Smashing Fast: What the Science Says

An insight into the recent scientific studies focussed on the badminton smash, investigating what technique factors are important.

By Harley Towler

Much like the 100 m sprint is the blue-ribboned event in athletics, the badminton jump smash is the shot in badminton, and players are always on the lookout for ways they can improve their smash and in particular, smash faster. The world record stands at 426 km/h, and a well-performed, fast and steep smash is a key weapon in any player’s repertoire. 

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All things being equal, it should be of no surprise to people that the biggest predictor of smash speed is racket head speed [1,2], especially when comparing across a large range of ability levels (Figure 1). However, an imperfect relationship exists between racket head speed and smash speed because of factors such as the racket properties (mass, mass distribution, geometry, stiffness), impact location (‘timing’) and stringbed properties (string type, tension), all of which interact with each other and can affect racket head speed [3]. Could you swing a racket that weighs 200 g as fast as a racket that weighs 90 g, both of which are equally balanced? The simple answer, no!


Figure 1. Data from 102 participants, showing the relationship between racket head speed and shuttlecock speed for their fastest smash.

So, what can you do as a player with your technique to swing the racket faster and ultimately smash faster? To answer this question, we (Loughborough University) collected data on over 100 badminton players ranging from a county/regional standard all the way to the very best in the world (highest WR #5). The process involves placing a series of markers on the body, racket and shuttlecock which can be tracked using a series of special cameras (motion capture), and then a model of the human body can be created from the markers to understand how it is moving (Figure 2).

Figure 2. Process of data collection and processing

We can then look and see what techniques those with faster smashes use compared to those who produced relatively slow smashes. Other research groups have also used motion capture or a similar approach to gather data on the badminton smash.  

What do you think are the most important technique factors? Higher jump? More elbow extension? More wrist flexion (‘wrist snap’)?  

Body Positioning

Past research has found that being positioned behind the shuttle (approximately half a metre), as opposed to directly below the shuttle or in front of the shuttle with respect to the net, improves the quality of the smash: both the speed and angle i.e. steeper [4]. Our data support this finding and suggest that players who position themselves further behind the shuttle at the body’s lowest point, typically when the bending the knees before jumping, relative to where they make contact with the shuttle [5]. In theory, by getting into position early (behind the shuttle), you can create more momentum in the direction in which you are hitting the shuttlecock. A simple comparison is the tennis serve, in which you will see players drive their bodyweight forwards when delivering a fast serve.

We also found that players who jumped higher produced faster smash speeds, however it is unclear whether this is just a characteristic of ‘better’ players who tend to fast smash, who are physically stronger and capable of jumping higher and alongside generating faster smashes also aim to generate steeper smashes as an additional way to make returning the smash more difficult for the opponent(s). Unsurprisingly, a similar strong correlation was found between jump height and smash angle, where simply put jumping higher and achieving a higher point of contact allows a player to produce a steeper angle whilst still clearing the net. This is supported by Ferreira et al [6], who found that there was no difference in smash speed for jump vs. no jump conditions.

The Importance of the Trunk

The role of the trunk in driving overhead motion is sometimes overlooked. In golf and throwing, the importance of the trunk is well-known in the production of end-point speed [7,8]. Early indications within a small group of 19 experienced badminton players, found that those who could counter-rotate their trunk more during the end of the backswing produced greater smash speeds [1]. This is supported within our larger set of data in which players who were able to counter-rotate their trunk more and achieve a similar or more rotated position at contact, could smash faster (Figure 3). Ultimately, this means that the ‘faster’ players would rotate their trunk faster during the forward swing leading to greater racket head speeds. Our advice is that players should not compromise an appropriate impact position by counter-rotating too much and not having the required strength to then rotate the trunk quick enough and under control during the forward swing. Instead, players should gradually strengthen and improve the flexibility of the musculature of the trunk so that over time they can achieve a more counter-rotated position without compromising the position at impact.


Figure 3. Emphasis should be on creating ‘separation’ between the trunk and hips (trunk rotation). In this image, the upper trunk and shoulders relatively perpendicular to the net, whilst the hips are much closer to parallel.

Note: Counter-rotation of the trunk here would be the direction of rotation shown by the skeleton in Figure 2. Rotation would then be the direction required to achieve a typical position at impact. Try this: stand facing forward with your hips square. Now, keeping your hips square, try and bring your right shoulder backwards and your left shoulder forwards by rotating your upper body (left-handed players do the opposite!). This is counter-rotation. 

