Methodology

Test Courses & Surfaces

Test courses were designed and built using nine different types of exterior surfaces (Table 1). The ADAAG Accessible Course was used to evaluate subjects' ability to ambulate in the community. This "access route" was 574.2 ft (175.0 m) in length, and included two 137 ft (41.8 m) sections with grades of 4% to 5% (one uphill, one downhill), and two 30-foot (9.1 m) ramps with grades up to 8.3% (one uphill, one downhill). The two Straight Courses were 984.3 ft (300 m) in length with a 32.8 ft (10 m) turning radius at each end. The "P" shaped Turning Courses were designed such that one circuit around the course provided 328 ft (100 m) of walking distance and involved turning for 10% of the distance (both 90 and 180 degree turns). (See the Technical Report for course details.)

The test surfaces were objectively measured using the Wheelchair Work Measurement Method and the portable Rotational Penetrometer. To determine the energy required, persons with and without disabilities walked or wheeled across each of these surfaces. For reference and comparison purposes, objective measures were also obtained on a slip resistant ramp at different grades and seven carpet/pad combinations (Table 2).

Table 1. Test Surfaces

Test Course/Test Surface
  • ADAAG Accessible Course: Unpaved #2 Road Mix(3/4" Class 2 aggregate) Code:ADAG
  • Straight Courses: Asphalt with exposed 1-in.minus aggregate Code:ASPS
  • Native soil Code:DIRS
  • P-shaped Turning Courses: Asphalt with exposed 1-in. minus aggregate Code:ASPP
  • Native soil Code:DIRP
  • Unpaved #2 Road Mix (3/4" Class 2 aggregate)Code:RDMX
  • Path Fines California Gold DG Code:PAFN
  • Path Fines with Stabilizer (Road Oyl® resin modified emulsion binder by Road Products Corp*) Code:RDOL
  • Wood Chips (chipped brush, average size 3x1x1 in., compacted to a depth of 5 in.) Code:CPBR
  • Engineered Wood Fiber J (loose-fill processed wood fibers, compacted to a depth of 5 in.) Code:EWFJ
  • Engineered Wood Fiber K (loose-fill processed wood fibers, compacted to a depth of 5 in.) Code:EWFK
  • Sand (dry) Code: SAND

* Resin Pavement is a trademark of Road Products Corporation and Soil Stabilization Products Company, Inc. The Road Oyl registered trademark and patent are the property of Road Products Corporation.

Table 2 Reference Carpet and Pad

Carpet
  • Level loop, 100% nylon with a woven polypropylene backing; 0.16 in pile height; 28 oz pile weight Code: C1
  • Interweave cut and loop (cut pile with loop pile at a different height), 100% nylon with a polypropylene backing; 0.281 in pile height(avg.); 43 oz pile weight Code: C2
  • Level cut pile, 100% nylon; 0.50 in pile height Code:C3

Pad

  • No pad used Code: P0
  • 0.25 in. fiber Code: P1
  • 0.375 in. bonded urethane Code: P2
  • 0.5 in. bonded urethane Code: P3
  • 0.375 in. fiber Code: P4

General Usage

  • High traffic areas (e.g., lower level corridors,lobbies), for longer travel distances Carpet/Pad Combinations: C1P0, C1P1, C2P1
  • Upper level corridors Carpet/Pad Combinations: C2P2, C2P4
  • Executive offices and sleeping rooms, for shorter travel distances Carpet/Pad Combinations:C3P0, C3P3

Note: All carpet/pad combinations tested comply with current ADAAG

Objective Surface Measurements

For purposes of comparison, objective surface measurement data are included from the "Measurement of Surface Characteristics for Accessibility" NIH-funded research project at Beneficial Designs. A wheelchair work measurement system and a portable surface measurement device were designed to objectively measure surface firmness and stability.

