Figure 1 shows pedometer accuracy during stair ascending and descending. The average difference between the pedometer scores and the actual number of steps (average ± standard deviation) was -16.1 ± 25.0 % in KZ, -8.6 ± 18.5 % in YM and -48.8 ± 43.9 % in OM for the over all stepping rates of stair ascending and descending. During stair ascending at 40 to 60 steps·min^-1, the pedometers significantly underestimated the number of steps (p < 0.05). In contrast, at 80 to 120 steps·min^-1, the number of steps assessed by KZ and YM did not differ significantly in comparison to the actual number of steps, whereas OM significantly underestimated the number of steps at 80 steps·min^-1 (p < 0.05). The measurement error during stair ascending and descending at 80 to 120 steps per minutes were -1.5 ± 3.4 % in KZ, 1.4 ± 4.3 % in YM and -1.3 ± 3.8% for OM.

Figure 2 shows pedometer accuracy during the bench stepping exercise (Figure 2). The average difference between the pedometer scores and the actual number of steps (average ± standard deviation) was -20.7 ± 27.2 % in KZ, -10.9 ± 18.7 % in YM and -55.3 ± 40.4 % for OM for over all bench stepping exercise. Furthermore, the measurement error was -34.2 ± 27.6 % in KZ, -17.5 ± 21.3 % for YM and -64.8 ± 37.4 % for OM with a 10 cm high platform, -16.3 ± 28.0 % for KZ, -8.9 ± 18.8 % for YM and -52.5 ± 40.2 % for OM at a 20 cm high platform and -11.7 ± 20.5 % for KZ, -6.2 ± 13.7 % for YM and -48.6 ± 42.3 % for OM at a 30 cm high platform, respectively. The pedometer scores for KZ and YM did not differ significantly in comparison to the actual number of steps and the magnitude of measurement error was -6.0 ± 14.5 % for KZ, -5.6 ± 12.2 % for YM at a 60 to 120 steps·min^-1 of stepping rate with 20 and 30 cm high platforms. In contrast, the OM significantly underestimated the number of steps during most bench stepping exercises (p < 0.05).

Figure 3 shows Bland-Altman plots for the three pedometers. The limit of agreement (mean ± 2 standard deviations of error) was -29 to 46 steps in KZ, -29 to 40 in YM and -53 to 129 in OM during stair ascending and descending, and was -19 to 46 steps in KZ, -16 to 30 in YM and -13 to 80 in OM during the bench stepping exercise.

Pedometers are popular devices for measuring daily physical activity (Bassett and Strath, 2002; Tudor-Locke et al., 2002). The current study demonstrated that pedometers could assess the number of steps accurately during horizontal walking (Crouter et al., 2005; Schneider et al., 2003). In addition, the present study demonstrated that pedometers could also assess the number of steps within an acceptable error during climbing activities such as walking up and down stairs. An original finding of the present study was that the magnitude of the measurement error averaged during stair ascending and descending and the bench stepping exercises with 20 to 30 cm high platforms at an 80 to 120 steps·min^-1 stepping rate was -3.8 ± 10.8 % for KZ, -2.1 ± 9.8 % for YM and -11.0 ± 18.9 % for OM. These results indicate that the KZ and the YM could assess the number of steps within ±5% of measurement error during stair climbing using 20 to 30 cm high platforms at rates of 80 to 120 steps·min^-1.

The results of the present investigation clearly indicate that accuracy of pedometers during stair climbing as well as bench stepping depends on the speed of the stepping rate and the height of the platform. During stair ascending and descending, the measurement error ranged from ± 2 % at a stepping rate of 80 or faster steps·min^-1, whereas the pedometers significantly underestimated the number of steps at a stepping rate of 60 or fewer steps·min^-1. In addition, during the bench stepping exercise, the pedometer scores for KZ and YM did not differ significantly in comparison to the actual steps at a stepping rate of 60 steps·min^-1 or higher with 20 and 30 cm high platforms, whereas both pedometers significantly underestimated the number of steps at all stepping rates with a 10 cm high platform. These results indicate that KZ and YM seem suitable for assessing the number of steps during stair climbing, and a measurement error of +/- 5% is expected during stair ascending and descending and during bench stepping exercise with 20 to 30 cm high platforms at an 80 to 120 steps·min^-1.

