## 1 Introduction  
Foot pronation is a natural damping mechanism during walking and running, whereby the eversion--a part of pronation--plays a crucial role in reducing the acting forces on the lower limbs. Eversion velocity seems to be more decisive for critical loading than the maximum angular excursion. In this context, studies have reported that high version velocities could be associated with medial tibial stress syndrome [1; 2; 3]. Aside from investigating injuries, previous studies examined the influence of footwear construction or foot orthoses [1; 4; 5; 6; 7], exhaustion [8], and running pace [9] on maximum version velocity and the time until it occurs.  
To investigate kinematics, optoelectronic systems (e.g., Vicon, Qualisys) have been established as the gold standard [8; 10; 11]. However, time-intensive preparation of subjects, considerable laboratory size, and high prices are the disadvantages of these systems. Furthermore, data capturing is restricted to indoor laboratory measurements. Low sampling rates between 50 and 500 Hz and marker-artifacts due to wobbling can also influence the accuracy of calculated parameters, especially when observing kinematics in the frontal and transversal planes.  
In comparison, electrogoniometers are considered an easy-to-use alternative when investigating rearfoot motion in relation to the shank in the frontal plane [5; 10; 12]. The electrogoniometer is attached to the heel cap of the shoe and at the posterior lower leg to accurately measure the rotation about the subtalar joint axis at distinctly higher sampling rates of up to 1000 Hz [5,12]. The disadvantage of this system is the flexible arm between the shoe or foot and the attachment at the lower leg. During long-term measurements in the field, the system's mass can influence walking and running gait. Furthermore, material wear of the flexible arm connections can occur due to the continuous mechanical stress during prolonged runs.  
The third option is to use micro-electromechanical sensors (MEMS). Wearable motion sensors (e.g., gyroscopes and accelerometers) are an inexpensive alternative to optoelectronic systems [13]. These sensors are simple to handle, cost-effective, and suitable for field measurements [8,11,13].  
A few studies investigated the accuracy of MEMS when comparing angles or angular velocities with optoelectronic systems [8,10,14]. When examining the agreement of the maximum angular velocity of the shoe in the frontal plane (eversion velocity), they found moderate [8], acceptable [10], and good [14] agreement between the systems. Investigated running speeds were in a narrow range between 3.2 \(\pm\) 0.4 and 4.0 \(\pm\) 0.2 m/s. The influence of locomotion speed (walking or running) or footwear characteristics on the accuracy of the maximum angular velocity was not investigated. However, this information is necessary to determine whether differences in angular velocities between footwear conditions as well as between locomotion speeds are caused by measurement errors of the gyroscopes or by the investigated conditions themselves.  
Therefore, the aim of this study was to compare the accuracy of a gyroscope and an electrogoniometer in quantifying peak exversion velocity (evVel) and the time until evVel (t_evVel). To avoid effects due to different sampling rates and marker-artifacts, the gyroscope data in this study were compared to the electrogoniometer data. Four locomotion speeds and three different footwear conditions were investigated. We hypothesized that evVel measured with a gyroscope is related to evVel measured with electrogoniometer (H1). Furthermore, we hypothesized that t_evVel with the gyroscope is related to t_evVel with the electrogoniometer (H2).