PRINCIPLE 1. Equitable Use
5.7 GAIT ANALYSIS—VARIABLES AND THEIR SELECTION
Gait analysis is the term used to describe and analyze the process of producing the biomechanics of the movement. There have been a number of comprehensive studies conducted on “normal” walking [1–4], which characterize their gait. These allow for a framework to help in the understanding of the impact of disorders on the system and can help in the development of rehabilitation programs or the development of new assistive devices. Further, any deviation from the norm can be illustrated and can therefore help in the interpretation of the data collected for those with some pathology. Generally, a biomechanical analysis of human movement investigates variables, which can be identifi ed as outcome—is the result successful, i.e., is stable effi cient progress achieved; and process—how does the body operate mechanically in order to achieve this outcome.
As outcome variables relate the success of the movement, they are often more easily measured. The complexity of the process variables can mean that sophisti-cated measuring tools are required. Over the past 30 years advances in technology have resulted in the widespread availability of measurement systems and as such the collection and analysis of biomechanical data in gait laboratories is reasonably com-monplace. Nonetheless, the accurate collection and interpretation of this data refl ects its complexity and requires specialist knowledge in the fi eld.
5.7.1 OUTCOME VARIABLES
As the main aim of walking is to safely transport the body, these are the key outcome variables, which should initially be assessed. Linear displacement of the CoM is the fi rst assessment of gait. Safety in transport is usually related to stability in stance, which requires a net extensor moment at the three lower limb joints.
Outcome measures that further elucidate the extent to which the displacement of the CoM was successfully achieved are often referred to as temporal and spatial measures (TS). These give more information on the components which make up the overall displacement of the CoM. TS variables are widely used to describe normal and pathological gait. The variables are well defi ned in the literature and are broadly accepted. Typical TS variables are velocity, cadence, step, and stride length. Others that are frequently reported are step and swing period, single and double support time, and percentage of stride. Stance and swing are initially defi ned; stance when in the limb is in support and swing with in the limb is in the air (Figure 5.2). Stance makes up about 60% of the gait cycle and the remaining 40% is in swing. In total,
double support is about 20% of the gait cycle, equally divided between initial double support and terminal double support. Single support is about 40% (the same duration as the contralateral swing). Subphases of stance and swing are also defi ned, though the phasing is somewhat more variable (Section 5.9).
5.7.2 TEMPOROSPATIAL VARIABLES
A stride is the distance (along the direction of progression) from the initial contact of one foot to the next initial contact of that (ipsilateral) foot. Initial contact is often heel strike, but for some pathological conditions, the heel does not necessarily con-tact the ground. Typically, normal stride length is about 1.46 m in men and 1.28 m in women [2]. Children have established an adult stride length by about 11 years [2].
Step length is the distance from initial contact of one foot to the initial contact of the other (contralateral) foot. Stride length, therefore, is the sum of the length of the two steps of which the stride is comprised. Stride length, when traveling in a straight line, is symmetrical. Step length need not necessarily be symmetrical, and in many patho-logical conditions, it is not symmetrical. Stride time is the interval between the foot contacts. Velocity of the CoM is often recorded and gives quality information regard-ing the displacement, i.e., it tells us how fast the person is walkregard-ing. Normal walkregard-ing velocity is approximately 1.3–1.6 m/s [1] with different age groups and pathologies achieving different velocities. Cadence refers to the number of steps or strides per minute or second and can refl ect the capacity to walk of the participant. Normal walking cadence is about 110–115 steps/min. The speed of walking is equal to the cadence times the step length, if the steps are shorter the cadence increases at the same velocity. The temporal characteristics of gait vary with walking speed. When walking speed increases the stance phase and double support period gets shorter and the swing phase increases. Eventually, walking is no longer sustainable and running must occur. Running is defi ned by a period of fl ight/no support. When the cadence reaches about 180 steps/min then gait switches from walking to running.
Comfortable walking speed declines with advancing age and the decline begins in approximately the seventh decade of life. Kerrigan et al. [22] found that the natural FIGURE 5.2 Timing of a single gait cycle. IC indicates initial contact, DS indicates double support, TO indicates toe-off.
velocity of elderly walkers was 1.19 m/s. Their cadence was 119 steps/min and stride length was 1.2 m. Younger walkers had the same cadence, but walking velocity was higher (1.37 m/s) due to a longer stride (1.38 m). Hyndman et al. [23] found that people with a stroke walked with a slower velocity and a shorter stride length than aged-matched controls.
