FIGURE 4.10: The muscular system of the human body


TRAPEZIUS DELTOID


PECTORELIS MEJOR RECTUS ABDOMINIS EXTERNAL OBLIQUE


TENSOR FASCIAE LATAE


ILLIOPSOAS


SARTORIUS QUADRICEPS


PERONEUS LONGUS PERONEUS BREVIS


ADDUCTOR MUSCLES


MULTIFIDUS SEMITENDINOSUS


TIBIALIS POSTERIOR TIBIALIS ANTERIOR


SOLEUS BICEPS TRICEPS SERRATUS


LONGISSIMUS THORACIS


LATISSIMUS DORSI ERECTOR SPINAE GLUTEUS MINIMUS


GLUTEUS MAXIMUS


BICEPS FEMORIS SEMIMEMBRANOSUS GATROCNEMIUS


MUSCLES Muscles are bands of soft tissue fibers that contract and relax in order to stabilize or move joints. Working in groups, muscles regulate tension for performing complex movements. Muscles move joints through three types of tension: concentric, eccentric, and isometric.


Muscle cells contain protein fibers that slide past one another, connecting with cross- bridges that attach to other filaments. Tis produces muscular tension and contraction, changing both the length and the shape of the fibers. You may envision this action as the arms of tug-of-war participants, pulling opponents toward them on a rope. With ankle dorsiflexion, filaments sliding past each other cause the muscle to shorten. As this occurs, the foot is literally pulled toward the shin in a concentric contraction. Sticking with the tug-of-war analogy, when the external force (the rope) overcomes the tension (the arms of the tug-of-war participants), the muscle is lengthened. Tis muscle lengthening under tension is called eccentric contraction. Because snowboarding is a gravity sport, riders end up performing a lot of eccentric muscle activity to push against the forces constantly bombarding the body. Muscles are more capable of lowering heavier weight than they are able to raise. During a turn, a rider’s body tends to continue in a straight line, as acceleration from the turn essentially pulls the rider toward the outside of the turn. If you are going to resist the strong pull, it is more effective to extend in the opposite direction of the force than to flex in the


64 AASI SNOWBOARD TECHNICAL MANUAL


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