Source: Quintic Sports
Anyone who plays cricket to a degree where you go out and take some care on buying your bat should know that the choice is based mostly on subjectivity. We work out through trial and error what our preferred bat weight is and use the term ‘pick up’ or ‘swing weight’ to reach that decision.
Note: here we are not concerned with impact performance of the bat related to the material properties. That is another story no less important for bat performance, but this article is about player performance with the bat.
Gunn and Moore advises “Always select a bat based on its pick up, how it feels to you, not on its scale weight.”
‘Pick up’ or ‘swing-weight’ is your feel for the bat when you swing it through the air with pretend shots. Some start with a bat weight they feel is what they should play with, the bigger the better, then see if they can swing it comfortably. Most go through the classic trial and error process.
In the end you probably have a bat that is at best, and somewhat fortunately, perfect for you. At worst it will be too heavy, unlikely to be too light, and most likely somewhere in the middle. Your preferred bat is more than likely sub-optimal for player performance, based on several somewhat sub-optimal preconceptions and cognitive bias.
The barrier to swing optimisation is that you don’t have enough information to make an objective selection. You have one metric, bat weight, the rest is subjective. Experience can reduce the level of error in selection, such as that possessed by a professional specialist batter, who is likely to have an advanced level of feel for the bat.
However, through research I have carried out, fine tuning and even optimising your cricket bat selection is now a whole lot easier. When it comes to swinging something in sport for performance the real parameter of interest is the moment of inertia.
Moment of inertia is a mechanical property that describes an implement’s resistance to being swung. It is dependent on the distribution of mass through the object, and the position of hands when swung. A sledgehammer has most of its mass concentrated in the large metal head, which gives it a high MOI, and hence feels very heavy. Turn it around and swing it while holding the hammer head and feels nice and light because it has a very low MOI.
Measuring MOI of a cricket bat is not simple because of the complex 3D geometry of the blade. There are simple equations for uniform and regular shapes such as rods and beams, but these are not directly applicable to a cricket bat. Traditionally, and mostly in university settings, cricket bat MOI is measured using a specialist method that treats the bat as a simple pendulum (Figure 1). It is neither practical for the bat maker or consumer to use this approach, as it requires a bespoke test rig, accurate timing of swings for each bat, and some calculation to derive MOI.
Figure 1. Pendulum method to measure MOI
Source: Eftaxiopoulou T, Persad L, Bull AM. doi:10.1177/1754337116638970
But while selecting a bat on MOI is definitely an improvement, it is not the complete answer
My paper on this has been peer-reviewed and published open access in the journal Sports Engineering. [Methods for estimating moment of inertia of cricket bats | SpringerLink]. In short, all you need to do is make a few simple but careful measurements with a ruler and some kitchen scales and put those values into a set of equations. To make it easy, I’ve created a website called Cricket Bat MOI that provides a tool to make the calculation of MOI, and all the instructions on how to make the measurements.
I would encourage bat makers to add this measure to their bats. There is a practicality that must be addressed by bat makers in terms of what resolution they are able to offer, as there is a stock control implication. The easiest approach would be to just add the MOI measure to the label for each bat they produce currently. Alternatively, if bat makers can’t or won’t do this, then retailers could.
Players can start by measuring the MOI of their current bat. Even if bat makers do not provide this information, you may still be able to do a measurement on a new bat and return this before use if it’s MOI is too far off. On knowing whether an MOI is ‘too far off’ your preferred value, it is worth noting that human sensitivity to MOI varies from around 3% for professionals to 20% for non-cricketers. Familiarity of use determines your sensitivity. As a useful rule of thumb, a 5% variation on your preferred MOI is probably a good starting point to give you some room to manoeuvre as bat makers are unlikely to provide resolution greater than this. A 5% MOI variation is equivalent to a 1.5oz difference in bat mass.
Custom made bats to a player’s specification is best for an optimum bat, and there are plenty to choose from. Off-the-shelf purchase from a bat maker stock, either direct or through a retail outlet, will mean that a player can only get near-optimum. Main-stream bat brands sold through retail outlets now provide bats in only three sizes: light, medium and heavy, which generally have a 1 to 2oz range in the light and medium weights.
The next piece in the puzzle of optimising swing performance is a system to characterise your own batting capabilities to identify the best MOI for you. Obtaining maximum batted-ball speed is a trade-off between swing speed and a measure called effective mass. The latter is a theoretical point mass at the point of ball impact. A paper by Nathan & Cross has shown that the ‘intrinsic power’ of an implement is dependent on the effective mass at the point of impact. Calculation of effective mass is a simple function incorporating bat mass, MOI at the centre of mass, and the distance of ball impact from the centre of mass. You would calculate this once at the approximate sweet spot of the bat.
A higher swing speed is enabled by a lower MOI, but for conventional shaped bats this is most likely to lower bat mass and therefore bat power. You can keep mass static and lower MOI by raising the balance point of the bat. This is only achieved by moving wood higher up the bat, and essentially results in a bat with a ‘higher middle’, which are good for play on hard bouncy wickets, but on soft green UK wickets where ball bounce is lower, your sweet spot could be in the wrong place (too high). It’s a tricky balancing act, and such refinement is probably only found within the professional ranks, through trial and error or approximation, if at all.
To aid the visualisation of this trade-off, I defined a parameter called effective momentum that combines swing speed with effective mass (recall that momentum is a product of speed and mass). What we begin to see from pilot experiment data is the shape of the curve that describes how effective momentum changes with MOI, and how its position will change depending on the level of skill of the player. It indicates the maximum useful MOI, where going any higher will be detrimental to performance.
Finding a practical way of implementing this for players is the next stage, whether by me or others.
