Muscle Function and Metabolism

Adenosine Triphosphate (ATP)• ATP is the source of energy for muscle contraction. • Muscles store a very limited amount of ATP (4-6 sec. worth at

most).• ATP must be regenerated if contraction is to continue• ATP can be generated by one of three pathways….• ATP video

Aerobic Metabolism/Cellular Respiration1.) Description• Occurs in the mitochondria, requires oxygen, and involves acomplex sequence of chemical reactions.

2. Chemical Formula: Glucose + oxygen carbon dioxide + water+ energy (36 ATP)

3. When this system is used:• Used during prolonged, endurance activities which maintain a constant heart rate

• As long as there is enough oxygen available relative to ATPdemand, a muscle will utilize aerobic metabolism.

• Posture, most daily movements, marathon runs, bike riding

Anaerobic Metabolism/Glycolysis1. Description:

• When muscles contract vigorously, the bulging muscles compress blood vessels within, impairing oxygen delivery.

• This pathway can occur in the absence of oxygen.

2. Chemical Formula:

Glucose lactic acid +energy (2 ATP)

3. When this system is used:

• When large amounts of ATP relative to available O2 are needed. Usually for exercise about 30-40 seconds long.

• Tennis, soccer, 100 meter swim

Anaerobic Metabolism/Creatine Pathway1. Description:

• Utilizes the molecule creatine phosphate to regenerate ATP, after stored ATP is depleted.

2. Chemical Formula:

Creatine phosphate + ADP Creatine + ATP (1 ATP)

3. When this system is used:

• Moblized at the beginning of exercise, before other pathways ‘kick in’.

• Creates enough energy for about 15 seconds of contraction.

• 100 meter dash, weightlifting

Summary of Muscle MetabolismCreatine pathway Glycolysis

PathwayAerobic pathway

Requires oxygen no no yes

Amount of ATP produced

1 ATP 2 ATP 36 ATP

Duration 15 seconds 30-60 seconds hours

By product creatine lactic acid CO2 and H2O

Advantages • Rapid energy• Easily mobilized

• Quick energy• Does not

require oxygen

• More ATP/glucose

• Waste products are easy to excrete

Disadvantages • Small amount of creatine available

• Small amount of ATP

• less ATP/glucose

• Lactic acid produces muscle fatigue

• Slower• Limited by

oxygen

Fast Twitch vs. Slow Twitch MusclesSprinter vs. Marathon Runner

Slow Twitch/Fast Twitch

Analogy: birdsWhite meat-fast twitch, found in breast and wings,

used for flying-quick movements. Dark meat-slow twitch, found in legs, used for walking.

Fast Twitch Slow Twitch

Lighter in color-less blood Darker in color-rich in blood

Few mitochondria Many Mitochondria

Mostly anaerobic Primarily aerobic

Easily fatigue Fatigue slowly

More forceful contractions Less forceful contractions

Increase in size with training Don’t increase in size with training

Sprinters Distance runners

Muscle Fatigue

Definition: the state of physiological inability to contract

Causes:1. Occurs when ATP production fails to keep up with ATP use.• Deficiency of ATP, as opposed to total absence of ATP which leads to a continuous state of contraction (rigor mortis, writers cramp)

2. Accumulation of lactic acid and ionic imbalances alsocontribute.• decreases muscle pH• causes burning sensation• interferes with actin/myosin binding

Muscle conditions

• Muscle cramps- (charley horse)sudden involuntary contraction of muscles due to injury, deficiency in calcium or phosphate, lack of blood flow, nerve tissue damage or dehydration.

• Muscle twitches -often cause by a single nerve, due to fatigue, lack of water, stress and anxiety.

• Lou Gehrig’s disease (ALS)- damages motor neurons, leads to loss of movement.

• Muscular dystrophy (MS)-skeletal muscle progressively weaken.