- For the 2-month-old infant:
- Injection Site: Vastus lateralis (lateral thigh).
- Muscle Targeted: Vastus lateralis.
- Origin: Greater trochanter and linea aspera of the femur.
- Insertion: Patella via quadriceps tendon, tibial tuberosity via patellar ligament.
- Action: Knee extension.
- Location: Mid-thigh, outer side between the hip and knee.
- For the 65-year-old grandfather:
- Injection Site: Deltoid muscle (upper arm).
- Muscle Targeted: Deltoid.
- Origin: Lateral third of the clavicle, acromion, and scapular spine.
- Insertion: Deltoid tuberosity of the humerus.
- Action: Arm abduction, flexion, extension, and rotation.
- Location: 2-3 fingers below the acromion process in the upper arm.