Reliability of the GPS devices was determined by comparing the data collected by two Viper 10 Hz GPS units carried by one participant. To this end, a 20 m distance was marked on the athletics one-lane track, using a 50 m tape. The participant performed an intermittent maximal effort of 10 x (20 m + 20 m) sprints, with a 180º change of direction and a 10 s inter-set (InterS) rest interval. During the drill the athlete carried two 10 Hz GPS units (GPS1 and GPS2, one above the other), positioned between the shoulder blades on the upper-back region.
Once the reliability was determined, validity of the Viper 10 Hz GPS was assessed by comparing practical speed from the previously mentioned devices with following criterion speeds: instantaneous speed by the radar gun, and mean speed by timing gates.
A 40 m distance was marked on the track with a 50 m tape, where timing gates were placed at 0, 10, 20, 30 and 40 m. The radar gun was placed on a tripod 10 m behind the start-point at a 1 m height, corresponding approximately to the participants’ centre of mass. Participants were instructed to begin in their own time and run from a starting point placed 0.5 m behind the first timing gate. Each subject decided freely on his sprint speed. Speed values were registered by the radar gun from the beginning of the movement (detected by an increase in speed), to the end of the drill, which was determined by the time recorded at the last photocells (40 m).
Each of the eight participants carried one Viper 10 Hz GPS unit in an individual specialized vest, placed between the shoulder blades on the upper-back region. After the reliability was checked, a total of 20 GPS units were included in this part of the study and randomly assigned to participants.
Firstly, all participants involved in the study performed 21 x 40 m sprints at a submaximal incremental speed (IncS). Secondly, the same athletes performed 21 x 40 m sprints with a submaximal incremental speed in the first stage and a subsequent submaximal decreasing speed during the second stage (Inc-DecS). Instantaneous speed was measured in each split by the radar gun. Time required to cover 10 m was taken under IncS conditions by timing gates.
Every test was performed after a standardized 10 min warm-up (5 min of light jogging, dynamic stretching exercises and 5 submaximal sprints).
Instantaneous speed was determined by a radar system following filtering in custom software designed for ATS II use (SATS version 5.0.3.0). The Viper 10 Hz GPS position and speed were taken from Doppler-shift using STATSport Viper Software Version 1.2. To obtain instantaneous speed from raw data, a logarithmic transformation was implemented. This transformation reduced bias derived from the radar’s non-uniformity error of measure. To calculate mean speed, the 10 m distance was divided by timing gates split record.
Once the reliability was determined, validity of the Viper 10 Hz GPS was assessed by comparing practical speed from the previously mentioned devices with following criterion speeds: instantaneous speed by the radar gun, and mean speed by timing gates.
A 40 m distance was marked on the track with a 50 m tape, where timing gates were placed at 0, 10, 20, 30 and 40 m. The radar gun was placed on a tripod 10 m behind the start-point at a 1 m height, corresponding approximately to the participants’ centre of mass. Participants were instructed to begin in their own time and run from a starting point placed 0.5 m behind the first timing gate. Each subject decided freely on his sprint speed. Speed values were registered by the radar gun from the beginning of the movement (detected by an increase in speed), to the end of the drill, which was determined by the time recorded at the last photocells (40 m).
Each of the eight participants carried one Viper 10 Hz GPS unit in an individual specialized vest, placed between the shoulder blades on the upper-back region. After the reliability was checked, a total of 20 GPS units were included in this part of the study and randomly assigned to participants.
Firstly, all participants involved in the study performed 21 x 40 m sprints at a submaximal incremental speed (IncS). Secondly, the same athletes performed 21 x 40 m sprints with a submaximal incremental speed in the first stage and a subsequent submaximal decreasing speed during the second stage (Inc-DecS). Instantaneous speed was measured in each split by the radar gun. Time required to cover 10 m was taken under IncS conditions by timing gates.
Every test was performed after a standardized 10 min warm-up (5 min of light jogging, dynamic stretching exercises and 5 submaximal sprints).
Instantaneous speed was determined by a radar system following filtering in custom software designed for ATS II use (SATS version 5.0.3.0). The Viper 10 Hz GPS position and speed were taken from Doppler-shift using STATSport Viper Software Version 1.2. To obtain instantaneous speed from raw data, a logarithmic transformation was implemented. This transformation reduced bias derived from the radar’s non-uniformity error of measure. To calculate mean speed, the 10 m distance was divided by timing gates split record.
