wrong
heavier: therefore more strain on muscles
Skeletal Muscles
Skeletal muscles can be consciously controlled during exercise, whereas cardiac and smooth muscles cannot be consciously controlled.
Skeletal muscles do not operate involuntarily; they are primarily under voluntary control, allowing for conscious movement. They also do not have a single nucleus per cell, as they are multinucleated due to the fusion of myoblasts during development. Additionally, skeletal muscles are not responsible for internal organ function, which is managed by smooth and cardiac muscles.
Skeletal muscles generate heat during physical activity through a process called muscle contraction. When muscles contract, they use energy from ATP molecules, which produces heat as a byproduct. This heat helps to maintain the body's temperature during exercise.
The diaphragm and intercostals for breathing
When a runner uses her leg muscles to run, she is primarily using skeletal muscles. Skeletal muscles are under voluntary control and are responsible for movement by contracting and relaxing. These muscles work in coordination to provide the strength and agility needed for running. In addition to skeletal muscles, some smooth muscles may be involved in regulating blood flow and digestion during exercise.
skeletal muscle
During contraction the two articulating bones move equally
the brain has 2 powerful systems work together to paralyze skeletal muscles during rapid eye movement sleep according to reaserch scientist may have better understanding
Though the skeletal does come under pressure during exercise, the movements are beneficial for strengthening the muscles and bones. Exercise also enhances flexibility.
The contractile units of skeletal muscles are called sarcomeres. Sarcomeres consist of actin and myosin filaments that slide past each other during muscle contraction, causing the muscle to shorten and generate force.
Once you start to exercise, your body has to make sure that the muscles that are now working much harder receive the oxygen and fuel they need to keep contracting. The various body systems must begin to work faster and harder to meet this extra demand. The muscles start to work harder, requiring more oxygen and producing more carbon dioxide, which needs to be removed