Fitness and Low Back Pain

Original Editor ­ - Peter Copeland, George Smith, Bryn Roberts as part of the Nottingham University Spinal Rehabilitation Project
Top Contributors - Peter Copeland, George Smith, Lucinda hampton, Bryn Roberts, Kim Jackson, Laura Ritchie, Evan Thomas, 127.0.0.1, WikiSysop, Wanda van Niekerk, Fahad Bin Aftab, Admin, Shaimaa Eldib and Aminat Abolade

Introduction

Low back pain is an umbrella of conditions with 80% of adults estimated to experience LBP at some point during their life . Low back pain refers to pain between the bottom of the ribs and the buttock crease.

• A high physical fitness level, and especially muscle endurance in the back muscles, is associated with lower risk of back pain
• A harmful misconception is that exercise should be avoided when LPB is present. Understandably, many patients are reluctant to exercise out of the fear that any exercises or stretching will aggravate their existing back pain. They may become reluctant to exercise and rely on medications.

Fitness 

Physical fitness is a set of attributes that people have or achieve. Being physically fit has been defined as:- the ability to carry out daily tasks with vigour and alertness, without undue fatigue and with ample energy to enjoy leisure-time pursuits and meet unforeseen emergencies
In accordance with Hales in 2010, these are the five components of physical fitness and the Gold Standards for measuring each of these aspects:-

1. Cardiorespiratory Endurance - VO2 max per Kg of body mass   
2. Muscular Endurance - Currently no Gold Standard measurment for muscular endurance
3. Muscular Strength - Isokinetic Dynamometry  VO2 max normative values
4. Body Composition:- The current Gold Standard is a Four-Compartment model of measurements most commonly consisting of Mass, Total Body Volume, Total Body Water and Bone Mineral Content. There are however other potential methods such as Dual-energy Xray Absorptiometry (DEXA) and Air-Displacement Plethsymology which are being trialled to measure body composition 
5. Flexibility - Optical Gold Standards such as the Vicon Motion Tracking System

Cardiorespiratory Endurance

Cardiovascular Endurance is the ability of the circulatory and respiratory systems to supply fuel during sustained physical activity and eliminate fatigue products after supplying fuel. The pain-relieving mechanics of aerobic exercise on lower back pain are not clear since the intensity of the muscular contractions are not intense enough to promote muscular hypertrophy.
Cardiovascular (CV) fitness theoretically has many different influences on the prevention of lower back pain. Cardiovascular fitness may help prevent any unfavourable adaptations to the body associated with neuromuscular health, muscular endurance, muscular strengt,h and general loading through the lumbar spine.
The majority of these tend to be indirect effects as the association between cardiovascular fitness and LBP is not as discernible as that seen with muscular weakness, reduced flexibility, and reduced muscular endurance.
However, a more direct link to why high CV fitness can prevent lower back pain is that due to the avascular nature of the intervertebral discs they rely on osmosis for he ttransport of nutrients and the removal of waste products. The improved efficiency in circulation that directly stems from good CV fitness, will facilitate the osmosis required to maintain disc hydration, therefore, delaying the process of disc degeneration and reducing the risk of LBP.

Although VO2 max is the gold standard for measuring cardiovascular endurance there is no evidence that specifically associates VO2 max in the prevalence of LBP . It is used in more of the evidence surrounding deconditioning syndrome related to chronic LBP.

Smoking has also been shown to increase the likelihood of LBP. The causality of which can partially be explained by the physiological effects that smoking has on the CV system. The decreased arterial oxygen to the paraspinal muscles of the lower back will lead to muscle fatigue and increase the use of the lactic acid system, therefore lactic may build-up and stimulate the pain sensors in the area, also as mentioned in Muscular endurance, the muscular fatigue increases the likelihood of low back pain too.

Muscular Endurance 

Muscular Endurance is the ability of the muscle to exert a submaximal force repeatedly over a sustained period of time. In a study conducted by Biering-Sorenson in 1984, it was discovered that patients with low back pain had reduced levels of muscular endurance in the lumbar extensors in comparison with non-sufferers, recent research by authors such as Andersen (2007) supports this as they showed a similar association in a large sample of healthcare workers and students.

