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1 This article was downloaded by: [National Sport Info Centre] On: 28 February 2011 Access details: Access Details: [subscription number ] Publisher Routledge Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Sports Biomechanics Publication details, including instructions for authors and subscription information: Cricket Marc R. Portus ab ; Bruce R. Mason b ; Bruce C. Elliott c ; Max C. Pfitzner d ; Richard P. Done d a Cricket Australia, Melbourne, Australia b Biomechanics Department, Australian Institute of Sport, Canberra, Australia c School of Human Movement and Exercise Science, University of Western Australia, d Australian Institute of Sport-Cricket Australia Cricket Academy, Adelaide, Australia To cite this Article Portus, Marc R., Mason, Bruce R., Elliott, Bruce C., Pfitzner, Max C. and Done, Richard P.(2004) 'Cricket', Sports Biomechanics, 3: 2, To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Technique Factors Related to Ball Release Speed and Trunk Injuries in High Performance Cricket Fast Bowlers MARC R. PORTUS, 1,2 BRUCE R. MASON, 2 BRUCE C. ELLIOTT, 3 MAX C. PFITZNER, 4 and RICHARD P. DONE 4 ABSTRACT In this study we analysed technique, ball speed and trunk injury data collected at the Australian Institute of Sport (AIS) from 42 high performance male fast bowlers over a four year period. We found several notable technique interrelationships, technique and ball speed relationships, and associations between technique and trunk injuries. A more front-on shoulder alignment at back foot contact was significantly related to increased shoulder counter-rotation (p < 0.001). Bowlers who released the ball at greater speeds had an extended front knee, or extended their front knee, during the front foot contact phase (p < 0.05). They also recorded higher braking and vertical impact forces during the front foot contact phase and developed those forces more rapidly (p 0.05). A maximum hip-shoulder separation angle occurring later in the delivery stride (p = 0.05) and a larger shoulder rotation to ball release (p = 0.05) were also characteristics of faster bowlers. Bowlers suffering lower back injuries exhibited typical characteristics of the 'mixed' technique. Specifically, the hip to shoulder separation angle at back foot contact was greater in bowlers who reported soft tissue injuries than in non trunk-injured bowlers (p = 0.03), and shoulder counter-rotation was significantly higher in bowlers who reported lumbar spine stress fractures than non trunk-injured bowlers (p = 0.01). The stress fracture group was also characterised by a larger hip angle at front foot contact and ball release, whereas a more flexed front knee at ball release characterised the non trunk-injured group. Keywords: cricket, fast bowling, injuries, release speed, technique. 1Cricket Australia, Melbourne, Australia 2Australian Institute of Sport Biomechanics Department, Canberra, Australia 3School of Human Movement and Exercise Science, University of Western Australia 4Australian Institute of Sport-Cricket Australia Cricket Academy, Adelaide, Australia Sports Biomechanics Vol.3 (2)

3 264 MARC R. PORTUS et. al. INTRODUCTION Previous fast bowling research has studied the relationships between fast bowling technique and injury (e.g. Foster et al., 1989; Elliott et al., 1993; Burnett et al., 1996). These studies have presented clearly the higher risk of lower back injury that the mixed technique presents over the side-on (Figure 1A) and front-on techniques (Figure 1C). The National Pace Bowling Program Resource Kit (ACB, 1998) also advocates the use of the semi-open bowling action as a safe technique (Figure IB). The mixed technique is evident at back foot contact (Figure ID & E) or in the phase between back foot and front foot contacts, where a large shoulder counter-rotation occurs. Shoulder counter-rotation is the predominant factor in lower back injury. It is a rapid realignment of the shoulders from a relatively front-on position at back foot contact (BFC) in the delivery stride to a more side-on position before front foot contact (FFC). The term is derived from the shoulders rotating away from the batter before they rotate towards the batter to release the ball (Figure 2). Figure 1 Line drawings of the various fast bowling techniques at back foot contact: (A) the side-on technique, (B) the semi-open technique and (C) the front-on technique. In each case the shoulders and hips are in alignment. The mixed technique presents in a variety of ways at back foot contact, where the shoulders and hips are not aligned: (D) the shoulders are more side-on than the hipsand (E) the shoulders are more front-on than the hips (drawings permission of ACB, 1998).

