Pedometer step counting in South Africa: tools or trinkets?

Objectives. This study addressed (i) the accuracy of measuring ambulatory signals and (ii) the susceptibility to nonambulatory signals, of the Discovery Vitality Pedometer (VT) and the Kellogg's Special K Step Counter (KL) compared with three research-grade pedometers (DW: Yamax DigiWalker SW-401, MTI: MTI Actigraph AM-7164-2.2 , NL: New Lifestyles NL 2000). Design. One hundred instruments (20 instruments/brand) were tested at five level walking speeds on a motorised treadmill (3.24, 4.02, 4.80, 5.64, 6.42 km.hr-1) and during motor vehicle travel on tarred roads (62.9 km). Results. The KL was highly variable across all speeds, while the VT tended to be variable at the lowest speed. The DW, NL and VT significantly underestimated steps below 4.80km.hr-1 (41 - 94%, p < 0.02) but accuracy improved at speeds ≥ 4.80 km.hr-1 (98 - 102%). The KL displayed the highest variability (60% inter-instrument variance) followed by the VT (10% inter-instrument variance). The research-grade pedometers were the least variable (0 - 1% inter-instrument variance). At 4.80 km.hr-1, all research- grade pedometers measured within a 10% margin of error compared with the 90% of VT units and 42% of KL units. The VT was significantly more resistant to nonambulatory signals than the DW (p < 0.01). The KL was the most variable in its response to non-ambulatory signals while the NL was the most consistent. The MTI detected the most non-ambulatory signals (p < 0.05). Conclusions. The KL should not be used as a promotional pedometer. The VT achieved the minimum standards required of a promotional pedometer. Further testing is required for longevity, and performance under free-living conditions. South African Journal of Sports Medicine Vol. 18 (3) 2006: pp. 67-78