There is also evidence that players who smash faster producing faster motions of trunk flexion (leaning forwards), with the range of motion and position not of particular importance [5]. With both motions of the trunk (flexion and rotation), it is essential that these faster motions are performed with some level of control as to not compromise the precise timing required for a successful stroke. If these trunk motions are performed with little to no control, the impact location is likely to be very inconsistent which has implications for the speed and accuracy of the stroke [3].

Techniques of the Racket Arm  


Similar to the trunk counter-rotation mentioned above, the role of the shoulder external to internal rotation (Figure 4) is critical in determining racket head speed and ultimately shuttlecock speed. Those players who adopted more externally rotated shoulder positions at the end of the backswing produced greater smash speeds, this is likely due to the upper arm being able to rotate through a larger range of motion and have a larger acceleration path [9], resulting in greater peak rotational speeds of shoulder internal rotation during the forward swing, which is typically the largest contributor towards the development of racket head speed [10]. The angle of shoulder internal rotation across our large sample of participants was not significantly different [5]. 


Figure 4. Description of shoulder internal/external rotation (left). A player at (or close to) maximum external rotation during the smash, which roughly coincides with the racket head at its lowest vertical position (right).



Figure  5 . Notice how the trunk has already rotated through, but the upper arm is ‘held’ back and delayed in terms of when it pulls through.

Another important technique factor is the delayed forward movement of the upper arm (Figure 5). This means keeping the elbow ‘back’ whilst the trunk is rotating through. This causes the stretching of the musculature of the chest, which means that the eventual contraction that pulls the elbow forward is stronger, and the elbow comes through faster.

A technique point that readers may find interesting is the role of pronation. Firstly, it is worth mentioning that “forearm rotation/pronation” and “elbow pronation” (elbow pronation is technically radio-ulnar pronation) are two different things. Many people will talk about the importance of forearm rotation in generating fast smashes, however understanding why this may or may not be the case takes careful consideration. The forearm itself is just a segment of your body, like your hand or foot – it is NOT a joint! The joint involved in this motion is the elbow (more specifically the radio-ulnar joint), and this simply means that elbow pronation is the movement of the forearm with respect to the upper arm. Try extending your arm, so that it almost straight, and then perform shoulder internal/external rotation (Figure 4), and you will notice that this movement alone will cause the forearm to rotate.

So, much of the rotation of the forearm actually derives from the internal rotation of the shoulder. In addition to this, elbow pronation is NOT a major contributor towards racket head speed [10], and instead is indirectly related to the speed by orientating the racket into position to achieve a desirable impact location and shuttlecock trajectory [11]. On top of this, think about when elbow pronation mainly occurs, it is generally just prior to racket-shuttlecock contact, and at this time point, the forearm and racket have a large angle between them (Figure 6), which we found was around 140-150º. What this simply means that the elbow pronation does not add much additional speed to the racket head. This angle is affected by the grip a player adopts, and if a player has a racket-forearm angle closer to 90º the contribution from elbow pronation would increase, however by doing this you would limit the height at which you could make contact with the shuttle.

Figure 6. Explanation of the racket-forearm angle

Recently, it was found that having a more bent elbow at contact was significantly correlated with greater shuttlecock speed amongst a group of 19 elite male Malaysian badminton players [12], and it was suggested that this put the shoulder in a more favourable position to generate greater rotational speeds and maximise the contribution towards racket head speed. Finally, the position of the wrist has bene found to have little importance on smash speed. The contribution from the wrist flexion rotational speed is a major contributor towards racket head speed, however, this is not generated by the musculature surrounding the wrist but is transferred through segments in a proximal-to-distal nature [13].  

In addition to the above, a whole-body technique that can provide consistently ‘good’ impact locations is essential for repeatedly producing fast smashes. Data from 65 elite badminton players, performing 2386 smashes, concluded that impact location alone could explain 26.2% of the variance in shuttlecock speed (% of participant maximum), and deviations as little as 5.6 cm from the optimal location could result in up to 26.9% reduction in shuttlecock speed [3]. More recently, using more control of the rackets used, impact location was able to explain 62% of the variance in shuttlecock speed (% of participant maximum) for 1500 smashes performed by 20 elite players [10]. It is therefore recommended that any alterations to technique should be cautious that the ability to achieve consistently ‘good’ impact locations is not affected.