                                        (Sorenson test)

Studies have also reported that abdominal muscular endurance in low back pain sufferers is significantly decreased in contrast to those in the normal health population , although a more recent study by Lewis (2009) showed that adolescents with LBP presented with significantly higher trunk flexor muscle endurance compared to adolescents without LBP. The argument is made that the ratio between flexor’s and extensor’s muscular endurance is more important in terms of LBP than endurance and strength measurements alone . The increase in flexion endurance and decrease in extension endurance could be linked to having a poor posture and loss of the neutral position, therefore leading to LBP. ()

Lumbar fatigue as a result of low muscular endurance has been shown to reduce the person’s ability to sense the positioning of the lumbar spine and that 25% of people with chronic LBP (n=57) had severely impaired ability in controlling the position of the lumbar spine after a fatiguing task. This loss of control again links back to the fact that not being able to hold a neutral position is strongly associated with LBP. ()

Physiologically in patients with lower back pain, it has been shown they have a higher percentage of fast type I glycolytic fibres compared to the slow oxidative fibres, this can be expected to render them less resistant to fatigue, where-as non-LBP people have a much higher percentage of type II glycolytic fibres giving them better muscular endurance helping prevent lower back pain.

Body Composition  

This is the relative amounts of muscle, fat, bone and other vital organs in the body. The prevalence of low back is undoubtedly related most commonly with body fat content/obesity. Numerous studies have been conducted highlighting the relationship between increased fat content and the likelihood/prevalence of lower back pain. A study conducted in 2003 found that there was a moderate positive relationship between obesity and lower back pain, however the results were based on the BMI calculation which does not definitively measure body fat content. In a study conducted by Urquhart 2011 it was also evident that there was a relationship between obesity and lower back pain. The difference with this study , however,is that not only was the BMI calculation used as a measure of obesity but Lean Fat Mass and Lean Muscle Mass were also calculated to determine whether it was fat content or general increase weight that was directly proportional to the potential for LBP. It is the common belief that an increase in body weight alters spinal biomechanics and loading creating excess strain to be put through certain structures. This picture displays how obesity can lead to altered body positions such as exaggerated lumbar lordosis which will cause an alteration in spinal loading mechanics.

The theory behind why back pain was less prevalent in those with high lean muscle mass was that the increase in muscle mass was there to compensate for the excess spinal loading and therefore would not alter loading mechanics. The studies conducted however have all been cross-sectional studies and longitudinal studies will need to be completed to assess if a higher fat mass predisposes the development of lower back pain later in life. There has been a meta-analysis completed  reviewing the literature surrounding obesity and low back pain. In the cross-sectional studies analysed, there was a strong link between obesity and the increased prevalence of LBP in the last 12 months, subjects seeking LBP care and chronic LBP sufferers. There was an increase in prevalence for overweight subjects in comparison with the non-overweight subjects however subjects classified as obese had the highest incidence rate of LBP. Of the cohort studies, there was only a relationship highlighted between obesity on LBP. Results were adjusted for publication bias and only studies who controlled for potential confounding variables were included. The results remained the same after being subjected to these criteria.  There have also been a number of studies investigating the relationship between bone mineral density (BMD) and the predisposition to low back pain. In a study conducted in 2011 , relationships were discovered between positional asymmetry, motion restriction and objective measurable increases in the BMD of affected vertebrae.  

The studies conducted however have all been poor quality cross-sectional studies, and to truly assess the implications of each aspect of body composition on the prognosis of LBP, longitudinal studies will need to be completed to investigate the subjects over a longer period of time.

