Age-Related Changes in Gait Characteristics

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LITERATURE REVIEW

Epidemiology

The proportion of elderly individuals in our society has been increasing (US Census Bureau, 2001) . The U.S. Census Bureau reported in 2001 that there was an increase in the population of 75 to 84-year-olds by 23 %, and the population of 65 to 74-year-olds by approximately 2 % between the years of 1999 and 2000. Further, according to these studies (American Geriatrics Society, British Geriatrics Society, & American Academy of Orthopaedic Surgeons Panel on Falls Prevention, 2001; Campbell, Reinken, Allan, & Martinez, 1981), the number of accidents due to falls increases with age.
Most falls among the elderly occur indoors (Kochera, 2002; Sjorgen & Bjornstig, 1991; Tinetti, Speechkey, & Ginter, 1988). Hornbrook et al. (1991) indicate that 56.6% of falls occur inside the home, 14.7% immediately outside the home, 17% away from the home in a familiar place, and 11.7% away from the home in an unfamiliar place. Additionally, Sjorgen et al. (1991) noted that most falls among the elderly occur indoors (71%) and the most common site (28%) for the falls are the living area such as the living room, hall ways, and other rooms rather than the kitchen (12%) and the bedroom (7.5%).
Indoor fall accidents are more likely to be caused by tripping, stepping wrongly, and intrinsic factors than are those that occur outdoors (Sjorgen et al., 1991). Indoor falls due to slipping are considered a small proportion of all falls (Sjorgen et al., 1991). On the other hand, the major reason of outdoor falls is slipping (Sjorgen et al., 1991).
The most common indoor floor covering, carpet, is considered a causative factor of indoor falls. According to Davidsen (1995), 70% of indoor floors in the United States are covered with carpet. Falls among the elderly predominantly occur indoors. Previous studies suggest that carpet could cause dangerous situations resulting in falls (Dickinson, Shroyer, & Elias, 2000; Gibson, 1998).
Although epidemiological studies suggest increases in fall accidents among the elderly indoors, mechanisms regarding these fall accidents remain elusive.

Gait Pattern

Gait Cycle
The gait cycle with one leg consists of two periods; namely, a stance and swing period. The stance is the time when the reference leg is on the ground; the swing is the time when the reference leg is off the ground.
He stance phase constitutes 60% of the gait cycle and the swing phase takes 40% of the gait cycle. The two phases are distinguished into several steps. The stance period consists of ground contact (0% of the normal gait cycle), foot flat (15%), heel off (40%), contralateral ground contact (50%), and toe off (60%). The swing period consists of early swing (60-75 %), mid swing (75-85 %), and late swing (85-100%).
Gait Parameter
Stride and Step Length
Step length is referred to as the distance from the heel contact of one foot to the following heel contact of the opposite foot (Oatis, 2004). Stride length is the distance from the heel contact of one foot to the following heel contact of the same foot (Oatis, 2004). Previous studies (Bunterngchit et al., 2000; Willmott, 1986) examined the stride and step length for steps taken on two different floor surfaces (e.g., a carpeted and vinyl floor hsurface). Both stride length and step length of the elderly walking on carpeted floor surfaces increased compared to walking on vinyl tile floor surfaces.
Toe Clearance
Foot clearance is defined as the height of markers on the heel or the toe from the ground (Bunterngchit et al., 2000; Gehlsen & Whaley, 1990). A considerable number of falls among the elderly are due to trips which occur when the foot contacts the floor during the swing phase (Tinetti et al., 1988). According to Startzell and Cavanagh (1999), the risk of a trip can be analyzed with the measurement of foot clearance in the sagittal plane during the swing phase of the gait cycle. A previous study (Winter, 1990) compared elderly participants’ toe clearance with younger participants’ toe clearance. The older participants in this study showed shorter toe clearance (1.12 cm) than their younger counterparts (1.29 cm).
Heel Contact Velocity over Different Floor Surfaces
According to previous studies (Karst, Hageman, Jones, & Bunner, 1999; Myung R. & Smith J.L., 1997; Winter, 1991), high horizontal heel contact velocity increases the likelihood of slipping. Cham and Redfern (2002) studied gait characteristics on different floor materials, such as vinyl and rough tile floor surfaces. They observed that heel velocity in the direction of motion at heel contact is greater on vinyl surfaces (mean velocity=0.19 m/s, S.D.=0.39) than on the rough floors (mean velocity=0.15 m/s, S.D.=0.31). However, in their study, age effects were not considered. On the other hand, Winter (1991) and Lockhart (1997) state that the elderly group have higher heel contact velocity in the horizontal direction than the younger group. It is worth noting, though, that they conducted the experiment without considering carpeted floor surfaces. Thus, in this study, the age and floor types will be considered for heel contact velocity in order to identify the relationship between heel horizontal contact velocity and slip-induced falls.
Velocity of the Whole Body Center-of-Mass (COM)
Sagittal and frontal 3-D link (14) segment models (Lockhart et al., 2003) are used to examine the velocity of the whole body center-of-mass (COM). Twenty- seven markers on landmarks of the body are utilized to define a whole body model. There is a contradictory result associated with walking velocity of the elderly. According to Willmott (1986), the elderly (mean 76.05 years of age) walk faster on a carpeted floor (mean velocity = 0.48 m/s, S.D. = 0.19) than on a vinyl floor (mean velocity = 0.40 m/s, S.D. = 0.17). However, Dickinson et al (2000) and Stephens et al (1999) suggest that elderly people walk slower on a carpeted floor than on a vinyl floor. McGibbon et al. (2001) examined gait patterns of the elderly (mean 70.67 years, S.D. =8.66) on a 10m carpeted walkway. The gait speed of elderly participants was 1.13 ± 0.2 (m/s). On the other hand, the walking velocity of the elderly was 1.2 (m/s) on the vinyl floor (Kim, 2003). The elderly walked slower on the carpeted floor than the vinyl floor.

