Non-specific low back pain (LBP) is a common con-dition that results in considerable discomfort and dis-ability for patients and high health and social carecosts.1–3 Numerous interventions commonly pre-scribed by physiotherapists and other healthcareproviders can play a role in the prevention and treat-ment of LBP. However, a definitive answer in respectof the most effective and efficient treatment for LBPis still the topic of much debate and research.4–6
Exercise has been suggested as an effective treatmentfor LBP,7–9 but research in this area has been plagued
by methodological challenges, the wide diversity inexercise interventions and the presence of possibleconfounders in the diverse group of patients withnon-specific LBP.10,11
Multiple clinical guidelines have been compiled to assistpractitioners with providing effective and efficient treat-ments for back pain.12–14 Where available, randomisedcontrolled trials (RCTs) and systematic reviews (SRs)have provided the basis for these guidelines. However,many of these RCTs have a number of limitations, mostnotably: (i) small sample size; (ii) low methodologicalquality; and (iii) inadequate or inappropriate statisticaltests to analyse the results.11,15,16 Most SRs in the area of
A SYSTEMATIC REVIEW AND SYNTHESIS OF HIGHERQUALITY EVIDENCE OF THE EFFECTIVENESS OF
EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOWBACK PAIN OF AT LEAST 6 WEEKS’ DURATION
DRIES M. HETTINGA1, ANNE JACKSON1, JENNIFER KLABER MOFFETT2, STEPHEN MAY3, CHRIS MERCER4, STEVE R. WOBY5
1Research and Clinical Effectiveness Unit, Chartered Society of Physiotherapy, London, UK2Institute of Rehabilitation, University of Hull, Hull, UK
3Faculty for Health and Wellbeing, Sheffield Hallam University, Sheffield, UK4Physiotherapy Department, Worthing and Southlands Hospitals NHS Trust,
Upper Shoreham, Shoreham-by-Sea, UK5Physiotherapy Department, North Manchester General Hospital, Manchester, UK
Systematic reviews and randomised controlled trials (RCTs) generally support the use ofexercise interventions to reduce pain and improve function in patients with chronic non-specific low back pain (LBP). However, many RCTs in the field of LBP include small numbersof subjects, have significant methodological limitations and use diverse exercise interventions.This review shows that the smaller RCTs often overestimate the true effectiveness or fail to detect truebenefits. Also, statistically significant results from RCTs of low methodological quality might not bevalid. This review showed that evidence from RCTs that are larger (≥ 40 subjects in exercise group),score high on the adapted van Tulder methodological quality criteria (≥ 5/10) and have used adequatestatistical tests, support the use of exercise for patients with LBP of at least 6 weeks’ duration, althoughthe effect sizes tend to be smaller. This higher quality evidence particularly supports the use ofstrengthening exercises, (organised) aerobic exercises, general exercises, hydrotherapy and McKenzieexercises for back pain of at least 6 weeks’ duration.
Keywords: Exercise, low back pain, systematic review
Physical Therapy Reviews 2007; 12: 221–232
LBP fail to recognise all three limitations or the effect ofeach limitation has not been clarified.
In addition to these potential shortcomings in thedesign of RCTs, individuals with non-specific LBP repre-sent a heterogeneous group of patients, which conse-quently means that large sample sizes are required inorder to detect clinically and statistically significantresults.11 Combining results of multiple smaller RCTs inSRs or meta-analyses can be difficult due to the greatvariation in exercise interventions employed in the variousRCTs.7 Moreover, research in other areas has shown thatevidence from large RCTs might contradict evidence fromsystematic reviews on multiple smaller RCTs.17
The limitations described above might explain whymany previous SRs on exercise for non-specific LBP haveonly found exercise to be of moderate benefit.7,18 Recentattempts to extract more specific information on whatexercise programmes should be prescribed for LBP haveshown promising results.8,9 However, limitations in theprimary studies that formed the basis of these reviewsremain an obstacle for compiling high-quality recommen-dations that can be widely generalised. It is, therefore, ofinterest to explore the effect of sample size, methodologi-cal quality and statistical rigour on the recommendationsfor exercise interventions in the treatment of LBP.
