**2. The relationship between walking efficiency and life‐space assessment in elderly people**

#### **2.1. Life‐space assessment**

The increased metabolic cost of walking can detract from the activity and quality of life of elderly people as a decline in physical activity rapidly degrades physical and psychological functions [8, 9]. Life space has been reported to have good construct and criterion validity for measuring the severity of mobility limitations, and achieving effi‐ cient walking plays a crucial role in the extension of life space. Life‐space assessment (LSA) is a tool that measures mobility and reflects participation in society based on the distance through which a person reports moving during the 4 weeks prior to the assessment [10, 11]. Life space, a relatively understudied concept in gerontology, can be defined as the size of the spatial area a person intentionally moves through in daily life, as well as the frequency of travel within a specific time frame [10]. Also, a reduced frequency of going outdoors could represent reduced life space, which has been hypoth‐ esized to be a risk factor in future physical disability. Murata et al. reported that life space was related not only to age or health status but also to environmental or psychosocial factors [12]. Shimada et al.'s reports confirm that LSA was more strongly associated with gait speed than the other gait variables [13] and also show that these declines in physical performances were apparent at age 80 years and over in women and at age 90 years and over in men [13].

LSA may reflect the physical activity status indirectly in elderly people because the LSA score is associated with physical performance, Activities of Daily Living (ADL), and sociodemo‐ graphic factors [11].

Life‐space mobility was measured using a Japanese translation of the LSA [14]. The LSA provided a score based on the distance a person reported moving during the 4 weeks before the assessment [10, 13].

The LSA scores range from 0 ("completely room‐bound") to 120 ("travel out of town every day without assistance") [13].

#### **2.2. Walking efficiency in elderly people**

of walking [1, 2]. In addition, a defect or slowing of this mechanism has been suggested to explain the difficulties experienced by older persons when trying to control their posture [3, 4]. Moreover, both muscle strength and lower postural stability decline with aging [5, 6]. Therefore, aging is characterized by changes in the neuromuscular system that decreases

Meanwhile, this progressive decline in physical capacities reduces the ability of elderly peo‐ ple to perform complex motor tasks and is associated with impaired mobility and a reduction in the ability [7]. Assessment of motor function contributes to the identification of factors that generate impairments to the performance of daily activities and an increase in the risk of falls for elderly people. Moreover, assessment of motor function by physical therapist provides important information about age‐related progressive reduction in muscle strength, ability to

This chapter provides an overview of the assessment method on motor function in elderly

**2. The relationship between walking efficiency and life‐space assessment** 

The increased metabolic cost of walking can detract from the activity and quality of life of elderly people as a decline in physical activity rapidly degrades physical and psychological functions [8, 9]. Life space has been reported to have good construct and criterion validity for measuring the severity of mobility limitations, and achieving effi‐ cient walking plays a crucial role in the extension of life space. Life‐space assessment (LSA) is a tool that measures mobility and reflects participation in society based on the distance through which a person reports moving during the 4 weeks prior to the assessment [10, 11]. Life space, a relatively understudied concept in gerontology, can be defined as the size of the spatial area a person intentionally moves through in daily life, as well as the frequency of travel within a specific time frame [10]. Also, a reduced frequency of going outdoors could represent reduced life space, which has been hypoth‐ esized to be a risk factor in future physical disability. Murata et al. reported that life space was related not only to age or health status but also to environmental or psychosocial factors [12]. Shimada et al.'s reports confirm that LSA was more strongly associated with gait speed than the other gait variables [13] and also show that these declines in physical performances were apparent at age 80 years and over in women and at age 90 years and

LSA may reflect the physical activity status indirectly in elderly people because the LSA score is associated with physical performance, Activities of Daily Living (ADL), and sociodemo‐

muscle strength, balance, and proprioception.

walk, and postural control.

**in elderly people**

over in men [13].

graphic factors [11].

**2.1. Life‐space assessment**

people.

26 Clinical Physical Therapy

It may be that the decline in walking efficiency is a common result of the decrease of many bodily functions that capture the overall impact of life space and is an important indica‐ tor of life space. However, the mechanism by which older people's life space and walking efficiency decline is not well investigated and remains poorly understood. Also, the specific mechanisms that explain the difference between the decline in walking efficiency and life space in early elderly and late elderly are not yet clear. Additionally, little is known about the relationship between the walking efficiency decline and confined life space to influence on aging.

In older adults with mobility limitations, abnormalities in posture and gait contribute to the greater energy cost of inefficient gait, with adjustments for age and gait speed [15]. Limitations in life space, as measured by the University of Alabama at Birmingham (UAB) life‐space assessment, reflect lifestyle as well as walking efficiency and may be a valuable measure of functional decrease for community‐dwelling elderly people, especially since life space specifi‐ cally relates to mobility and a person's participation in society.

#### *2.2.1. Walking efficiency assessment*

Walking efficiency during the 6MD trials was measured using the Cosmed K4b2 (Rome, Italy), an indirect calorimetry system specifically designed to measure energy expenditure in nonlaboratory settings (**Figure 1**).