Tribology

Tribology is a study focusing on friction, wear, and lubrication of interacting surfaces in relative motion (Stachowiak & Batchelor, 2001). The slip resistance between shoe soles and floor surfaces is considered important in order to decrease the risk of slipping. For slip resistance, the coefficient of friction (COF), defined as the ratio of the foot’s horizontal shear force to the foot’s vertical normal force (Chaffin, Woldstad, & Trujillo, 1992), must be examined.
There are two kinds of COF, namely static COF and dynamic COF (Lockhart, Woldstad, Smith, & Ramsey, 2002b; Hanson et al., 1999; Redfern & Bidanda, 1994; Swensen, Purswell, & Schelegel, 1992). Static COF is referred to as the shear force required to initiate movement of an object on a floor divided by the vertical force on the object. On the other hand, dynamic COF is the shear force that is required to sustain movement of the object over the vertical force (Redfern et al., 1994).
RCOF represents the ratio of the horizontal foot force to the vertical foot force, indicating the minimum coefficient of friction available at the interface between shoe and floor to avoid initiation of slipping (Lockhart et al., 2002b). Foot slip can be avoided when the COF is higher than RCOF. McVay and Redfern (1994) noted that the peak RCOF is used to predict the slipperiness of the floor. Additionally, the peak RCOF has been employed to indicate the requirements of walking on various floor surfaces (Hanson et al., 1999; McVay & Redfern, 1994).
A previous study (Bunterngchit et al., 2000) investigated RCOF when participants walked on carpeted and soapy vinyl floor surfaces. The results indicate that the participants have higher RCOF values on a carpeted floor than on a soapy vinyl floor. Additionally, Lockhart et al. (2002b) observed that younger participants have higher RCOF values than older participants on a non-slippery floor surface.

Subjective Perception of Floor Slipperiness

Besides tribological effects, subjective perception of floor slipperiness is essential as well to prevent from a slip, trip, or fall accident (Li, Chang, Leamon, & Chen, 2004).When people walk on a slippery floor surface, they change their gait patterns to reduce the propensity of a slip.
Myung, Smith, and Leamon (1993) stated humans are able to distinguish floor slipperiness, which is reliable but risky. False subjective perception of slipperiness might lead to an inappropriate gait pattern, which results in higher probability of a slip-induced fall accident (Li et al., 2004).

Age-Related Changes in Gait Characteristics

The elderly show several gait adaptations, such as reductions in stance duration and loading speed on the supporting foot, and shorter stride length (Cham & Redfern, 2002; Edelstein, 1988). Additionally, studies (Cham et al., 2002; Dobbs et al., 1993; Winter, 1991; Edelstein, 1988) have found that walking velocity decreases with advancing age. Winter (1991) mentioned the lower walking velocity of the elderly, comparing levels of ankle plantar-flexor power during push-off. The elderly showed 2.478 W/kg at 1.29m/s while the young showed 3.266W/kg at 1.44m/s (Winter, 1991). These statistics indicate that the elderly have less vigorous push-off power (Kavanagh et al., 2004; Judge, Davis, III, & Ounpuu, 1996; Judge et al., 1995).

Summary

The elderly population who is more likely to suffer from a slip, trip, or fall is experiencing a rapid growth rate. The rate of indoor falls among the elderly is much higher than outdoor falls and many of theses falls are due to hazardous conditions associated with floor coverings. Seventy percent of indoor floor covering materials in the United States are covered with carpet (Davidsen, 1995) and the elderly spend most of their time indoors often encountering transitions from carpeted floors (e.g., bedroom and living room) to vinyl floors (e.g., kitchen and bathroom) or vice versa. There have been a number of studies trying to determine what factors affect older individuals in terms of balance and gait characteristics on vinyl or carpet. However few have tried to find the effect of transitioning over different floor surfaces on gait characteristics even though indoor falls exist predominantly. People exhibit several changes in gait characteristics (e.g., gait speed, stride length, toe clearance, heel contact velocity, walking velocity, and RCOF) when they walk over different floor surfaces (e.g., vinyl and carpeted floor surfaces). In conclusion, gait adaptations associated with different floor surfaces may influence the outcome of a slip, trip, or fall accident.

ABSTRACT.
DEDICATAION
ACKNOWLDEGEMENTS
1. INTRODUCTION
1.1 Background.
1.2 Statement of the Problem
1.3 Objective of the Study
2. LITERATURE REVIEW
2.1 Epidemiology
2.2 Gait Pattern
2.3 Tribology
2.4 Subjective Perception of Floor Slipperiness
2.5 Age-Related Changes in Gait Characteristics
2.6 Summary
3. METHODS
3.1 Participants Population
3.2 Apparatus.
3.3 Procedure
3.4 Experimental Variables
3.5 Data Analysi
4. RESULTS
4.1 Data Analysis
4.2 ANOVA Results
4.3 Paired-Comparison t-Test
4.4 Summary of Results
5. DISCUSSION AND CONCLUSION
5.1 Hypotheses and Experimental Findings
5.2 Conclusions
5.3 Design Guidelines/Design Recommendation
5.4 Limitations and Assumptions
5.5 Summary of Future Research
Reference List
APPENDIX
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The Effects of Transitioning Between Different Floor Surfaces on Gait Characteristics of the Elderly

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