Bat Sensor Numbers, Explained

1. What a bat sensor measures, and what it cannot

A bat sensor is a small motion sensor that clips to the knob of the bat (Blast Motion and Diamond Kinetics are the two M4P uses) and records how the bat moved on every swing: how fast the barrel was going, the direction it was travelling at contact, and how long the swing took. It measures the bat. It does not measure the ball.

The ball is a different set of tools. HitTrax and Rapsodo report what happened after contact: exit velocity, launch angle, distance. A radar such as Pocket Radar reports exit velocity alone. A sensor can tell you a swing was fast and on a good path; only a ball-tracking tool can tell you the ball came off hard.

Sources: S1, S2, S3, S4

2. Bat speed

Bat speed is how fast the barrel is moving through contact, reported in miles per hour. The apps measure it at a point on the barrel, not at the hands, and each app's help screen says exactly where and when; read that definition once so you know what your number means. The barrel matters more than the hands: the hands can move at the same speed on two swings while the barrel arrives at very different speeds, depending on how the swing was sequenced.

Read a round, not a swing. One hero swing tells you what the athlete can do once; the average of a full round tells you what the swing actually is today. When we log bat speed at M4P we log the round average, with the best swing noted separately.

• Log the round average, not the best swing.
• Keep the same bat. A different bat is a different number.
• Note the sensor model and the app version in the log.

Sources: S1, S2

3. Attack angle versus launch angle

These two get mixed up constantly because they are both angles and both involve the word up. They are not the same thing.

• Attack angle is the swing. It is the direction the barrel is travelling at the moment of contact, measured against level ground: positive means the barrel was moving upward through contact, negative means downward. The sensor reports it.
• Launch angle is the ball. It is the angle the ball leaves the bat after contact. HitTrax and Rapsodo report it. It depends on the attack angle and on where the bat met the ball.

Which one can you coach? The swing. A hitter cannot decide a launch angle; they can only build a bat path and a point of contact that produce it. That is why M4P films contact depth and the swing plane on assessment day instead of chasing a launch-angle target. The biomechanics page at movement4power.com/m4p/biomechanics shows how contact depth and the sequence show up on film.

Sources: S1, S3, S4

4. Time to contact and peak hand speed

Time to contact is how long the swing takes from the start of the forward move to contact, reported in fractions of a second. Peak hand speed is the fastest the hands move during the swing; both apps report a hand-speed number, under slightly different names. Together they tell you about sequencing, pillar three of the M4P Hitting Development Guide: a swing that is both short in time and fast at the barrel usually means the lower half led and the hands fired last.

A long time to contact with low bat speed is the most common youth pattern we see on film: the hands start early, the barrel drags, and the athlete muscles the swing. The fix is rarely a hands cue. It is usually the order.

Sources: S1, S2, S5

5. Rotational acceleration, on-plane efficiency and the other composites

Your app will show more than these four numbers: rotational acceleration, on-plane efficiency, power, connection scores and others. They are useful, and they are vendor-defined composites, each built from the raw motion data in a way the vendor describes in its own glossary. We do not paraphrase those definitions here, because a paraphrase can drift from how the number is actually computed. Read the definition in the app's help screen, and ask your coach which of them they use and why.

Sources: S1

6. How to take a reading you can trust

A number is only worth logging if it can be compared with the next one. Hold everything the same except the athlete:

• Same bat, same sensor, same app settings.
• Same tee height, or the same soft-toss feed from the same spot.
• Same ball.
• Warm-up swings excluded from the round.
• Same round size every time. Round size: ________ swings.
• Sensor model and app version written in the log.
• Round average logged, best swing noted separately.

M4P runs a fixed protocol on assessment day. If your athlete has been assessed, use the round size and setup from their report so your home numbers line up with ours.

Sources: S4

7. Reading change over time

Swings vary. Inside one round the fastest and slowest swings are never the same number, and that spread is normal. A change in the round average that is smaller than the spread inside the round is not yet a change; it is noise. A change that holds across two retests, measured the same way, is real.

• Compare round averages, never single swings.
• Retest on a schedule, not on a feeling. The free 4-week program that comes with an M4P assessment ends with a re-test in week 4; at home, retest at the end of each 4-week block.
• Write down what changed in training between tests, so a jump has a reason attached to it.

The Baseline and Progress Worksheet (free at movement4power.com/resources) is built for exactly this: one page for the baseline, a retest log with a change column, and a line for what the athlete worked on.

Sources: S4, S6

8. Is there a good number for my athlete's age?

The honest answer: published tables vary by device, by how the swing was measured and by who was measured, and most were not measured the way you will measure. Two tables from two vendors will not agree, and neither will match a round you took in the garage with a different bat.

So M4P does not print a benchmark table in this guide. What we do instead is take a baseline the same way every time, write a plan against the biggest limiter, and re-test. Progress against your own baseline is the number that matters, at every age.

If you want context for where an athlete sits for their class year, ask the coach who measured them. They know the device and the setup, which is what makes the comparison fair.

Sources: S1, S4

9. The limits of a sensor

• A knob sensor sees the bat, not the body. It cannot tell you the hips started late; film and a coach can.
• Pairing drops and mis-tagged swings happen. A round with a missing swing is not the same round; re-take it.
• A swing the sensor likes is not always a swing a coach likes. Fast and on plane can still be early, late or out of order.
• Numbers describe; they do not prescribe. The drill choice comes from what the film and the coach see, with the numbers as the check.

That is the whole reason the M4P assessment pairs the sensor with HitTrax, slow-motion film and, on assessment days, 3D motion capture: each tool covers a blind spot in the others.

Sources: S4