For this review, we defined persistent or chronic LBPas pain persisting for 6 weeks or more. Although otherdefinitions have been used, 6 weeks is beyond the periodof spontaneous recovery for much back pain.2,19
Moreover, specific exercise interventions have shown tobe of limited value for individuals with acute LBP (i.e.less than 6 weeks’ duration).7,12,13
The aim of this review is, therefore, to summarise thebest available evidence for exercise interventions for thetreatment of non-specific LBP of at least 6 weeks’ dura-tion. In an attempt to overcome the limitations inherentwith existing reviews, only those RCTs that included alarge sample size, were of good methodological quality,and employed adequate statistical analysis were includedin this review. Since the majority of the RCTs have moni-tored changes in pain and function, these two outcomeshave been used for detailed quantitative analyses.
METHODOLOGY
This review was part of a project aimed at developingphysiotherapy specific guidelines for the treatment ofpersistent low back pain, which will be published bythe Chartered Society of Physiotherapy (UK).
Literature search
An extensive literature search was conducted in 2003 toidentify SRs and RCTs on physiotherapy interventions
for the treatment of LBP. This search in MedLine,EMBASE, CINAHL, AMED, Cochrane, PEDro andthe library collection of the Chartered Society ofPhysiotherapy (UK) resulted in 5065 articles. In 2005, anupdated search was conducted using the same databasesto identify any new SRs or RCTs published before 1 June2005. This search resulted in an additional 2660 articles.SRs were used to identify relevant RCTs, while the searchon RCTs was aimed at finding RCTs not included in theSRs or published after the last search date of the SRs.
RCTs were included if they met the following criteria:
1. Patients (> 18 years of age) with non-specific lowback pain of at least 6 weeks’ duration.
2. Exercise was used as the single physiotherapy inter-vention for at least one group in the trial. RCTs werenot excluded if exercise was combined with othernon-physiotherapy interventions (e.g. general practitioner [GP] care, medication).
3. The effectiveness of exercise was tested in at leastone of the following areas: pain, function,psychological status or return to work/sick leave.
The methodological quality of the included trials wasassessed by two reviewers using an adapted version ofthe van Tulder criteria.20 The original scale consists of 24criteria, 10 were thought to be the most relevant for thisreview. Nine of the criteria relate to the internal validityof the RCT and one criterion relates to the similarities ofmain baseline characteristics/predictors (see Table 1 fora list of all criteria). The other criteria included withinthe original 24-item van Tulder list were not used tocalculate the score in this review, because they wereeither already included in the scope of this review (e.g.eligibility criteria, description of interventions) orqualitatively assessed (e.g. statistical criteria). Samplesize was considered separately since this is not includedin the van Tulder criteria. Instead of using the totalnumber of subjects in the RCTs, we have used thenumber of subjects in the exercise group as an indicationof sample size. This controls for RCTs with a relativelylarge sample size, but multiple subgroups. The smallestRCTs (≤ 15 subjects in the exercise group) that alsoscored very low on the methodological quality scale (≤ 2out of the 10 points) were not considered in this review.
Quantitative analysis
Most of the RCTs monitored pain and function beforeand after intervention; therefore, these two outcomeswere analysed quantitatively. Any outcome measure forpain and function was included in this analysis. Forevery RCT, the change in pain and function (after anyfollow-up period) was calculated as a percentage of the
222 HETTINGA, JACKSON, KLABER MOFFETT, MAY, MERCER AND WOBY
baseline score of that group. These percentage changeswere plotted so that the change in the exercise group wasdisplayed on the x-axis, and the control or alternativegroup on the y-axis (Figs 1 and 2). Some RCTs reportedP-values for this difference in change, while in other casesthe statistical significance of this value was unknown.These L’Abbe plots give a clear picture of all the data inthe included RCTs and facilitate identification of possibleoutliers.21 Points towards the bottom-right corner of theplots indicate that the exercise intervention was better,
while points towards the top-left corner favour the con-trol interventions. Points along the line y = x indicatethat the effectiveness of the exercise intervention wassimilar to the control intervention.