4 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 265 Figure 2 Line drawings of a fast bowler displaying shoulder counter-rotation, a major characteristic of the mixed technique. The shoulders quickly re-align from a more front-on position at (A) back foot contact (not necessarily fully front-on), to (B) a more side-on position, normally just prior to front foot contact. The shoulders then rotate normally to (C) ball release. That is, the shoulders have counter-rotated between (A) and (B), and rotated between (B) and (C) (drawings adapted with permission from ACB, 1998). Although the results of these studies have influenced the coaching literature, no published study to date has both analysed fast bowling technique threedimensionally and examined the relationships with injury. Using a threedimensional analysis to determine the orientation of the shoulder and hip segments and, therefore, the hip-shoulder separation angle, may permit the etiology of back injuries to be further clarified. Previous three-dimensional research reporting the hip-shoulder separation angle in fast bowling (Stockill and Bartlett, 1992; Burnett et ah, 1995) has not related this measure to back injuries. Limited research has been published on the critical factors associated with faster ball release speeds (Davis and Blanksby, 1976; Burden and Bartlett, 1990; Stockill and Bartlett, 1993). It has been inconclusively suggested that a more extended front leg at ball release will enable faster ball release speeds to be attained. As the name of the skill implies, it is a fundamental component to successful performance for high ball release speeds to be attained by fast bowlers. It is, therefore, important that research further examines fast bowling from injury and performance perspectives holistically, particularly when dealing with the professional high-performance cricketing population, whose careers depend on being relatively injury free and consistently achieving high standards of performance. The objectives of this study were to identify technique factors associated with a higher ball release speed and to identify the critical technique factors associated with trunk injuries.

5 266 MARC R. PORTUS ef. a/. METHODS Three-dimensional kinematic data for 42 fast bowlers (mean age ± standard deviation: 22.4 ± 3.5 years) between the years of 1996 and 1999 were collected (1996 at 100 Hz; other years at 50 Hz). Film or video footage was manually digitized in two synchronised views and transformed using a direct linear transformation procedure. Data from all years included segment angular displacement in the transverse plane for the hip segment (line joining each hip joint centre) and the shoulder segment (line joining each shoulder joint centre). Three-dimensional joint displacement data were available for both the knee and hip joints. Delivery stride length, ball release height, ball speed and whole body centre of mass location were also generated in the kinematic analyses over these years. Kinematic data were filtered using a Butterworth digital filter, cut-off frequencies being selected on the basis of smooth second derivative curves. Two force plates captured kinetic data (1000 Hz; Kistler Inc.) for all years for back foot contact and front foot contact simultaneously during the delivery stride, which was defined as back foot contact to ball release. Much of the previous research literature on fast bowling back injuries has applied a set of criteria to classify technique as either side-on, front-on or mixed. When using these criteria, the angles are calculated by viewing the hip and shoulder segments in the transverse plane. The zero line runs directly down the pitch from the left hip and shoulder, with the alignment angle measured in an anti-clockwise direction. The hip-shoulder separation angle is calculated by subtracting the hip alignment angle from the shoulder alignment angle; hence a positive separation angle refers to the shoulders being in a more front-on alignment than the hip segment, a negative separation angle refers to the hip segment being more front-on than the shoulder segment. The maximum hipshoulder separation angle refers to the greatest difference between the hip and shoulder segments that occurs between back foot contact and ball release. To classify the fast bowling techniques, a modified criteria from Burnett et al. (1995) and Portus et al. (2000) was used: Side-on: a shoulder segment angle less than 210 at back foot contact, a hip-shoulder separation angle less than 30 at back foot contact, and, shoulder counter-rotation less than 30. Semi-open: a shoulder segment angle from 210 to 240 at back foot contact, a hip-shoulder separation angle less than 30 at back foot contact, and, shoulder counter-rotation less than 30. Front-on: a shoulder segment angle greater than 240 at back foot contact, a hip-shoulder separation angle less than 30 at back foot contact, and, shoulder counter-rotation less than 30. Mixed: a hip-shoulder separation angle equal to or greater than 30 at back foot contact, or, shoulder counter-rotation equal to or greater than 30. As the role of the front lower limb during the front foot contact phase has been implicated as a mechanistic factor in the development of lower back

