This was a pair of studies by the same authors that have some great, real world implications with regards to prevention and physical therapy treatment of low back pain and neck pain.
Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder. J Electromyogr Kinesiol. 2005 Feb;15(1):37-52. Courville A, Sbriccoli P, Zhou BH, Solomonow M, Lu Y, Burger EL.
The objective of this work was to study the effect of rest periods of various durations applied between six 10-min sessions of static flexion on the development of cumulative low back disorder (CLBD). Three experimental groups of a feline model were used, and the rest duration between sequential static load periods was set to 5, 10, and 20 min, with a corresponding load-to-rest ratio of 2:1, 1:1 and 1:2, respectively. The reflex electromyographic (EMG) activity from the multifidus muscles and supraspinous ligament displacement (creep) were recorded during the flexion periods and over 7 h of rest following the load-rest cycles. It was found that a minor disorder developed in all the groups whereas a severe neuromuscular disorder including a delayed hyperexcitability was observed only in the group subjected to 5 min rest. The two-way ANOVA showed a significant effect of time post loading (p<0.001) and rest duration (p<0.001) on the Normalized Integrated EMG (NIEMG) recovery data; a significant effect of time post loading on the Displacement data (p<0.001) was observed as well. The post hoc Fisher test performed on the NIEMG data during the recovery phase showed a significant difference between the group subjected to 5 min rest and the other two groups (p<0.001). These results suggest that while a short rest period of 2:1 load-to-rest ratio leads to CLBD, longer rest at 1:1 and 1:2 load-to-rest ratio are more favorable for preventing or attenuating the development of CLBD. Short rest periods between sessions of static lumbar flexion, therefore, are a risk factor for the development of CLBD.
Work to rest durations ratios exceeding unity are a risk factor for low back disorder; a feline model. J Electromyogr Kinesiol. 2007 Apr;17(2):142-52. Epub 2006 Apr 4. Sbriccoli P, Solomonow M, Zhou BH, Lu Y.
Low back disorders are prominent among the work force engaged in static anterior flexion during the workday. As a continuing part of a long-term research aimed to identify the biomechanical and physiological processes and corresponding risk factors leading to such cumulative trauma disorder (CTD), we ventured to assess the effect of rest and the work-to-rest duration ratios that may prevent CTD. Three groups of the feline model were subjected to three load/rest paradigms: two 30 min loading periods spaced by 10 min rest in Group I, two 30 min loading period spaced by 30 min rest in Group II and one 60 min loading period for Group III. The cumulative loading duration in the three groups was 60 min. Each of the groups were allowed 7h of rest while monitoring EMG and lumbar viscoelastic tissue creep each hour. The results demonstrate that for two 30 min load periods with a 30 min in between rest, an acute neuromuscular disorder was not present whereas for two 30 min loading with a 10 min rest it was. Similarly, for a 60 min loading with long-term rest, the disorder was present. Post hoc Fisher analysis demonstrated significant differences in the delayed hyperexcitability between the first and second group (P<0.0001) and the third and second (P<0.0001) group. Statistical difference in the displacement data of the three groups was not present. ANOVA showed a significant effect of time post-loading (P<0.0001 and different rest durations (P<0.0001) on the EMG data during the 7h recovery. The new data allow us to conclude that a work-to-rest duration ratio of 1:1 can prevent the development of CTD as long as the work periods are not too long (<60 min). Longer static flexion durations do not respond favorably to rest even if it is of equal or longer duration. It is suggested that appropriate durations of rest may be a viable tool to avert CTD in a certain range whereas long static flexion durations should be avoided at all cost.
I have a lot of comments on this one because these are really great studies, though perhaps not so much if you are a cat.
The idea is that spine flexion on the job or in some sports leads to low back pain secondary to damage to lumbar discs, overstretching spine ligaments and facet joint capsules. An objective sign of such damage is an increase in hypertonicity (excessive tension) of the spine extensor muscles following pathological durations of end range spine flexion with low to moderate loads. The findings were that a total time of 60 minutes of sustained back flexion would not induce a severe neuromuscular disorder so long as it was broke up in to six 10 minute segments with at least 10 minutes rest in between them or as long as two 30 minutes segments of stretch with at least 30 minutes rest between. Thus the 1:1 ration. However if the stretch was a sustained 60 minutes, there was an increase in hypertonicity regardless of how long the rest was afterwards. So a take home message is that if you are going to partake in a spine flexion posture perhaps during work or sport, you can minimize and hopefully avoid damage if you keep the flexed posture periods 30 minutes or less to be relatively safe, and certainly less than an hour, with necessary rest periods needing to be as long as the stretch time.