To assess the effect of sample size and methodologicalquality, the difference in change (percentage changein the exercise group minus the percentage change inthe control/alternative intervention) was plotted ver-sus the quality score of the trial and the number ofsubjects in the exercise group (Figs 3 and 4).
EFFECTIVENESS OF EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOW BACK PAIN 223
Fig. 1. Percentage improvement in pain (on any outcomemeasure at any follow up point) for the exercise group and thecorresponding control/alternative group. Each point representone observation on the difference in change: filled squares,statistically significant; open squares, non-statistically signifi-cant; open triangles, unknown level of statistical significance.
Fig. 2. Percentage improvement in function (on any outcomemeasure at any follow up point) for the exercise group and thecorresponding control/alternative group. Each point representone observation on the difference in change: filled squares,statistically significant; open squares, non-statistically signifi-cant; open triangles, unknown level of statistical significance.
Fig. 3. Association between number of subjects in the exercise group and the difference in percentage change between theexercise group and the control/alternative group. Each point represent one observation on the difference in change: filled squares,statistically significant; open squares, non-statistically significant; open triangles, unknown level of statistical significance.
In the above mentioned figures, outcomes after anyfollow-up period are grouped in one graph. To evaluatethe effect of follow-up period on outcome, the changeover time was plotted versus the follow-up period (Figs5 and 6).
Qualitative analysis
Since small sample size, low methodological quality andinadequate statistical testing can distort the results ofRCTs, only results from large, good quality RCTs withadequate statistical tests comparing the difference in
change between intervention groups were considered forthe qualitative analysis. To distinguish larger from smallertrials and low quality from higher quality trials, arbitrarycut-off points were agreed. Methodological quality wasassessed on a 10-point scale and RCTs were considered tobe of lower methodological quality if they scored fewerthan the median score on the 10-point quality score.Consequently, RCTs scoring the median score or betterwere considered to be of higher methodological quality.
Although a power analysis should determine ade-quate sample size, a pragmatic approach was used in thisreview due to limited resources for this project. An RCTwith ≥ 40 subjects in the exercise group was defined as
224 HETTINGA, JACKSON, KLABER MOFFETT, MAY, MERCER AND WOBY
Fig. 4. Association between methodological quality score and difference in percentage change between exercise group andcontrol/alternative group. Each point represent one observation on the difference in change: filled squares, statisticallysignificant; open squares, non-statistically significant; open triangles, unknown level of statistical significance.
Fig. 5. The percentage change in pain over time. R2 of the best-fitted trend line is 0.0016.
large. This cut-off point was adapted from work byMoore et al.15 on the effect of random chance on vari-ability in patients’ response to pain relief interventions.
The third criterion for best available evidence in thisreview is adequate statistical testing to determine thelevel of statistical significance for the difference inchange between the exercise group and control/alter-native group. Given that LBP is known to improve inmany patients over time,2,19 comparing pre- and post-scores within one group is not sufficient to test theeffectiveness of an intervention. This review will onlyconsider the difference in change between the exercisegroup and the comparator group and the level of sta-tistical significance for that difference in change.
Although all RCTs that fulfilled the three inclusion cri-teria were included in the quantitative analysis (minus thevery small RCTs that also scored low on the quality scale),only RCTs that were large, high quality and employedadequate statistical tests were used to recommend specificexercise interventions for chronic non-specific LBP.
RESULTS
Table 1 displays the 31 included RCTs with the qual-ity score and sample size for each trial. The medianmethodological quality score was five and 16 RCTswere considered to be of higher methodological qual-ity (≥ 5 out of 10). None of the included trials scoredthe maximum score. The total number of subjects var-ied widely between the included RCTs (n = 36–1334),but 20 of the 31 included RCTs had fewer than 40subjects in the exercise group. Only seven trials wereboth of high quality (≥ 5 on quality score) and large
(≥ 40 subjects in exercise group). All of these sevenRCTs reported adequate statistical tests that directlycompared the change in the intervention group withthe change in the control/alternative group.
