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Please, don't buy this: Zip Trainer

A few months back, I posted an entry about the Zip Curveball Trainer and why it is an awful product. At the time, I was aware that the regular Zip Trainer existed, but I assumed it couldn't possibly be worse than the Zip Curveball Trainer. I finally read about it, and I was dead wrong.

The Zip Trainer (Source: product is "designed" to promote wrist flexion as a proper part of a powerful pitch release. Like the Zip Curveball Trainer, though, the Zip Trainer teaches it backwards. The device actually trains its users to extend their wrists as they prepare to release the ball.

The tension applied by the Zip Trainer creates an eccentric contraction that strengthens the extensor muscles of the forearm rather than the muscles of the flexor-pronator mass.

One advantage of increased strength in the extensor muscles is that the muscles will be able to handle greater loads during deceleration. This means that after using the Zip Trainer, a pitcher will likely develop faster, more powerful wrist action because the forearm will be better conditioned to slow the hand down after the pitch is thrown.

So why is this bad? When a muscle or group of muscles contracts during joint action (flexion or extension), the brain prevents the opposing muscle(s) from contracting simultaneously. This is called reciprocal inhibition. This means that while the extensor muscles are extending the wrist, the flexor-pronator mass can not contract to support the ulnar collateral ligament.

Because this device teaches wrist extension prior to pitch release, pitchers who use this device "properly" place themselves at an increased risk for UCL injuries.

But wait! There's more!

The product page also offers tips on how to use the Zip Trainer to throw a slider. By moving the finger loops onto different fingers, the Zip Trainer can also teach its users to throw sliders with supinated releases.

Supinated releases do not protect against the forearm flyout flaw that is present in the arm action of most pitchers with traditional pitching mechanics. When unprotected, this flaw causes the back of the elbow to "slam closed." The collision between the olecranon of the ulna and the olecranon fossa of the humerus irritates cartilage and leads to irregular bone growth (lengthening of the ulna, bone spurs, bone chips, etc.).

To have a look at this questionable product for yourself, click here, but please, don't buy this.

Do you know of another stupid pitching product out there? Tell me about it.

Reader Comments (6)

on the subject of the reciprocal inhibition...

agonists and antagonists are often active at the same time...

think of bodybuilders flexing their biceps... the biceps contract (albeit isometrically) creating a tension that propagates into the tendons of the flexors. if this were the only force acting about the joint, the arm would go through a flexion motion... the triceps muscles have to be active in order to keep the segments in static equilibrium.

but antagonists and agonists are often contracting at the same time for reasons beyond cosmetics. When muscles make forces, the angle at which the tendon attaches to the bone is not perpendicular to the shaft of the bone. The component of the force that is parallel to the longitudinal axis will push the head of the bone into the joint, aiding in joint stability. The perpendicular component will cause the bone to rotate about the joint capsule, but will also cause a tendency to translate slightly. If this becomes too large, the bone can actually translate out of the socket.
this is where the antagonist comes in. the antagonist will make similar forces, one component perp. and another par. to the long axis. Only this time the perp. component will cause translation in the opposite direction as that of the agonist. So this is important because the forces will cancel out.

but i'll agree that in the case of the zip trainer the contribution from the other muscle group is minimal, as it often is. but it is still not negligible.

this is actually a problem when biomechanists report joint torques... even with emg (which doesn't do a good job of telling you magnitudes of muscle contractions, instead they really only tell you when a muscle is 'on' or 'off') a biomechanist can really only report NET TORQUE about a joint. this would be fine if only one muscle group were active at one time. but that's not the case.

a biomechanist would look at the bodybuilder and say that because the joint is in static equilibrium the net torque is zero. that doesn't mean that the muscles aren't making forces. and again, emg wouldn't solve this, because all it would tell us is "yep, both muscles are active, but we don't know how big the forces are."

Just a heads up.

Wow. that was wordy and i didn't intend it to be.

June 16, 2009 at 9:18 PM | Unregistered Commenterrick

You are correct on a lot of points, but the biceps and triceps are not a paired agonist and antagonist. The triceps antagonist is the brachialis. If a body builder wanted to flex his brachialis and triceps at the same time, the joint would have to be in a static position (complete isometry).

In a ballistic exercise, like throwing, the antagonist muscle group does not begin to contract until the agonist muscle is no longer contracting. *This* is reciprocal inhibition.

In the example of the Zip Trainer, this principle only applies while the wrist is moving backward to full extension. Once the wrist stops moving backward, your brain allows the antagonist flexor-pronator mass to contract.

As far as translating a bone out of socket is concerned... Neuromuscular fitness plays a large role there. Your brain isn't supposed to let your triceps accelerate your forearm beyond what your brachialis is capable of decelerating. That said, these things do not happen at the same time unless your nerves/neurons are misfiring.

When joint translation begins to occur, the brain relaxes the agonist muscle and contracts the antagonist muscle. This, of course, assumes a certain level of neuromuscular fitness and healthy joints.

In just about every case of serious joint translation or full out dislocation, an outside force is to blame.

