Here's something I've only thought about superficially, and I'd like your views. There is no doubt that body rotation is an important element in producing powerful shots in badminton. But I have yet to see a believeable explanation as to why it actually works. Many try to explain it by using the "kinetic link" principle, where the hip, shoulder, elbow, forearm are viewed as links in a chain, with movement being transferred from one link to the next, and speed increasing by each link. This sounds good and plausible, but once I started to think about it doesn't seem to hold. Think about it: how fast can you move rotate your hip, for instance? 5 km/h? Maybe 10? And the shoulder? Another 5 km/h perhaps? The chain principle is additive, so that would add up to a speed increase of at most 15 km/h. I read an article recently where they referred to a test carried out at the Stockholm University College of Physical Education and Sports. They tested the speed of different body parts in the shotmaking proces of male Swedish badminton players at elite level. The results were only briefly mentioned in the referring article (I will try to get a copy of the test report, though) but a number of interesting facts were revealed: to propel a shuttle at 275 km/h, one must achieve a racquet head speed of about 200 km/h. (So it is clear that the strings provide quite a bounce.) Even more remarkable is that in such a shot, the hand merely travels at a speed of about 25 km/h! (and according to my reasoning, perhaps 15 of those would come from the hip and shoulder) The remaining racquet head speed of 175 km/h is all generated by the pronative movement of the forearm. To sum it all up: according to scientific tests, body rotation has almost no effect on racquet head speed. In fact, forearm rotation stands for about 85% of the achieved head speed... And yet, most of us know that body rotation works. So, if the kinetic link principle is bogus, then why does body rotation make it easier to produce powerful shots? Comments?
Oppositional vs. Rotational Interesting thread. My initials thoughts concern rotational dynamics. If the hips/body rotate at a set speed (eg. 5km/h) and the arm is kept in constant relation to the body then the hand will be travelling much faster. So do not discount the overall effect that body rotation has. I came across an old book recently that discussed the difference between rotational and oppositional power. Briefly, rotational power is achieved purely by turning the body, eg. if you hold a ball in your arm and hold your straight arm out to your side, throwing the ball by merely rotating the body (no arm movement) produces a weak and innacurate throw. Oppositional power builds power and releases it. To throw a ball you would bend your back and pull both shoulders back and release them forward to throw the ball. This movement is much more powerful. Applying this to badminton, a rotational shot (even with arm movement) would mean the body is rotating around the vertical central point of your body. An oppositional shot would use the left side (notably the shoulder) as the centre point of the bodies rotation, making it more of a 'turn' than a 'spin'. This type of movement allows much of the body weight to be utilised in shot production. Perhaps 'body rotation' is not a causal factor in shot technique. But it could be the result of the oppositional principle working properly. I am, of course, theorising on subjective evidence and would welcome any thoughts others may have on this principle.
Re: Duh! Should read "kinetic", of cours Coming from a squash point of view, rotation is very important. Rotation is used to transfer additional kenetic energy to the ball; therefore, a harder stroke. I am not sure if the same can be said for badminton, because the rotation is quite different and the kenetic transfer thus would be different as well. I am no physicist, but I am quite sure that the roations are different. Different rotations can produce different results.
Re: Oppositional vs. Rotational So, what you are suggesting is that body rotation -- rather than contributing directly to racquet head speed -- would have more of a counter-balancing function, thus enabling one to apply greater force in the forearm pronation? By the way, in my club, as a first warm-up excercise (after the "proper" warm-up), we do still-standing clears from baseline to baseline, facing the net, feet placed firmly on the floor, keeping the racquet arm up and using nothing but forearm pronation. It's hard work, but not as difficult as one would think... although once you allow the footwork back in it gets much less taxing! In any case, it's a good test to ensure that the pronation works...
Re: Questioning the linetic link principle Applying science to us mortals, you are extrapolating from elite players and assuming the same variables. For example, you give your exercise of hitting the shuttle from the baseline as maximal use of forearm pronation. If we take a less skilled player to do the same exercise, they may have lesser proportion of power generated from pronation and more from body rotation. Thus, we would need to repeat the experiment with non-elite players to get the true proportions. Unfortunately, the non-elite players will have many more differences in techniques and it may be difficult to draw the firm conclusions. i.e. amateurs may need to use more body rotation compared to elite players.
It is true that some top players don't use much body rotation. Simon Archer is an excellent example. He often smashes standing almost still. But I would say that most top players do use a lot of body rotation. I hope you see what I am getting at here. Most coaches (and most text books on badminton for that matter) emphasize the role of body rotation in producing power, but I am suggesting that it does not contribute significantly to increased racquet head speed, and that it maybe has more to do with counter-balancing your gravity for a follow-up forward to the net.