If all RCTs were pooled, exercise resulted in similarimprovements in pain and function as alternativeinterventions (30–32%), while control interventions(i.e. no treatment or placebo) resulted in considerableless benefit (1–16%). When only considering evidencefrom large, good quality RCTs with adequate statisti-cal testing, the effect of exercise on pain and functionwas slightly smaller (26–28%), while the effect ofalternative interventions remained similar (30–32%)and the effect of control interventions was slightlyhigher (8–22%). It should be noted, however, that theeffect of control interventions was based on a small num-ber of observations. Full details are presented in Table 2.
The (percentage) change in pain in the exercisegroup and the corresponding control/alternativeintervention is displayed in Figure 1. A large numberof the points are located around the line of no differ-ence (y = x), although there is a tendency for signifi-cant differences (displayed as black squares) to favourthe exercise intervention. This is more evident for thefigure displaying the effect on function (Fig. 2).
Figure 3 gives the number of subjects in the exercisegroup on the x-axis and the difference in change (per-centage change in exercise group minus percentagechange in control group) on the y-axis. Any blackdots appearing above the x-axis, therefore, representtrials where a statistically significant finding wasreported in favour of the exercise intervention; anyblack dots appearing below the x-axis represent a sig-nificant finding in favour of the control/comparative
EFFECTIVENESS OF EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOW BACK PAIN 225
Fig. 6. The percentage change in function over time. R2 of the best-fitted trend line is 0.0068.
226 HETTINGA, JACKSON, KLABER MOFFETT, MAY, MERCER AND WOBY
Table 1. Characteristics of included RCTs
Reference Interventions Methodological n in exercise Stat. test Outcome measuresquality score group to compare included in
(criteria) (total n) changes? this review
Callaghan et al. General exercise (8 sessions) vs 2 (B,I) 30/30 (80) Yes Pain (VAS)(1994)31 general exercise (4 sessions) vs control
Donchin et al. Strengthening exercise versus 5 (A,B,H,I,J) 46 (142) Yes Pain (painful months), et al. (1990)22 backschool versus control function (Oswestry)
Elnagger et al. Mobilising exercise (flexion) vs 5 (A,B,G,I,J) 28/28 (56) Yes Pain (Modified McGill PQ)(1991)36 mobilising exercise (extension)
Gur et al. General exercise vs general exercise 5 (B,E,G,H,I) 25 (75) Yes Pain (VAS), function (2003)37 + laser therapy versus laser therapy (Roland DQ, Oswestry)
Helmhout et al. Strengthening exercise (high intensity) 3 (A,G,I) 41/40 (81) Yes Function (Roland DQ, (2004)38 vs strengthening exercise (low intensity) Oswestry)
Hemmila et al. General exercise versus physical 7 (A,B,D,G, 35 (132) Yes Pain (VAS)(1997)33, (2002)34 mixed methods versus bone setting H,I,J)
Johannsen et al. Aerobic exercise versus 1 (I) 20/20 (40) Yes Pain (0–4 scale for pain), function(1995)39 co-ordination exercise (patient’s rating of impairment),
return to work (sick days)
Jousset et al. General exercise versus functional 4 (B,E,H,I) 41 (86) No Pain (VAS), function (impact (2004)40 restoration on activities Dallas Pain Q),
return to work (sick leave)
Kankaanpaa General exercise versus placebo 3 (E,H,I) 30 (59) Yes Pain (VAS), function (Pain et al. (1999)28 (massage + thermal therapy) and Disability Index)
Kendall & Strengthening exercise (extension) 2 (H,I) 14/14/14 No Pain (presence of pain onJenkins versus general exercise versus (42) 3-point scale)(1968)41 strengthening exercise (isometric)
Klaber Moffett General exercise versus GP care 7 (A,B,E,G, 89 (187) Yes Pain (Aberdeen Back Pain et al. (1999)27 H,I,J) Scale), function (Roland DQ),
psychological status (Fear Avoidance Q)
Koumantakis General exercise versus core 7 (A,B,E,G,H, 26/29 (55) Yes Pain (McGill, VAS), function et al. (2005)42 stability exercise I,J) (Roland-Morris DQ),
psychological status (TampaKinesiophobia scale)