6 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 267 injury (Mason et al., 1989; Foster et al., 1989) and faster ball speeds (Burden and Bartlett, 1990), we used a classification criterion to differentiate between styles of front lower limb actions during the front foot contact phase, defined as full foot contact to ball release. The criteria were: Flexor: knee flexion 10 or more followed by less than 10 of knee extension. Flexor-extender: flexion and extension of the knee by 10 or more. Extender: knee flexion less than 10 followed by knee extension by 10 or more. Constant brace: both flexion and extension of the knee less than 10. Pearson product moment correlations (SPSS Inc.) were used to identify interrelating technique factors and the relationships between technique and ball release speed. A qualitative description for the strength of correlations was adopted: correlation coefficient (r) values 0 to 0.1 were 'trivial', r values greater than 0.1 were 'small', greater than 0.3 'moderate' and greater than 0.5 'large' (Cohen, 1988). As the study sample consisted of a highly homogenous athletic group of Australian high performance adult male fast bowlers, we hypothesized that any significant correlations were likely to be only small to moderate in strength and, therefore, the chance of making Type II familywise errors was increased if a conservative significance level was set. Correlations significant at the 0.05 alpha level were therefore included, provided there could be a logical postulation about their association in an effort to avoid an opposing Type I familywise error. To assess the relationships between fast bowling technique and trunk injury, four injury groups were created based on the history of injuries suffered by the bowlers. Trunk injury histories were available for 30 bowlers; 27 trunk injuries were recorded from 24 of these 30 bowlers. The four trunk injury groups were: Group 1; stress fracture of the lumbar spine pars interarticularis (n = 9), Group 2; back sprain, including injury to disc, facet joint or ligaments (n = 11), Group 3; muscle side strain (n = 7), and Group 4; no trunk injury in = 6). Two bowlers suffered a soft tissue injury to the lower back (group 2) and trunk muscle side strain (group 3); one bowler suffered a lumbar spine stress fracture (group 1) and trunk muscle side strain (group 3). These bowlers were included in both relevant injury groups in an attempt to identify a possible mechanism for the recently reported common incidence of trunk side strains in Australian fast bowlers (Orchard et al., 2002). Bowlers suffering from both forms of back injury (groups 1 and 2) were classified by injury severity and were, therefore, assigned to group one only. All bowlers suffered these injuries either in the year previous to or following biomechanical technique analysis, with the exception of the stress fracture group (group 1). Table 1 outlines the injury history of the lumbar-spine stressfracture group relative to their biomechanical technique analysis. In all cases injuries were diagnosed by a qualified sports physiotherapist and sports physician working in the cricket environment. Radiological investigations were undertaken as deemed necessary by these medical personnel.

7 268 MARC R. PORTUS et. al. Table 1 History and site of lumbar spine stress fracture incidence relative to biomechanical technique analysis. Bowler number Year of incidence of lumbar spine stress fracture(s) Site and side (relative to bowling arm) of lumbar spine stress fracture Year of technique analysis * recurrence recurrence recurrence 2000 L5 L5 contra lateral L2 & L5 concurrently L2 & L4 concurrently L5 bilateral L4 L4 L4 & L5 concurrently L5 contra lateral L3 & L4 contra lateral, concurrently *Bowler number 5 had surgical repair of this injury in Although he did not suffer a recurrence of lumbar spine stress fractures he was continually plagued with back pain and sprains associated with bowling between 1990 and From each injury group, a technique profile was created using mean data; descriptive statistics were used to assess group differences. Characteristics appearing to differ were further analysed using a one-way analysis of variance and Scheffe post hoc analysis where required. Homogeneity of variance was assessed and satisfied with the Levene statistic (SPSS Inc.). An alpha level of 0.01 was adopted for the analysis of variance because of the multiple comparisons and to reduce the probability of making a Type I familywise error. Fifteen comparisons were made which resulted in the familywise error rate rising from 0.01 to 0.14 (Vincent, 1999). RESULTS Technique inter-relationships The alignment of the shoulders at back foot contact had a large correlation with shoulder counter-rotation (r = 0.72, p < 0.001), which is a relationship that has been previously reported (Portus et al., 2000). Descriptively, bowlers who landed with a more front-on shoulder alignment, counter-rotated their shoulders more than bowlers who had a more closed shoulder orientation at back foot contact. Further analysis of the hip and shoulder orientations at back foot contact revealed that 11 of the 14 bowlers who were classified as adopting a mixed

8 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 269 posture at this time had a 30 or more front-on shoulder alignment than hip alignment. The role of the lower limb during the front foot contact phase has been discussed as being important in the attenuation of impact forces (Foster et al., 1989; Mason et al., 1989). In support of this we found a series of significant moderate relationships between various lower limb kinematic and kinetic factors (Table 2). Knee angle at ball release had a significant moderate relationship with the vertical and braking impact forces on the front foot. That is, bowlers who had a more extended front knee when releasing the ball, as opposed to those who had a more flexed front knee at this time, tended to experience higher braking and vertical impact forces. Furthermore, bowlers who extended their front knee more during the front foot contact phase to ball release experienced higher braking forces. Table 2 Knee angles, peak braking and vertical impact forces and their correlations during the front foot contact (FFC) phase (n = 41) (mean + standard deviation). Time of knee angle measure Front Foot Contact Minimum Knee Angle Ball Release Knee extension during FFC phase *p<0.05. Angle n ±20 10±9 Peak impact forces during the FFC phase (body weights) Braking Vertical ±1.8 Knee angle - impact force correlation (r) Braking Vertical * 0.31* 0.33* 0.29 Bowlers using an extended or extending lower limb during the front foot contact phase not only experienced higher peak forces, they also developed these peak forces more rapidly. Significant moderate correlations were observed between the knee extension range during the front foot contact phase and the time to peak braking and vertical forces (r = -0.41, p<0.01 and r = -0.41,/?<0.01 respectively). Technique and ball speed relationships Several technique characteristics had moderate to large relationships with faster ball release speeds (Table 3). There was a trend for bowlers who extended their lower limb at the knee during the front foot contact phase to bowl faster than those who flexed or extended their front knee less. This supports data from Burden and Bartlett (1990), who reported that faster ball release speeds were related to a more extended front lower limb at ball release. The peak braking force at front foot contact and the time to peak braking

