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 11MUSCLE

2. MECHANICS OF SINGLE-FIBERCONTRACTIONGROUP 2 YA

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

4. ISOMETRIC - are contractions in whichthe muscle is developing force but not shortening and no visible movement is seene.g. weight lifting, sprintingISOTONIC - a muscle is generating aconstant force to move a loade.g. jogging, dancing, aerobics

6. TWO TYPES OF ISOTONIC CONTRACTIONCONCENTRIC ISOTONIC - the muscle is shortening while it is contractinge.g. picking up an objectECCENTRIC ISOTONIC - the muscle is lengthening while it is contractinge.g. lowering the object back to place

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

8. THREE PHASES OF TWITCH CONTRACTION1. LATENT PERIOD - lasts about 2 msec (milliseconds)and is the time between stimulation of muscle cells and force generation2. CONTRACTION PERIOD - lasts about 10–100 msecand is the period during which force (measured in grams) is increasing3. RELAXATION PHASE - the period when force is decreasing; lasts 10–100 msec

12. Isotonic twitch depends on the magnitudebeing liftedHeavier loads:Latent period is longer

13. Velocity of shortening is slower

14. Duration of a twitch is shorter

15. Distance shortened is less