Friday, 8 November 2013

What Exercise is Best for the Lumbar Extensors?

Ok so things have been pretty hectic for me at the moment. I am coming to a critical point in my PhD work, I have been moving about regarding jobs, and have had plenty of other projects on the go. Hence little activity on the blog recently. 

I have a few posts lined up and will get to them in the near future. In the meantime I wanted to highlight the paper that we have just had published. As most may be aware my PhD research involves the use of a specialised form of exercise for the lumbar extensors that utilises a specific restraint system in order to prevent concurrent hip extension and thus involvement of the hip extensor musculature during the exercise. Although in theory this should make for a more specific means of exercising and thus conditioning the lumbar extensors to date no one has reviewed the literature in this respect, nor have they compared studies examining other exercises aimed at conditioning the lumbar extensors.

So as part of my PhD literature review I wanted to examine whether or not evidence showed that isolated lumbar extension (ILEX) was indeed more specific in conditioning the lumbar extensors. Understanding this may go some ways towards understanding the mechanisms through which such exercises are effective at reducing pain and disability in CLBP as it seems ILEX is more effective than unrestrained trunk extension (see Smith et al., 2011).

As a note, and this is discussed in the article, ILEX is essentially allowed by having the pelvis restrained against a posterior pelvic restraint,  a semi-seated position and thigh belt, such as in the picture below.


So we first reviewed the literature pertaining to what effects different exercises aimed at conditioning the lumbar extensors had upon acute activation of this musculature. Although acute activation measured using EMG is not necessarily indicative of the effectiveness of a particular exercise or approach in inducing chronic adaptations it is a good place to start to generate hypotheses or to understand mechanisms. 

Finally we reviewed the literature pertaining the to what effects different exercises aimed at conditioning the lumbar extensors had upon chronic adaptation of this musculature. These studies give us the real information regarding how specific exercises may or may not be for conditioning the lumbar extensors.

Here's the abstract: 
A review of the specificity of exercises designed for conditioning the lumbar extensors
Abstract
Objective To review the specificity of exercises designed to condition the lumbar extensor musculature (ie, lumbar erector spinae and multifidus).
Methods A review of studies examining effects of exercises designed to condition the lumbar extensors was conducted. Included were studies that examined the acute activation and chronic adaptation of the lumbar extensor musculature in response to benches and roman chair trunk extensions, free weights exercises (ie, deadlifts, squats, good-mornings, etc), floor and stability ball exercise (ie, trunk extensions, bridging, four-point kneeling, etc) and resistance machines (ie, those with and without pelvic restraints).
Results Evidence suggests that the reviewed exercises designed to condition the lumbar extensors all may result in significant activation of this musculature during their performance. However, examination of training studies shows that for benches and roman chair trunk extensions, free weights exercises, floor and stability ball exercise and resistance machines without appropriate pelvic restraints, evidence suggests that they may be less effective for inducing chronic adaptations in the lumbar extensors as a result of their performance. Contrastingly, resistance machines that employ appropriate pelvic restraint to isolate lumbar extension are better evidenced to confer specific adaptations to the lumbar extensors.
Conclusions Numerous exercise approaches have been designed with the intention of conditioning the lumbar extensors. Those examined appear to activate the lumbar extensors; however, the specificity of many of these exercises for producing chronic adaptations may be questionable, potentially due to the compound nature of them allowing involvement of other musculature such as the hip extensors. Many of the reviewed exercises offer potential to condition the lumbar extensors, however, isolation of lumbar extension through appropriate pelvic restraint appears important for optimising specific adaptations in the lumbar extensors.
The results of our review indeed did suggest that ILEX may be most optimal for conditioning the lumbar extensors, however, some of the other exercises examined (particularly trunk extension based movement i.e. roman chair, swiss ball or floor trunk extensions, deadlifts, other 'unrestrained' back extension machines) may induce some degree of conditioning the lumbar extensors. It just might not be as effective as ILEX.

This publication was timely with respect to another in British Journal of Sports Medicine recently. We highlighted in our review that the ability to identify which exercises were most specific for the lumbar extensors may be important from a prehabilitative perspective. A few days later the following study was also published indicating the effectiveness of resistance training in preventing injury:
The effectiveness of exercise interventions to prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials
Abstract
Background Physical activity is important in both prevention and treatment of many common diseases, but sports injuries can pose serious problems.
Objective To determine whether physical activity exercises can reduce sports injuries and perform stratified analyses of strength training, stretching, proprioception and combinations of these, and provide separate acute and overuse injury estimates.
Material and methods PubMed, EMBASE, Web of Science and SPORTDiscus were searched and yielded 3462 results. Two independent authors selected relevant randomised, controlled trials and quality assessments were conducted by all authors of this paper using the Cochrane collaboration domain-based quality assessment tool. Twelve studies that neglected to account for clustering effects were adjusted. Quantitative analyses were performed in STATA V.12 and sensitivity analysed by intention-to-treat. Heterogeneity (I2) and publication bias (Harbord's small-study effects) were formally tested.
Results 25 trials, including 26 610 participants with 3464 injuries, were analysed. The overall effect estimate on injury prevention was heterogeneous. Stratified exposure analyses proved no beneficial effect for stretching (RR 0.963 (0.846–1.095)), whereas studies with multiple exposures (RR 0.655 (0.520–0.826)), proprioception training (RR 0.550 (0.347–0.869)), and strength training (RR 0.315 (0.207–0.480)) showed a tendency towards increasing effect. Both acute injuries (RR 0.647 (0.502–0.836)) and overuse injuries (RR 0.527 (0.373–0.746)) could be reduced by physical activity programmes. Intention-to-treat sensitivity analyses consistently revealed even more robust effect estimates.
Conclusions Despite a few outlying studies, consistently favourable estimates were obtained for all injury prevention measures except for stretching. Strength training reduced sports injuries to less than 1/3 and overuse injuries could be almost halved.
So there we have it. Strengthening looks to be most effective for reducing injuries in sport and being that ILEX is most specific in conditioning the lumbar extensors may be best for reducing low back injuries and LBP. Though prospective ILEX exercise has been used in occupational settings and shown reducec low back injury rates ideally future work should look to actually conduct prospective interventions utilising follow-ups to rigorously test this in athletic populations. 

Obviously not everyone has access to equipment capable of providing ILEX but they shouldn't fret. Utilising some type of trunk extension exercise and attempting to focus on lumbar extension through the movement will likely provide some degree of conditioning and some is better than none in this respect.