Core stability training: performance cure-all or just a con?

Core stability training has become universally accepted as an integral and essential part of many sports conditioning programmes. But just how effective is it? Andrew Hamilton looks at the evidence

What are core muscles?

The core stabiliser muscles are (mostly) deeply placed muscles, whose job is to stabilise the joints and maintain correct anatomical alignment, while the bigger, more powerful mobiliser muscles do their stuff during activity (see panel 1). In particular, core muscles help anchor and ‘lock’ the vertebrae of the spine in the correct position, thus protecting the back from injury during powerful movements of the trunk. They’re also active when the body is stationary – eg when standing upright to maintain correct posture.

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Panel 1: Some of the key ‘core stabilising muscles’

Spinal

• Multifidus (see figure 1): Stabilise the vertebrae of the spine and also co-contract with the abdominals to increase trunk stiffness.
• Erector spinae: Stabilise the vertebrae of the spine, helping to control decelerate trunk flexion and rotation.

Abdominal

• Rectus abdominis: Controls trunk flexion.
• Internal and external obliques: Helps control trunk rotation.
• Transverse abdominis (see figure 1): Works with multifidus (above) to increase intra-abdominal pressure and provide stability to the lumbar spine.

Hip

• Gluteus medius and minimus: Primary lateral stabilisers of the hip. Control abduction of the hip and help stabilise the pelvis.
• Gluteus maximus: Helps control hip extension and the transmission of forces from the lower extremities to the trunk.

Figure 1: Transversus abdominis and multifidus muscles

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Over time, these core stabilising muscles can become less active and/or weakened for a number of reasons such as inactivity, poor posture or (the most common reason in athletes) because of injury. However, weak core muscles can soon lead to dysfunctional movement patterns, which increase the risk of further injury. The theory behind core stability training is to train the core muscles to function optimally in order to help prevent injury and to correct any dysfunctional movement patterns.

Patchy evidence

Although core training is very popular across a number of sports, the evidence for the benefits of core training is unfortunately far from clear-cut. For example, US scientists found that collegiate athletes who participated in a core-strengthening program experienced no significant reduction in back pain compared to those that didn’t⁽¹⁾ while Australian scientists found that although core training on a stability ball increased measures of core stability in runners, no changes were observed in activity of the abdominal and back muscles, maximum aerobic power or running posture⁽²⁾.

A similar study examined the effects of a 6-week stability ball training program on swimming performance and although it reported improved core stability, again, there was no enhancement of swimming performance⁽³⁾. In another study, the link between core muscle strength and sports performance in 29 collegiate football players was found to be moderate to poor⁽⁴⁾ and a follow up study found that while there was some correlation between core strength and isolated strength measures, there was no correlation between core strength and functional movement⁽⁵⁾.

In another study on this topic, researchers investigated the relationship between core stability, functional movement, and performance⁽⁶⁾. A number of sportsmen and women underwent core strength assessments in three categories: flexion (leaning forwards), extension (leaning backwards) and left/right lateral movements. They then performed a number of functional movement tests to see if higher levels of core strength helped in these tests, which consisted of:

• Deep squat
• Single leg squat
• Trunk-stability push-up
• Right and left hurdle step
• In-line lunge
• Shoulder mobility
• Active straight leg raise
• Rotary stability
• Backward medicine ball throw

The results showed that while there was some moderate to weak correlation between core strength and functional movement ability, this was not significant, suggesting that core stability is not a strong predictor of functional performance. The researchers concluded by adding: “Despite the emphasis fitness professionals have placed on functional movement and core training for increased performance, our results suggest otherwise. Although training for core and functional movement are important to include in a fitness program, especially for injury prevention, they should not be the primary emphasis of any training program.”

Benefits of core training

As we’ve seen, the evidence that core training significantly boost performance is patchy to say the least. However, not all the studies carried out have produced negative results. For example, a study on 41 female athletes showed that six weeks of plyometric, core strengthening, balance, resistance, and speed training reduced the risk of knee injury⁽⁷⁾. Unfortunately, because these elements were combined in the study, it’s difficult to know which of these training components was responsible for the reduced injury risk.

Meanwhile, core training consisting of multifidus, transversus abdominis and pelvic floor exercises resulted in an improvement in multifidus muscle strength in Australian cricketers and a subsequent decrease in back pain⁽⁸⁾. Also, a study on the effects of abdominal stabilisation manoeuvres on spinal stability found that performing the abdominal bracing manoeuvre prior to an external perturbation to the trunk was effective in reducing spinal motion⁽⁹⁾. Overall though, there’s still considerable debate in the scientific community about just how effective core training is.

Core endurance and running efficiency

One possible benefit of core training that seems to have been hitherto overlooked is an increase in ‘core endurance’. Core endurance is a crucial component in core training because improved endurance helps support the core muscles to maintaining an efficient trunk position. Research suggests that core endurance is important to spinal stability during prolonged exercise. In particular, there’s good evidence that improved core endurance benefits running kinematics (running gait and limb coordination) and that core muscle fatigue might be reduced during high-intensity running, which leads to improved running performance^(10,11).

To test this theory, a newly published study has examined the effects of an 8-week core training programme on core endurance and running economy in college athletes⁽¹²⁾. Running economy is a measure of how efficiently the energy expended by the running muscles is converted into forwards motion. All things being equal, improved running economy means that less energy is required to sustain a given running speed – ie a given level of workload becomes less fatiguing. It’s a fact that all top performing athletes whose sports involve running will have good levels of running economy.

In this study, 21 male college athletes were randomly divided into two groups:

• A control group who carried on with their normal training but did no core training
• A core training group who also maintained their regular training, but who also attended three extra core training sessions per week for eight weeks.

The participants were assessed before and after the training program for measures of core strength, static balance and running economy using a 4-stage treadmill incremental running test.

The key finding was that the core trained runners not only exhibited better core strength and static balance, they also used less oxygen in the later stages of the running test, which indicated improved running economy. This study suggests that while core training might not help functional strength, it could help improve running kinematics, leading to improved economy – an obvious benefit to any sportsman or women whose sport involves significant amounts of running!

Practical advice for sportsmen and women

Okay, let’s sum up. What role should core training play in your sports training programme? The current evidence suggests that:

• Sportsmen and women with a history of back injury may benefit from some carefully targeted core training as a preventative measure. This article provides a good introduction to the type of core training exercises that should be incorporated into a core programme.
• Recent research also suggests that maintaining core strength can improve running economy, which will help reduce fatigue during longer sporting activities where running is a key activity.
• However, for sportsmen and women who are normally injury-free, spending large proportions of training time engaged in core training is unlikely to improve sporting performance. Where this is the case, athletes may be better off investing that training time elsewhere.

References

1. Med Sci Sports Exerc. 2002 Jan;34(1):9-16
2. J Strength Cond Res. 2004 Aug;18(3):522-8
3. Master’s Thesis, University of North Carolina, Chapel Hill 2001
4. J Strength Cond Res: Nov 2008; 22(6)1750-1754
5. Okada T, Huxel KC, Nesser TW, Graduate Thesis, Indiana State University 2007
6. Journal of Strength & Conditioning Research. 2011; 25(1):252–61
7. J Strength Cond Res. 2005 Feb;19(1):51-60
8. J Orthop Sports Phys Ther. 2008 Mar;38(3):101-8
9. J Electromyogr Kinesiol 2007;17(5):556-567
10. Journal of Science and Medicine in Sport. 2014; 17(4):419–24
11. Journal of Sports Science & Medicine. 2014; 13(2):244–5
12. PLoS ONE 14(3): e0213158. https://doi.org/10.1371/journal.pone.0213158

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