Intra-Trial Reliability and Usefulness of Isometric Mid-Thigh Pull Testing on Portable Force Plates

The aim of this study was to assess the intra-trial reliability and usefulness of portable force plates and a customised Isometric Mid-Thigh Pull rig. Twenty males (age: 24.1 +/- 2.5 years, body height: 177.7 +/- 0.09 cm, body mass: 88.4 +/- 17.9 kg) with weightlifting experience +/- 12 months attended 1 familiarisation session and 1 testing session where 4 isometric mid-thigh pulls were performed. Maximum force, absolute peak force (PF), relative PF, allometrically scaled PF, and force (150, 200, 250 ms) were deemed reliable (ICC >= 0.91 and CV <= 9.8%) based on predetermined criteria (ICC >= 0.8 and CV <= 10%). The impulse and the rate of force development (RFD) were deemed unreliable (ICC <= 0.91 and CV >= 10 %) at all time points. Maximum force, absolute PF, relative PF to body weight and body mass, rand allometrically scaled PF, had a typical error (TE) lower than the smallest worthwhile change small effect (SWC0.2) and moderate effect (SWC0.5) and were rated as good with regard to usefulness. The TE for force at selected time points (150, 200, 250 ms) was also higher than the SWC0.2, achieving a rating of marginal, but TE was higher than SWC0.5, achieving a rating of good with regard to usefulness. Portable force plates and customised rigs can reliably determine peak force and force output at different time points and for detecting the SWC in maximum and absolute force measures, greater familiarisation may be required to establish reliability of other variables such as the impulse and the RFD.