Kuukkanen & General exercise versus control 4 (B,E,H,I) 29 (90) No Pain (Borg scale), function Malkia (intensive training group excluded (Oswestry)(2000)43 due to non-random allocation)
Martin et al. General exercise (strengthening and 1 (I) 12 (36) Yes Pain (0–5 point scale for hourly (1986)31 mobilising) versus strengthening pain rating), function (VAS for
exercise (isometric) versus placebo difficulties with ADL)
Manniche et al. General exercise (high intensity) vs 7 (A,B,D,G, 27/29 (105) No Pain (0–10 point scale), function (1988)44 general exercise (low intensity) H,I,J) (15 ADL questionnaire)
versus physical mixed methods
Manniche et al. Strengthening exercise (high intensity) 2 (G,I) 33/36 (105) Yes Pain (LBP Rating scale for pain),(1991)45 versus strengthening (low intensity) function (LBP Rating scale for
versus control (massage + disability and physical hot compresses + mild exercise) impairment)
EFFECTIVENESS OF EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOW BACK PAIN 227
Reference Interventions Methodological n in exercise Stat. test Outcome measuresquality score group to compare included in
(criteria) (total n) changes? this review
Mannion et al. Aerobic exercise versus general 9 (A,B,D,E, 44/47 (148) Yes Pain (VAS), function (Roland (1999)24, (2001)46 exercise versus physical mixed F,G,H,I,J) Morris DQ), psychological status
methods (Modified Zung Questionnaire for depression, Fear Avoidance Beliefs Questionnaire)
McIlveen & Hydrotherapy versus control 6 (A,B,E,G,H,I) 45 (109) Yes Pain (McGill Pain Questionnaire), Robertson function (Oswestry)(1998)27
Petersen et al. Strengthening exercise versus 6 (A,B,E,H,I,J) 128/132 (260) Yes Pain (Manniche LBP Rating scale), (2002)23 McKenzie function (15 ADL items), return
to work
Rasmussen-Barr Core stability exercise versus 2 (B,I) 24 (47) Yes Pain (VAS), function (Oswestry, et al. (2003)47 manual therapy VAS for disability rating)
Reilly et al. General exercise (supervised) versus 2 (H,I) 20/20 (40) No Pain (VAS)(1989)48 general exercise (unsupervised)
Risch et al. General exercise versus control 4 (B,H,I,J) 31 (54) Yes Pain (West Haven Yale Multi-(1993)19 (waiting list) dimensional Pain Inventory),
function (Sickness Impact Profile)
Rittweger et al. Strengthening exercise versus 4 (B,E,H,I) 30/30 (60) Yes Pain (VAS), psychological status (2002)49 vibration exercise (Allgemeine Depression Skala)
Shaughnessy & Core stability exercise versus control 2 (B,I) 20 (41) Yes Function (Oswestry, Roland-Caulfield (2004)29 (no intervention) Morris DQ)
Snook et al. General exercise versus prevention of 6 (B,E,F, 36 (85) No Pain (0–10 scale), function (Mean (1998)50 early morning lumbar flexion G,H,J) disability/impairment)
Storheim et al. Aerobic exercise versus cognitive 5 (A,B,G,I,J) 30 (93) Yes Pain (VAS, pain diary), function (2003)51 intervention versus GP care (Roland-Morris DQ), psycho-
logical status (Fear Avoidance Belief Questionnaire), return to work (Sick-listing)
Torstensen et al. General exercise versus aerobic 8 (A,B,D,E, 71/70 (208) Yes Pain (VAS), function (Oswestry), (1998)25 exercise (walking) versus physical G,H,I,J) return to work (Return to work)
Turner et al. General exercise versus general 4 (B,G,H,I) 24 (96) Yes Pain (McGill), function (Sickness (1990)32 exercise + operant-behaviour versus Impact Profile), psychological
operant-behaviour status (CES Depression Scale)
UK BEAM General exercise + GP care versus 6 (A,B,D, 310 (1334) Yes Pain (Von Korff scale), function (2004)4 general exercise + manual therapy + H,I,J) (Roland DQ, Modified Von Korff
GP care versus manual therapy + scales), psychological status (Fear GP care versus GP care Avoidance Questionnaire)
Yozbatiran et al. General exercise (land-based) vs 5 (B,E,H,I,J) 15 (30) No Pain (VAS), function (Oswestry)(2004)53 general exercise (in the pool)
