Four groups of muscles that contribute to proper posture to avoid low back pain are the

a) flexors

b) extensors

c) abdominal

d) Lower back muscle

Explanation:

The flexors group of muscles along with abdominal muscles are responsible for flexing motion of the body. It also enable a person to bend forward and helps in lifting and controlling the arch in the lower back. These muscles lie on the front side

While the extensor muscles lie on the backside and allows one to lift object and  stand upright. These muscles work together to stablize body posture

Lower back muscle along with abdominal muscles prevent low back pain.