Overview of the Muscular System

The muscular system is responsible for movement of the human body, maintaining posture, and circulation of blood.
It is composed of three types of muscles: skeletal, smooth, and cardiac.
Skeletal muscles are responsible for movement and are directly attached to bones.
Smooth muscles are found in organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, blood vessels, and the arrector pili in the skin.
The cardiac muscle is specific to the heart and allows it to contract to pump blood.
Each muscle is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves.

Structure of Muscles

Muscles cells, also known as muscle fibres, are long and cylindrical.
A single skeletal muscle such as the biceps brachii contains hundreds of muscle fibres.
Myofibrils are composed of two protein filaments: myosin (thick filament) and actin (thin filament) which allow for muscle contraction.
Each muscle fibre is surrounded by a plasma membrane called the sarcolemma, and the cytoplasm of a muscle fibre is known as the sarcoplasm.
Tendons are strong, fibrous structures that attach muscle to bone.

Muscle Contraction and Relaxation

Muscle contraction occurs through a process known as the sliding filament theory.
The filaments of actin and myosin slide past each other to create muscle contraction, powered by the hydrolysis of ATP.
During relaxation, the filaments slide back to their original position.
The entire process is regulated by calcium ions and proteins called troponin and tropomyosin.

Types of Muscle Contractions

Three types of contractions possible are; isotonic, isometric, and isokinetic.
An isotonic contraction occurs when a muscle changes length as it contracts and causes a movement of a body part.
An isometric contraction occurs when a muscle contracts but does not change length and does not cause movement.
An isokinetic contraction is one in which a muscle shortens at a constant speed.

Role of the Muscular System in Sport Performance

The muscular system is integral to all human movement, hence critical to all sports.
Personal trainers and athletes must have a deep understanding of muscle physiology and how to condition specific muscles to improve performance or recover from injury.
Understanding the properties of the muscular system also allow for the formulation of targeted training regimes, such as resistance training for hypertrophy or endurance training for stamina.

Muscular Disorders and Injuries

Muscular injuries are common in sports, including strains, tears, and cramps.
Muscular dystrophy, stress-induced myopathy, and myasthenia gravis are amongst various muscular disorders that can impair physical performance.
Understanding muscle physiology allows for a better understanding of injury prevention, management and rehabilitation.

Remember to incorporate knowledge about muscles and their properties when improving physical performance in your answers. Don’t forget to reference relevant sports, injuries or disorders to demonstrate an understanding of the broader application of this knowledge.