Validity and reliability of a novel iPhone app for the measurement of barbell velocity and 1RM on the bench-press exercise

The purpose of this study was to analyse the validity and reliability of a novel iPhone app (named: PowerLift) for the measurement of mean velocity on the bench-press exercise. Additionally, the accuracy of the estimation of the 1-Repetition maximum (1RM) using the load-velocity relationship was tested. To do this, 10 powerlifters (Mean (SD): age=26.5 +/- 6.5years; bench press 1RMkg(-1)=1.34 +/- 0.25) completed an incremental test on the bench-press exercise with 5 different loads (75-100% 1RM), while the mean velocity of the barbell was registered using a linear transducer (LT) and Powerlift. Results showed a very high correlation between the LT and the app (r=0.94, SEE=0.028ms(-1)) for the measurement of mean velocity. Bland-Altman plots (R-2=0.011) and intraclass correlation coefficient (ICC=0.965) revealed a very high agreement between both devices. A systematic bias by which the app registered slightly higher values than the LT (P<0.05; mean difference (SD) between instruments=0.008 +/- 0.03ms(-1)). Finally, actual and estimated 1RM using the app were highly correlated (r=0.98, mean difference (SD)=5.5 +/- 9.6kg, P<0.05). The app was found to be highly valid and reliable in comparison with a LT. These findings could have valuable practical applications for strength and conditioning coaches who wish to measure barbell velocity in the bench-press exercise.