The rectus abdominis is indeed the most well-known and prominent muscle of the abdominal region. It is a paired muscle, meaning there is one on each side of the midline, and it extends vertically from the pubic bone (pubis) to the lower ribs (fifth, sixth, and seventh ribs).

The rectus abdominis is commonly referred to as the "six-pack" muscle because it is responsible for the appearance of the abdominal muscles in a well-toned individual. It is divided into segments by fibrous bands called tendinous intersections, which give it a segmented or "six-pack" appearance.

At the superior (upper) end, the rectus abdominis connects to the xiphoid process. The xiphoid process is a small, cartilaginous extension at the lower end of the sternum (breastbone). It serves as an attachment point for various muscles and ligaments, including the rectus abdominis.

The rectus abdominis plays a crucial role in trunk flexion, which involves bringing the chest towards the pelvis. It is involved in various movements such as sit-ups, crunches, and other exercises that require bending or flexing the trunk forward.

It's worth noting that the abdominal region is composed of several other muscles as well, including the external and internal obliques, transversus abdominis, and the deeper muscles of the core. Together, these muscles provide stability, support, and contribute to various movements of the trunk.

Stretching and exercising the hip muscles can indeed help improve flexibility and loosen them up. It's always important to ensure proper form and technique when performing any exercise to avoid injury.

Based on your description, it seems like you're performing a variation of the lower body crunch where you lie on your back, lift one leg up onto the knee, and perform a crunch motion. Remember to support your neck during the exercise to prevent strain.

Starting with a small range of motion is normal, especially if you're just beginning or have tight hip muscles. Gradually, as you continue to perform the exercise and improve flexibility, you should be able to achieve a deeper lower body crunch.

While exercise is beneficial for overall health, it's important to consult with professionals such as a local family physician, physiotherapist, registered dietitian, or athletic therapist for personalized advice and guidance, especially if you have any existing health conditions or concerns.

Additionally, a balanced diet plays a crucial role in maintaining good health. If you're looking for dietary advice, a registered dietitian can provide tailored recommendations based on your specific needs and goals.

Remember to listen to your body, start with a comfortable range of motion, and gradually progress as you feel more comfortable and flexible. If you experience any pain or discomfort during the exercise, it's advisable to consult with a healthcare professional for proper evaluation and guidance.