Some time ago I set off on a mission to clarify the muddy waters that surround 'core stability'. The concept has been subject to harsh criticism from some corners while others still view it as a panacea for all. The truth probably lies somewhere in the middle, which is often the case. With so many options involved – traditional core, core 'stability', gym balls/ core devices, free-weights, abdominal bracing, Pilates etc etc – I wanted to determine if these exercises have a role and which are most effective for runners.
It seems that there is little evidence that core work will improve performance or reduce injury risk but there may be a group of people more likely to benefit. The first question to ask yourself though is why do I want to improve my core? If it's for back pain this may not be the article for you. The role of 'core stability' in back pain is a complex one and the research is yet to give clear guidance on whether core exercises will help and which ones to use. This article is for those who want to include some for of 'core work' in their strength and conditioning exercises rather than as treatment for back pain. Whether it will help those with movement control problems mentioned in our previous article (linked above) is unclear.
There have been over a thousand studies on core stability and yet it is an area that is poorly defined and includes many conflicting opinions. Hot off the press to help this is a systematic review by Martuscello et al. (2013) due to be published soon in the Journal of Strength and Conditioning Research.
Martuscello et al. compared studies of a variety of 'core' exercises to see which achieved the most activity in three 'core' muscles – multifidus, transversus abdominis and quadratus lumborum. The research they reviewed used EMG to determine muscle activity, they found 1681 studies and of these just 17 met their inclusion criteria. Exercises were divided into 5 categories;
Each of these categories were compared with regard to their recruitment of each of the 3 core muscles;
Moderate quality evidence was found showing greater muscle activity during free weight exercises than ball/ device exercises. 'Core stability' (plank, side bridge etc) had similar results to ball/ device exercises.
Limited quality evidence suggested free weight exercises (squats, deadlifts etc) had more recruitment than 'traditional core' (back extensions, sit ups). Greater activity was found during 'core stability' than 'traditional core' exercises.
Conclusion – exercise with free weights appear to be most effective in recruiting multifidus.
Moderate quality evidence was found suggesting 'core stability' and ball/ device exercises achieved similar results.
Limited quality evidence suggested 'traditional core' and 'core stability' achieved similar recruitment and 'non-core free weights' (shoulder press, bicep curls etc) were more effective than free weights.
There was conflicting evidence between 'traditional core' and ball/ device exercises and many areas had no evidence.
No firm conclusions can be made on recruitment of transversus abdominis.
No studies of quadratus lumborum were found that met the inclusion/ exclusion criteria.
Systematic reviews are considered one of the highest levels of evidence in research. They review the results from multiple studies to reach conclusions. The issue with these types of reviews is they can only be as good as the research they include. In this case the research was often of poor quality with a number of methodological limitations and conflicting results were seen in many areas. Martuscello et al. weren't able to use the data to perform a meta-analysis (pooling the results of multiple studies and examining statistically) to help reach more robust conclusions.
Reviews of this type are useful but only provide theoretical evidence. There is a big difference between this and clinical trials showing a change in a desired outcome using these exercises. For example we might conclude that free weights are most effective for recruiting multifidus but we don't know whether doing them will reduce back pain or improve performance. All the included studies were done on healthy subjects which means conclusions can't be drawn on their effects on various injuries. The use of EMG as a method of recording recruitment also has its drawbacks – they tend to record mainly surface muscle activity and may not tell us a great deal about other aspects of muscle function such as force production or movement control. Also there is a huge question of whether we really want increased core activity, what will we gain from working multifidus and transversus abdominus? The jury is still out on that one!
With little clear guidance from the research it's hard to draw an evidence based conclusion on what core exercises to use. With all factors considered though, my current advice would be that free weight exercises such as squat and deadlift are the best core exercises for runners.
Free weight exercises appear to achieve the most recruitment of multifidus but perhaps more importantly actually have some evidence that shows they can improve your running. Free weight exercises can be used as part of a resistance training programme which research suggests improve running economy and performance. By contrast studies on other types of core exercises have not shown these improvements such as Stanton et al. (2004) who found Swiss ball training did not significantly improve running economy or performance. More here on the role of core stability in performance and injury prevention and resistance training for runners.
In addition to showing reasonable core recruitment free weight exercises give you a lot of bang for your buck! We all have limited time and want to know our work outs are useful to us. Free weight work can create a number of benefits not usually associated with other types of core work. Free weights are more likely to improve strength in other key muscle groups such as quadriceps, calf and hamstrings. They are easier to add weight too and this load can be modified to achieve changes in power, muscle bulk or endurance. In terms of function free weight work is closer to the activity of running than sitting on a ball or maintaining a plank. Many have questioned whether maintaining a rigid position in prone or sidelying is useful for an upright activity like running that doesn't involve long periods in one position (until you pass out at the end of a race!). We may disregard function somewhat if an exercise helps in recruiting a specific target muscle but if it is neither functional nor specific to a muscle you have to ask what its role is. The exception with these exercises may be side bridge which research suggests is very effective in recruiting gluteus medius, a muscle vital to hip stability.
Free weight exercises are multi-functional and can easily be included in your strength and conditioning programme. The exercises included in Martuscello et al. were deadlift, lateral step up, lunge and squats (squat-front, squat-back and squat free weight). Many of these were also included in training programmes recommended by Eriksen (2005) in his article on strength training for endurance athletes in the NSCA's Performance Training Journal.
Pictures from Eriksen (2005) – article freely available online.
If I were to add to these exercises then I would suggest single leg balance and single knee dip. Both were included by Kibler (2006) in his piece on core stability in athletes and both have links to glutes activity and movement control. For more information (including videos) see our article on rehab of balance.
Unanswered questions remain as to a number of other aspects of core stability work. Does it have a role in treating back, hip or knee pain? How does 'stability' link to 'movement control'? How best do we improve movement control of the lumbar spine? Should we included abdominal bracing or 'hollowing' in our exercises? Who's eaten the last of the cheese? All important questions but beyond the scope of this piece. Hopefully we'll have answers on RunningPhysio in the not too distant future (especially regarding the cheese, my suspicion is that FMG ate it…)
Closing thoughts: the concept of core stability appears to be gradually unravelling. First its role in back pain was questioned then whether it had any place in sport. Now it seems that what we thought these 'core' exercises were doing is not what happens in practice. The aim of core specific work was to recruit muscles such as multifidus and transversus abdominis which were thought to be important for stability. Now we see these exercises don't appear to recruit these muscles as well as free weight exercises the strength and conditioning community has used for years. Further research is needed to tell us more about this complex area and I urge caution in making too strong a conclusion until we have better quality evidence.