Muscle tension and load are opposing forces that determine the type of muscle contraction. There are three main types of contractions: isometric contractions where the muscle generates force without shortening, and two types of isotonic contractions where the muscle shortens or lengthens while generating force - concentric contractions where the muscle shortens, and eccentric contractions where it lengthens. A single muscle twitch has three phases - a latent period after stimulation, a contraction period where force increases, and a relaxation period where force decreases. Heavier loads result in longer latent periods, slower velocities of shortening, and shorter twitch durations with less shortening distance. As load increases, the velocity of muscle fiber shortening decreases until it reaches zero at maximal isometric

1. CHAPTER 11 MUSCLE

2. MECHANICS OF SINGLE-FIBERCONTRACTION GROUP 2 YA

3. TENSION – is the force exerted on an object by a contracting muscle LOAD - the force exerted on the muscle by an object Muscle tension and load are opposing forces.

4. ISOMETRIC - are contractions in which the muscle is developing force but not shortening and no visible movement is seen e.g. weight lifting, sprinting ISOTONIC - a muscle is generating a constant force to move a load e.g. jogging, dancing, aerobics

6. TWO TYPES OF ISOTONIC CONTRACTION CONCENTRIC ISOTONIC - the muscle is shortening while it is contracting e.g. picking up an object ECCENTRIC ISOTONIC - the muscle is lengthening while it is contracting e.g. lowering the object back to place

7. TWITCH CONTRACTION TWITCH - is a single stimulus contraction–relaxation sequence in a muscle fiber

8. THREE PHASES OF TWITCH CONTRACTION 1. LATENT PERIOD - lasts about 2 msec (milliseconds) and is the time between stimulation of muscle cells and force generation 2. CONTRACTION PERIOD - lasts about 10–100 msec and is the period during which force (measured in grams) is increasing 3. RELAXATION PHASE - the period when force is decreasing; lasts 10–100 msec

13. Velocity of shortening is slower

14. Duration of a twitch is shorter

16. LOAD-VELOCITY RELATION Velocity at which a muscle fiber shortens decreases with increasing loads

17. The shortening velocity is maximal when there is no load Zero when the load is equal to the maximal isometric tension Loads greater than the maximal isometric tension, the fiber will lengthen at a velocity that increases with load