9 270. MARC R. PORTUS et. al. force were moderately related to ball release speed, although the most convincing support for the role of the front lower limb in ball speed generation was the large correlation between time to peak vertical force during this phase and ball release speed (Table 3). Bowlers who had higher braking forces, and developed their peak braking and vertical forces more rapidly at front foot contact, recorded higher ball release speeds. A moderate relationship was evident between ball release speed and the timing of the maximum hip-shoulder separation angle. That is, bowlers whose maximum separation angle occurred after front foot contact bowled faster than those who recorded a maximum before contact. The range of shoulder girdle rotation preceding ball release was also moderately related to ball release speed (Table 3). Shoulder rotation appeared to be significantly more important to produce faster ball release speeds than shoulder counter-rotation, which had a near zero or 'trivial' correlation with ball release speed (r = 0.009, p = 0.95). Table 3 Technique characteristics that were related to faster ball release speeds (FFC = front foot contact; HSS = hip-shoulder separation). Technique Variable FFC phase knee extension FFC peak braking force FFC time to vertical peak force FFC time to braking peak force Time of maximum HSS angle Shoulder segment rotation Correlation Coefficient (r) Number of bowlers (n) Technique Classification Statistical Significance (P) 0.02 <0.01 <0.01 < After our trunk technique classification, 31 of the 42 bowlers were classified as mixed. Of the 31 mixed bowlers, nine had a misaligned hip and shoulder posture at back foot contact and an excessive shoulder counter-rotation; eight of the nine were more front-on in the shoulders than the hips at back foot contact, see Figure IE. Five of the 31 mixed bowlers had a misaligned hip and shoulder posture at back foot contact and did not excessively counter-rotate their shoulders; three of the five were more front-on in the shoulders than the hips, and 17 were mixed owing solely to an excessive counter-rotation of the shoulders after having a well aligned posture at back foot contact (Figure 3). From the other 11 bowlers two were classified as side-on, six were semi-open and three were front-on. We also classified the 42 bowlers in this study by the front lower-limb style they used during the front foot contact phase. Four bowlers were flexor-extenders, four were extenders, nine bowlers used a constant brace and 25 were flexors. These results illustrate how few bowlers adopted the flexor-extender front

10 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 271 Figure 3 Seventeen of the 31 mixed fast bowlers were classified as mixed solely owing to an excessive counter-rotation of the shoulders. Their hips and shoulders were in good alignment at (a) back foot contact, but they excessively counter-rotated their shoulders to (b) a more side-on position just prior to (c) front foot contact. The conclusion of the delivery stride is at (d) ball release. The bowler pictured recorded a hip-shoulder separation angle of 17 at back foot contact (a) and a shoulder counter-rotation of 53 (a)-(b). Table 4: Mean and standard deviations for peak ground reaction forces (bodyweights), time to peak force (s) and ball release speed (m.s" 1 ) when grouped according to the front lower limb technique used during the front foot contact (FFC) phase. Ground reaction force characteristic Flexor Front lower limb technique grouping Extender Flexor- Extender Constant Brace FFC vertical force Time to peak FFC braking force Time to peak Ball release speed ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±2.5

11 272 MARC R. PORTUS ef. al. lower limb technique advocated by Bartlett et al. (1996). Table 4 shows the bowlers when grouped by these categories with their associated impact forces and ball release speeds. Although there were no statistically significant differences, ball speeds were generally faster for extenders and flexor-extenders, and impact forces lower for flexors. 8 30" egre Q Technique and trunk injuries The technique profile of the four injury groups revealed that shoulder counterrotation was significantly higher in the stress fracture group than the no trunk injury group (F = 4.5, p = 0.01) (Figure 4). This supports previous research findings in which shoulder counter-rotation has been the most important technique factor in the etiology of lower back bony, tissue and disc injuries (Foster et al, 1989; Elliott et al., 1992, 1993; Burnett et al, 1996) ^ Hip-Shoulder Separation BFC Q Shoulder Counter-Rotation ~] Hip Counter-Rotation T I I _HI i 41* ill 9 I i " il _l 36 I T 27 I I 8 I i * I T ^M 19 B T2 Stress Fracture Back Sprain Side Strain No Injury Trunk Injury Group Figure 4 Selected technique factors (mean and standard deviation) for the four trunk injury groups. *Shoulder counter-rotation was significantly higher in the stress fractured bowlers than the no injury bowlers (p = 0.01). Note: BFC = back foot contact. When the shoulder segment alignment throughout the delivery stride was analyzed, it was quite obvious that the stress fracture group had the most front-on shoulder orientation at back foot contact. Thereafter, these bowlers achieved a more side on shoulder alignment at the time of minimum shoulder alignment, which was approximately 80% of the time between back and front

