According to common knowledge, one of the key muscles in anterior pelvic tilt are the abdominal muscles. The most prominent of these muscles is the rectus abdominis, a paired muscle that runs vertically on both sides of the abdomen:

The rectus abdominis muscles

The rectus abdominis muscle is what you see when someone has a "sixpack". Since the ambdominal muscles are involved in tilting the pelvis backwards (i.e. posterior pelvic tilt), it has been assumed that the strength of these muscles is related to the degree of anterior pelvic tilt during standing.

Anatomically, this idea makes sense on the surface. In anterior pelvic tilt, where the pelvis is tilted forwards, the abdominal muscles would appear to be stretched downwards, which would in turn cause them to lengthen and become weak over time. This is why several people, including physiotherapists, recommend training the abdominal muscles when there is an excessive anterior pelvic tilt.

The problem is that it's based on a anatomical hypothesis of what should happen when the pelvis is tilted forwards, not what actually happens. Empirically, it remains to be proven that abdominal muscle strength is related to anterior pelvic tilt in any way. Furthermore, even if abdominal muscle weakness did correlate with anterior pelvic tilt, it would not prove that training the muscles would fix anterior pelvic tilt.

One of the standard ways of measuring abdominal muscle strength is the leg-lowering test. To perform the leg-lowering test, lie on your back and raise your feet into the air so that your torso and legs are in a 90 degree angle and your knees are straight. Flatten your spine to the ground. Then, lower your both legs together while keeping your knees straight and your back flattened against the ground. The lowering part should take 10 seconds. The point where you notice your lower back start to arch or come off the ground is the cut-off point for the test. Here's a video showing the leg-lowering test:


In one study, 31 healthy men and women were measured for abdominal muscle strength, lumbar lordosis (i.e. the curvature of the spine) and pelvic tilt (1). To measure abdominal muscle strength, the leg-lowering test was performed. The correlation between the variables was so low that according the authors, abdominal muscle function, lumbar lordosis and pelvic tilt were not linked.

Part of the reason for this lack of link is that the abdominal muscles are not active during standing and walking. The strength or weakness of the abdominal muscles is therefore not likely responsible for the degree of pelvic tilt or lumbar lordosis, even though this relationship has often been assumed.

The authors note that while the leg-lowering test is a standard test for measuring abdominal muscle function, it has not been proven to measure muscle strength accurately. A different measurement might have given different results. Furthermore, the length of the abdominal muscles was not measured. Thus, it is possible that the structure of the abdominal muscles is involved in pelvic tilt and lumbar lordosis.

What this study does show, however, is that much of the information out there on anterior pelvic tilt is not based on empirical evidence.

References

(1) Walker ML, Rothstein JM, Finucane SD, Lamb RL. Relationships Between Lumbar Lordosis, Pelvic Tilt, and Abdominal Muscle Performance. Physical Therapy, 1987; 67(4): 512-516.