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>>> YOU HAVE THREE TYPES OF MUSCLES IN YOUR BODY.
>> SKELETAL MUSCLES HELP YOU MOVE.
>> SMOOTH MUSCLES HELP YOU EAT AND BREATHE.
>> AND CARDIAC MUSCLES MAKE YOUR HEART BEAT.
>> YOU HAVE ABOUT 650 MUSCLES IN YOUR BODY.
AND THEY COME IN ALL SHAPES AND SIZES.
SOME ARE WIDE SHEETS OF TISSUE LIKE THE MUSCLES IN YOUR BACK.
OTHERS ARE CIRCLES OR TRIANGLES.
SKELETAL MUSCLES ARE MADE UP OF LOG-SHAPED FIBERS WITH HUNDREDS
AND HUNDREDS OF STRANDS.
THE THINNEST STRANDS OVERLAP ONE ANOTHER, LIKE FINGERS LACED
TOGETHER.
THERE ARE TWO TYPES OF FIBERS, FAST TWITCH FIBERS CONTRACT
QUICKLY, GIVING YOU A BURST OF ENERGY, AND SLOW TWITCH FIBERS
PROVIDE YOUR MUSCLES WITH A SUSTAINED RELEASE, SO THE
MUSCLE CAN ACT LONGER.
SOME SKELETAL MUSCLES ARE ATTACHED TO YOUR SKIN OR OTHER
MUSCLES, BUT MOST ARE ATTACHED TO BONES WITH TENDONS.
WIGGLE YOUR FINGERS.
YOU CAN SEE CORDS JUST UNDER YOUR SKIN.
THESE ARE THE TENDONS CONNECTING MUSCLES IN YOUR
LOWER ARM TO YOUR FINGER BONES.
SKELETAL MUSCLES WORK IN PAIRS.
WHEN YOU LIFT SOMETHING, ONE MUSCLE CONTRACTS OR TIGHTENS
AND THE OTHER MUSCLE RELAXES OR LOOSENS.
THE CONTRACTING AND RELAXING ACTION PULLS UP THE MUSCLE AND
YOUR ARM BONE.
>> AND IT TAKES MORE THAN 300 MUSCLES WORKING TOGETHER JUST
TO TAKE ONE SINGLE STEP.
>> MUSCLES ARE THE MEAT OF THE BODY.
THEY MAKE UP ABOUT A THIRD TO HALF YOUR BODY WEIGHT.
MUSCLES ARE LOADED WITH BLOOD VESSELS AND NERVES.
BLOOD BRINGS MUSCLES FOOD AND OXYGEN SO THEY CAN WORK AND
TAKE AWAY WASTE PRODUCTS.
AND SIGNALS FROM YOUR BRAIN TRAVEL THROUGH THE NERVES TO
TELL YOU MUSCLES WHAT TO DO.
SKELETAL MUSCLES ARE VOLUNTARY, THAT IS YOU CAN CONTROL THEM.
SMOOTH MUSCLES ARE INVOLUNTARY, THAT IS THEY WORK WITHOUT YOU
HAVING TO THINK ABOUT THEM.
SMOOTH MUSCLES ARE FOUND IN PLACES LIKE THE WALLS OF YOUR
STOMACH AND BLOOD VESSELS.
WHEN YOU GET COLD, TINY SMOOTH MUSCLES PULL ON THE HAIRS OF
YOUR SKIN AND YOU GET GOOSEBUMPS.
CARDIAC MUSCLES ARE ALSO INVOLUNTARY AND THEY EXIST ONLY
IN YOUR HEART.
AND UNLIKE OTHER MUSCLES, IT NEVER GETS TIRED.
CARDIAC MUSCLES CONTRACT TO SQUEEZE BLOOD OUT OF YOUR HEART
AND RELAX TO FILL YOUR HEART WITH BLOOD.
YOU CAN INJURE YOUR MUSCLES.
MUSCLE STRAINS HAPPEN WHEN MUSCLE FIBERS STRETCH TOO FAR
OR TEAR.
BUT WITH ICE AND REST, YOUR BODY CAN USUALLY HEAL ITSELF IN
TIME.
YOU CAN KEEP YOUR MUSCLES HEALTHY BY EATING RIGHT, LOTS
OF VITAMINS, MINERALS AND PROTEIN, BY DRINKING WATER AND
BY KEEPING YOUR MUSCLES STRONG.
AND THE BEST WAY TO DO THAT IS TO EXERCISE.
>> IF YOU DON'T EXERCISE, YOUR MUSCLES CAN SHRINK AND LOSE
STRENGTH.
SO GET ACTIVE EVERY DAY.