B6–B8 Responses, Adaptations and Additional Factors Typeit

Responses of the muscular system occur immediately at the onset of exercise. The level and type of response depend on the activity undertaken, be that aerobic or anaerobic, endurance-based or resistance-based. Long-term adaptations to regular exercise are also dependent on the type of training and energy systems used. 

Responses of the muscular system to a single exercise session include:

• The increase in energy demand at the muscle in order to contract during exercise is met by an increased  supply. This occurs as a result of an elevated heart rate and stroke volume, and thus cardiac output.
• The reactions that take place when making energy available to the muscle release heat, increasing muscle . This, in turn, increases the activity of enzymes involved in these reactions.
• At the onset of exercise, the muscles might seem stiff to start with but there is generally an increase in the range of movement they allow around a joint. This is due to an increased  of muscles and ligaments, reducing their risk of being overstretched and causing injury.
• During isotonic contractions, which is prominent during (weight) training, the muscle undergoes micro- that disrupt the normal structure of muscle fibres. These are often accompanied by onset muscle soreness (DOMS), symptoms of which include pain and swelling which can last up to 72 hours post exercise.
• During high-intensity exercise (i.e. that which predominantly works the anaerobic energy system), the demand for oxygen at the muscle exceeds its supply, and the subsequent reaction that takes place results in an accumulation of . This potentially harmful by-product is associated with impaired muscle contraction and uncomfortable sensations in the muscle.

• Progressive overload of muscles during regular resistance training will increase muscle size, known as muscular . This is because resistance training stimulates muscle protein synthesis, which is augmented by protein consumed as part of the diet.
• Increased strength of – These are the tough bands of connective tissue that attach muscle to bone. Although this adaptation is not visible like the increase in size of superficial muscles, the individual would benefit from a reduced risk of injury and greater range of movement.
• Training that places a significant demand on the aerobic system will result in many structural adaptations within the skeletal muscle. This includes an increase in storage of , which is the oxygen-binding pigment in muscle cells that enhances its uptake from the surrounding capillaries. More oxygen can then be delivered to the  (organelles found in the muscle cells), the powerhouses of aerobic respiration, which increase in size and number following regular aerobic training. Muscles are also capable of storing a greater amount of , used in both aerobic and anaerobic respiration, as well as  – used exclusively during aerobic activity.
• High-intensity training that taxes the anaerobic energy system will improve the body's ability to  lactate, allowing exercise of this type to continue for longer periods before the build-up becomes limiting.