The key idea is identifying the hip muscles that actively provide external rotation and are emphasized for steady, propulsive gait. The deep external rotators of the hip—six short muscles (the piriformis, superior and inferior gemelli, obturator internus and externus, and quadratus femoris)—work together to externally rotate the femur and stabilize the hip joint during walking. The posterior fibers of the gluteus medius and the gluteus maximus also contribute external rotation, especially when the hip is extending or when stabilizing the pelvis through the gait cycle. This combination is the set most associated with controlling internal rotation tendencies that occur during stance and progression. That’s why the described group includes the six short external rotators plus the posterior fibers of gluteus medius and gluteus maximus. The other options don’t fit because they involve hip flexors (iliopsoas and rectus femoris), ankle/foot dorsiflexors (tibialis anterior and EHL), or muscles that mostly act as abductors/internal rotators (gluteus minimus and TFL) rather than the emphasized external rotator group for gait.

The timing of fibularis longus and brevis activation is tied to their role in controlling foot stability during weight bearing and preparing for push-off. After heel contact, these muscles briefly start contracting to resist sudden inversion and to help progress the foot into stance, while also contributing to plantarflexion. They remain active through the majority of the stance phase, up to just before toe-off, when propulsion begins and other plantarflexors take over. This timing fits the need for lateral stabilization and controlled pronation as the body moves over the stance limb. The other options either truncate activation to a tiny moment or place it in phases (late swing or the entire swing) where these muscles aren’t functioning in weight-bearing, so they don’t best describe their usual activity pattern.

During heel contact through early stance, the body’s weight tends to flex the hip and tip the trunk forward. The gluteus maximus acts as a powerful hip extensor and stabilizer to oppose that tendency, keeping the pelvis and trunk upright and controlling the forward collapse of the thigh. This stabilization also sets up the limb for forward progression into midstance, contributing to propulsion by extending the hip as weight is borne. That’s why the best choice describes both supporting body weight and producing hip extension. The other options don’t fit: knee flexion isn’t the gluteus maximus’s role, pelvis elevation of the swing side is handled by other hip abductors, and toe extension occurs in the foot, not at the hip.

Hip flexion during gait is driven mainly by the iliopsoas, a powerful hip flexor formed by the iliacus and psoas major. It crosses the front of the hip joint, allowing the thigh to rise and move the leg forward into the swing phase, which is essential for advancing the limb. The gluteus maximus extends the hip, not flexes it, so it opposes this action. The tibialis posterior and soleus act on the foot and ankle, not the hip. So, the iliopsoas is the best answer because it is the primary muscle responsible for initiating and controlling hip flexion during walking.