This is the second in our multi-part series all about ‘the Core’. A term that has been used across the health and fitness world to loosely describe the muscles that stabilise the trunk. But what is it exactly? And what role does it have to play in injury and performance? Here’s Chews Health Physiotherapist Rich Saxton with some of the ‘science’ behind it. Part 1 is available here.

What is value of assessing and training the core in sport?

As discussed, the core incorporates varied and complex interactions between musculature and non-contractile structures. To assess core stability, strength or function, multiple tests have been developed and are regularly used.  Throughout the literature there is no one reliable or valid dynamic assessment of core strength or stability (Shinkle et al. 2012).  The common clinical assessments of the core include isometric endurance and isokinetic strength tests coupled with functional sport specific assessments (Cowley et al. 2007).  There is limited evidence in large controlled studies on the efficacy of core stability exercises compared to that of other exercises to improve athletic performance (Standaert and Herring, 2007).  Moreover, due to the varying demands placed on the body during dynamic sport, like field hockey, static core exercises incorporated into non-elite participant trials cannot be generalised into the elite population (Hibbs et al. 2008).

The principle of training the core should address both the local and global musculature in order to maintain control of the trunk and pelvis.  An effective co-ordination of the multi-role muscles is based around integrating functional control with breathing, postural and movement functions (Key, 2013).  In contrast, an analytical model showed an increase in abdominal pressure increased spinal stability but this was not influenced by TrA, IO or EO. Moreover, increasingly activating TrA resulted in a reduction in spinal stability.  However this study did not involve human participants and only measured three pure movements about a central axis (Stokes et al. 2011) and thus not representative of a dynamic sporting movement but highlights the contradiction in the research.

An elite athlete requires central stability during the multidirectional dynamic movements that occur to perform their sporting activities (Hibbs et al. 2008).   Field hockey is a low intensity with intermittent high-intensity team sport that places high demands on aerobic system as well as muscular strength, endurance and proprioception (Lythe and Kilding, 2011).  A field hockey match lasts 70 minutes with the average athlete playing for between 48-57 minutes (Spencer et al. 2005).  During a field hockey match an average player will run 8.1km mainly at low and moderate intensities with high intensity activity only 4.5% of total player running time (Lythe and Kilding, 2011).  Moreover, hitting, tackling and passing the ball require a combination of spinal flexion and rotation mainly in a semi-crouched position (Fenety and Kumar, 1992). Thus a generalised hockey player will be used when discussing the value of assessing and treating the core to aid performance and injury prevention.

In studies reviewing other sports and the importance of the core in performance, a study reviewed the implementation of a six-week core strengthening exercise programme alongside proprioception exercises in 5km running performance (n=28).  The control group were asked to complete the same lower limb stability exercises but not the core-strengthening programme, this included abdominal crunches, hip raises and back extension on a stability ball, supine leg and opposite arm raises and a Russian twist on a stability ball.  The study showed that there was no significant difference between the control and the core strengthening exercise group in balance, proprioception, and ground reaction forces. However, the 5km running time was significantly improved after core exercises compared to that of the control group (Sato and Mokha, 2009).  This improvement was reported to be as a result qualitative feedback of runners who suggested they used their core to stabilise their running technique improving performance.

As discussed, within field hockey, players are required to maintain low intensity activity with high intensity activity.  Therefore, the effect of an increase in core strength was evaluated in relation to sprint times as players are required to have short, high intensity sprints especially if playing in a forward position (Vescovi and Frayne, 2015).  Participants who had completed the specific hip flexion resistance exercises (which can be defined as the core over 8 weeks, 3 times a week) improved their 40-yard dash and shuttle run time and isometric hip strength compared to the control (Deane et al. 2005). However the participants were not elite athletes and their normal training regimes were not altered or recorded; therefore there was no standardised control group and it cannot be concluded the targeted hip flexor exercises specifically resulted in an improved sprint time. 

In attempting to train the core multiple exercises are used within the literature in an attempt to increase core strength and stability. Multi-strength exercises are required to increase overall core strength as different exercises affect different core musculature. An 80% one-repetition squat seen to increase lumbar-sacral erector spinae most effectively with an 80% one repetition deadlift activating the upper lumbar erector spinae musculature. In contrast the squat, deadlift, body weight squat or deadlift, swiss ball sidebridge and superman exercises did not significantly activate core muscles (Hamlyn et al. 2007).  However this study had a small number of participants (n=16) and exclusion criteria included previous and current low back pain which has established effects of core muscle strength and activation patterns.

The use of an unstable surface during core training exercises with a 10 repetition maximum stable load results in the largest EMG activity of the RA, lower erector spinae and the upper erector spinae musculature in trained participants.  However the EO recorded a high EMG recording when trained on a stable surface with an unstable load, however these values were not significantly different. Moreover it has been suggested increasing the strength of the RA beyond optimal can have a destabilising effect on the spine in a frontal plane (Kohler et al. 2010). 

A study attempted to assess core stability in relation to athletic performance in a functional test, the double leg-lowering test (DLL).  This test requires high levels of muscle activation and trunk stabilisation has been described as a functional test for core stability.  The participants who recorded a higher core stability in the DLL test only saw a significantly better throwing distance, all other measures of performance including an agility test, forty yard dash and vertical jump were not correlated with a higher DLL measurement (Sharrock et al. 2011).  However, the study used the DLL test to measure core stability, this test is a static singular plane movement and not representative of a dynamic multi-directional sport such as hockey.

In field hockey upper limb strength and control is vital, as unlimitedly force generation will be transferred to the stick and ball.  The role of the core is to provide a dynamic stable base to enable upper limb movements. Participants who completed three different core exercises showed a significantly reduced postural sway, as measured by a stabilometer, when completing upper limb tasks such as turning pins in a slight forward lean posture.  This indicated improved trunk stability when completing an upper limb functional task after 20 minutes of core exercises (Miyake at al. 2013).   However the results cannot be generalised to the elite hockey player, as the upper limb functional task used in the study was not sport or hockey specific and the participants were not athletes.

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