2. Methods
In order to compare the swing weight and swing speed relationships across several sports an analysis
was carried out using data from existing literature. Published data was analysed for nine different sports
as listed in Table 1. In the case of tenpin bowling, the 'implement' was defined as being the bowler's arm
and ball as one fixed unit which rotates around the shoulder joint. The moment of inertia data for bowling
was created using mean body segment data as presented by de Leva [8]. Specific shots chosen were the
badminton smash; front foot drive in cricket; field hockey hit; golf drive; ice hockey slap shot; overhead
lacrosse shot and forehand ground stroke in tennis. The swings were considered up to the impact event or
ball release, as appropriate.
In order to study the effect of swing weight on swing speed both variables need to be explicitly defined
to ensure that all data describes the same property. These definitions are important as they needed to be
such that the data provides a fair comparison across all nine sports. The immediate choice of parameter
for swing weight was the second moment (m2), or moment of inertia (I) to describe the implement's
rotational resistance, as defined by Brody [9]. There were however, four possible parallel axes which the
moment of inertia could be defined about, which were all considered. The axes were all perpendicular to
768 Dave Schorah et al. / Procedia Engineering 34 ( 2012 ) 766 – 771
the handle and in plane with the implement's face. The locations were: the centre of mass; the end of the
handle; the location of the distal hand; an assumed centre of rotation.
A correlation matrix was created using the variables in Table 1 and alternatives, which provided a
clear understanding of the most strongly related variables in the data set and informed decisions as to
which were the most suitable definitions.
The moment of inertia about the handle end (IHE) was chosen as the most appropriate definition. This
was because it is a definite location on every implement which will not change, as the location of the
distal hand or the instantaneous centre of rotation could. It was also possible to calculate, using the
dimensions of the implements, the moment of inertia about the centre of mass and the parallel axis
theorem. The handle end moment of inertia has a relatively significant relationship (p