Mechanics of hit acceleration

The tactical value of a spike in volley-ball rests on the production of a trajectory:

  • straight line
  • plunging
  • precise

Each spike manages a compromise between these three parameters according to conditions. The spike should give the opponent a problem of speed and control.

From a physical point of view the hit is an shock between the hand and the ball. The resulting speed depends on several factors like the density of the two elements and their speed. Veterans have noticed a few years ago that the regulatory drop in ball pressure has forced spikers to hit harder to obtain the same speed.

We also know that an "active" tonic hand transmits more speed than a soft and relaxed hand. Here we are going to focus on a central question: How to give speed to the hitting hand to transmit some to the ball? At the same time we will relate this to the spontaneous productions of beginners.

Note that the mechanisms in play stay valid in other sporting skills like the service or the spike in tennis and in badminton for example. This makes the spike a relatively widespread technical element. It is very important to understand that it's a matter or coordination and not pure force.

Lift, push, whip?

Initial behaviour: The beginner tries to secure contact with the ball by placing himself below it which stops him from accelerating it and forces him to push it from below.

See the resource on
the spike

Evolution 1:

The intermediate player, better placed, can hit the ball but he generally does it with a locked arm (straight or bent), which means that mobility is reduced to that of the shoulder. It's the 'hit with a stick" model. It's neither efficient nor precise.

Evolution 2:

Most of the time the player stays facing the net and finds himself limited in his movement range by the limited mobility of the shoulder towards the back (the back of the player, or his own back). He sometimes transfers the mobility to a lower level using the lower back to arch /bend and his spine will remember that later... But at the time this corresponds to the representation "demonstration of force" linked to the spike.

This mechanism does produce more amplitude and power. The tension of fore muscles can recall the image of a bow.

The effort supplied is important in relation to the speed transmitted to the ball. Often these hits will end up out of the court for lack of rolling towards the target.

Evolution 3:

If we ask a pupil if he would rather be hit (absurd hypothesis) by an 80 cm long stick or a nunchaku of 2x40 cm he will prefer the first solution. He is however unable to explain that in the first case the speed of the end of the stick depends on the rotation speed at the base and on the length of the stick and that in the second case the combination of a shorter lever and an additional level of mobility allows a much bigger acceleration at the extremity.

Of course these examples are over simplified. In reality biomechanical movements occur in all three dimensions and the limits of joint mobility are specific to articulation. However, unlike with a nunchaku, the human body possesses a chain of muscles enabling to accelerate the different segments and thus accumulate speeds.

If the shoulder acquires a speed (Vs), that on this acquired speed the elbow is projected forward (Ve), that based on the elbow's speed the forearm (Vfa) and finally the hand (Vh) are accelerated we witness an addition of the speeds (Vs+Ve+Vfa+Vh) that we will never obtain with only one level of mobility at the shoulder. At the end the "hand overtakes everyone" with maximum speed.

From this point of view the image of the nunchaku even if it is simplistic happens to be a useful technical metaphor to understand that the release and the use of the different joint movements allow to produce more speed than an effort blocked at the shoulder. A high elbow (arm against the ear) is a useful marker to facilitate the last accelerations: forearm and hand. If the elbow drops in front of the hand there is no acceleration

The elbow's anatomy requires an internal rotation of the hand and the arm at the end of the gesture to avoid a blocking of the elbow which can cause a trauma. This rotation happens naturally if the elbow stays high at the end of the gesture and if the latter is executed in a relaxed manner.

The hand trajectory resulting from the acceleration movement is much more adaptable and better oriented to adapt to the distance of the ball to the net and vary the points of impact on the ball and therefore the trajectories.

See the resource on
hits and distances
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