Muscles, Muscle Contraction and Strength

How Muscles Work The muscles arranged along the skeletal frame of the body, always act as a group rather than contracting individually. Therefore the movements performed about a joint are produced by several muscles, with different roles.

How Muscles Work ROLES: Agonists: muscles that work together to perform a movement (ex. Bicep, Antagonists: muscles that during motion act in opposition to the agonists Stabilizers: smaller muscles which contract to anchor, or steady, a bone so that the prime movers have a firm base to pull on

How Muscles Work Types of Muscular Contraction: Concentric (positive): contractions in which the muscle length shortens. Eccentric (negative): contractions in which the muscle length increases Isometric (static): the muscle develops tension without changing its length

How Muscles Work Energy Sources for Contraction: ATP is the fuel that supplies energy to our muscles. (ATP  ADP + P + energy) There is a limited amount of ATP stored in the muscle cells thus they must continuously be restored.

How Muscles Work The Three Energy Systems: Anaerobic Systems (No O 2 ) 1.ATP-CP system 2.Lactic Acid System Aerobic System (O 2 ) 3.The Oxygen System (O 2 )

ENERGY SYSTEMS ATP – CP (Anaerobic) In addition to ATP, small amounts of creatine phosphate (CP) are stored in the muscle. It can restore ADP to ATP This system can only restore energy for seconds. It takes 60 sec to restore 70% of the CP and 3-5 minutes to restore 100% of the CP.

ENERGY SYSTEMS The Lactic Acid System (LA): For intense events between seconds. The LA system breaks down glycogen which is stored in the muscle and liver cells, releasing energy to reconvert ADP + P to ATP. However due to a lack of O 2 LA builds up. This LA causes fatigue, which eventually leads to cessation of exercise.

ENERGY SYSTEMS The Lactic Acid System (LA): It takes 30 min of rest to remove 50% of the LA. However, this time can be reduced to 10 min with active rest. Restoration of the glycogen takes hours. Depending on the intensity and repetition of the activity and the fitness level of the person.

ENERGY SYSTEMS Aerobic System: Predominant energy source for activities 2min-3hours. Breaks down glycogen in the presence of O 2. Due to the O 2 little lactic acid is produced with the aerobic system. But instead C O 2 and H 2 O. The rate at which the ATP is replenished is limited by ones aerobic capacity. (heart and respiration capacities)

Muscle Fiber

Fiber Types: Type I (slow-twitch): aerobic 50% Type IIa (fast-twitch): oxidative anaerobic 25% Type IIb (fast-twitch): non-oxidative 25% Your ability to use specific fiber types is dependant upon your nervous systems ability to recruit them and how you have trained them.

Muscular Adaptation Adaptation is the sum of modifications brought about by the systematic repetition of exercise. Hypertrophy: enlargement of muscle size Fiber Type: Type IIa acts as Type I or Type II depending on training Nervous system: ability to recruit fibers increases with training as does coordination