MEASUREMENT OF PLANTAR PRESSURE DURING HIGH IMPACT-SHORT CONTACT TIME SPORTS ACTIVITIES

INTRODUCTION Force Measurement is an important part of biomechanical research. Until now the measurement of plantar force during the more dynamic sports events have been primarily limited to the laboratory because the available systems capable of accurately measuring 'high impact-short contact-time' forces are not very portable. The purpose of this study was to evaluate the use of soft Parotec pressure sensors inside the shoe as a means of portable and reliable force measurement during jumping sport movements. METHODS The subjects (n =14) performed a series of 'depth jump' exercises simulated by a falling pendulum. Force curves were generated with the use of 4 soft Parotec force sensors (data collection rate 1000 Hz) which were held to the underside of the right fore-foot (Hallux, Metatarsals 1, 3, and 5) using tape and gymnastic shoes. Force curves were simultaneously generated using Kistler force sensors (data collection rate 1000Hz) which were used as control in evaluating the accuracy of the Parotec sensors. The following temporal aspects of the force curves were compared: total contact time (CT), time to first peak (TI), and time to second peak (T2). Further parameters were force at first peak(Fl), force at the saddle (FS) between the first and second peaks, and maximum force (F2). The times between initial contact and T1 and T2 were consistently (approx 70%) identical (+I- Oms) for both systems, although a variance of lms in either direction was seen in approximately 30% of the trials for both values. Although the time of initial contact was consistantly recorded the same by both systems the comparison of the exact total contact time was not usually possible because indistinct 'take-off' times were often measured by Parotec due to residual pressure in the shoe. As expected the force measured by the Parotec sensors recorded considerably less of the total force than the Kistler system. The Parotec sensors recorded force most accurately for the FS and F1 values where they captured up to 48% and 47% respectively of the force measured by the Kistler sensors. For the F2 force values they captured up to 32% of the force measured by Kistler. Greater discrepancies in force values were seen at higher total force values. CONCLUSIONS The comparison of the force curves in this study indicate that Parotec sensors, as used in the above described configuration for high impact-short contact time movements, are accurate in measuring important force parameters. This accuracy was best for the various time measurements. More experimentation is required in the of number of sensors and sensor placement to better measure the force for these type of movements