• weak, transient muscle contracton
• results from a single action potention in a muscle fiber

• incomplete= progressively greater force in which the muscle fiber only relaxes slightly between subsequent contractions
• complete= only in maximal contractions, such as lifting the heaviest weight possible for a single reetition in which action potentials arrive so frequently that the fiber does not relax at all between contractions

• "same length" contractions
• contractions that do not alter muscle length
• force is generated and the muscle tenses; however, the myofibrils do not slide and the muscle does not change length
• maintain our upright body posture

• "same tone" or "same force"
• everyday movement
• constant foce is maintained over the course of a contraction, but the length changes

• shorten the muscle, bring the muscle attachment closer to the origin
• bicep curls
• myofilaments slide; sarcomeres, fibers, and muscles shorten
• movement occurs

• generate a restraining force as the muscle lenthens
• enable weight to be smoothly and controllably lowered following a biceps curl
• myosin heads grab onto the actin filaments and slow the rate of movement

• state of subconscious isometric contraction that occurs even in voluntarily relaxed muscle.
• maintains muscle in a healthy state
• if nerve supply is interrupted, muscle loses this and become flaccid. 

Activators of smooth muscle

1. mechanical signals- prevents overstretching
2. autonomic nerves- 
3. chemical signals- 
4. pacemaker activity- self stimulating action potentials, move food