RCTs in bold have fulfilled the three criteria of higher quality trials (large, good methodological quality and adequate statistical testing).Methodological quality criteria: (A) Treatment allocation: Was the treatment allocation concealed? (B) Were the groups similar atbaseline regarding the most important prognostic indicators? (e.g. age, duration of complaints, value of main outcome measures). (C)Was the care provider blinded to the intervention? (D) Were co-interventions avoided or comparable? (E) Was the compliance rate (ineach group) unlikely to cause bias? (F) Was the patient blinded to the intervention? (G) Was the outcome assessor blinded to theintervention? (H) Was the withdrawal/drop-out rate unlikely to cause bias? (I) Was the timing of the outcome assessments in bothgroups comparable? (J) Did the analysis include an intention-to-treat analysis? These criteria are derived from van Tulder et al.21
group. It appears that smaller studies report morevarying differences in change than the larger studies.Similarly, although less evident, RCTs scoring loweron the quality scale report more variation in differ-ence in change than RCTs scoring higher on the samescale (Fig. 4).
When all observations are grouped, no clear effectof follow-up period on the percentage change can beidentified (Figs 5 and 6). Best-fitted, linear trend linesin both occasions had R2 of close to zero.
For the qualitative analysis, exercise interventionswere grouped according to the type of exercise usedand the following exercises were identified (based onthe descriptions given in the original articles): mobil-ising exercises (2 RCTs), strengthening exercises (7RCTs), aerobic exercises (6 RCTs), general exercises(15 RCTs), core stability exercise (3 RCTs), hydrother-apy (1 RCT), McKenzie exercises (1 RCT) and co-ordination exercises (1 RCT). The individual RCTs inthese groups are noted in Table 1. There was evidencefrom at least one large, good quality RCT with robuststatistical analyses to support the following statements:
1. Strengthening exercises are more effective than notreatment or back schools in reducing pain.22
Also, strengthening exercises are equally aseffective as McKenzie exercises in reducing pain,although the short-term effect is less clear.Strengthening exercises are equally as effective asMcKenzie exercises in improving function andimproving psychological status.23
2. Organised aerobic exercises are more effectivethan physical mixed methods in improvingpsychological status, although the short-termeffect is less clear. Organised aerobic exercises areequally as effective as physical mixed methods inreducing pain and improving function.25
Organised aerobic exercises are also equally aseffective as muscle reconditioning exercises inreducing pain and improving function andpsychological status.25 However, unsupervisedaerobic exercises are less effective than physicalmixed methods in reducing pain, but moreeffective in improving function25 and, in
comparison to general exercises, unsupervisedaerobic exercises are less effective in reducing painand improving function.25
3. General exercises are more effective than GP carein reducing pain and improving function,especially in the long-term.26 In addition, there isevidence from a very large trial that generalexercises are more effective than GP care inreducing pain and improving function andpsychological status.4 Compared to physical mixedmethods, general exercises are equally as effectivein reducing pain and improving function24,25 andmore effective in improving psychological status,although short-term psychological benefits areequal.24 In addition, general exercises are moreeffective than unsupervised aerobic exercises inreducing pain and improving function,25 butequally as effective as organised aerobic exercisesin reducing pain and improving function andpsychological status.25
4. Hydrotherapy is more effective than no treatmentin improving function and equally as effective inreducing pain.27
5. McKenzie exercises are equally as effective asstrengthening exercises in improving function,although in the short-term it might be moreeffective, and McKenzie is equally as effective asstrengthening exercises in reducing pain andimproving return to work.23
Note: For the qualitative analysis, timing of follow-upmeasurements was not taken into consideration,except where discrepancies in short-term (< 6months) and long-term results existed.
