Which of the following is a common cause of poor posture?

Weak abdominal muscles are indeed a common cause of poor posture because the abdominal muscles play a crucial role in stabilizing the core and maintaining proper alignment of the spine. When these muscles are weak, it can lead to an imbalance where the pelvis tilts or shifts. Consequently, other muscle groups may become overactive or strained in an attempt to compensate for the lack of support. This can result in poor posture, often presenting as excessive arching of the lower back or slumping of the shoulders.

Additionally, while excessive flexibility of the back can contribute to a lack of stability and thus affect posture, the primary issue typically stems from a lack of strength, particularly in the core area. Strength in the hip flexors is important for overall functioning, but if they are strong without balanced abdominal support, they can contribute to a tilting posture. High activity levels generally promote better alignment and strength unless poor movement mechanics are consistently practiced, which is not commonly seen as a direct cause of poor posture in itself.