Although global positioning systems and inertial measurement unit systems are often used to quantify physical variables in training, both types of systems need to be compared, considering their frequent use in measuring physical loads. Thus, the purpose of our study was to test the reliability and validity of speed and distance run measurements at different intensities in indoor and outdoor conditions made by Polar Team Pro and Playermaker. Four participants (age = 30.0 ± 5.1 years, body mass = 76.3 ± 5.3 kg, height = 1.79 ± 0.09 m), each wearing three Polar Team Pro and two Playermaker sensors, performed 100 m runs with different prescribed intensities (i.e., criterion measure) varying from 8 to 24 km h⁻¹, in a straight line and/or rectangle under indoor and outdoor conditions. Both systems underestimated total distance; Playermaker underestimated speed, the extent of which increased as speed increased, while Polar Team Pro overestimated mean speed at 8 km h⁻¹ for the straight-line condition. No differences emerged in mean speed estimated by Polar Team Pro at any intensities other than 20 km h⁻¹, which was underestimated by 2%. The reliability of the sensors was good, given a coefficient of variation (CV) of <2% for all conditions except when measuring indoor conditions with Polar Team Pro (CV ≈ 10%). Intraclass correlations (ICCs) for consistency within the sensors varied from 0.47 to 0.99, and significantly lower ICCs were documented at 8, 10, and 12 km h⁻¹. Both systems underestimated distance measured in indoor and outdoor conditions, and distance validity in different intensities seemed to worsen as speeds increased. Although Polar Team Pro demonstrated poor validity and reliability in indoor conditions, both systems exhibited good reliability between their sensors in outdoor conditions, whereas the reliability within their sensors varied with different speeds.

Physical variables from soccer training are commonly quantified by using global positioning systems (GPS) and/or inertial measurement unit (IMU) systems. More studies are needed to compare both systems, taking into account that both are frequently used to measure physical load. The purpose of this study was to (i) compare IMUs (PlayerMaker™) to ten Hz GPS (Polar Team Pro) units during a square running protocol (SRP) to investigate the accuracy of distance measured and intra-unit reliability of the devices and (ii) compare IMUs and GPS units for measurements of total distance (TD), very high intensity running (VHIR), accelerations and decelerations during small-sided games (SSGs) in semi-professional soccer. Four subjects ran theSRP whilst wearing two IMU units and three GPS units to compare the accuracy of distance measured and examining the intra-unit reliability. Fifteen male soccer players participated in the SSGs where the players’ physical variables were simultaneously captured by a foot-mounted IMU in addition to GPS units. IMU and GPS were respectively 2% and 1% from actual distance, whereof both systems had a coefficient of variation at~1%. In the SSGs, the IMU measured~4% higher TD compared to the GPS. VHIR measured by the IMUs were around 18% lower while the IMUs measured~39% more accelerations and~35% more decelerations compared to the GPS. Both systems measure close to actual distance. In SSGs, IMU measures higher distances below VHIR while the GPS measures higher distance above VHIR. IMUs measure a higher number of accelerations and decelerations during SSGs.

The intermittent work in soccer demands rapid changes in velocity and direction due to the unpredictable events that occur during match play. Hence, the players’ ability to accelerate and decelerate are important indicators for physical performance and load. It is common for elite teams to use inertial measurement units (IMU) to monitor the external training load, of which accelerations and decelerations are considered important variables. Accelerations and decelerations have traditionally been determined relative to a fixed threshold (e.g., >2.0 m·s ⁻² ). The aim of this study was to examine accelerations and decelerations in several zones (graded from low to high) in two different levels of sensitivity and in three different thresholds for determination of accelerations and decelerations. Thirty-five semi-professional soccer players were monitored with a foot-mounted IMU (Playermaker) during 60 official matches, where number- and meters of accelerations and decelerations were distributed from low to high in sensitivity level 1 (6 zones), sensitivity level 2 (3 zones), and three different thresholds for determination of accelerations and decelerations. Sensitivity and threshold are shown to influence positional differences when acceleration and deceleration values are relatively low but appear to be absent when the values are relatively high. High sensitivity leads to positional differences that are not present for low sensitivity, whereas low sensitivity polarizes differences between zones. For thresholds, the use of acceleration meters leads to greater positional differences compared to number of accelerations. These findings should be considered in the interpretation of the data output and in decisions regarding training load management.