Accessible Exterior Surfaces Technical Article

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).

¹ 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.

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.

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.