Barbell VBT: are we really measuring what counts?


by Scott Damman, Assess2Perform.  Being in the VBT technology space with the Bar Sensei we look beyond simply displaying a number.  We study training outputs to see if there is valuable information that maybe is getting missed.  Sometimes we need to challenge the traditional way and ask questions -- is the standard metric, or what I call legacy data, the right metric?  In June I guest wrote on SimpliFaster an article Is It Time for Coaches to Rethink Velocity-Based Training?  The point of the article was to create some fresh conversation related to the VBT metrics that have been used traditionally, and challenge those metrics.

I want to come back to one metric in particular, MPV (mean propulsive velocity).  There is a compelling argument for MPV to replace AVG (aka mean) velocity, yet I see very little attention to this point.  AVG speed (interchangeable with velocity) is the legacy metric used during VBT (bar speed tracking) for lifts such as squat, bench, and deadlift.  These are non-ballistic movements and include an acceleration phase, a point of peak speed, then a deceleration phase.  AVG takes into account the time during that full range of motion, and small changes in time have a significant effect on the meters per second display of AVG (i.e. 0.84 m/s).

 

 This data collected with the Bar Sensei shows bar speed metrics during a Squat:  peak, average, distance, MPV, and a ratio of MPV into AVG.  Look as Column N (Avg to MPV ratio) tightens as the load goes from 95 to 220, then starts to open back up at 250.

 

Flip side, MPV looks at the Propulsive Phase, the point of the barbell accelerating until the lift hits peak speed.  The mean (average) of MPV is the time from the start of the concentric phase to where acceleration hits zero (point of peak speed).  MPV does not give a rat's --- of what happens after that point of the lift.  Why is this important?  Because the deceleration phase of the lift (slowing the barbell down for a squat or bench) is not part of the MPV equation, as this deceleration phase is not relevant and can actually penalize (or misrepresent) an explosive lifter.  AVG bar speed takes into account the full range of motion, MPV only cares about the time you are accelerating (the propulsive phase).

Think about this, since time is the controlling factor for AVG bar speed and MPV metrics, an explosive lifter who takes longer to decelerate the barbell -- whether it is because they are efficient at braking, they are longer levered, or other factors -- could have a higher percentile MPV but a middle-of-the-road AVG.  Or, two lifters can hit a similar Squat 1RM -- lifter 1 hits pk speed early (short window of acceleration) and grinds through the rep; while lifter 2 accelerates throughout most of the range of motion.  They both finish the rep and have a similar 1RM, but they get there two very different ways.  Are you looking to develop grinders or explosive athletes?  

I am not saying MPV is the holy grail of VBT metrics; in fact, when this all washes out I bet it will be a VBT composite index of a few telling metrics -- MPV, peak speed, and POP-100.  I do not see AVG being relevant when we now have more innovative metrics available.  All I ask today is do not be comfortable with how it has always been; rather, ask questions and look at the path of logic during your VBT tracking and training.  Look at what you are trying to develop, then work backwards to see if your VBT metrics are representing your outcome goals.