12 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES , Back Foot Contact Most side-on position Front Foot Contact 240- V) 170- Stress Fracture Back Sprain Side Strain Trunk Injury Group No Injury Figure 5 Shoulder segment alignment (mean and standard deviation) in the transverse plane at key instants during the delivery stride. Most side-on position occurs between back and front foot contacts. One hundred and eighty degrees indicates the shoulders are exactly side-on. I 216 foot contacts, and subsequently carried this more side-on position on to front foot contact. The general shoulder alignments for the different groups are illustrated in Figure 5. Hip segment kinematics showed a similar pattern to that of the shoulder for all injury groups, in that hip counter-rotation was highest in the stress fracture group and lowest in the no injury group. However, the magnitudes of these hip counter-rotations were far lower than shoulder counter-rotations. Figure 4 illustrates these kinematic patterns and indicates that a concurrent counter-rotation of similar magnitudes of the hip and shoulder segments was not common. Figure 6 shows an example of an international fast bowler who sustained lumbar spine stress fractures with a moderate to large shoulder counter-

13 274 MARC R. PORTUS et. al w sacs' Hip segment Shoulders are counter-rotating Shoulder segment o c\i - in i~- Q o o Time (s) ^ CD OS i - T t C \ J C V J C M C O C O o d d d o CO - CO r- C O C O ^ ; Figure 6 Line graph illustrating an international fast bowler counter-rotating, or closing, his shoulders between back foot contact (BFC) and front foot contact (FFC) while his hips were rotating, or opening, thereby probably increasing the torque experienced by the lumbar spine. This bowler was counter-rotating his shoulders between 26 and 31 for analysed deliveries and suffered a stress fracture to lumbar vertebrae 3 on the contra-lateral side four months later. One hundred and eighty degrees indicates the segment is exactly side-on. rotation and no hip counter-rotation, that is hip rotation only, after back foot contact. At back foot contact the back sprain group did exhibit a larger hip-shoulder separation angle than the no injury group, although this was not statistically significant (p = 0.03). The maximum hip-shoulder separation angle was similar for all groups (Figure 7), although it is noteworthy that the back sprain group had more bowlers recording their maximum separation angle before front foot contact than other groups (Figure 8). Table 5 displays the hip-shoulder separation angles at back and front foot contacts, shoulder counter-rotations and technique classifications for the stress fracture and no injury groups.

14 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 275 Table 5 Key kinematic parameters and general technique classification for bowlers in the lumbar spine stress fracture and no trunk injury groups. Bowler Number Shoulder HSS Angle at BFC Counter- Rotation HSS Angle at FFO Technique Classification 2 Lumbar Spine Stress Fracture Group Mean (± SD) No Trunk Injury Mean (± SD) Group ± ± ± ± ± ±9 Mixed Mixed Mixed Mixed Front-on Mixed Mixed Mixed Mixed Side-on Semi-Open Semi-Open Semi-Open Semi-Open Mixed 'A negative hip-shoulder separation (HSS) angle indicates the hip segment is more front-on than the shoulder segment. 2 AII bowlers classified as mixed in the table were classified so primarily due to an excessive counterrotation of the shoulders (3= 30 ). Note: BFC and FFC are, respectively, back and front foot contact. No other technique factors were statistically different for any of the groups, although the stress fracture group was characterised by a more upright hip joint angle at front foot contact and ball release, whereas a more flexed knee characterised the non-trunk injured group. Concomitant with these kinematic characteristics, the stress fracture group displayed a series of non-significant trends in their ground reaction forces - higher vertical forces at back foot contact and a faster rate of peak braking and vertical force development during the front foot contact phase (Table 6).

15 276 MARC R. PORTUS ef. al. Table 6 Knee and hip joint angles ( ) and ground reaction force characteristics (body weights; time in s) for the four trunk injury groups (mean ± standard deviation). Technique Characteristic Stress Fracture Trunk Injury Croup Back Sprain Side Strain No njury Knee angle at FFC Knee angle minimum Knee angle release Hip angle FFC Hip angle release BFC vertical force Time to peak (s) FFC vertical force Time to peak (s) FFC braking force Time to peak (s) 167±9 143 ± ± ± ± ± ± ± ± ± ±9 149 ± ± ± ± ± ± Note: BFC and FFC are. respectively, back and front foot contacts. 167 ±7 151 ± ± ± ± ± ± ± ± ± 0.02 Back Foot Contact Front Foot Contact Maximum ± ± ± ± ± ± ± ± ± ±0.06 Ball Release Stress Fracture Back Sprain Side Strain Trunk Injury Group No Injury Figure 7 Hip-shoulder separation angle (mean and standard deviation) in the transverse plane occurring at key times during the delivery stride. Maximum is the largest hip-shoulder separation angle occurring at any time during the delivery stride. At each instant the shoulder segment is more front-on than the hip segment (a positive separation angle), except at front foot contact where the hip segment is more front-on than the shoulder segment (a negative separation angle but graphed as a positive for easier comparison).

