Role of muscles
Muscles can shorten their length by contraction.visibly, they become shorter and thicker. This is not bad for showingoff, but there is much more to muscle contraction than justimpressing someone. Muscles are meant to squeeze or move somethingwhen they contract. In example, the heart muscle squeezes the bloodout, while skeletal muscles move the bone to which the insertiontendon is attached to (the one that does not move is the origintendon). This causes motion.
Types of muscle contractions
There are two main types of muscle contraction. Thefirst type is isotonic contraction. This is type of contraction inwhich the muscles contract and shorten while they produce force whichcauses movement of a body part. The second type is isometriccontraction, when muscles produce force but do not change theirlength, as happens with muscles of your lower arm when you grip andhold something heavy.
How muscles work
Muscles are mostly water (over 70 percent) andprotein (almost 22 percent). Proteins of muscle tissue are in form ofthin strands of actin, and thick strands of myosin, which run thelength of each muscle cell. Muscle contraction is basically slidingof actin and myosin protein strands over each other, which causesreduction of the length of the cell, and in turn, shortening of theentire muscle.
Muscle contractions are regulated by the centralnervous system, and can be voluntary and involuntary (automatic, doesnot require - or offer - a conscious "order" to the muscleto contract). when a muscle should be contracted, the nerves whichinnervate its fibers receive the signal to act and transmit a weakelectric impulse to the muscle cells. Once the impulse reaches thecells, it causes them to begin contraction. force of the contractionis determined by frequency of impulses that keep arriving from thenerve while the contraction lasts - the more impulses, the strongerthe contraction.
How isotonic contraction works
In this type of contraction, tension remains constantwhile the muscle becomes shorter. these contractions are the mostcommon in a majority of exercises and physical activities. All weightlifting exercises are based on isotonic contractions. to test howthat works, flex and bend your biceps and measure its length beforeand after contraction. you will notice the significant decrease inlength when it is contracted.
There are two types of isotonic contractions:concentric, where tension of the muscle increases to match theresistance and then remains on that level while the muscle shortens.The external force on the muscle is weaker than the force generatedby the muscle in this case, and contraction causes muscle shortening.The other type is eccentric isotonic contraction, where the musclelengthens as it contracts. this type of contraction typically servesto control or decelerate movement caused by the eccentriccontraction. This type of contraction is stressful to the muscle andcan cause injuries.