Muscle Physiology Skeletal muscle function

Muscle Strength A motor unit is one motor neuron and all of the muscle fibers it controls The force with which a whole muscle contracts depends on how many motor units the nervous system stimulates.

All or None….. A muscle will either completely contract, or not at all. This means the stimulus only needs to pass the threshold.

What is the threshold? The minimum amount of stimulation that will cause a muscle fiber to completely contract. The amount of work that a muscle is being asked to perform is directly proportional to the threshold of the stimulus.

Types of muscle contractions Isometric: Muscle increases in tension but does not shorten Isotonic: The muscle shortens and the amount of tension is constant. Most muscle movement is a combination of both types of contractions.

Muscle Fatigue Fatigue is the decrease in ability to do work Psychological fatigue is when a person thinks he/she cannot do any more muscular work Muscle fatigue means the muscles have trouble, or are unable to respond to stimuli

Energy for muscle contraction Creatine phosphate can be used as an energy source for ATP production. Most ATP is produced during aerobic respiration

Oxygen and exercise Heavy exercise creates EPOC – excess post- exercise oxygen consumption The time spent in EPOC depends on each person’s level of fitness Fat metabolism is also a factor because more oxygen is required to generate energy from fats

Hypertrophy and Atrophy Hypertrophy is an increase in a muscle’s size Most hypertrophy is due to exercise Atrophy is a decrease in muscle size This is usually due to disuse.