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Throwing a baseball overhead
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Deltoid
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Action: The deltoid muscle is responsible for the abduction of the arm, primarily by its middle fibers. The anterior fibers contribute to flexion and medial rotation, while the posterior fibers assist with extension and lateral rotation of the shoulder.
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Innervation: The axillary nerve, which arises from the C5 and C6 nerve roots, innervates the deltoid muscle.
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Pectoralis Major
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Action: Flexion, adduction, and medial rotation of the arm at the shoulder joint. It helps bring the arm across the body, which is important during the throwing motion.
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Innervation: Lateral and medial pectoral nerves (C5, C6, C7, C8, and T1).
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Kicking a ball
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Quadriceps
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Action: The quadriceps group (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius) primarily extends the knee. The rectus femoris also assists in hip flexion since it crosses both the hip and knee joints. These actions are crucial when kicking a ball, as they powerfully extend the knee.
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Innervation: The quadriceps are innervated by the femoral nerve, which originates from nerve roots L2, L3, and L4.
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Hamstring
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Action: The hamstrings (biceps femoris, semitendinosus, and semimembranosus) flex the knee and extend the hip. This group is particularly active in the backswing of kicking and also helps stabilize and control the leg as it follows through after the kick.
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Innervation: The hamstrings are innervated by the sciatic nerve, which has contributions from nerve roots L5, S1, and S2.
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Doing sit-ups
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Rectus Abdominis
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Action: Flexion of the vertebral column (primarily lumbar flexion), which brings the ribcage towards the pelvis during a sit-up. It also stabilizes the pelvis during movement.
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Innervation: Lower six thoracoabdominal nerves (T7–T11) and subcostal nerve (T12)
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Obliques
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Action: The external obliques and internal obliques work together to flex and rotate the vertebral column. During sit-ups, they assist in trunk flexion and rotation (especially when performing twisting sit-ups or similar exercises). The external obliques rotate the trunk to the opposite side, while the internal obliques rotate the trunk to the same side.
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Innervation: Lower six thoracoabdominal nerves (T7–T11), subcostal nerve (T12), and iliohypogastric nerve (L1)
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Breathing
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Diaphragm
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Action: The diaphragm contracts and flattens during inspiration, increasing the vertical diameter of the thoracic cavity, which allows the lungs to expand and air to be drawn in. During exhalation, the diaphragm relaxes and returns to its dome shape.
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Innervation: Phrenic nerve (C3, C4, C5)
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External Intercostals
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Action: The external intercostal muscles elevate the ribs during inspiration, increasing the transverse and anteroposterior diameters of the thoracic cavity, which helps in lung expansion.
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Innervation:Intercostal nerves (T1–T11)
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