In every action, we perform we create asymmetries and adaptations between the left and right sides of the body. Hand and foot dominance often create asymmetries of range, strength, and power. The body will find a way to achieve movement even if that if not the most efficient way and creates compensations. It will do whatever it needs to do. The body has the most incredible means of protecting itself, by adapting to the load applied to it through a variety of muscular and bony processes.
Think of the stability of the body as a pop-up tent. It has intrinsic stability but requires more stability on a windy day. The tent may then need guide ropes. To keep the tent “stable” the tension in those ropes would need to be symmetrical. If they are not, torsion may develop affecting the stability of the tent. However, if the wind only blew from one predictable direction, creating more tension in certain ropes might enhance the stabilising mechanism and create greater protection. The same might be so in the human body to adapt to the demands of certain sports and habits.
Many sports, such as pace bowling in cricket and serving at tennis are by nature asymmetrical involving varying rates of repetitive trunk extension, contralateral side-flexion, and rotation. In golf and hockey, one hand is placed below the other creating trunk side flexion to one side. Over time, these “habits” may create an imbalance in either bone or muscular responses.
But, do the asymmetries pose an injury risk or do asymmetrical adaptations develop to meet the demands of the sport and protect against injury (Gray et al., 2016)
Muscular asymmetry
Quadratus lumborum is a side flexor of the trunk and as such may hypertrophy in response to repetitive side bending motion of the trunk such as cricket pace bowling actions. Studies have reported conflicting findings as to whether hypertrophy of QL is more prevalent on the dominant side or non-dominant side in fast bowlers and it varies between adults and juniors.
Excessive lumbo-pelvic lateral flexion load during bowling has been linked to increases in lumbar bone stress injuries (LBSI) on the non-dominant side. Those bowlers who exhibited greater lateral flexion load had greater than 10% asymmetry of QL on the dominant side (Crewe et al., 2013). This asymmetry of quadratus lumborum cross-sectional area therefore may have potential value in use as a screening tool to spot those bowlers who are at risk of sustaining LBSI.
Engstrom et al (2007) investigated QL asymmetries in adolescent fast bowlers reporting asymmetries with greater QL hypertrophy on the dominant side of the trunk. However, in another study involving junior cricketers, the results highlighted a similar distribution of QL asymmetry between the dominant and non-dominant side (Kountouris et al., 2012). The techniques for evaluating the cross-sectional area were different in each study.
Potentially, the hypertrophy observed in adult pace bowlers may not develop until a greater degree of maturity or greater longevity of bowling has occurred in adulthood.
Asymmetries in abdominal muscles have been observed in injury-free adolescent cricket pace bowlers Those with thicker non-dominant internal obliques (IO) at rest remained injury-free (Martin 2017). In another study, involving a small sample group of adolescent pace bowlers, all abdominal muscles were thicker on the non-dominant side in controls but symmetrical in those who had low back pain (LBP) (Gray et al 2016). This might suggest that the asymmetry develops in response to repetitive loading and might offer protection against LBSI.
Do we need symmetry in return to play post lumbar bone stress injury?
In Anterior Cruciate Ligament injury, we aspire to achieve limb symmetry index across strength, power and other such metrics. But do we take account of imbalances that are a result of compensations built up over time to offer protection to the body part in question? When doing a rehabilitation protocol for a junior athlete following a lumbar bone stress injury, do we consider the symmetry of the trunk, hip, and lower limb musculature both in terms of range, strength, and endurance? Do we apply the same rigorous protocols designed for ACL rehab to the junior athlete with LBP or do we return them to sport under prepared for the demands of their sport? If we consider the number and quality of research papers around ACL rehab and the number around LBSI one might assume that the answer is NO, we don’t have adequate knowledge or understanding of the return to play protocols for lumbar bone stress injuries in youth athletes.
With the recurrence of LBSI rates as high as 45.5% in junior athletes, more high-quality papers are needed to test out the best indices for a safe return to sport following a lumbar bone stress injury. If anyone is looking for a research project, let me know and they can scrutinise my protocol!!
Bone mineralisation
Bone has the capacity to adapt to the load placed upon it through a cycle of bone remodeling stages. Bone mineral density (BMD) and bone mineral content (BMC) are indicators that have been used to evaluate bone health (Scerpella et al.,2018).
Increases in bone mineral density (BMD), bone mineral content (BMC), and bone mass have been observed at the site of greatest strain to enhance bone strength and therefore protect against bone stress injuries (Christen et al 2014; Scerpella et al., 2018).
Greater bone mineral density (BMD) and bone mineral content (BMC) have been observed in response to repetitive forces such as the dominant arm in tennis when compared to their nonplaying arm (Ireland et al., 2013) and in the lumbar spine in rugby players (Seminati et al., 2017).
Micklesfield et al. (2012) found a higher whole-body BMD in fast bowlers compared to spin bowlers and higher BMD in the spine and hips compared to control non cricketing populations. Fast bowlers in cricket had greater BMD (14.6%) and BMC (18.1%) on the non-dominant side of the spine compared with the dominant side, specifically at L4, whereas rugby players had bilateral increases in BMD in the posterior vertebral elements at L1-4 (Alway et al., 2019a).
Research has indicated that there may be lower BMD in the contralateral vertebrae in fast bowlers who have a current or previous lumbar bone stress injury than those who have never had one (Alway et al., 2019b). Those bowlers who had not had a LBSI had less BMD on the dominant side and greater BMD on the non-dominant side of the lumbar spine compared to those who had experienced a past or current BSI. The degree of asymmetry increased in magnitude from L1 peaking at L4 and the authors stated that these changes were above the expected bone modeling threshold and likely therefore to be a result of a positive osteogenic response to loading (Alway et al., 2019b).
In a study of adult fast bowlers, (Alway et al., 2019b) who had a lumbar stress fracture (LSF), the BMD and BMC were observed post-injury. At 8 weeks post-injury, there was a reduction of 2.48% of BMD and 2.41% BMC at L1-L4. This reduction in BMD and BMC did not recover by 21 weeks. This timing often coincides with the timing of a return to sport and caution should be applied when considering the rate of return to bowling post-injury (Alway et al., 2019b).
The recurrence rate in LBSI is as high as 45.5% in junior athletes and a return to sport that does not account for the relative loss in BMD and BMC may be a factor (Selhorst et al., 2016).
If following injury, a reduction in BMD and BMC is observed, then this might also be the case after relatively low exposure to sport such as during the off season and during periods of inactivity seen during the recent COVID-19 pandemic.
Might this be the cause of the recent spike in lumbar bone stress injuries being witnessed across both adult and junior athletes, where previous robustness to high loads had been built up over time and then was reversed during the period of relative inactivity? Junior players missed nearly 2 years of building up that bony robustness but returned to the sport with longer levers, and greater body mass, and yet no muscular and bony adaptation developed to account for the greater gains in height and strength. Many of these junior players, moved up to adult sport post-pandemic, without the gradual increase in load and intensity that would have naturally occurred in previous cohorts. The relative loss of BMD or BMC post-pandemic might not be possible to assess, but is worthy of consideration should such a period of inactivity be enforced again.
References on request – email info@angelajacksonphysio.com
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