Wheelchair Work Measurement Method. Wheelchair work per meter values for straight and turning were determined for all test course surfaces except sand, under dry conditions using the Wheelchair Work Measurement Method in accordance with ASTM F1951-99 (formerly PS 83-97). Work per meter values were also determined for the reference ramp grades and carpet/pad combinations.

Rotational Penetrometer. The Rotational Penetrometer (Figure 1) is a portable device that provides accurate measurements of firmness and stability on a wide variety of surfaces. It can be used easily in the field, is suitable for trail use, and does not require a level surface for testing.

Figure 1. Rotational Penetrometer:  A vertical shaft, supported by a frame, with 8-inch wheelchair caster on the bottom.  Pressure is applied downward on the top and a lever midway down the shaft is used to rotate the shaft/caster assembly.

Figure 1. Rotational Penetrometer

All of the test courses were measured using the Rotational Penetrometer under wet and dry conditions. Firmness was determined by applying a given force to the penetrator and then measuring the depth of penetration into the surface. The stability of a surface was measured by applying a given force, rotating the penetrator left and right 90 degrees, for a total of 360 degrees, and then measuring the final depth of penetration into the surface.

Human Subject Testing

Subject Recruitment. Subjects were recruited by gender and mobility limitation (no known disability, ambulatory with limited mobility, ambulatory with assistive devices, and manual wheelchair use). Informed consent was obtained from each participant. Prior to beginning their participation in this study, subjects were screened for "at risk" conditions for exercise. To characterize the study population, background information was collected, including age, gender, disability, assistive device use, independence in activities of daily living, and physical activity participation.

Standardized Tests of Physical Fitness and Community Ambulation. Energy expenditure at rest and during ambulation can be significantly affected by the individual's level of fitness. In order to characterize the fitness levels of study participants, standardized tests of aerobic endurance (PWC170) and strength (hand grip) were completed.

Resting heart rate and energy consumption were measured with the subject seated or reclining on a couch. Heart rate was measured with a Polar heart rate monitor (Polar Vantage XL). Energy consumption was measured using a portable Aerosport KB1-C metabolic analyzer.

Subjects were asked to complete two laps of the ADAAG Accessible Course while their heart rate, energy consumption and velocity were recorded. Data were recorded during the second lap of the course. Upon completion of the ADAAG course, subjects were asked to rate their level of perceived exertion using the RPE Scale (Borg, 1974). Subjects were also asked to rate the difficulty they had walking or wheeling on the ADAAG course. Perceived difficulty was designed to consider factors such as the security of footing, obstacle negotiation, and effort required on slopes. The subjects rated the level of difficulty from 1 to 10 for both straight travel and turning on the surface using the Level of Difficulty Rating Scale. Subjects were instructed that a rating of "1" represented a hard, level, indoor surface. A rating of "10" was the difficulty level for walking on sand.

Energy Consumption During Ambulation. Measurements were recorded for subjects walking on the Straight and Turning Courses. Subjects walked on each surface at their preferred pace, until the physiological variables (energy consumption, heart rate, velocity) had stabilized (2-3 minutes) and the data collection period (an additional 2 minutes) had been completed. Rating of perceived exertion (RPE) and level of difficulty were recorded after the subject had completed each course. Subjects were instructed to rate the difficulty of each surface for both straight travel and turning. A combined level of difficulty rating was calculated as the weighted total of the straight and turning scores in relation to the amount of turning required for each course (10% turning for "P" course, no turning for the straight courses). The order of the surfaces tested was randomly assigned and a 10-15 minute rest interval was permitted between tests to ensure that the physiological measures had returned to resting levels.

Data Analyses

Net energy consumption - the additional energy utilized during walking in excess of resting levels - was calculated for each surface. Relative oxygen consumption values (ml O2/kg weight/min) measured during the data collection period (stable, plateau phase) were averaged for the resting data and each test surface. The net energy consumption (ml/kg/min) was calculated by subtracting the average resting value from the value for each test surface. The net energy consumption was divided by the velocity of walking in order to standardize the data for comparison between subjects. Thus, the energy consumption for each surface (oxygen consumption/kilogram of body weight/meter) was standardized relative to subject size (body weight), resting metabolic levels and speed of ambulation.

