Abstract
The purpose was to compare step-by-step kinematics measured using force plates (criterion), an IMU only and a combined laser IMU system in well-trained sprinters. Fourteen male experienced sprinters performed a 50-m sprint. Step-by-step kinematics were measured by 50 force plates and compared with an IMU-3D motion capture system and a combined laser+IMU system attached to each foot. Results showed that step kinematics (step velocity, length, contact and flight times) were different when measured with the IMU-3D system, compared with force plates, while the laser+IMU system, showed in general the same kinematics as measured with force plates without a systematic bias. Based upon the findings it can be concluded that the laser+IMU system is as accurate in measuring step-by-step kinematics as the force plate system. At the moment, the IMU-3D system is only accurate in measuring stride patterns (temporal parameters); it is not accurate enough to measure step lengths (spatial) and velocities due to the inaccuracies in step length, especially at high velocities. It is suggested that this laser+IMU system is valid and accurate, which can be used easily in training and competition to obtain step-by step kinematics and give direct feedback of this information during training and competition.
Highlights
Sprinting performance is very important in many sports
Post hoc comparison showed that step velocity and step length measured with the IMU-3D system were lower in each step and followed another development trajectory over the 24 steps compared to that measured with force plates (Figures 2 and 3)
There were no significant differences found between the laser+IMU system and the force plate system for any of the kinematics (Figures 2 and 3), except when evaluating per step; in the first two steps, a significant lower step velocity was found in the laser+IMU system compared with the force plates
Summary
Sprinting performance is very important in many sports. The two main variables, step length and frequency, determine sprint performance. Taller athletes have longer step lengths and a lower frequency compared with shorter athletes who show the opposite [1]. It is natural to enhance one of the two variables, while keeping the other constant [2]. The easiest way to measure mean step length and frequency is just by counting the number of steps over a certain distance and time, and dividing the distance by the number of steps. During a sprint, step length and frequency are not constant and differ during the different phases of a sprint [3,4]. Coaches and scientists it can be important to know the step-by step kinematics to check how they respond to a stimulus (e.g., a que or training session/period)
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