DISCUSSION
The aim of this review was to use the best availableevidence to evaluate the effectiveness of exercise inter-ventions for patients with non-specific low back painof at least 6 weeks’ duration. Only evidence from
228 HETTINGA, JACKSON, KLABER MOFFETT, MAY, MERCER AND WOBY
Table 2. Change in pain and function after any follow-up duration. Change is expressed as a percentage of the baseline value
Exercise interventions Alternative interventions Control interventionsChange (%) Observations (n) Change (%) Observations (n) Change (%) Observations (n)
PainAll RCTs considered 30.95 3408 30.46 2743 16.26 264Only best available evidence 25.80 2021 29.98 2042 22.00 50
FunctionAll RCTs considered 30.73 4204 32.31 4376 1.31 175Only best available evidence 27.65 24.97 33.56 3606 8.00 50
RCTs that were large (≥ 40 subjects in the exercisegroup), had good methodological quality (≥ 5/10 onthe quality score) and had directly compared andanalysed the change in the exercise group with thechange in the control/alternative group were used inthe qualitative analysis of this review. Although mostsystematic reviews assess methodological quality ofthe included trials, the effect of sample size and statis-tical quality on the conclusion has often not beenexplored. When only considering evidence from large,high-quality RCTs with adequate statistical testing,support was found for the use of strengthening exer-cises, (structured) aerobic exercises, general exercises,hydrotherapy exercises and McKenzie exercises forpain and disability reduction. Psychological statusand return to work were not always reported in theincluded RCTs; however, there was evidence to sup-port the use of strengthening exercise, McKenzieexercises, (structured) aerobic exercises and generalexercises for improving psychological status and theuse of McKenzie exercises and strengthening exercisesfor improving return to work.
Justification for only considering large, good qual-ity RCTs with adequate statistical testing came fromthe quantitative analysis of all potentially eligibleRCTs. Many RCTs reported changes in pain andfunction in the exercise group that were similar to thechanges on the same outcomes in the control or alter-native interventions (Figs 1 and 2). Statistically signif-icant differences between the changes in the exercisegroup and the comparator group have been reportedfor trials that found large differences between thetwo19,28–31 or trials that included large samplessizes.4,25,26 Figure 3 shows that large differencesbetween exercise and comparator differences havebeen reported mainly in the smaller trials, while thelarger trials reported statistically significant differ-ences that were much smaller.4,25,26 Smaller, but statis-tically significant, differences in effectiveness found inthe larger trials were of similar magnitude to resultsof some of the smaller trials. However, the smaller tri-als failed to show statistical significance of theseresults, probably resulting from insufficient statisticalpower. Moreover, the smaller trials and the lowerquality trials tended to report more often positiveeffects for the exercise intervention (shown by the factthat more points in Figs 3 and 4 are above the liney = 0). This might suggest publication bias as smallertrials with negative results are less likely to be pub-lished. Another explanation might lie in differences indifferences in subject characteristics. The smallerRCTs might have recruited subjects from a smallerand more specific population, while the larger trialsby definition have to recruit from a larger and, there-fore, probably more representative population.
It is also noteworthy that large superior effects ofexercise over comparator interventions have moreoften been reported in RCTs that score low on themethodological quality criteria (Fig. 4), possibly lead-ing to an overestimation of the true effectiveness ofexercise. Low methodological quality in RCTs limitsthe internal and external validity of the results andmay potentially mislead the clinician.
Justification for pooling all follow-up points in theabove quantitative analyses came from Figures 5 and6. There was no clear correlation between timing offollow-up and the change in pain or function. Itshould be noted, however, that these figures neithersupport nor refute long-term effects of exercise inter-ventions since the data presented in Figures 5 and 6are derived from multiple RCTs and do not representfollow-up data of individual treatment groups.