Flexibility

This is the range of movement available at any particular joint of the body. Patients presenting with low back pain often display significant reductions in degrees of several movements at the pelvis and trunk. Adequate flexibility of the lumbar spine enhances functional mechanical advantage, while spasmodic or shortened back muscles adversely affect spinal mechanics . Tightness in the hip flexors can reduce pelvic mobility and therefore put excess strain on the lumbar spine during certain disciplines of movement – especially into flexion, following that, tight hamstring and hip extensors can also contribute to an exaggeration in the lordotic curve, which can potentially affect spinal loading mechanisms and lead to injury . The tightness in hip flexors and hamstrings can lead to a Sway Back posture (see figure). In this posture the muscular tightness causes an anterior pelvic tilt and therefore excessive lumbar extension which compresses the lumbar vertebra - this position can predispose patients to lumbar facet sydnrome.

The relationship between flexibility and lower back pain, however, is still largely based around theory and there are yet to be a number of high-quality experiments/investigations to either support or refute this hypothesis.

Strength and Low Back Pain

Muscle strength is the contractile force a muscle is able to produce.
The large muscles of the back (See anatomy section) are often thought of as synonymous with back strength. It is a commonly held belief that having 'strong' back muscles will support the back and prevent back pain however there is conjecture in the literature surrounding this theory. 

Many common exercises such as prone extensions, deadlifts, and low-rows are thought to strengthen the back muscles and 'stabilize' the spine and help prevent future back pain.  

Muscle strengthening exercises form part of the NICE treatment guidelines for Early management of persistent non-specific low back pain.



                                                                                

Measures of Back Strength

There are a variety of measures targeted at assessing muscular strength e.g. one rep max, isokinetic dynamometry, manual muscle testing etc.

Muscle strength with regards to the lower back is commonly researched as a proxy measure of ‘physical capacity’ which also includes muscle endurance and joint mobility ( ) although there is a lack of sufficient high quality evidence surrounding reproducibility of current physical capacity measures in healthy subjects and in patient groups. ( ). When researching lower back strength in relation to the prevalence of LBP, isokinetic maximal flexion and extension, calculated with an isokinetic dynamometer, isoinertial dynamic testing and isokinetic lifting force are commonly used ( There is some evidence to show that isokinetic measurement is reproducible and valid ( )

Evidence Review

A systematic review from 2007  evaluated evidence on the relationship between physical capacity and future low back and neck/shoulder pain. It was the first systematic review of longitudinal studies assessing the link between physical capacity and LBP.
Thirteen high-quality studies reported no association between trunk muscle strength and future risk of low back pain. The risk ratios were insignificant between low and high isometric strength (0.6 and 1.2 respectively), however, five high-quality studies have shown that poor trunk muscle strength is a significant predictor of LBP and two other high-quality studies found high strength as a risk factor. The results of this systematic review, therefore, are inconclusive one way or another in terms of the relationship between trunk strength and LBP. The review is further summarised in the table below.

A more recent study looking into LBP in male adolescents found isometric and isoinertial trunk performance was not significantly associated with LBP although they did find that regular sports participation was associated with LBP (93.9%:67.9% LBP + sport: No LBP + sport) . 
Another paper by evaluating the strength and cross-sectional area of extensor muscles in chronic LBP patients states that ‘weakness of the back muscles can lead to LBP’. The evidence this paper has used to support their own research actually contradicts the basis of their paper and is highlighted here as a good example of low-quality research in the area based on commonly held beliefs rather than evidence-based theory. 

Clinical Relevance

The research is inconclusive with regards to strength and low back pain however there is good evidence that poor trunk muscle strength is a risk factor for LBP. The evidence has so far failed to establish causality. Clinical guidance e.g. NICE guidelines still recommend strength exercises as part of a rehab program for BP.

Bottom Line

An argument can be made for or against using strengthening exercises as a preventative measure for back pain More high-quality research is needed to determine if either low or high strength is a risk factor for LBP.

Overall we have found that there is insufficient high-quality evidence in the area of fitness and prognosis of future back pain due to the lack of prospective studies. Many of the studies fail to use gold-standard measures as a reference, though we have shown with lower quality evidence that obesity, low isometric strength, and reduced muscular endurance are related to LBP however the literature is indecisive of the causality.