In contrast to KZ and YM, accuracy of OM was sometimes problematic. The measurement error during the climbing activities with 20 cm or higher platforms at a stepping rate of 80 to 120 steps·min^-1 was also above 10 % for OM (-11.0 ± 18.9 %), whereas that for KZ and YM was below 5% (-3.8 ± 10.8 % in KZ and -2.1 ± 9.8 % in YM).Therefore, KZ and YM seem to be more suitable for the assessment of the number of steps during stair climbing than OM. This result is supported by previous investigations where the KZ and YM also showed superior accuracy in comparison with other pedometers during horizontal walking (Schneider et al., 2003; 2004). However, when limited to stair ascending and descending at 80 steps per minute or higher, OM was able to assess the number of steps within ± 2 % (-1.3 ± 3.8 %) as well as KZ (-1.5 ± 3.4 %) and YM (1.4 ± 3.4 %).

Teh and Aziz (2002) reported the usual stepping rate for stair climbing to be 95 ± 14 steps·min^-1 for stair ascending and 106 ± 14 steps·min^-1 for stair descending in 103 middle-aged individuals using a public-access staircase with steps that were 15 cm high. Since the results of the present investigation demonstrated that the magnitude of the measurement error with pedometers was below 2% during stair ascending and descending at 80 to 120 steps·min^-1 (Figure 1), pedometers would be expected to assess the number of steps accurately during normal stair ascending and descending. Furthermore, the bench stepping exercise at 80 to 120 steps·min^-1 with the 20 to 30 cm high platforms also provides an appropriate intensity for young to older individuals in order to obtain health benefits (Ayabe et al., 2003; 2004). Since the present study confirmed validity of KZ and YM during the bench stepping exercise at 80 to 120 steps·min^-1 with 20 to 30 cm high platform (Figure 2), the pedometers would be expected to assess the number of steps accurately during the normal bench stepping exercise. These results indicate that pedometers seem to be sufficiently accurate for general stair climbing activities.

However, the present investigation demonstrated that the pedometer underestimated the number of steps during stair climbing with a lower height platform at a slower stepping rate. Therefore, pedometer accuracy may be problematic for a light intensity workout during stair climbing. Similarly, recent studies demonstrated that pedometer accuracy significantly decreased during walking at slower speed (Cyarto, 2004; Melanson et al., 2004). Furthermore, a recent publication also demonstrated pedometer accuracy to decrease at a higher step frequency such as a running at above 240 steps·min^-1 (3.5 Hz; Rowland et al., 2007).Therefore, pedometer accuracy may decrease during stair climbing corresponding to light- and very vigorous-intensity.

Thus, based on the present investigation as well as the results of previous findings (Melanson et al., 2004; Schneider et al., 2003; 2004), pedometers can accurately assess the number of steps during ambulatory activity. Furthermore, it also seems desirable to evaluate the number of steps associated with stair climbing separately from that of horizontal walking. Since stair climbing is a body bearing exercise, in comparison to horizontal walking, stair climbing may, therefore, provide some unique health benefits such as increasing lower limb muscle power and improving the bone density (Mori et al., 2006; Olson et al., 1996). Furthermore, if a pedometer can successfully detect horizontal walking and stair climbing separately, then accuracy for assessing calorie expenditure will be improved.

There are some limitations in regard to the present investigation. First, since the subjects of the present study consisted of 10 young men, the results of the present investigation should also be confirmed in women as well as in middle- to older aged individuals in future studies. Second, body mass index of the subjects was below 25 kg·m^-2. Since accuracy of a spring-levered pedometer could be affected by the body mass index, accuracy of YM during stair climbing may, therefore, decrease in overweight and obese individuals. Furthermore, the present investigation used pedometers based on the spring lever (YM) or a one-axial accelerometer (LC and OM). However, it is unclear whether different make pedometers can accurately assess the number of steps during stair climbing. Another type of pedometers based on a uni-axial accelerometer and an omni-directional accelerometer has recently been released (Rowland et al., 2007; Esliger et al., 2007). Therefore, while the KZ and YM have, up to now, been used as standard pedometers, further studies should, therefore, examine pedometer accuracy during stair climbing using other types of pedometers in a heterogeneous group of people.

• " Pedometers can assess the number of step accurately within an acceptable range of measurement error during the stair climbing activities at a stepping rate of 80 step·min^-1 or faster with 18 cm or higher stairs.