Gait: definition, what's normal, what's not

Walking is one of the most natural, frequently used and essential human movement patterns. Abnormalities in walking can indicate potential muscular and postural imbalances ....

Definition
 
In simple terms, gait is walking forward. If we want to get more sophisticated, it is propulsion of the erect body forward with the lower extremities. This movement of the body’s mass in space requires energy. The energy expenditure is determined by the body’s weight and to what extent it is displaced around its centre of gravity. The centre of gravity of the human body is 1cm anterior to the first sacral segment of the spine (S1) when a person is erect with his feet a few inches apart and arms at the side.
 
Normal gait
 
Efficient movement of the body forward is normal gait. When the gait is efficient energy expenditure is minimised. ‘Abnormal gait patterns’ are any deviations from this minimum. So, the technical definition of ‘normal guide’ is: “the forward locomotion of the body during which the body’s centre of gravity describes a sinusoidal curve of minimum amplitude in both the Y and X axes.” (Gross et al., Musculoskeletal Examination, 2016)
 
Displacing the body’s centre of gravity further away from this optimal pattern increases energy expenditure. This makes locomotion less efficient and increases fatigue.
 
The repetitive positioning of the limbs forms a cyclical pattern. This cycle is divided into stance and swing.
 
The stance phase has five discrete stages: heel-strike > foot-flat> midstance > heel-off > toe-off. It comprises 60% of the time of a normal gait cycle.
 
The swing phase constitutes the remaining 40% and is encapsulated in the following phases: initial swing (acceleration) > mid swing > terminal swing (deceleration).
 
When both feet are on the ground, this is called double support. The distance between the two feet when they are in contact with the ground is called step length. Stride length, on the other hand, is the distance between two subsequent heel strikes of the same leg.
 
Gait is determined by 6 postural factors making the movement efficient and reducing energy expenditure. The first 5 minimise the displacement of the body’s centre of gravity vertically, while the 6th one minimises it laterally.

1. Pelvic tilt – approximately 5 degrees on the swing side
2. Pelvic rotation – approximately 8 degrees in total on the swing side
3. Knee flexion – to approximately 20 degrees in the early stance phase
4. Plantar flexion – to approximately15 degrees in the early stance phase
5. Another plantar flexion – this time to approximately 20 degrees in the late stance phase
6. Narrow walking base – accomplished thanks to normal knee valgus and foot placement

 
Gravity pulls the body down throughout the whole cycle causing rotation in the joints of the legs. This rotational movement is termed moment. Its magnitude is a function of the perpendicular distance between the centre of gravity and the axis about which the force of gravity acts (or the moment arm) and the size of the force.
 
Using the vertical axis (Y axis) as the moment arm, the rotation toward the midline is termed varus and away from the midline – valgus. When a joint closes as a result of the moment, this is called flexion. For example, during heel-strike, there is spontaneous closing (flexion) of the thigh on the torso. Conversely, when there is an opening (increase) in the joint angle when the moment arm acts, this is extension. The quadriceps extend the knee during walking when it contracts.
 
Understanding the concept of moment helps with analysing each joint throughout the cycle. It is possible to predict in theory when each muscle must be active and where it must be positioned by examining the relative positions of the joint in question and the body’s centre of gravity.
 
Abnormal gait
 
Knowledge of optimal biomechanics is essential in order to identify abnormal gait. The three key causes of abnormal guide are:

• Pain – Usually, this leads to a decrease in the duration of the stance phase and avoiding contact with the ground where the pain is.
• Weakness – There is an observable decrease or increase in the motion in the affected joint during muscular contraction. Usually, other joints compensate for this by adjusting the location of the centre of gravity to prevent falling.
• Leg length discrepancy and abnormal range of motion – Other joints would try to compensate to allow weight bearing, clearance of the limb or the displacement of the centre of gravity.

 
These factors are interconnected and can occur together or separately. A weak muscle and cause pain in a joint, which will limit its range of motion, for example. When these factors appear in isolation, however, they result in classified gait abnormalities.
 
Gait disorders, however, can also be caused by diseases of the nervous system or injuries. Cases of spastic, ataxic, or parkinsonian gait would be such examples.
 
The ability to recognise movement symmetry is key to identifying abnormal gait. It is therefore essential to observe a client’s walking over an extended distance sometimes. Subtle abnormalities may take some distance to show up and the space of the treatment room may not be enough. Ideally, the patient must be observed without their conscious knowledge so they don’t try to modify their gait.
 
Therefore, the observant therapist can learn a lot about the health and alignment of the body just by the way a person walks.