When all the results of only the large, good-qualityRCTs with adequate statistical testing are pooled, itappears that the effectiveness of exercise is similar toalternative interventions. Previous reviews that havepooled all exercise interventions found only moderatebenefits of exercise for LBP. However, clinically moreuseful recommendations can be made if the type ofexercise is specified. Hayden et al.8 concluded in theirreview and accompanying meta-regression analysisthat individually designed, supervised exercise pro-grammes that include strengthening and stretchingmay improve pain and function in chronic LBP.Discrepancies between the conclusion from Haydenet al.8 and the present review can probably beexplained by differences in exercise characteristicsincluded in the analysis (i.e. stretching was notincluded in our analysis, although it might overlapwith mobilising exercises) and by differences in weightgiven to methodological quality, sample size and sta-tistical rigour. Interestingly, some of the RCTsincluded in our review found exercise to be inferior toalternative interventions for chronic LBP,25,31–34
although only in one instance did such a findingemerge from a large, high quality RCT.25 Torstensenet al.25 reported that unsupervised walking was lesseffective than medical exercise therapy or conven-tional physiotherapy. The lack of supervision mightexplain this, as suggested by Hayden et al.8
Although this review gives valuable guidance forclinical practice, some limitations should be noted.First, the authors relied on information supplied inoriginal publications, which in some cases wasambiguous. In such cases, consensus was soughtbetween the authors of the present review, who are allfamiliar with the LBP literature. Second, this reviewincluded some outcome measures for pain, function,psychological status and return to work that had notundergone adequate psychometric testing. Despite
EFFECTIVENESS OF EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOW BACK PAIN 229
this, it should be noted that the higher quality studiesincluded within this review employed valid and reli-able measures for pain and function such as McGillPain Questionnaire, Aberdeen Back Scale, Roland-Morris Disability Questionnaire. Consequently, theuse of less well-established outcomes measures islikely to have had only a minimal impact upon thefinal conclusions of this review. Finally, whilst pre-senting the effectiveness of interventions as a percent-age of the baseline score enabled us to group variousoutcomes measures, this approach has a number ofdisadvantages. For instance regression to the meanmight have over-represented the larger changes.
CONCLUSIONS
Many RCTs on exercise for chronic, non-specific LBPhave limitations in methodological quality, samplesize and/or statistical rigour. This review has shownthat these limitations might have resulted in mislead-ing conclusions. Specifically, the results of RCTs withsmaller samples sizes, lower methodological qualityand inadequate statistical testing should be inter-preted with caution. Nevertheless, evidence fromlarger, higher quality RCTs with adequate statisticaltesting support the use of exercise interventions forpersons with LBP of at least 6 weeks’ duration. Inparticular, it would seem that strengthening exercises,(organised) aerobic exercises, general exercises,hydrotherapy exercises and McKenzie exercises are aneffective form of exercise intervention for individualswith persistent LBP.
Future RCTs on exercise for LBP should includelarge sample sizes, based on appropriate power calcu-lations, follow strict methodological guidelines anduse adequate statistical testing in order to allow forthe true effectiveness of exercise for non-specific LBPto be detected.11 Moreover, sub-classification of non-specific LBP and exploring what exercises might ben-efit which sub-group, might improve effectiveness andfurther guide clinical practice.
ACKNOWLEDGEMENTS
The authors would like to thank the people who assistedwith conducting this review (Katherine Dean, Jo Jordan,Jenni Hall and Sharlene Ting), the Library staff at the CSP(Samantha Molloy, Linda Griffiths, Andrea Peace, AnnaSewarniak and Alison Jinks), other staff at the CSP (AlexWarne, Helen Whittaker, Susan Williams) and all mem-bers of the Guideline Development Group (Panos Barlos,Sarah Ferguson, Susan Greenhaulgh, Vicki Harding,
Deirdre Hurley-Osing, Denis Martin, Jude Monteath,Lisa Roberts, Nia Taylor). Funding for this project wasreceived from the Chartered Society of Physiotherapy andthe CSP’s Charitable Trust, London, UK.
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EFFECTIVENESS OF EXERCISE INTERVENTIONS FOR NON-SPECIFIC LOW BACK PAIN 231
232 HETTINGA, JACKSON, KLABER MOFFETT, MAY, MERCER AND WOBY
DRIES M. HETTINGA
School of Health Sciences and Social Care, Brunel University, Uxbridge UB8 3PH, UK
ANNE JACKSON (for correspondence)
Research and Clinical Effectiveness Unit, Chartered Society of Physiotherapy, 14 Bedford Row, London WC1R 4ED, UK
