Abstract
The number of validation studies of commercially available foot pods that provide estimates of running speed is limited and these studies have been conducted under laboratory conditions. Moreover, internal data handling and algorithms used to derive speed from these pods are proprietary and thereby unclear. The present study investigates the use of foot contact time (CT) for running speed estimations, which potentially can be used in addition to the global positioning system (GPS) in situations where GPS performance is limited. CT was measured with tri axial inertial sensors attached to the feet of 14 runners, during natural over ground outdoor running, under optimized conditions for GPS. The individual relationships between running speed and CT were established during short runs at different speeds on two days. These relations were subsequently used to predict instantaneous speed during a straight line 4 km run with a single turning point halfway. Stopwatch derived speed, measured for each of 32 consecutive 125m intervals during the 4 km runs, was used as reference. Individual speed-CT relations were strong (r2 >0.96 for all trials) and consistent between days. During the 4km runs, median error (ranges) in predicted speed from CT 2.5% (5.2) was higher (P<0.05) than for GPS 1.6% (0.8). However, around the turning point and during the first and last 125m interval, error for GPS-speed increased to 5.0% (4.5) and became greater (P<0.05) than the error predicted from CT: 2.7% (4.4). Small speed fluctuations during 4km runs were adequately monitored with both methods: CT and GPS respectively explained 85% and 73% of the total speed variance during 4km runs. In conclusion, running speed estimates bases on speed-CT relations, have acceptable accuracy and could serve to backup or substitute for GPS during tarmac running on flat terrain whenever GPS performance is limited.
Highlights
Speed is the primary performance parameter for running
We could compare 125m-interval-speed estimates based on contact time (CT) and global position system (GPS) to the reference speed obtained with stopwatch timing for every 125m during the 4km runs
There are strong individual relations between running speed and CT during outdoor over ground running on flat terrain
Summary
Speed is the primary performance parameter for running. In practice, training schedules are largely based on running speed, often in combination with heart rate. Small inertial sensors can be used to provide runners with estimates of their running speed. Such speed estimations can serve as backup whenever GPS reception is poor or absent (indoors). The protocols and algorithms used to derive running speed from the inertial sensors in these commercial devices are proprietary, it is unclear how running speed is estimated. Direct integration of these sensors’ acceleration signals to obtain measures of running speed is not yet accurate enough [5]
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