Muscles and Actions in Gait
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Direct answer
Walking is a controlled fall repeated with every step: each cycle, just over a second long, divides into stance (about 60 per cent) and swing (about 40 per cent), and each phase has its own muscle script. Quadriceps contracts eccentrically at loading response to stop the knee buckling, soleus and gastrocnemius restrain then drive the tibia through mid and terminal stance, gluteus medius and minimus hold the pelvis level in single support, the hip flexors launch swing, the dorsiflexors hold the foot up to clear the ground, and the hamstrings decelerate the swinging shank before heel strike. Read the failing muscle and the gait names itself — Trendelenburg, high-stepping, waddling, hemiplegic circumduction.
What you must remember
- Cycle arithmetic: stance about 60 per cent, swing about 40 per cent; two brief double-support intervals separate the single-support phases; cadence near 100 steps per minute is typical adult walking.
- Loading response (0-15 per cent): quadriceps works eccentrically to absorb knee flexion; gluteus maximus and hamstrings decelerate the limb's forward momentum at heel strike.
- Mid and terminal stance: soleus performs eccentric then concentric work to control and finally push the tibia; the intrinsic windlass mechanism tensions the arch as the heel lifts.
- Pelvic stability: gluteus medius and minimus (with tensor fasciae latae) abduct the stance hip so the pelvis does not drop on the unsupported side — the Trendelenburg test and sign.
- Swing phase: iliopsoas and rectus femoris initiate flexion, the dorsiflexors (tibialis anterior, extensors) keep the toe cleared, and hamstrings brake knee extension before contact.
- Named pathological gaits: Trendelenburg waddle (hip abductor weakness, myopathic or superior gluteal nerve), high-stepping foot drop (common peroneal palsy or L5), hemiplegic circumduction with equinus, parkinsonian festination with reduced arm swing, scissoring from adductor spasticity, and antalgic (short stance on the painful limb).
- Viva rule: timing beats naming — say which phase the abnormality appears in, then name the muscle and its nerve.
Analysing a limp at the bedside
Stand the patient, ask for a few lengths of corridor, and watch from the front, then behind. First the pelvis: if it dips toward the swing side in single stance, the stance-side abductors have failed — positive Trendelenburg sign; when both hips fail the child develops the classic myopathic waddle, body lurching side to side over each weak hip. Then the feet: a foot slapping at heel strike or dragged with toes scraping the floor points to dorsiflexor weakness, and the patient lifts the knee excessively to clear the ground — high-stepping gait of a common peroneal palsy at the fibular neck. Then the knees: a back-knee thrust or a hand pressing the thigh downward on forward stepping signals quadriceps weakness, the patient locking the knee in extension to accept weight.
Timing converts observation into anatomy. Pain appearing in stance shortens the stance phase on that side (antalgic gait). A drop-foot that clears by hip hiking is a swing-phase problem; a pelvis that lurches laterally in stance is an abductor problem. The viva sequence examiners reward is phase, muscle, nerve, then the commonest cause at that age — muscular dystrophy in children, poliomyelitis residua in older patients, peroneal palsy in adults, Parkinson's disease or stroke in the elderly.
Where students slip
Two confusions dominate. The first is assigning gluteus maximus the central role in level walking — its peak is brief at and just after heel strike, and it dominates climbing, rising from sitting and running; pelvic control in level gait belongs to the abductors. The second is calling every drooping foot pattern a "Trendelenburg gait"; the names are not interchangeable, and mixing the abductor weakness pattern with the dorsiflexor failure pattern is the quickest way to lose the viva. A third, quieter slip is forgetting that quadriceps activity in loading response is eccentric — a lengthening contraction that absorbs energy — which is why its weakness produces the hand-on-thigh, back-knee compensations rather than simple collapse.
Frequently asked questions
What is the role of the gluteus medius during the stance phase?
It abducts the stance hip to hold the pelvis level over the single supporting limb; weakness produces a positive Trendelenburg sign and a lurching gait.
Which muscles prevent foot drop during the swing phase?
The dorsiflexors — tibialis anterior, extensor hallucis longus and extensor digitorum longus, deep peroneal nerve — failing in common peroneal palsy.
Why does quadriceps weakness cause the patient to press the thigh while walking?
The eccentric quadriceps control of knee flexion at loading response is lost, so the patient keeps the knee locked in extension and pushes it back with a hand for security.
What is a high-stepping gait and what causes it?
Excessive hip and knee flexion to clear a dropped foot, caused by dorsiflexor weakness — classically common peroneal nerve injury at the neck of the fibula.
Which gait is typical of Parkinson disease?
Festination — short, quick shuffling steps with stooped posture, reduced arm swing and difficulty starting and stopping, with turns made en bloc.