#separator:tab #html:false #tags column:4 Biceps brachii Front of the upper arm; bends the elbow bio-muscles Triceps brachii Back of the upper arm; straightens the elbow bio-muscles Deltoid Shoulder muscle that lifts the arm bio-muscles Pectoralis major Large chest muscle bio-muscles Latissimus dorsi Broad muscle of the back bio-muscles Trapezius Muscle across the upper back and neck bio-muscles Abdominals Muscles of the belly that help the trunk bend and twist bio-muscles Gluteus maximus The largest muscle in the body, in the buttock bio-muscles Quadriceps Four muscles at the front of the thigh that straighten the knee bio-muscles Hamstrings Muscles at the back of the thigh that bend the knee bio-muscles Gastrocnemius The big calf muscle bio-muscles Soleus Calf muscle lying below the gastrocnemius bio-muscles Tibialis anterior Muscle on the front of the shin bio-muscles Sartorius Long strap-like muscle of the thigh bio-muscles Masseter Chewing muscle in the jaw bio-muscles Orbicularis oculi Muscle that closes the eyelids bio-muscles Diaphragm Muscle that helps you breathe bio-muscles Intercostals Muscles between the ribs bio-muscles Rotator cuff Group of shoulder muscles that stabilize the joint bio-muscles Achilles tendon Strong tendon that connects the calf muscles to the heel bio-muscles Skeletal muscle Voluntary muscle attached to bones; striped bio-muscles Smooth muscle Involuntary muscle in organs such as the stomach bio-muscles Cardiac muscle Muscle of the heart bio-muscles Voluntary muscle One you can control bio-muscles Involuntary muscle One that works without you thinking bio-muscles Tendon Connects muscle to bone bio-muscles Ligament Connects bone to bone bio-muscles Contraction When a muscle shortens bio-muscles Muscles can only Pull; they cannot push bio-muscles Antagonistic pair Two muscles that work in opposite ways, like biceps and triceps bio-muscles Flexor A muscle that bends a joint bio-muscles Extensor A muscle that straightens a joint bio-muscles Muscle fiber A long muscle cell bio-muscles Myofibril Thread-like part inside a muscle fiber that contracts bio-muscles Actin and myosin Proteins that slide to make muscles contract bio-muscles ATP The energy molecule muscles use bio-muscles Lactic acid A by-product that can build up in tired muscles bio-muscles Muscle tone The small constant tension in resting muscles bio-muscles Atrophy Muscle shrinking from not being used bio-muscles Hypertrophy Muscle growing larger from use bio-muscles Cramp A sudden painful tightening of a muscle bio-muscles Sprain An injury that stretches or tears a ligament bio-muscles Strain An injury that stretches or tears a muscle or tendon bio-muscles Warm up Gentle exercise before activity to prepare muscles bio-muscles Protein A nutrient that helps build and repair muscle bio-muscles Fast-twitch fibers Muscle fibers that contract quickly for sprints bio-muscles Slow-twitch fibers Muscle fibers that work for a long time without tiring bio-muscles How many muscles do people have, about? More than 600 bio-muscles Which muscle in the body never rests? The heart bio-muscles Neuromuscular junction Where a nerve meets a muscle to tell it to contract bio-muscles Extraocular muscles The six muscles that move each eye bio-muscles Sphincter A ring-shaped muscle that opens and closes an opening bio-muscles Peristalsis Waves of smooth muscle squeezing food along bio-muscles Sarcomere The basic contracting unit of a muscle fiber bio-muscles