Caveats worth knowing is that the cats in this study were apparently without prior injury so someone who already has some degree of spine degeneration might not tolerate as long of flexion periods and might need greater rest periods before they can tolerate flexed postures again. Since I am unaware of any occupations that allow employees a 1-1 ratio of work and rest times, it’s probably best to minimize spine flexion in the first place by having office workers sit in chair with good lumbar support, and make periodic use of standing work stations. More active occupations need a greater emphasis on learning to hinge and bend at the hips and knees while preserving a neutral spine to prevent damage, which is what people learn by using proper technique with multi-joint weightlifting movements. Also while the authors said the resulting hypertonicity was indicative of “severe neuromuscular disorder” all the spines, even with the longer rest periods, displayed hypotonicity (less than normal muscle tone) for hours after all the stretch protocols, which the authors still called a minor disorder. I would expect this minor disorder and hypotonicity would put workers at increased risk of low back injury for as long as this hypotonicity was observed, which in these studies was at least 7 hours. So, only when spine flexion is unavoidable should the above work to rest ratios be endured.
Important to note is regardless of rest period length there was an increase in spine ligament elongation, thus decreasing passive support to the spine. Only when the rest periods were less than the stretch periods (up to 30 minutes) was there a combination of a still greater increase in spine ligament elongation combined with hypertonicity. I think this hypertonicity best explains why many of my back pain patients complain of feelings of stiffness and feel they need to stretch it out. In such cases the stretch that feels good leads to further damage of the spine and in the long run further increases hypertonicity. So I really like these studies as they make the principle considerably more concrete and easier to explain, with some “here’s exactly what happens” examples.
So the counterintuitive answer is to eliminate the flexion stretch in physical therapy and elsewhere, thus allowing the spine to heal and muscle tone to normalize. Patients might still need to increase range of motion around the hips and shoulders so that tasks can still be accomplished without over-stressing the spine. So stretch itself isn’t bad, it just needs to be applied to the right place. The above studies, and a number of others tend to show that the spine itself is the wrong place to stretch. This research likely also explains why massage and soft tissue mobilization generally feels good immediately afterwards, perhaps by normalizing tone, but leads to no long-term relief of prevention of further spine damage because it does not address any of the underlying problems. This is why I much prefer electric muscle stimulation (EMS) as my modality of choice for pain relief, because you not only get pain reduction, but a direct increase in muscle strength and endurance. So it’s a great 2 for 1 that you just don’t get from ASTYM, Graston Technique, Dry Needling or what ever else soft tissues technique of the day.
Increasing core and extremity strength and endurance allows people to better avoid compromising positions thus decrease strain on the spine. Only then will hypertonicity decrease, the spine not feel so stiff, and likely the spine won’t be as stiff. This was objectively found in cervical spine research where rehabilitation programs focusing on strength led to better improvements in range of motion than those that focused on stretching, indicating that the above principles apply to the treatment and prevention of neck pain, much as they do in low back pain.
So it’s an exciting time in spine rehabilitation. These studies are really leading to conservative treatment programs that are very effective at lessening and eliminating back and neck pain. What’s frustrating is that most physical therapists still promote spine stretching treatments that are objectively harmful, and a number of passive modalities that provide only short term relief at best, so that a good number of back and neck pain patients just don’t get better. They then go back to their doctor and say “physical therapy didn’t work”, and eventually they end up with what should have been unnecessary surgery that in the long term does not fix what caused their pain in the first place. Later they end up in pain management, doped up for life, with a diagnosis of spinal stenosis or failed back syndrome. So it’s kind of a big deal.
As always, if you have any further questions or need for clarifications, please don’t hesitate to ask. Being aware that some of my blog ideas are contentious and occasionally a bit out of the field of my expertise, I encourage my readers to come forth with any questions/comments that are of interest or concern. Your comments are valued and welcomed.
Chad Reilly is a licensed physical therapist, located in North Phoenix, practicing science based medicine with treatment protocols unique and effective enough to proudly serve patients from Phoenix, Scottsdale, Mesa, Chandler, Tempe, Peoria, and Glendale.