June 16, 2009 at 11:28 PM | Registered CommenterTrip Somers

that's the textbook definition of reciprocal inhibition, and to a good approximation yes, opposing muscles groups aren't active during throwing, but they rarely shut off *completely*. i think there's some misinterpretation of how that works.

as far as joint translation, that happens often to throwers. but in the normal throwing motion the forces are seldom large enough to cause complete subluxation, but it occurs slightly on every pitch. throwing is basically an attempt to dislocate your shoulder. luckily we have soft tissue and connective tissue across the joint that resist this and keep our humeral head where it's supposed to be.

but like you said, if you were to, say, compound this with an external force of maybe hitting the ground as you throw or if someone were to slide into you with enough force, then the risks of dislocation could become larger.

and come on, isn't that being a little nitpicky with the biceps-triceps thing? haha the biceps can do a few things, including flexion of the elbow

June 17, 2009 at 3:39 AM | Unregistered Commenterrick

It's not picky at all, it's a scientific fact. That's how your brain interprets the relationship between the biceps, triceps, and brachialis, not my opinion of how they pair up. The fact that your biceps can "do a few things" is the very reason the brain doesn't reciprocally inhibit it while the triceps is contracting. The brachialis only does one thing - flex the elbow. (Wikipedia's example is wrong in this case.)

Ballistic activities typically involve maximal contractions from agonist muscles. Sprinting is the perfect example. The hamstring and quadriceps muscles contract extremely powerfully and in alternating fashion. The hamstring is typically a weaker muscle, but it is still strong enough to tear itself apart. When your brain fires the command to contract the hamstring at sprinting speed *before* your quadriceps is done extending your knee, your hamstring will strain, pull, or even tear itself.

These reciprocally inhibited pairs of muscles exist across every joint. Wrist action is important during pitching because the muscles that flex the wrist help stabilize the elbow joint by virtue of their origins on the medial and lateral epicondyles of the humerus.

I agree with you on the shoulder. Rotator cuff muscles tear fairly easily compared to most muscles because two powerful muscles that oppose their contraction are not antagonistically paired with them - primarily the pectoralis major but also the deltoids and some of the back muscles. When I write about rotator cuff injuries, there's going to be a lot more detail.

June 17, 2009 at 10:41 AM | Registered CommenterTrip Somers

yeah, i'm not going to argue motor control (a subject that is admittedly a weakness of mine), but I am positive that even agonist-antagonist pairs do not operate with only one active at one time...

with your sprinting example (a subject I AM familiar with)... in a perfect world you wouldn't have competing muscle groups. so you're right, the hamstrings and quadriceps do work in alternating fashion... BUT (and this is a big but) it's not as simple as 'off' and 'on' for a muscle these muscles. there is a delay from the time a muscle is activated until it is capable of taking up the slack and actually making a tension, let alone a maximal force. if it were possible to go from 'off' to making a maximal contraction in an infinitely small time increment that would be fantastic, but it doesn't work that way... for that reason there is almost always a constant overlap of muscle activation from the agonist and antagonist.

this is part of the reason why countermovements are so valuable. the execution of a jump from a squat position is a good example. if you were to start in a squat position and attempt to jump, by the time your feet left the ground your muscles would be making some force F. The range of motion would have allowed them to develop some force, but with muscle's limited rate of force development and the path of motion, their is limited time and range to generate large forces.

if you were to start in a standing position and then quickly lower yourself into the same squat position, you would find that your hip and knee extensors were the active muscles, both contracting eccentrically to basically "catch" your body. eccentric conditions produce remarkable amounts of force due to stretching of passive elements and almost as important, the muscles are already active by the time you reach the squat position. so now, instead of starting with zero muscle tension and inactive extensors, you have this baseline level of force already generated. Over the course of the range of motion this force will probably decrease as the muscles shorten, but the point is that you will be able to achieve a greater vertical velocity by the time your feet leave the ground, allowing you to achieve a higher peak.

on an unrelated note, i read your "about the author" link and it said you have an MBA. i don't know anything about what you do for a living, but have you considered returning to school to study biomechanics or a similar field? A) you have a computer science background so i can't imagine the math would ever be out of your league B) you obviously have a passion for the subject so i can't imagine you'd ever get tired of the learning process... i mean, with a little know-how you could be hunting for more than just visual and temporal cues in your videos... and you wouldn't have to stop with pitching either... just a thought

June 17, 2009 at 4:22 PM | Unregistered Commenterrick

Longest... comments... ever. Keep 'em comin' as you see fit, man.

For the brain, it actually is as simple as "off" and "on." Other factors, though, such as calcium and potassium intake, can affect the response of the muscle.

For the sprinting example, there is a *gap* in muscle activity, not an overlap. Of course, it's very small and hardly noticeable even on slow-motion video. The first stage of the contraction is eccentric. Before it can concentrically contract, the hamstring has to slow down and stop the knee action eccentrically. When the foot hits the ground the quadriceps fires to keep you from falling on your face before once again yielding to the hamstring's concentric contraction.

This extra little bit of firing by the quadriceps (in between the eccentric and concentric hamstring contractions) is what causes hamstring tears. When a player is confused about whether to stop or start or speed up or slow down, he confuses his muscles, and they try to do too many things at once, overloading the weaker muscle in the process.

Your jumping example refers to what kinesiologists call the stretch-shortening cycle; however, I'm not sure that it applies to the concept of reciprocal inhibition. Were you trying to connect it to reciprocal inhibition or were you further explaining your sprinting comments about countermovement?

Regarding school: I'm actually re-enrolled for pre-med classes starting in the fall. The path is longer and rougher than kinesiology, but I feel that actually "fixing" these injuries will be more rewarding emotionally (as well as financially, of course).

June 17, 2009 at 5:34 PM | Registered CommenterTrip Somers

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