Advancing the use of the load-velocity profile for resistance training prescription: methodological comparisons and device validation

The main aim of this doctoral work was to delve deeper into the implementation and use of the load-velocity profile (LVP) for resistance training prescription by addressing three interrelated dimensions: the methodological impact of different LVP testing protocols, the influence of LVP construction on regression parameters, and the technological validity of emerging measurement tools. These investigations aimed to advance the understanding of how methodological and technological factors affect the LVP-derived outcomes. To achieve this goal, the research was developed into three interconnected studies. The STUDY 1 investigated whether different LVP testing procedures such as the velocity-based LVP (LVPVB), the percentage-based LVP (LVPPB), and the 2-point LVP (LVP2-POINT) affect the determination of the one-repetition maximum (1-RM) load and the velocity associated with that load (V1-RM) expressed as mean velocity (MV), mean propulsive velocity (MPV), and peak velocity (PV). STUDY 1 revealed a large effect of protocol on 1-RM load, with the LVP2-POINT yielding the highest value. On the other hand, although only small average differences in V1-RM were observed across protocols, the high intra-individual variability and wide limits of agreement indicate that the different LPV testing procedures cannot be used interchangeably to measure V1-RM. STUDY 2 further examined the influence of the aforementioned LVP protocols (i.e., LVPVB, LVPPB, and LVP2-POINT) on the slope and intercept of the load-velocity relationship using created between load and MV, MPV, and PV. The results demonstrated that the exercise testing protocol significantly affected LVP slopes and intercepts. Specifically, the LVP2-POINT protocol yielded steeper slopes and higher intercepts than the longer multiple-point methods across all velocity metrics, resulting in a higher theoretical 1-RM load values compared to LVPVB. Therefore, STUDY 1 and STUDY 2 indicated that the LVP was affected by the testing procedure, highlighting the importance of maintaining consistency in protocol use, as it may influence the accuracy of exercise testing and prescription. The LVP2-POINT protocol resulted as a time-efficient option for estimating 1-RM load, consistently producing slightly higher values than the multiple-point methods. Finally, STUDY 3 evaluated the concurrent validity of the MetricVBT smartphone camera-based application relative to the Vitruve linear position transducer for assessing barbell MV and PV during 1-RM test performed with the Smith-machine bench press. The MetricVBT smartphone application showed that although excellent and moderate concurrent validity with the Vitruve for assessing PV and MV, the limits of agreement revealed moderate variability, indicating that the two systems should not be used interchangeably. Overall, this doctoral work revealed that both methodological and technological factors substantially influence the estimation and interpretation of load-velocity relationships. Therefore, to effectively apply the LVP in exercise testing and prescription, it is required an accurate assessment methodology based on a standardized and valid protocol, a consistent velocity metric, and a reliable measurement device.