Final answer:
The part of triple extension involved in backside sprint mechanics that is not included is A) Hip flexion.
Step-by-step explanation:
In backside sprint mechanics, the aspect not involved in triple extension is Hip flexion, as triple extension includes extension of the ankle, knee, and hip, not shoulder abduction. Triple extension refers to the simultaneous extension of the ankle, knee, and hip joints, which are required during explosive movements such as sprinting, jumping, and lifting.
This extension includes B) Knee extension, as the knee joint straightens; C) Ankle dorsiflexion, as the toes are pulled up towards the shin; and the hip joint extends to propel the body forward. D) Shoulder abduction, the movement of the shoulder joint away from the midline of the body, is not part of the triple extension.
Thus, the correct option is A.