Frequency tabulations were used to identify data entry errors. T-tests and correlations were used to evaluate the relationships between numerical data. The impact of categorical data was evaluated using analysis of variance (ANOVA) statistics. Statistical significance was set at p < 0.05 for all analyses.

 

EXPLANATION OF STUDY DESIGN

What was measured and why?

Energy Consumption - Measuring the oxygen a person consumes indicates how much energy the body is producing. When the oxygen consumption is measured at rest (i.e., with the person sitting or lying down), the amount of energy the body is using to function (e.g., for making the heart pump, organs function) can be determined. If an individual walks at a steady pace for 3 to 4 minutes, energy consumption will stabilize at a level that is equal to the energy required to negotiate that environment. By subtracting the resting oxygen consumption from the oxygen consumption while walking/wheeling, the amount of energy being used specifically for walking can be determined.

Walking Speed - If adults are asked to walk at their freely chosen speed they automatically select the type of movement and speed that requires the least amount of energy. If an individual is forced to walk either faster or slower than this chosen pace, the amount of energy used will increase. Therefore, for this study, subjects were allowed to determine their own preferred pace so that energy consumption in its "most efficient" state could be measured.

Heart Rate and Rating of Perceived Exertion - Rating of perceived exertion (RPE) is a research scale used to document the individual's perception of how difficult it is for his/her body to perform an exercise (i.e., how hard the individual's lungs are breathing, and heart is pumping). RPE scores have been shown through research to be consistently related to measures of heart rate and amount of exercise, regardless of the type of exercise. In general, the RPE score is equal to the steady state heart rate divided by 10.

Level of Difficulty - Level of difficulty is similar to the rating of perceived exertion in that it attempts to quantify the individual's subjective perception of the activity. However, it differs from the rating of perceived exertion in that it is not specific to how the heart and lungs are performing. Often, an unstable surface, for example, may be perceived as very difficult because of the unstable footing, even though the individual does not have to exert him/herself. Level of difficulty was recorded to evaluate factors (e.g., ease of slipping, uneven surfaces) that would not necessarily affect the energy consumption but may impact the overall "accessibility" of the surface.

Why test on straight courses and P-shaped turning courses?

Constructing long test courses enables comparison of subject data with research done by other investigators in which subjects walk on a straight linear course or in large diameter circles or ovals. However, the cost for producing these course designs with a number of surface materials would be very large. As a compromise, the construction of two long courses enabled some comparisons with published research without generating prohibitive surface construction costs. In this study, there was also a desire to have the subjects walk on the test surfaces in a manner that would reflect the types of ambulation that would represent functional mobility. This functional mobility includes both turning and walking in a straight path on any given surface. The "P" courses were designed so that the subject was turning for approximately 10% of the total distance.

What happens when people walk under more difficult conditions?

In general, when people walk under more difficult conditions there is: 1) a decrease in speed (to decrease the energy required), 2) an increase in heart rate (to pump more oxygen to the muscles), and/or 3) an increase in total energy consumption (when the other compensating mechanisms are not sufficient).

Which surfaces are accessible to everyone?

There are no surfaces that are accessible to everyone, because there is an infinite range of abilities among the population. Participants in this study were recruited to represent a variety of disabilities. They completed standard tests of fitness to ensure that a variety of ability levels was represented. Currently, our society has made a decision on what is considered "sufficiently accessible," that being environments that comply with the current ADAAG. Although it is recognized that not all individuals have independent access in an ADAAG environment, these standards have been designated "accessible enough" for most people. It should be noted that all powered mobility technologies are able to negotiate ADAAG environments and represent an option for persons without the functional mobility to negotiate these environments.