One category of gait measurements proven powerful in scientific literature is spatiotemporal parameters (STP). All STP are derived from a few basic variables, reflecting the spatiality and temporality of foot-based placements.
In measuring gait analysis, the first step is to isolate the gait cycle. Computerized systems such as the Zeno Walkway collect key events during gait and then separate it into different phases and quantify measurements to characterize movement. Specifically, The Zeno Walkway System collects data based on the direct acquisition of the spatial coordinates of the feet on the ground and the contact times.
(This is part 1 of 2 – link to part 2 is below)
Measuring Time Parameters
These parameters are the raw time values that reflect the patient’s walk. In the final analysis, these raw values are not used directly, in seconds or milliseconds, as it’s not very expressive and are in direct connection with the frequency of locomotion. The analysis of the relative durations of each phase as a percentage of the total duration of the gait cycle is more usual.
- Duration of step (s): period between the first contact of a foot and the first following contact of the contralateral foot.
Duration of the left step = first contact on the left – first contact on the right
Example: 10.358 – 9.775 = 0.583 s
- Stride duration (s): total duration of the gait cycle which is equivalent to the time taken to make two successive steps; this duration is used to express the walking phases in relative duration (%). The duration of the cycle is calculated as the time elapsed between the first contact of a foot and the first following contact of the same foot.
Duration of the left cycle = first contact for left footprint n°2 – first contact for left footprint n°1
Example: 10.358 – 9.167 = 1.167 s
- Stance phase (s): period when the foot is in contact with the ground (single support + double support). This is measured by subtracting the instant of first contact of the foot from the instant of the last contact of the foot, duration to which is added a temporal sample to have all the support. The temporal sample is added because at the last moment, the foot is still in contact with the ground.
Stance phase = last contact – first contact + 1 sample
Example for a system at 120 Hz: 9.933 – 9.167 + 0.00833 = 0.77433 s
- Swing phase (s): the period during which the foot is not in contact with the ground.
Swing phase = cycle time – stance phase
Example: 1.192 – 0.775 = 0.417 s
- Single support (s): period during which only one foot is in contact with the ground; it is equivalent to the swing phase of the contralateral lower limb for the considered cycle.
- Double support (s): initial and final periods of the support phase, where both feet are in contact with the ground; it can be considered as a global duration or by differentiating initial double support and terminal double support.
Initial double support = (last contact of the previous foot + 1 sample) – first contact of the current foot
Example for a system at 120 Hz: (9.933 + 0.00833) – 9.775 = 0.16 s
Final double support = (last contact of the current foot + 1 sample) – first contact of the next foot
Total double support = initial double support + terminal double support
Once expressed as a percentage of the cycle time (simple cross product), the proportions of the different phases become easier to work with, but they do vary in changes with speed.
Measuring the Stance Phase
The stance phase includes the initial double support; the phase of single support; and the final double support. This phase represents a global component of the support of a foot on the ground.
The duration of the stance phase at spontaneous speed is about 60% of the walking cycle. This proportion decreases when the speed increases, in favor of the duration of the oscillating phase which represents the remaining 40% of the cycle where the leg is no longer in contact with the ground and is brought forward.
The stance phase is often prolonged when the subject presents a problem of balance. When the gait disorder affects one side more than the other (hemiplegia, prosthesis, pain), the stance is shortened on the (more) affected foot and increased on the other member.
It should also be noted that the stance phase is shorter during a walk with shoes compared to a barefoot walk, as shoes provide a slightly larger ground surface and improve the balance (Eisenhardt et al., 1996).
The most relevant information in measuring the stance phase is the ratio between the single support phase (40%) and the two phases of double support (twice 10%).
The single support phase is equivalent to the swing phase of the contralateral limb. When walking is symmetrical, reducing the phase of single support increases the proportion of double support. This is the case when a person is led to walk more slowly than at spontaneous speed and/or when there is a problem of dynamic balance. In either case the subject increases the time spent on the two supports to allow more time to control the center of mass. On the contrary, if a subject is asked to walk faster, double support will be reduced in favor of single support. Although the double support phase is often studied in its entirety, differentiating between initial and terminal double support makes it possible to specify a problem during the transfer from one limb to the other.
- Cadence (steps/min): number of steps taken during a given time; the unit used clinically is usually the number of steps per minute.
The cadence is given in steps per minute or in cycles per minute, information once again more exploitable. However, mathematically, the cadence, which is a frequency (number of events per second), is calculated as the inverse of the cycle time. It is then assigned a factor of 60 to obtain a number in cycles per minute or a factor of 120 for the number in steps per minute.
The spontaneous cadence is usually between 98-138 steps/min for women and 91-135 steps/min for men aged 18-49. Women compensate for the shortest step length with a greater frequency of steps. In general, an increased cadence occurs regardless of sex for adults who are shorter than average.
Read part 2, Measuring Spatial Parameters, Speed and Walk Ratio