Final answer:
The hamstrings, pectoralis major, hip flexors, and erector spinae are muscles that commonly tend to be tight from factors such as poor posture and insufficient stretching.
Step-by-step explanation:
Frequently, certain muscles may become tight due to a variety of factors including poor posture, lack of stretching, or strenuous activities. Four common muscles that are prone to tightness include the hamstrings, which are located on the back of the thighs; the pectoralis major, which is found on the chest; the hip flexors, which include the iliopsoas group at the front of the hips; and the erector spinae, which run along the spine and are responsible for maintaining an upright posture.