16 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES S o \ " Stress Fracture Back Sprain i i Trunk Injury Group Side Strain Mo Injury Figure 8 The mean and standard deviation time of the maximum separation angle between the hip and shoulder segments in the delivery stride. Front foot contact is at zero (0) seconds. DISCUSSION AND IMPLICATIONS Technique interrelationships The relationship between shoulder alignment at back foot contact and shoulder counter-rotation highlights two potential problems with the techniques analysed. First, bowlers trying to bowl with a very front-on technique could rarely maintain their front-on orientation throughout the full delivery stride. Secondly, bowlers trying to bowl with one of the more closed actions, such as semi-open or side-on, often did not align their upper body to match their lower body orientation at back foot contact. Coaches should note that a very front-on bowling action was rarely executed properly; also, if a bowler was using a semi-open or side-on technique, a common technique error was the shoulders not aligning, that is being too open at the critical time of back foot contact. Both these scenarios can lead to excessive shoulder counter-rotation, which has been consistently linked to lumbar injuries (Foster et al., 1989; Elliott et al., 1993; Burnett et al, 1996). Significant moderate associations between kinematics and impact forces at front foot contact highlights how an extended or extending lower limb during this phase can lead to higher peak forces being experienced more rapidly. As will be discussed in the following sections, this has implications for ball release speed and trunk injury.

17 278 MARC R. PORTUS ef. al. Technique and ball speed relationships Sufficient evidence was forthcoming to suggest a moderate interaction between front knee technique, ground reaction forces and ball release speed. A front lower limb that extends, or is extended, at the knee during the front foot contact phase may permit a more efficient transfer of kinetic energy to the ball to facilitate a higher ball release speed. However, there is probably a trade off present for bowlers who have a propensity to back injury, as they may need to flex during this phase, which reduces peak impact forces and increases the time to peak force by allowing the force to be attenuated over a longer period. It is for this reason that it has been proposed that the ideal front leg technique is one in which the knee flexes at initial front foot contact to help attenuate impact forces, then extends before ball release to enable increased delivery speeds (Bartlett et al., 1996). The extension component of this front leg technique (flexor-extender) may also enhance the work output contribution from the quadriceps musculature through stretch-shortening cycle mechanisms (Walshe et al., 1998), as well as increase the height of ball release for extra bounce. In terms of trunk technique contribution to ball release speed, our findings suggest that an optimal sequence of hip and shoulder rotations were performed, which also may reduce stress in the lumbar region. Foster et al. (1989) suggested a properly timed summation of segmental velocities was important in reducing the stress in the lumbar region. Our results tend to support this for ball release speed. It seems that a well-timed hip to shoulder segmental summation was important to generate a positive maximum hip-shoulder separation angle closer to ball release (after front foot contact) both to reduce injury risk and to increase ball release speed. Generally, faster bowlers had their maximum separation angle occurring after front foot contact and closer to ball release with their shoulders being more fully rotated than the hips to generate the positive maximum separation angle. Within the coaching domain, the previous observation seems to be true anecdotally, as it is often suggested that higher ball speeds are attained when technique is smooth and rhythmical as opposed to an extreme effort to bowl fast; the latter may lead a bowler subconsciously to increase shoulder counterrotation. It might be speculated that increasing shoulder counter-rotation will enhance the contribution to segmental summation from the stretch-shortening cycle of the trunk rotator muscles. However, a smooth proximal-to-distal segmental summation of hip rotation leading shoulder rotation should derive a significant contribution from the elastic action and pre-tension of the trunk rotator musculature (Walshe et al., 1998) to aid in the efficient summation of segment velocities to the ball. Technique classification Currently there is no standard classification criterion for fast bowling technique, which has led to different research groups applying different criteria (e.g. Elliott et al., 1992; Portus et al., 2000). Issues such as sampling rate and a precise definition for fast bowling of foot contact or impact, thorax alignment,

