To our knowledge, this is the first study that examined the reproducibility of GymAware, PUSH2 and Vmaxpro velocity monitoring devices during the free-weight back squat exercise while also examining their sensitivity for detecting true changes in RT performance. The main findings of this study were 1) fixed and proportional bias was not observed for any of the devices and velocity metrics examined in this study; 2) only MV from GymAware and Vmaxpro, but not PUSH2 devices were sensitive enough to detect true changes in RT performance according to the apriori established criteria; 3) GymAware (MV and PV) and Vmaxpro (MV), but not PUSH2 (neither MV nor PV) devices demonstrated high levels of within-unit agreement (i.e., equivalence) concerning SDC for load-velocity profiles in the free-weigh back squat exercise previously reported in the literature. Collectively, these findings support the use of MV and PV from GymAware LPT and MV from Vmaxpro devices for RT monitoring and prescription due to their low magnitudes of error; thus, allowing for sensible detection of meaningful changes in neuromuscular status and functional performance during RT.
Most of the available studies examining the reliability of velocity monitoring devices including PUSH2 and Vmaxpro have quantified inter-individual or intra-individual variability in movement velocity during the same testing condition (e.g., velocity against the same relative load for all individuals) or during the “same” testing condition separately by a specific amount of time (e.g., 48–72 hours; test-retest reliability), respectively. However, this study design fails to separate biological (i.e., human) and technological variation and, as such, does not reveal any information about the true source of measurement error14. An effective approach to examine devices’ reproducibility (i.e., their true technological error) is to simultaneously use two or more devices of the same brand under the same testing conditions18–20. This approach was taken in the current study and revealed that GymAware devices possess almost perfect reliability for MV as evidenced by low RSE, high PPER and sensitivity to detect meaningful changes in performance (i.e., SDC%1RM), and the absence of fixed and proportional bias. In comparison, PV from GymAware devices demonstrated small, but practically non-significant fixed and proportional bias, and slightly lower PPER and SDC%1RM. These findings are in partial agreement with the only previous study18 examining the reproducibility of GymAware while simultaneously using two devices under the same testing conditions. More specifically, Jovanovic and Jukic18 found PV from GymAware to be a more sensitive metric compared to MV in detecting changes in performance during the hex-bar deadlift exercise, although both velocity metrics were found to be highly sensitive and reliable. It is important to highlight that although PV from GymAware was less sensitive than MV in the present study, it was still sensitive enough to detect meaningful changes in RT performance. Namely, when investigating the equivalence of PV recorded by two GymAware devices, upper and lower LoA were within the lowest SDC for the individualised load-velocity profiles reported by Banyard et al.10 during the free-weight back squat exercise. Therefore, it can be concluded that both MV and PV from GymAware are reliable and sensitive to detecting meaningful changes in neuromuscular status and functional performance during the free-weight back squat exercise.
In the present study, fixed and proportional bias was not an issue for body mode PUSH2 devices. However, somewhat higher RSE, PPER and SDC%1RM compared to GymAware – especially for MV – and apriori established criteria, suggest that caution should be exercised when using PUSH2 devices in practical settings. In the previous study18 which examined the reproducibility of bar mode PUSH2 devices, the authors reported worse RSE, PPER, and SDC%1RM. Therefore, although the reproducibility of body mode PUSH2 devices examined in the present study was unacceptable, reproducibility was greater than for previously reported bar mode PUSH2 devices. It is important to note that several software updates may have played a bigger role in the improved reproducibility of the PUSH2 devices observed in the present study compared to the differences between the body and bar mode of PUSH2 devices. In addition to previous findings, we also observed a lack of agreement for both MV and PV between two PUSH2 devices concerning the SDC of the individualised load-velocity profiles in the free-weight back squat exercise. Therefore, while substantial fixed and proportional bias were not present for PUSH2 devices, they do seem to possess a considerable amount of random error which negatively affects their sensitivity in detecting practically relevant changes in performance regardless of the velocity metric used. Nevertheless, it should be noted that MV from PUSH2 had a reasonably high PPER and low SDC%1RM, suggesting that practitioners who are only interested in detecting changes in performance greater than ~ 7% 1RM could still benefit from using PUSH2 devices. Though, caution should again be exercised when using these devices for monitoring neuromuscular status or terminating training sets based on velocity loss.
