Encoder reliability and calculated metrics
Why Vitruve uses a linear position transducer, what the validation research found, and how each velocity, force, power, and fatigue metric is defined.
Vitruve encoders are linear position transducers (LPTs): a string physically follows the bar, so the device measures real displacement over time. This page explains how reliable that is and what each calculated metric means.
Reliability
Vitruve describes its encoder as one of the most reliable VBT devices available. For VBT, a reliable device must meet two criteria:
- It never misses a rep.
- It gives consistent data with minimal error from one rep to the next.
Vitruve's position is that linear position transducers are the only truly accurate devices for velocity-based training. Devices based on other sensors, such as accelerometers or cameras, may have scientific validation, but that does not necessarily make them accurate enough for VBT.
The validation research
Vitruve's reliability material refers to Pérez-Castilla et al. (2019), a study that compared seven commercial velocity-measuring devices:
- Participants: fourteen men.
- Sessions: one session to find their one-repetition maximum (1RM) in the bench press, and a second with repetitions at several loads.
- Reference: movement velocity was recorded at the same time by an optical motion-capture system (Trio-OptiTrack) and by all seven devices.
- Result: the devices showed varying levels of reliability, which matters when choosing a device for practical weightlifting assessment.
Download the full validation research from vitruve.fit/reliability-of-vitruve.
Metrics the current app calculates
The current Vitruve app uses these definitions for each rep and set. Values use m/s for velocity, m/s² for acceleration, N for force, and W for power. Range of motion and load follow your metric or imperial unit setting.
| Metric | Definition |
|---|---|
| Mean Propulsive Velocity (MPV) | Average velocity during the propulsive part of the concentric phase, before the bar starts to slow down. The braking phase is not used. It is the main VBT velocity. |
| Mean Velocity (MV) | Average velocity across the whole concentric phase, including slowing down at the top. |
| Peak Velocity (PV) | Highest instantaneous velocity in the concentric phase. |
| ROM | Range of motion: the distance the bar travels. |
| Mean Acceleration | Average rate of change of velocity during the concentric phase. |
| Peak Acceleration | Highest instantaneous acceleration during the concentric phase. |
| Acceleration Index | Peak Velocity divided by Time to Peak Velocity: how quickly the athlete reaches top speed. |
| Time to Peak Velocity | Time from the start of the concentric phase until Peak Velocity. A shorter time means a more explosive push. |
| Mean Force | Force needed to lift the external load against gravity (load mass × gravitational acceleration). |
| Peak Force | Highest force during the concentric phase, from peak acceleration and the external load (force = mass × acceleration). |
| Mean Power [MPV] / [MV] | Mean Force × Mean Propulsive Velocity, or Mean Force × Mean Velocity. |
| Peak Power | Peak Force × Peak Velocity. |
| Set Avg Mean Velocity / Mean Propulsive Velocity | The average of the mean velocities of every rep in the set. |
| Fatigue [MPV / MV / PV] | Velocity loss: the percentage drop from the fastest rep of the set so far to the current rep. |
| 1RM | Estimated one-repetition maximum, from a load-velocity profile. See Create equations and manual 1RM. |
Force and power depend on the load you enter. Check the load and unit before comparing them between sets. Jump metrics, such as jump height and modified RSI, are explained in Record jump workouts.
Concentric and eccentric data
The encoder measures both directions of a rep. To show eccentric data in the app as well, turn on Eccentric phase (Include eccentric phase in repetitions) in the VBT training settings. You do not need to change anything on the encoder. See Training settings.
Differences from the older apps
The older Vitruve and Vitruve Teams apps listed some metrics differently:
- They calculated mean force as the entered load × mean acceleration. The current app calculates Mean Force as the load × gravitational acceleration.
- They showed Dynamic Isometric Strength, which the current app does not list.
- Vitruve Teams showed the same metrics, with mean and peak acceleration included only in data exports.
Compare results only when they were calculated the same way. See Legacy apps for the older apps.
Buttons, menu, and screen
Use the older Vitruve Encoder's power switch and two buttons, including touch-sensitive ones, open its Menu screen, and read the rep data on its OLED display.
Troubleshooting
Fix an older Vitruve Encoder that is missing from Bluetooth, records eccentric reps instead of concentric, or restarts its rep count.