Healthy individuals who are asked to walk with assistive devices and load a limb to 50%, evidence a slower walking speed (1.281 m/s slows to 0.563–0.761 m/s depending on the type of device). The slower walking is as a result of both reduced cadence 110.9 reduced to 69.4–75.5 steps/min and stride length 138.4 shortened to 112.9–124.3 cm. In early unilateral osteoarthritis, patients walked at a signifi cantly slower speed (1.05 m/s) than an equivalent nonclinical group (1.18 m/s). The slower walking speed was as a result of both a signifi cantly reduced stride length (1.16 against 1.24 m) and a signifi cantly reduced cadence (108.62 against 114.27 steps/min). Total hip arthroplasty patients monitored preoperative and at 4 and 8 months postoperatively showed an increase in walking speed over time and a signifi cant difference was found preoperatively (0.95 m/s) and at 8 months postoperation (1.08 m/s). When using a cane, the subjects walked 3% slower than when walking independently [18]. Table 5.1 indicates the mean velocity, cadence, and stride length for different groups. All data are presented in the same units, so some calculations have been made to facilitate comparisons.
Table 5.1 illustrates the wide range of values for different populations. The TS variables of gait can change depending on the environment, size of the room, and even if the data are collected inside or outside. As a result many studies complete their own control trials in order to understand the normal range of the group if an
TABLE 5.1
Temporospatial Characteristics for a Normal and Nonpathological Populations
Velocity (m/s) Cadence (step/min) Stride Length (m)
Men [1] 1.3–1.6 110–115 1.4–1.6
Women [1] 1.2–1.5 115–120 1.3–1.5
Elderly [22] 1.19 119 1.2
Adult [22] 1.37 119 1.38
Poststroke [8] 0.23–0.73
Poststroke hemiparetic [24] 0.346 83.4 0.52
Early OA [25] 1.05 108.62 1.16
Elderly fallers [26] 0.89 107 138
Elderly nonfallers [26] 1.21 120 1.22
TTA SACH foot [27] 1.32 118 1.36
Hip arthroplasty before surgery [18]
0.95
Hip arthroplasty after surgery [18]
1.08
alteration is being made to that group, or if comparing disability to nondisability.
Control groups should be age and activity level matched as much as possible. When it is not possible to height match patients, it may be more appropriate to try to normal-ize the data. The most appropriate way is to convert the variables to dimensionless quantities (e.g., Ref. [1]).
When assessing the process by which the TS variables have been affected, i.e., how did the joint mechanics alter as a result of a pathology or of aging, it is important to ensure that the altered mechanics are not simply an effect of the slower walking, but as a result of the disability or aging. It is reasonably common to make allowances in interpreting pathological gait results in comparison to normal gait to account for the different walking speed. A relationship between many variables and speed has been established [28], which can be helpful in making diagnostic decisions.
It can be useful to ask the controls to walk at the same speed as the disabled group (e.g., Ref. [24]).
Gait performance has been seen to deteriorate when participants carry out a sec-ondary task. Tasks such as talking, carrying a tray/glass, stepping over obstacles, and responding verbally to sounds have been shown to slow gait. Hyndman et al. [23]
introduced a cognitive task—remembering a seven-item shopping list—to the task of walking 5 m. Both stroke patients and control groups walked more slowly, with a shorter stride length. Further, stride length was reduced for fallers compared to non-fallers in the stroke group. Walking speed has been shown to be affected when the environment is changed such as walking in a mall. Lord et al. [29] showed that gait speed of stroke patients in the clinic was 0.68 m/s while this slowed to 0.60 m/s in a mall. This was related to the unpredictability of the constraints imposed by the envi-ronment. Step length and step frequency were not signifi cantly different between the clinic and mall, but were much more stable in the clinic. This can have implications for rehabilitation, which is confi ned to the clinic as the skill may not be suffi ciently malleable to cope with the unpredictability of natural environments.
5.7.3 TS VARIABLESAND FUNCTIONAL MOBILITY
In order to achieve community mobility, people need to be able to walk at a 1.22 m/s (in order to be able to cross a street controlled by a traffi c light) for 332–360 m [30,31].
They also need to be able to negotiate a 17.8–20.3 cm curb, manage stairs, and a ramp. Older people with disabilities are more likely to take fewer trips and more likely to have more days in which no trips outside the house were taken compared to older people without disabilities [32]. On those trips, the people with a disability were not able to maintain the speed of those around them and they completed the trips accompanied by someone, while those without a disability were able to keep up with those around them and complete 95% of the trips unaccompanied.