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Deadlift : Validity of different devices to measure the force-velocity relationship

by P. Debraux | 29 May 2018

deadlift, validity, accuracy, science, data, sensor, inertiel, sport, training, push, gymaware, tendo, linear transducer,comparison, test

With the democratization of inertial sensors that measure acceleration (PUSH, The Beast, to name only the newest) and linear transducers that measure displacement (GymAware, Open Barbell, Tendo Sport), Velocity-Based Training (VBT) has become increasingly popular in weight training. The general idea is that there is a relation between the loads relative to the 1RM and the velocity of displacement, and that this relation is linear and stable in time. This load-velocity relationship would allow a better way of training more in accordance with the level of form of the moment since the load would be selected according to the velocity of exertion fixed on a given exercise ( read our complete review on the subject).

Inertial sensor PUSH

Figure 1. Inertial sensor PUSH.

However, velocity-based training depends mainly on the validity of sensors (their ability to give correct values relative to reference devices) and their sensitivity (their ability to distinguish velocity differences from hundredth of m/s), whether linear or inertial transducers. The GymAware is the validated linear transducer of reference in comparison to the force plate ( read our article on the subject), on guided and non-guided movements. Inertial sensors, on the other hand, are based on accelerometry and algorithms that detect the different movements realized. Their main advantage is their price, lower than that of linear transducers, and the fact that they are wireless, and therefore very practical to use. However, despite the attractive appearance of such devices, their reliability is not clearly demonstrated. The validation of these devices is not always obvious, some devices like the Push show good validity on guided exercises but the opposite when it comes to non-guided exercises, especially at very fast and very slow bar velocities. What about the validity of the Push during a deadlift?

The Study

To answer this question, the authors of this study compared measurements obtained using different devices (GymAware, Tendo and PUSH) during a deadlift at different relative loads of 1RM. For this, they recruited 10 strength trained male who each could deadlift a load at least equivalent to 1.5 times their body weight. The protocol consisted of 3 sessions separated by at least 72 hours. During the first session, in addition to the anthropometric data, the participants evaluated their 1RM deadlift. In the following two sessions, all participants performed 3 repetitions at 20, 40 and 60% 1RM and 1 repetition at 80, 90 and 100% 1RM. For each repetition, measurements were simultaneously performed with GymAware, Tendo and PUSH to compare the reliability and sensitivity of the 3 devices.

Results & Analyzes

The main results of this study show that the PUSH is not valid in comparison to the GymAware either on all 120 repetitions tested or on the 6 relative intensities for the measurement of the mean velocity and the maximal velocity. In comparison with GymAware, the velocity measurements obtained via Tendo are strongly correlated with that of GymAware when the 120 repetitions tested are combined, but when the relative intensities are observed separately, moderate to large differences are found at 80 and 90% of 1RM for mean velocity, and at 20, 40 and 60% 1RM for maximal velocity(Figure 2-3).

Comparison of the mean velocity between the 3 different sensors during all the repetitions in deadlift

Figure 2. Comparison of the mean velocity between the 3 different sensors during all the repetitions in deadlift.

Comparison of the maximal velocity between the 3 different sensors during all the repetitions in deadlift

Figure 3. Comparison of the maximal velocity between the 3 different sensors during all the repetitions in deadlift.

These results are in line with a study that used PUSH in a non-guided back squat and concluded that it was invalid. On the other hand, two other studies studied PUSH and found that this sensor was valid. But these two studies did not report validity at specific relative intensities and one of them validated PUSH in a smith machine back squat. The main reason for these differences in results is in the type of exercise used (guided vs. non-guided) and in the exercise itself (squat vs. deadlift). The algorithm of inertial sensors is supposed to recognize the exercise performed to better adapt its measurement. In addition, the accelerometers are sometimes not sensitive enough to detect the weakest movements of the bar.

Practical Applications

In comparison with the GymAware, reference of the linear transducers, this new study shows that the PUSH inertial sensor is not valid in a conventional deadlift, regardless of the relative intensity of 1RM used. It is therefore strongly recommended not to use this device if you wish to base your training on the velocity of execution. In terms of reliability, these small wireless sensors (like the old Myotest or the new Beast) are very limited, although they seem very practical. It is not uncommon that some repetitions are simply not counted or that the values indicated are completely out of standard (because the velocities will be too important or too weak to be correctly analyzed or even recognized).

In addition, even if the price is very attractive compared to devices such as GymAware or Tendo, and the device implementation is much simpler and convenient, all this is at the expense of measurement reliability. In this case, how will you be sure that you progress (or regress / or stagnation) over time is simply not the device playing you tricks ? Note that an interesting alternative (in terms of price) linear transducer has emerged : Open Barbell and the company that marketed this product will soon launch a new product : RepOne Strength. It remains to know if it's reliable...

References

  1. Chéry C and Ruf L. Reliability of the load-velocity relationship and validity of the PUSH to measure velocity in the Deadlift. J Strength Cond Res Article in Press, 2018.

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