Concurrent validity and reliability of a functional electromechanical dynamometer to assess isometric mid-thigh pull performance

The aim of this study was to examine the concurrent validity and reliability of a functional electromechanical dynamometer (FEMD) to assess the isometric mid-thigh pull (IMTP) kinetic variables: peak force (PF), rate of force development (RFD), and time-specific force values (50-, 100-, 150-, and 200-ms). Twenty-seven male collegiate athletes (age: 22.9 +/- 1.9 years; stature: 184.8 +/- 10.4 cm; body mass: 84.2 +/- 11.8 kg) performed four IMTP trials simultaneously on a force platform and the FEMD. The PF variables calculated from performance of the IMTP on both devices were reliable (CV < 3%; ICC > 0.90) and valid (bias < 13.9 N; random error < 52.1 N; r = 1.00), but they showed heteroscedasticity of the errors (R-2 > 0.23). The RFD (CV > 10.88%; ICC < 0.76) and initial force (CV > 8.81%; ICC < 0.76) variables did not reach an acceptable reliability for any device, but they showed strong associations between them (r range = 0.53-0.69). These results indicate that the FEMD is an acceptable alternative to assess athlete's maximal force production (i.e. PF), but the data collected with FEMD and force plates should not be used interchangeably.