Ask ten different coaches to describe a 'heavy jab', and I suspect you'll get somewhere close to ten different answers.
Some refer to heavy jabs as 'stiff jabs'. For others, a 'stiff jab' relates more to technique and for others still, it relates to the 'natural' power some fighters' jabs generate.
To address the jab demonstrated by your instructor:
I'm not a big fan of telegraphing at any time, but there are instances in which it might be deemed acceptable by some. These instances are those in which your opponent is overwhelmed and/or overly defensive, presenting no obvious offensive threat. Some fighters take this as an opportunity to 'wind up' a little more, especially if they themselves are fatigued and losing coordination and power. Occasionally though, these lapses of discipline cost them dearly.
Your instincts about the instruction may well be right. No well-thrown punch (or kick) I can think of ever looks ridiculous. It looks honed, the ultimate evolution of centuries (millennia?) of trial and error and design. The time it takes to retract or 'cock' an arm, and then to return it to it's ordinary starting position is a very long time in the lightning-fast context of expert striking. Was any advice given as to the occasion in which you might use such a punch? I'm not aware of any great fighters who routinely telegraph the jab (except perhaps when exhausted).
Clearly, all punches exist on a power spectrum. Jabs can be thrown as feints, quick distracting flicks, sharp stun shots, stiff range-holders, and yes, as very heavy blows (of knock-out effect in skilled hands). So, a 'heavy' jab is arguably any in which the power intended and/or delivered is close to maximal.
A very heavy jab can be developed without resort to retracting the arm. The best heavy jabs are motions of violent beauty which shun unnecessary movement and achieve maximum effect through efficiency of movement.
Key ingredients to a truly heavy jab include (in no particular order):
- Speed
- Body-weight transference
- Timing
- Range
- Accuracy
These elements can be understood in the context of force.
Force = Mass x Acceleration.
Speed and range: The faster you punch, the faster the acceleration of your fist will be, usually just before the end of the jab. The vital thing to remember here though, is to realise that the range from which you throw the jab and the way you envisage your target have a massive impact here. Why? Because if your target is merely the surface of the body, your fist will have moved beyond its maximal accelerative phase by the time contact occurs. Inhibitory mechanisms designed to prevent overextension of the elbow come into play and slow the fist down towards the very end of its motion. To counter this effect, it is necessary to aim beyond the surface of the body (about the depth of your fist). In other words you want to be punching into or through your opponent, to cause maximum damage via the maximisation of force, which is partly achieved through maximising the acceleration of your fist at the point of impact. By punching through your opponent, the inhibitory processes described above have not yet interceded and the transferral of your body mass's momentum is allowed to 'penetrate' the opponent's body.
Timing, accuracy and body weight transferral also work together. You want your punch to represent the accumulation of the power generated by your feet, legs, torso, shoulders and arms. If there is a staggering of these motions - if the flow of this kinetic chain is broken/hindered in any way - maximum weight transferral is diminished.
Timing is maximised when the successful execution of this complex movement coincides with forward momentum via a step and via the rotation of the trunk and shoulders, the tensing of the arm and shoulder at the precise moment of impact, the position and motion of your opponent at the moment of impact, the grounding of the body's weight at the moment the stepping foot lands, and the accuracy of the blow (ie. onto a part of the face from which it does not lose force because of glancing caused by inaccuracy).
There is much more detail to go into, but if you work on these principles consistently, you should go a long way to maximising the potential power of your jab and no 'winding up' should be necessary.
I realise your question is about jabbing in a Muay Thai context, but the jab-specific Muay Thai footage available is relatively scarce, so I thought you'd enjoy this video of 'The 10 Best Jabbers in Boxing History'. Some of these fighters threw extremely heavy jabs, and you'll notice they keep telegraphing to an absolute minimum.