For Vmaxpro devices, neither fixed nor proportional bias was observed in the present study. Importantly, very low RSE and SDC%1RM, and high PPER were observed for MV. Interestingly, these values for RSE, SDC%1RM, and PPER were superior in comparison to GymAware and PUSH2 devices. In addition, MV between the two Vmaxpro devices was highly equivalent concerning SDC in load-velocity profiles suggesting their sensitivity in detecting very small changes in performance. However, RSE and SDC%1RM for PV were twice as high compared to MV of this device, but still slightly superior to those of PUSH2, but not GymAware devices. This finding was further reflected by the equivalence analysis for PV of Vmaxpro where upper and lower LoA always sat just outside (~ 0.007 m/s) the practically equivalent margin of ± 0.11 m/s which corresponds to a real change in daily readiness to train during the free-weight back squat exercise when assessed by PV10. Therefore, MV from Vmaxpro devices can be used for RT monitoring, prescription, and performance evaluation, whereas caution should be exercised when using PV from Vmaxpro as it does not seem to be sensitive enough to detect the smallest changes in performance that could be relevant in practical settings.
Traditional interpretations of correlations and linear relationship coefficients (i.e., values > 0.90 as very high) previously failed to confirm devices’ reliability19,20. Similarly, MV and PV between pairs of the same device in the present study all showed high r and ICC values (i.e., ~ 0.98). However, this just means that the faster the movement on the first device, the faster the movement on the second device, giving no information about the magnitude of errors in absolute values. Since velocity monitoring devices, among other purposes, are used to leverage the utility of the load-velocity relationship it is crucial to evaluate their magnitudes of error in both absolute (i.e., m/s) and relative, practical terms (i.e., %1RM), as done in the present study. Furthermore, for the assessment of technological variability stricter criteria than previously used should be adopted, as recently recommended by Courel et al.19 For instance, if one considers CV values of < 10% and ICC values > 0.90 to represent good reliability of a given device, then one also must accept the remaining 10% error in the measurement. While these criteria could be seen as more than rigorous in social sciences, it is not enough for the assessment of technological devices. In this regard, Courel et al.19 suggested ICC > 0.99, CV < 3.5%, RSE < 0.03 m/s for velocity monitoring devices to be considered reliable and possess acceptable sensitivity. Following these recommendations, only MV and PV from GymAware and MV from Vmaxpro can be used for RT monitoring and prescription, as previously concluded based on other statistical parameters provided in the present study. Finally, future research should also consider evaluating a wide range of statistical parameters rather than relying on traditional correlation, CV, and ICC coefficients to provide more nuanced insights into the reliability and sensitivity of velocity monitoring devices.
The present study is the first to examine the reproducibility of GymAware, body mode PUSH2 and Vmapro devices during the free-weight back squat exercise while evaluating and interpreting the magnitudes of errors according to pre-established, practical criteria. A relatively large number of males and females with different training backgrounds and experience levels performed ecologically valid RT sets with a range of different loads and repetition ranges. However, it should be noted that the validity of these devices was not evaluated in the current study due to the absence of a gold standard (i.e., the MOCAP system). In addition, the validity of GymAware, PUSH2 and Vmaxpro devices has been examined in previous studies using different approaches with conflicting findings reported, especially for PUSH2 and Vmaxpro devices16,17. Therefore, future research is required to comprehensively examine the validity of these devices. Nevertheless, if the reproducibility and sensitivity of a given device are proven sound, they can safely be used for RT monitoring and prescription purposes. Finally, it should be noted that manufacturers of velocity monitoring devices are very frequently releasing new software updates for devices and increasing the accuracy and stability of the algorithms used. This further suggests that the reproducibility of devices should be examined regularly to ensure that the measurements obtained are reliable and sensitive enough for the intended purpose.
The findings of the present study suggest that GymAware is highly reproducible and sensitive in detecting the smallest changes in RT performance, regardless of the velocity metric used. Vmaxpro can be considered as an equivalent, cheaper alternative to GymAware, but only if the MV metric is used for RT monitoring and prescription since PV from Vmaxpro was found to be a slightly less sensitive metric compared to PV from GymAware. Caution should be exercised when using PUSH2 devices in practice due to their comparatively higher, unacceptable measurement error and generally low sensitivity to detecting meaningful changes in neuromuscular status and functional performance during a free-weight back squat exercise.