1.1 Background
Fall related injuries are a serious public health issue in many countries all over the world (Lord, Ward, Williams and Anstey 1993; Kannus, Parkkari, Koskinen, Niemi, Palvanen, Jarvinen and Vuori 1999; Scuffham, Chaplin and Legood 2003). Falls could cause moderate to severe injuries such as bruises, hip fractures, or head traumas. Falls also generates psychological trauma and vast burden of health system. Falls not only reduce living independency, but also increase the risk of early death. In fact, falls are the most common cause of traumatic brain injuries (Jager, Weiss, Coben and Pepe 2000). As the population ages, fall accidents become more and more considerable affair we have to face.
In the United States, one-third of adults aged sixty-five years and older fall at least once each year (Hornbrook, Stevens, Wingfield, Hollis, Greenlick and Ory 1994; Hausdorff, Rios and Edelberg 2001). Falls in the home and community caused or led to 20,600 deaths in 2007. All age groups are vulnerable, but older adults are most at risk. The rates of fall-related deaths among older adults rose significantly over the past decade. Moreover, in the year of 2000, the direct medical cost totaled $0.2 billion ($197 million) for fatal falls and 0.19 billion for nonfatal fall-related injuries (Stevens, Corso, Finkelstein and Miller 2006). The annual cost of fall injuries is even expected to reach $54.9 billion by 2020 (Englander, Hodson and Terregrossa 1996). In Taiwan, accidental injury was the fifth leading cause of death from 1999 to 2006.
According to the survey of Executive Yuan in 2005, falls were the second most common cause of unintentional injuries within the last three months, only inferior to traffic accidents. However, for people aged sixty-five years and older, falls are the most common cause (up to 72.8%) of unintentional injuries.
Previous study also indicated that in Taiwan about one-fifth of adults aged
sixty-five years and above fall at least once each year and 44.4% of latest falls occurred at home (Directorate-General of Budget Accounting and Statistics 2007). Apart from the fall-related physical injuries and the vast burden to the health care system, falls also could generate psychological trauma. Many people, who experienced a fall, even a non-injury fall, develop fear of falling. The fear may cause them to limit their activities leading to reduced mobility and physical fitness, and increasing their risks of fall in the future (Vellas, Wayne, Romero, Baumgartner and Garry 1997). In a word, falls commonly occur at home, especially for people aged sixty-five years and above. Fall-related accidents could lead to both physical and psychological trauma, even death. Besides, the resultant medical cost is a heavy burden to the sufferers and the health care system.
In Taiwan, that population aged sixty-five years and above was more than 7% by 1993 (Directorate-General of Budget Accounting and Statistics 2007), which means that Taiwan has become an aging society since then, and is expected to be over 20% in 2026 (Department of Manpower Planning 2008).
Therefore, fall-related injuries and resultant medical cost in people aged sixty-five and above would be a crucial concern. If we could reduce the occurrence of falls, fall-related injuries and health care expenses would inevitably diminish so does corresponding scocio-economic cost. Suitable living environments could prevent people from falls or slips and further guarantee their quality of life against the fall-related threats. Among the most important environmental factors related to falls are the frictional and material properties of the floor and shoes (Redfern, Cham, Gielo-Perczak, Gronqvist, Hirvonen, Lanshammar, Marpet, Yi-Chung Pai and Powers 2001; Cham and Redfern 2002).
A study, about the circumstances of falls in the elderly in Taiwan in year 2005 and those in year 1999, indicates that about 40% of falls are caused by environmental factors, and within which the two most common factors are
slippery floor and obstacles on the ground (Tsai, Yeh, Lan, Chang and Tseng 2008).
In many industrial countries such as Taiwan, multiple floor materials are commonly used in living environments. Since frictional and material properties of the floor and shoes are important environmental factors of falls, many researches have studied the effects of floor materials on gait. However, floor transition (i.e. from one material to another) has been paid less attention, as well as resultant accidents. The understanding of floor transition is still insufficient and the effects of floor transition on locomotion and gait stability needs to be revealed more comprehensively. Therefore, we would like to investigate the influence of floor transition on gait stability in order to expand the knowledge in this field. Meanwhile, we expect the results of this study could provide a recommendation for people when choosing interior floor materials, which could practically avoid the transition-induced fall events
1.2 Objective
Falls are prominent among the external causes of unintentional injury and the frequency of falls increase with age and frailty level (World Health Organization 2008). In consideration of the increasing proportion of population aged sixty-five years and above in Taiwan, and the high ratio of fall-at-home events, we would like to improve home environment and make it safer and more suitable for all age. However, falls occur as a result of a complex interaction of risk factors which are usually categorized into four dimensions: biological, behavioral, environmental and socioeconomic factors. Factors related to the physical environment, such as floor materials, contaminants, are the most common causes of falls in older people, responsible for 30-50% of fall incidents (Rubenstein 2006). Furthermore, floor transition (for example: from living room to kitchen and from bedroom to bathroom) is a common yet frequently neglected
condition of indoor space when considering the factors of falls. Therefore, we want to reduce the floor material-induced fall risks. The purpose of this study is to examine the effect of floor transition on gait stability.
Many studies have used the motion of whole-body center of mass, center of pressure (COP) under feet and the interaction between the two variables to describe the gait stability (Jian, Winter, Ishac and Gilchrist 1993; Mackinnon and Winter 1993; Prince, Winter, Stergiou and Walt 1994; Winter 1995; Krebs, Jette and Assmann 1998; Polcyn, Lipsitz, Kerrigan and Collins 1998; Tucker, Ramirez, Krebs and Riley 1998; Chou, Kaufman, Brey and Draganich 2001;
Hof, Gazendam and Sinke 2005; Lee and Chou 2006; Parker, Ostering, Van Donkelaar and Chou 2006). Nonetheless, this method needs enormous anthropometry database and reconstruction of three-dimensional multiple segment biomechanical models as well. The complexity of calculation and high technical skill it needs may limit the practical utility of COM in evaluating the stability (Hahn and Chou 2003). Consequently, in addition to observing gait, we expect to find out other kinematics or kinetics variables that could efficiently represent the stability of locomotion without complicated calculating process.
1.3 Hypothesis
In order to examine the effect of floor material change on gait and gait stability, we first measure coefficient of friction (COF) of several commonly-used interior floor materials in Taiwan and then observe the locomotion on different floor material conditions. The kinematics variables of gait will be analyzed and the relationship between these variables and COM will then be examined. The research questions and hypotheses are listed below:
A. Does floor transition have any effect on gait stability?
We hypothesized that floor materials change would decrease the stability of locomotion.
B. If floor transition has effects on gait stability, does gait stability have positive/negative relationship with the difference of COF between two transition floor materials?
We hypothesized that the difference of COF between two connected floor materials has negative relationship with gait stability. Moreover, when the COF difference reaches a certain level, the risk of falls during walking would increase significantly.
C. Are there any age differences on movement adjusting strategy when encounter a floor transition condition?
We hypothesized that the elderly would need more time to adjust their gait and would start the adjustment earlier then young adults. Furthermore, they could only adjust their gait successfully within a lesser range of COF difference.
D. Is there any kinematics variable besides the whole-body COM that could be used to indicate gait stability?
We hypothesized that pelvic motion could be used for indicating the stability of locomotion.