18 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 279 choice of anatomical locations to create the shoulder and hip segments - such as acromion processes versus shoulder joint centres and surface pelvis markers versus hip joint centres - would need to be standardised to ensure that a single criterion could be reliably applied in all fast bowling research. The age of the athlete might also be important, and the style of analysis would also need to be considered, for example three-dimensional manual digitizing, two-dimensional overhead camera or three-dimensional kinematic modeling of joint centres. Elliott et al. (2002) have begun work in the latter area, showing reliability across some of these filming protocols between back foot contact and front foot contact, but not ball release, when filming at 50 Hz. The fact that the technique classification criterion in this investigation was more liberal than in previous studies (Elliott et al., 1992; Burnett et al., 1995) and classified 31 of the 42 bowlers as mixed is of concern, especially as these bowlers were associated with high performance programmes in Australian cricket. Given this, it seems difficult for coaches to detect or correct a mixed technique, whether with the naked eye or with regular video analysis. Furthermore, the problem is probably exacerbated by the lack of proven coaching methods to modify a mixed technique bowler. Possible solutions to this could be, first, to continue the research efforts of Wallis et al. (2002) investigating the most effective ways to modify fast bowling technique, particularly the mixed technique. Secondly, a greater and more thorough emphasis should be placed on educating coaches at all standards about detecting technique errors and developing individualised correction methods (Elliott and Khangure, 2002). The classification of bowlers by their front leg technique at front foot contact is, as far as we are aware, the first time bowlers in cricket have been reported in this way. As discussed for trunk classifications, there will be many similar issues to address for a standardised classification system to be adopted for all future fast bowling research. As would be expected, the constant brace group experienced relatively high impact forces, although they did not seem to gain a ball release speed advantage. The non-significant trend for flexors to experience less peak force and develop those peak forces more slowly illustrates a shock absorbing effect in this technique. It also appears that the less efficient transfer of run-up momentum, due to a flexing knee, may reduce a bowler's ability to achieve faster ball release speeds. Evidence has been presented and previously discussed on the benefits of using one of the extender techniques (extender or flexor-extender) for faster ball release speeds. However, it must be noted the small sample sizes for these two groups (n = 4) limited statistical power when we used the front leg technique classification system (Table 4). Technique and trunk injuries It seems clear the twisting of the trunk during shoulder counter-rotation is closely linked to lower back injury. However, the injury mechanism may be more than just the twisting of the spine during this movement. It is possible that bowlers who counter-rotate their shoulders are more predisposed to the adoption of a hyper-lordotic or laterally flexed posture at front foot contact,

19 280 MARC R. PORTUS ef. al. where the ground reaction forces are large (Burnett et al., 1998). It is generally accepted that lower-back stress fractures are common in sports that require repeated episodes of combined trunk rotation and hyperextension (Brukner and Khan, 1997). The measurement of back hyperextension and trunk lateral flexion, particularly at front foot contact, needs to be undertaken in future fast bowling injury studies as these are also likely contributors to the etiology of trunk injury in fast bowlers. Surprisingly, the hip-shoulder separation angles of the stress fracture group were generally similar to the no-injury group (Figure 7). The differentiating technique factor for stress fractured bowlers was after back foot contact where a large counter-rotation of the shoulders to a more side-on position took place (Figures 3 & 4). As the hip segment generally begins to rotate towards the batter well before front foot contact, it seems that the lumbar spine is exposed to a large torque due to the shoulder segment counter-rotating, or 'closing', and the hip segment rotating, or 'opening', between back and front foot contacts (Figure 6). A concurrent counter-rotation of the hip and shoulder segments after back foot contact would presumably reduce this lumbar torque. However, there were no bowlers who displayed similar magnitudes of hip and shoulder counter-rotations and, in all cases, hip rotation began well before shoulder rotation. This may indicate that in the everyday high-performance coaching environment where an overhead camera can be used, quantification of shoulder counter-rotation alone to indicate the torsion being experienced through the trunk, and hence the risk of trunk injury, is sufficient. The hip-shoulder separation angle at back foot contact for fast bowlers with a back sprain injury was non-significantly larger than no-injury bowlers (Figure 4). This result may have clinical significance for soft tissue injuries in the fast bowling population; dismissing its importance because of its alpha level of 0.03 might represent a Type II error. It should be noted, however, that in general terms, the trunk injury findings for body alignment at back foot contact suggest that a technique with the hip and shoulder segments well aligned ('in-line set-up'), can still be a technique causing lumbar spine injury if a moderate to large shoulder counter-rotation occurs after back foot contact. The analysis of the hip-shoulder separation angle at front foot contact, at which ground reaction forces were largest, was of particular interest in the investigation of back injury and technique. Of note was that this angle was not significantly different for the stress fractured group (Figure 7). Although eight of the nine stress fractured bowlers were classified as mixed (Table 5), the separation angle at any time in the delivery stride was not a significantly differentiating factor for these bowlers. This may be a reflection of the technique analysis protocol used; the separation angle is essentially a two-dimensional projection collected three-dimensionally. Facets of the fast bowling technique, such as lateral flexion and hyperextension, particularly at front foot contact where vertical impact forces averaged 7.3 times body weight (Table 2), are ignored in the calculation of the hip-shoulder separation angle. Other technique factors characteristic of bowlers were a larger hip angle at front foot contact for the stress fracture group and a more flexed knee at ball

