Fast and Furious
The biomechanics of fast bowling was the topic of my PhD research at the University of Western Australia from 2009-2012 – specifically, the lumbar loads experienced during bowling and the mechanism of lower back injury. Before starting my PhD, I worked in clinical practice in Johannesburg and treated many bowlers recovering from stress fractures and other back injuries. This, in part, fuelled my interest in the subject. Since returning to South Africa from Australia, I have analysed the actions of hundreds of bowlers, from junior school level right up to the very best cricketers in the world (Protea men and women players, as a consultant biomechanist for the Cricket South Africa Elite Fast Bowling Group) and worked with coaches to fine tune bowling technique, often with an emphasis on reducing the risk of injury. In this post, I’ll summarise the science on the topic and share my approach to simple field-based bowling technique analysis.
The fast bowling action is a unique skill. It differs from over-arm throwing because, according to The Laws of Cricket, the ball must be delivered without any straightening of the elbow after the arm has reached the height of the shoulder in the delivery swing. In comparison, baseball pitching, for example, relies on rotation at the shoulder joint with the elbow flexed and then straightening up to the point of release as a vital mechanism for the production of ball speed. Cricketers, therefore, need to find a different solution in order to bowl fast.
Bowlers do this, firstly, by employing a run-up, at the end of which is the “gather” where they set themselves up to start the circling motion of the bowling arm. During the delivery stride, from “back foot contact” to “front foot contact”, the torso rotates away from the batter into a relatively side-on position as the bowling arm circles backwards. Between front foot contact and ball release the front leg acts like a strut that the upper body pivots over, and the torso rapidly rotates towards the batter with simultaneous forward flexion and side bending, allowing the arm to circle over head to a vertical release position.
A Pain in the Back
Fast bowling-related injuries are a major headache for cricket coaches and medical support teams. In first-class and international level squads, one in five fast bowlers is likely to be unavailable for match selection due to injury at any point int time (data from injury surveillance in Australian men’s cricket over a ten-year period, showing an average prevalence of 20%) . Most of this lost playing time is due to lower back injuries. Stress fractures of the lumbar vertebrae in particular, which are near endemic in fast bowlers, require 6-8 months recovery time on average before a player can fully return to fast bowling.
Injuries happen when the load applied to the tissue (bone, in this case) is greater than the tissue’s capacity to withstand that load. The mechanism of injury refers to a biomechanical description of the “inciting event” that causes injury (or events – in the case of stress fractures, the injury develops through numerous repeated loads).
During fast bowling, the load on the lumbar spine is greatest just after front foot contact . This is because of the large ground reaction forces the bowler experiences on impact, typically five to eight times body weight, while the spine is undergoing combined flexing, twisting and side bending motions at high velocity. Of these three, the side bending (lateral flexion) motion is the most extreme. Biomechanics research has shown that bowlers exceed their “available range of motion” in this plane during the bowling action. Try this – stand upright with your arms at your sides and bend to one side as far as you can, keeping your feet anchored to the ground. This is your available range of motion. Now imagine bending 25% further – this is how much fast bowlers exceed their own available range by after front foot contact. In comparison, bowlers only “use” about a quarter of their available hyperextension range and 80% of their available rotation range .
As part of my PhD research, we analysed the bowling actions of junior male fast bowlers and calculated the load experienced at the lumbo-pelvic joint during bowling. Then, we monitored them for the duration of a cricket season, recording any new lower back injuries. Bowlers who went on to suffer a lower back injury had greater pelvis rotation beyond a ‘front-on’ position and greater trunk lateral flexion angle at ball release, and larger flexion and lateral flexion moments (or “torque”) at the lumbo-pelvic joint . This evidence points to lateral flexion between front foot contact and ball release as a key component of the injury mechanism. While it’s not feasible to measure 3D lumbo-pelvic joint motion and moments in a field setting, the lateral flexion angle of the trunk relative to the vertical can be measured using simple 2D video analysis .
This 2D trunk lateral flexion angle is one of the main metrics that I report on when analysing fast bowlers’ technique. However, the biomechanist’s job shouldn’t end at measuring a position or describing a movement. The next step is to diagnose why the player may be ending up in an undesirable position, because this is the information a coach needs in order to design a plan to improve the player’s action.
When I observe a player that finishes in an extreme lateral flexion position at ball release (>50°), I typically work backwards to find the point where things start to “go wrong”. Take a look at the sequence of images below. This is an example of a bowler who “kicks out” with the rear leg during the gather and “sits” into the back leg, pressing his centre of mass away from the stumps in the frontal plane (images 1-3). He then drifts inwards, towards the stumps, with the lower body between back and front foot contact as the upper body falls away (images 4-6). Because of the motion in the first part of the delivery stride, trunk lateral flexion might be necessary to (i) achieve a vertical arm position at ball release and (ii) avoid running across the pitch in the follow-through. Technical work should therefore focus on improving the set-up position at back foot contact and the direction of the centre of mass thereafter, which in turn should reduce the amount of lateral flexion at release. The bowler also needs to be strong enough to support and transfer their weight effectively during the delivery stride. Reduced back and hip muscle strength and control of the pelvis during single leg squatting tasks have also been shown to increase back injury risk in fast bowlers , so any technical intervention should also take the player’s physical capacity into account.
Some readers may be surprised to get this far into an article about bowling technique and back injuries without any mention of the “mixed action” or “counter rotation”. The mixed action is when the bowler positions themselves at back foot contact with a misalignment of the hips and shoulders, and thereafter “counter rotates” the upper body from relatively front on to more side on between back and front foot contact, and several research studies have identified this as a risk factor for lumbar injury. The role of this motion in the development of back injuries has been a topic of debate, because it occurs before the peak load on the spine and is therefore unlikely to be the mechanism of injury. In the series of images above, this bowler clearly displays the mixed action and, in this case, it likely contributes to the subsequent lateral flexion which is more mechanistically linked to injurious lumbar load during fast bowling.
Interestingly, recent research has shown an association between lumbar stress fracture risk in fast bowlers and increased hip and knee flexion of the support leg after back foot contact (also apparent image #3 in the sequence above) . This is another example of how a position or motion that is fairly removed from the injury mechanism can be linked to injury because it reveals something about the player’s physical and/or technical predisposition to end up at the “inciting event”.
I used this fast bowling example in a presentation I gave recently at the XIX Brazilian Congress of Biomechanics, to illustrate a framework for deciding what to evaluate and how to approach any technique intervention. First, specify the outcome you are concerned about - in this case lower back injury. Second, identify the key mechanisms that cause this outcome - lumbar load after front foot contact, in particular in the lateral flexion direction. Third, diagnose the factors that lead up to this mechanism - these are the things you can coach/train.
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