Validity, precision and reliability in power, strength and movement velocity measurements are fundamental characteristics for assessing sport performance in many sport disciplines. The main variables traditionally considered in strength training for stimulus control have been the type and order of exercises, the number of sets and repetitions, the intensity or training workload and the recovery time (Kraemer and Ratamess, 2004, MSSE, 36: 674–688). Movement velocity is another factor that may be useful for assessing and monitoring resistance training (González-Badillo and Sánchez-Medina, 2010, IJSM, 31: 347–2) characterising the type of neuromuscular response and the subsequent adaptations (Sánchez-Medina and González-Badillo, 2011, MSSE, 43:1725–34). The aim of this study was to test the validity and reliability of a Chronojump linear position transducer (CLPT) (Chronojump, Barcelona, Spain) compared to a reliable and validated one (T-Force System, Ergotech, Murcia, Spain). 19884 repetitions were analysed with two devices in order to compare the average velocity (AV) and average power (AP) measurements obtained with the two systems. An isoinertial dynamometer (T-Force Dynamic Measurement System®, Ergotech, Murcia, Spain) was used as a reference instrument to compare with the CLPT. For this purpose, bench press (BP) and back squat (BS) were selected, and validity and reliability were studied. The intraclass correlation coefficients (ICCs) for validity assessment were very high, with values ranging from 0.925 to 0.988. The absolute bias was calculated for AV and AP. Mean absolute bias were 0.018% (±0.001) and 0.024% (±0.027) for AV and AP, respectively. Correlations between the two devices were highly significant for AV and AP (r 0.99, p < 0.001). These results, and Bland and Altman analyses, support the validity of the CLPT as a valuable and reliable system for measuring movement velocity and for estimating power in strength and conditioning training exercises.
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