20 CRICKET FAST BOWLING TECHNIQUE, BALL SPEED AND INJURIES 281 release for the no-injury group. This lends support to previous findings in which a greater release height relative to standing height, caused by larger knee and hip joint angles, was statistically related to lumbar spine stress fractures (Foster et at, 1989; Elliott et al., 1992). The previously-discussed link between knee action and impact forces, combined with this hip joint finding, would suggest that knee and hip kinematics during the front foot contact phase influence impact forces experienced by the trunk. When ground reaction forces were analysed, peak braking and vertical impact forces were statistically similar for all groups, although there was a non-significant trend for the stress fracture group to develop their peak impact forces during the front foot contact phase more rapidly than the no-injury group (Table 6). Several key factors have been highlighted in this research as being important for the development and coaching of technique in young high-performance fast bowlers. The constant bane for fast bowlers is injury, while the need to maintain high performance - high ball release speeds and accuracy - is paramount for continued selection and success. This paper has presented and discussed the technique factors contributing to trunk injury and faster ball release speeds. It is hoped that coaches can use this information in their coaching programmes to assist young fast bowlers to minimise injury and improve performance. Limitations of this study The limitations of this study should be noted by the reader before using this information. Bowlers have only had one delivery analysed to represent their technique. This study design creates the potential for technique variations within the same bowler, which may or may not influence injury incidence or performance factors, to be unknown and unanalysed. Additionally, as the study was longitudinal, and much of it retrospective, the exact cause and effect between technique and injury is not clearly established. For example, many bowlers in this paper had suffered injuries before their technique analysis; this, it could be argued, leads bowlers to adopt a certain technique as a result of that injury. We have assumed that core movement patterns, such as hip and shoulder rotations, have not significantly altered pre-post injury when speculating on the links between bowling technique characteristics and trunk injury. In future studies, we recommend that researchers plan fast bowling studies to address the issues of technique variability - through within-bowler multi-trial analyses - and causal effects - through prospective and intervention programmes. CONCLUSIONS Several factors have been identified as contributing to faster ball release speeds. Those bowlers who extended their front knee during the front foot contact phase recorded higher braking forces and more rapid vertical force development, and, in turn, faster ball release speeds. Bowlers with a maximum positive hip-shoulder separation angle occurring after front foot contact, with

21 282 MARC R. PORTUS ef. al. the shoulders being more rotated than the hips to generate the maximum positive separation angle, also recorded faster ball release speeds. Coaches should consider that many of these characteristics in a fast bowler's technique will also create more stress on their body. Shoulder counter-rotation, a major characteristic of the mixed bowling action, was the technique factor most strongly associated with lumbar spine stress fractures in the current study. Bowlers who adopted a more open shoulder position at back foot contact were the most susceptible to excessive shoulder counter-rotation. Coaches and bowlers should be aware that correct alignment of hips and shoulders at back foot contact is one important factor to address to reduce shoulder counter-rotation. However, coaches should not assume that if a bowler is well aligned at back foot contact that the technique is safe, as shoulder counter-rotation occurs later. Indeed, the stress fracture group were characterised by a technique that featured reasonably aligned hip and shoulder segments at back foot contact and a counter-rotation of the shoulders from back to front foot contact. The mixed fast bowling technique was most prevalent among this group of high-performance fast bowlers. As this technique has been consistently linked, including in the current study, to a higher incidence of lower back injuries this should be a major concern to coaches and administrators. Several strategies are recommended: a yearly systematic technique screening programme, which encompasses all leading fast bowlers in each state and territory; a more thorough approach to coach education in technique error detection and correction; and an intervention research programme evaluating the most appropriate individualised coaching methods to modify the mixed fast bowling technique. ACKNOWLEDGEMENTS The authors would like to acknowledge the assistance and contribution of Cricket Australia, the staff of the Biomechanics Department of the Australian Institute of Sport, Dr Peter Barnes and Patrick Farhart. REFERENCES ACB (1998). Australian Cricket Board National Pace Bowling Program Resource Kit. Melbourne: Australian Cricket Board. Bartlett, R., Stockill, N., Elliott, B., and Burnett, A. (1996). The biomechanics of fast bowling in men's cricket: a review. Journal of Sports Sciences, 14, Brukner, P., and Khan, K. (1997). Clinical Sports Medicine. Sydney: McGraw- Hill. Burden, A., and Bartlett, R. (1990). A kinematic investigation of elite fast and fast medium cricket bowlers. In M. Nosek, D. Sojka, W. Morrison, and P. Susanka (eds.), Proceedings of the Vlllth International Symposium of the Society of Biomechanics in Sports (pp ). Prague Consport. Burnett, A., Elliott, B., and Marshall, R. (1995). The effect of a 12-over spell on fast bowling technique in cricket. Journal of Sports Sciences, 13,

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