In brief, it uses a breath‐by‐breath measurement of gas exchange through a rubberized facemask and a turbine for gas collection, secured by a head harness. A flexible facemask that the participants keep in place by a head harness covers the participants' mouth and nose. Flexible facemask is attached to a digital turbine flowmeter to measure the volume of expired air and inspired. Sampling line from the turbine to analyzer unit system delivers expired air for the measurement (O2 , CO2 content). Before test, the K4b2 was calibrated according to the manufacturer's guidelines. After warming up the unit for 60 min, the CO2 and O2 analyzers were calibrated against room air as well as a reference gas of known composition (4.94% CO2 , 16.07% O2 ). Before walking efficiency assess‐ ment, each participant was required to sit quietly for 10 min as a rest period. The speed and distance of the 6‐min walking distance test (6MD) was recorded using standardized procedures.

**Figure 1.** Expiration gas analyser.

Walking efficiency was calculated based on net efficiency as follows: Walking efficiency = (walking VO2  ml/kg ‐ resting VO2  ml/kg)/6MD average walking speed (m/s) (**Figure 2**) [16]. The Cosmed K4b2 system uses the increased VO2 /kg ratio after noise processing to predict walking effi‐ ciency from O2 consumption.

Breath‐by‐breath values from the Excel spreadsheet were calculated from the increased ratio over 1‐breath intervals. Outliers from the increased ratio were calculated from exploratory data analysis of participants. We defined outliers (noise) as values beyond an increased ratio of 100%. Data that were more than 100% of the increased ratio were removed, and a below‐100% value was calculated from the remaining test data. This method contributes to noise processing of the VO2 /kg signal. For each subject, walking efficiency was calculated by recording the noise‐processed VO2 /kg values.

#### **2.3. Relationship between walking efficiency and life‐space assessment**

Ito et al. reported the significant relationship between walking efficiency and LSA in late elderly [16]. Moreover, the data from this study suggest that as walking efficiency declines with age, life space increasingly declines (**Figure 3**). This suggests that the age‐related decline of walking efficiency is caused by physiological changes of the late elderly. Other studies have suggested that as aerobic capacity declines with age, walking at a habitual speed becomes an increasingly more intense and therefore difficult activity, resulting in a slowing of walking speed in an effort to reduce fatigue [17]. Also, the previous study has shown that the walking energy cost for a comparable speed is generally higher for healthy

**Figure 2.** Walking efficiency = (walking VO2  ml/kg ‐ resting VO2  ml/kg)/6MD average walking speed (m/s). Horizontal axis of blue shows the meaning of 10 min of the rest period and 6‐min walking trial. Vertical axis of red shows the meaning of last 3 min of the 6‐min walking trial. Following the transfer of data from the instrument, an Excel spreadsheet was used to calculate steady‐state VO2 /kg and mean counts per minute during the last 3 min of the 6MD trial and 10 min of the rest period.

Walking efficiency was calculated based on net efficiency as follows: Walking efficiency = (walking

Breath‐by‐breath values from the Excel spreadsheet were calculated from the increased ratio over 1‐breath intervals. Outliers from the increased ratio were calculated from exploratory data analysis of participants. We defined outliers (noise) as values beyond an increased ratio of 100%. Data that were more than 100% of the increased ratio were removed, and a below‐100% value was calculated from the remaining test data. This method contributes to

Ito et al. reported the significant relationship between walking efficiency and LSA in late elderly [16]. Moreover, the data from this study suggest that as walking efficiency declines with age, life space increasingly declines (**Figure 3**). This suggests that the age‐related decline of walking efficiency is caused by physiological changes of the late elderly. Other studies have suggested that as aerobic capacity declines with age, walking at a habitual speed becomes an increasingly more intense and therefore difficult activity, resulting in a slowing of walking speed in an effort to reduce fatigue [17]. Also, the previous study has shown that the walking energy cost for a comparable speed is generally higher for healthy

/kg values.

**2.3. Relationship between walking efficiency and life‐space assessment**

 ml/kg)/6MD average walking speed (m/s) (**Figure 2**) [16]. The Cosmed

/kg signal. For each subject, walking efficiency was calculated by

/kg ratio after noise processing to predict walking effi‐

VO2

ciency from O2

28 Clinical Physical Therapy

 ml/kg ‐ resting VO2

**Figure 1.** Expiration gas analyser.

noise processing of the VO2

recording the noise‐processed VO2

K4b2 system uses the increased VO2

consumption.

**Figure 3.** Schematic diagram of the incidence of walking efficiency decline in late elderly people.

elderly people, particularly those above 65 years, compared with younger people [18, 19]. Mechanisms related to the initiation and stepping patterns of gait, such as hip extension, step width, and cadence, have previously been reported to be related to the energy cost of walking in older adults with slow and variable gait [15]. Abe et al. reported that women of advanced age (75 years or older) have diminished pulmonary function, physical function, and mobility, and that diminished pulmonary function is associated with declining physical function [20]. Malatesta et al. reported that healthy octogenarians exhibited higher walking cost and greater stride time variability [21] and also reported that these declines in physi‐ cal performances were apparent at age 80 years and over in women and at age 90 years and over in men [13]. Shimada reported that increased VO2 in older adults manifests as walking becomes inefficient and reduced endurance capacity occurs [22].

This suggests that going activity to extension of LSA may better impact walking efficiency than efforts to improve gait speed and muscle strength.