Conclusions & Top Tips

1. Ensure early positioning behind the shuttle (approx. half a metre behind where you anticipate the make contact with the shuttle). There is no conclusive evidence as to whether jumping allows you to smash faster, however it certainly allows you to perform a steeper smash, which can also make a smash more likely to be successful.

2. Racket head speed is the biggest predictor of smash speed. Be careful when choosing rackets that may be too heavy or head-heavy, which may reduce your swing speed too much and negate the effects of having ‘more mass’ behind your stroke.

3. Greater rotational speed or trunk rotation and flexion are crucial towards to initial development of racket head speed. The focus should be on achieving a common ‘body shape’ at impact and maximising the counter-rotation during the backswing so that a larger range of motion (and rotational speed) is produced.

4. Similarly, maximising the acceleration path of the racket, by achieving a more externally rotated shoulder position during the backswing, will allow greater development of racket head speed. It’s important that players are capable of achieving these positions as well as being strong and stable in these ‘extreme’ ranges. Additionally, having a slight bend in the elbow at contact will increase the contribution made by shoulder internal rotation.

5. Avoid pulling the upper arm through too soon. Try and achieve a clear distinction between trunk rotation followed by the ‘forward pull’ of the upper arm.

6. Motions of the elbow and wrist are somewhat less important and not directly related to the development of racket head speed, but instead are crucial in the dexterity and coordination involved in ‘good timing’ and achieving a desirable impact location.

7. With all of the above points, any changes in technique, and in particular new motions/or more ‘extreme ranges’, should be gradual as to not avoid injury and so that impact timing is not significantly impacted.

References


[1] King, M. A., Towler, H., Dillon, R., & McErlain-Naylor, S. (2020). A correlational analysis of shuttlecock speed kinematic determinants in the badminton jump smash. Applied Sciences, 10 (4), 1248. https://doi.org/10.3390/app10041248.

[2] Kwan, M. Designing the World’s Best Badminton Racket (2010. Ph.D. Thesis, Aalborg University, Aalborg, Denmark.

[3] McErlain-Naylor, S. A., Towler, H., Afzal, I. A., Felton, P. J., Hiley, M. J., & King, M. A. (2020). Effect of racket-shuttlecock impact location on shot outcome for badminton smashes by elite players. Journal of Sports Sciences, 38(21), 2471–2478. https://doi.org/10.1080/02640414.2020.1792132

[4] Li, S., Zhang, Z., Wan, B., Wilde, B., & Shan, G. (2016). The relevance of body positioning and its training effect on badminton smash. Journal of Sports Sciences, 35(4), 310–316. https://doi.org/10.1080/02640414.2016.1164332

[5] Towler, H., Deshpande, Y., King, M.A. (2021). What techniques do elite male players use to smash fast? Unpublished manuscript.

[6] Ferreira, A., Górski, M., Gajewski, J. (2020). Gender differences and relationships between upper extremity muscle strength, lower limb power and shuttle velocity in forehand smash and jump smash in badminton. Acta of Bioengineering and Biomechanics, 22(4), 41-49.

[7] Hirashima, M., Yamane, K., Nakamura, Y., & Ohtsuki, T. (2008). Kinetic chain of overarm throwing in terms of joint rotations revealed by induced acceleration analysis. Journal of Biomechanics, 41(13), 2874–2883. https://doi.org/10.1016/j.jbiomech.2008.06.014

[8] Turner, J., Forrester, S.E., Mears, A.C., Roberts, J.R. (2020). The effect of golf club moment of inertia on clubhead delivery and golfer kinematics. Proceedings 13th Conference of the ISEA, 49(1), 96.

[9] Lees, A.; Cabello, D.; Torres, G. (2008). Science and Racket Sports IV; Routledge: London, UK.

[10] Towler, H. Unpublished thesis.

[11] Teu, K.K.; Kim, W.; Tan, J.; Fuss, F.K. (2005). Using dual Euler angles for the analysis of arm movement during the badminton smash. Sports Engineering, 8, 171–178.

[12] Ramasamy, Y., Usman, J., Sundar, V., Towler, H., King, M.A. (2021). Kinetic and kinematic determinants of shuttlecock speed in the forehand jump smash performed by elite male Malaysian badminton players, Sports Biomechanics, https://doi.org/10.1080/14763141.2021.1877336

[13] Rasmussen, J.; Kwan, M.; Andersen, M.S.; De Zee, M. (2010). Analysis of segment energy transfer using musculoskeletal models in a high speed badminton stroke. In Proceedings of the 9th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, Valencia, Spain, 24–27 February.