1. Unit: Muscular System Types of Skeletal Muscle Contractions & Fatigue

2. What you will learn: Learning Targets:
I can identify the types of skeletal muscle contractions; tonic, twitch, tetanic, isotonic, isometric
I can explain why a muscle fatigues

3. Types of Skeletal Muscle Contraction:
Twitch Contraction
Tetanic Contraction
Isotonic Contraction
Isometric Contraction

4. Types of Skeletal Muscle Contraction:
Reminder:
Tonic contractions: sustained muscle contractions that maintain muscle tone and posture.
- They can last several minutes & up to hours
- Example: Muscles of the lower back, hold vertebrae in place.

5. Types of Skeletal Muscle Contraction:
Twitch contraction: is a quick jerky response to a stimulus (not sustained).
- Plays minimal role in normal muscle activity, usually seen in controlled environments such as a research lab
- One stimulus (nerve impulse)
- Muscle contractions must be fluid and not jerky.

6. Types of Skeletal Muscle Contraction:
Tetanic Contraction: is a more sustained and steady response than a twitch.
- It is caused be a series of bombarding stimuli (nerve impulses)
- Thus, contractions melt together to produce a sustained contraction (or tetanus).
- ~ 30 stimuli/sec.

7. Types of Skeletal Muscle Contraction:
Two types of tetanic contractions:
1) Isotonic contractions
Concentric
Eccentric
2) Isometric contractions

8. Isotonic Contractions:
Tension remains unchanged but the muscle's length changes.
- Produces movement at the joint
- Insertion point moves relative to the origin point.
- Two types of isotonic contractions:
1) Concentric: muscle shortens
2) Eccentric: muscle lengthens
(think: extension)

9. Isometric Contractions
Tension changes but the muscles length remains the same.
- Contraction that does not produce movement.
- Iso + metric = same length
- Example: pushing against a wall, can increase myofilaments and thus increase strength.

11. Effects of Exercise on Skeletal Muscle:
Increases: muscle tone, posture, more efficient heart and lung function and reduced fatigue.
Disuse atrophy: occurs during prolonged inactivity, reduce muscle mass (loose myofilaments).
Hypertrophy: occurs during increased strength training (weight lifting), increases muscle mass (gain myofilaments).
- Isotonic & Isometric Contractions

12. Effects of Exercise on Skeletal Muscle:
Endurance training: (or aerobic training) increases a muscle's ability to sustain moderate exercise over a long period.
- Activities include: running, speed walking and bicycling.
- Isotonic movements increase the number of blood vessels to the muscle fibers.
- ↑ blood flow, ↑ oxygen, ↑ glucose,
- ↑ mitochondria (increased ATP production)

13. Muscle Fatigue:
Occurs when muscle cells are stimulated repeatedly with inadequate periods of rest (such during a tetanic contraction).
- During exercise the stored ATP required for muscle contraction becomes depleted.
- Therefore the body tries to replenish the oxygen debt, through increased oxygen intake (increased inhalation; aerobic respiration).

14. Muscle Fatigue:
- However, when that is not enough the body produces lactic acid through lactic acid fermentation (anaerobic respiration).
- This is only temporary, and the build up of lactic acid can cause muscle soreness after exercise.

15. Muscle Fatigue:
- Therefore, the strength of muscle contractions decreases, which results in muscle fatigue.
- Eventually muscle contraction will no longer occur (cease).
- After exercise, labored breathing will persist in order to “pay the debt” for the metabolic effort. This is an example of your body trying to maintain homeostasis (bringing your body back into a stable internal environment).

16. Muscle Fatigue: Homeostasis – repeated simulations – less
strength (use up stored ATP) – revert to lactic
acid fermentation (anaerobic respiration) to
make ATP – build up of lactic acid, causes
muscle soreness – Oxygen debt (increase
metabolism to replace ATP reserves - Homeostasis