What I am saying is that it may contribute significantly for the non-elite players! And I agree it may not be so for elite players. That would still be consistent with your last sentence on counterbalance.
Mmm... so you mean that beginners would need to use more body rotation to compensate for their poor forearm rotation? Yes, I suppose that sounds possible to me...
Re: Questioning the linetic link principle Mag, is this statement your or the test report's conclusion? **To sum it all up: according to scientific tests, body rotation has almost no effect on racquet head speed. In fact, forearm rotation stands for about 85% of the achieved head speed... And yet, most of us know that body rotation works.**
Re: Questioning the linetic link principle Mag, is this statement your or the test report's conclusion? **To sum it all up: according to scientific tests, body rotation has almost no effect on racquet head speed. In fact, forearm rotation stands for about 85% of the achieved head speed... And yet, most of us know that body rotation works.**
Re: Oppositional vs. Rotational "Applying this to badminton, a rotational shot (even with arm movement) would mean the body is rotating around the vertical central point of your body. An oppositional shot would use the left side (notably the shoulder) as the centre point of the bodies rotation, making it more of a 'turn' than a 'spin'. This type of movement allows much of the body weight to be utilised in shot production. " could u explain the 2nd sentence hoe can the shoulder be the centre point of body rotation & the difference between 'turn' & 'spin'
Yup, exactly what I was meaning. And it's not an "all-or-nothin" effect. Everybody has a different degree of body rotation for the power in the shot.
Physics What happens when a dump truck travelling at slow speed hits a motorcycle that is not or also moving slowly? The motorcycle will still fly pretty far (or in this case get damaged reallly badly) Same applies to this case of hitting the bird. The use of this rotational method to hit the bird, allows us to put the mass of our body into a badminton bird (instead of just the mass of say our arm when just swinging the arm). Although the resulting racket speed may not be as great, the resulting momentum and transfer of energy is a lot higher. Of course the human body is nowhere near perfect in terms of efficiency, but if we look at somekinetic energy and physics equations, we can derive the fact that the higher amount of mass and speed we are able to put into the badminton bird, the faster we will be able to hit it.
Re: Physics Jet, Well put. That's exactly what I'm thinking about too. Previous comments seem to have forgotten about the mass of the body. Kinetic energy = 1/2 mv**2. If we try to sectionalize every body part movement, and just focus on the body rotation part. And assume that the body, arm, racque combined is a rigid body. While the speed of the racque on impact may not seem fast, the transfer of energy (or should I say momentum) to the lighter birdy could cause the bird flying out at a speed faster than that of the racque. Of course the assumption that the whole body is rigid may not be true. On the other hand, I'm not sure if the racque has to travel 200km/h to generate a shuttle speed of 275km/h, due to mass differences. And finally, if you only throw your arm w/o body rotation, the mass of the previously presumed "rigid" body is much smaller. Thus its momentum also smaller.
Re: Physics some of you guys are pulling equation and concept out from thin airs with regard to Mag's topic. Mag's post is about rotational components in relation to racket speed, not about momentum energy. Even if i try to understand your (Jet) momentum argument about more mass will generates more momentum onto the bird, your logic still doesn't make sense at all. If u r right, then fat and obesed people would have the most powerful smashes. According to your argrument, a 450lb guy would smash 3x harder than a 150 lb player. However, most pros double players that i observed weigh no more than 180 lb.
Re: Physics I agree with Jet and Raymond about the maximal transfer of momentum energy of the body into the bird. I also agree that the rotation helps counterbalance. cooler, don't forget that the 450lb guy won't be able rotate his body and arm as fast as the 150lb person... and if he was able to, yes he will smash harder, but not likely 3x harder due to limitations of strings, air resistance etc. In order to understand this principle of transfer of momentum, try throwing a baseball overhand (as Slanter had alluded to earlier) because smashing and clearing is very similar to that. First, throw the ball only using your arm/wrist/finger power, ie. without shoulder/body rotation. Next, throw it with all your might (like a professional baseball pitcher does) using all of the above power available including your shoulder and body rotation. Which method allows you to throw further and harder? I am willing to bet dollars to donuts that the latter one will.
Re: Physics "To sum it all up: according to scientific tests, body rotation has almost no effect ... And yet, most of us know that body rotation works. So, if the kinetic link principle is bogus, then why does body rotation make it easier to produce powerful shots?" Oftentimes, just because we or "science" are/is unable to analyze/see/understand something completely and comprehensively doesn't mean that it doesn't work or doesn't exist...
