International Journal of Osteopathic Medicine 10 (2007) 42e49

www.elsevier.com/locate/ijosm

Research report

The effects of high-velocity, low-amplitude manipulationand muscle energy technique on suboccipital tenderness

Luke Hamilton a,*, Caitlin Boswell a, Gary Fryer a,b,c

a School of Health Sciences, Victoria University, Melbourne, Australiab Centre for Ageing, Rehabilitation and Exercise Science, Victoria University, Melbourne, Australia

c A.T. Still Research Institute, Kirksville, MO, USA

Received 25 March 2007; received in revised form 15 August 2007; accepted 21 August 2007

Abstract

Background and objectives: High-velocity, low-amplitude (HVLA) manipulation and muscle energy technique (MET) are commonlyadvocated by manual therapists to resolve pain and dysfunction. The aim of this controlled, single blinded study was to investigatewhether HVLA manipulation of the occipitoeatlantal (OA) joint and/or an MET stretch had an effect on pressure pain thresholds

(PPT) in the suboccipital musculature in an asymptomatic population.Methods: Participants (N¼ 90; mean age¼ 23� 5; 29 males and 61 females) were screened for suitability and PPT measurementswere made using a hand-held electronic algometer which was positioned centrally in the suboccipital region. Participants were ran-

domly allocated into three intervention groups and then received an HVLA thrust to cavitate the right and left OA joints, an METstretch applied to the suboccipital muscles bilaterally, or a sham ‘functional’ technique. Post-intervention PPT measurements wererecorded at 5 and 30 min.

Analysis: Analysis of the PPT data using a SPANOVA revealed a significant difference over time (F2,174¼ 8.80, P< 0.01), but nosignificant difference between the groups (F2,87¼ 0.08, P¼ 0.93). Within-group changes were further analysed using paired t-testsand repeated measures ANOVA which revealed significant changes at 5 min post treatment in the HVLA (P< 0.01) and METgroups (P< 0.01), but not in the control (P¼ 0.35). At the 30 min interval a significant change was calculated for the MET group

(P< 0.03), but not in the HVLA (P¼ 0.29) or control group (P¼ 0.21).Conclusion: Neither HVLA manipulation nor MET significantly changed the PPT of the suboccipital muscles in asymptomatic par-ticipants. Both techniques produced greater mean increases in PPT and effect sizes compared to the control group, and investigation

of the effect of these techniques in a symptomatic population is recommended.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Manipulation; Stretching; Suboccipital; Muscles; Occipitoeatlantal joint; Algometry; Osteopathic medicine

1. Introduction

High-velocity, low-amplitude (HVLA) manipulationand muscle energy technique (MET) are manual tech-niques advocated by osteopathic authors to restore spi-nal range of motion and to decrease pain.1e3 HVLA

* Corresponding author. 182 Fulham Road, Gulliver QLD 4812,

Australia. Tel.: þ61 402 908 631.

E-mail address: lukass5@hotmail.com (L. Hamilton).

1746-0689/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijosm.2007.08.002

involves the application of a fast non-forceful thrust,which is often associatedwith an audible ‘pop’ or ‘crack’.1

MET differs from HVLA in that it is an active techniquerequiring the patient to contribute the corrective force.2

MET has been described as a valuable treatment tech-nique because of the many claimed therapeutic benefitsresulting from a single procedure, including lengtheningand strengthening muscles, increasing fluid mechanicsand decreasing local oedema, mobilising restrictedarticulations and reducing pain and disability.2,4e6 The

43L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

application ofMET involves the voluntary contraction ofpatient muscle in a precisely controlled direction, at vary-ing levels of intensity and against a distinctly executedcounterforce which is applied by the operator.2

A small number of studies support the short-term hy-poalgesic effects of HVLA manipulation.7e10 Terretet al.7 reported an immediate rise in cutaneous painthreshold following spinal manipulation, and noted dis-tinct and progressive elevation in pain tolerance within2 min, lasting at least 10 min post-manipulation, in com-parison to the control group. Similarly, Vernon et al.8

found individuals suffering chronic neck pain who re-ceived HVLA manipulation experienced a significantrise (40e55%) in pressure pain thresholds (PPT) forall four points around the manipulated spinal segment,as compared to the small change following mobilisationtreatment. However, because of the small sample size(n¼ 9), the findings of this study should be treatedwith caution.

Fryer et al.9 reported that both HVLA and mobilisa-tion had a significant effect on perceived tenderness overthe thoracic spine in a group of asymptomatic partici-pants. However, HVLA was less effective for increasingthe PPTs when compared with mobilisation, and a signif-icant difference existed between the mobilisation andcontrol group (P¼ 0.01), but not between the manipula-tion and control group (P¼ 0.67). These findings con-flicted with those of Cassidy et al.10 who reported thata single HVLA technique was significantly more effec-tive in 85% of participants when compared to METfor treating neck pain. In recent systematic reviews, spi-nal manipulation has been recommended with someconfidence to be a viable option for the treatment ofboth low back pain and neck pain.11,12

The mechanisms by which HVLA produces a hypoal-gesic effect are largely speculative. Melzack and Wall13

proposed the gate control theory, where large diametermyelinated neurons from mechanoreceptors modulateand inhibit the smaller diameter nociceptive neuronal in-put at the spinal cord level. Joint manipulation wouldactivate mechanoreceptor afferents and may thereforeprovide pain relief by activating this spinal gate controlmechanism. Any technique that stimulates joint propri-oceptors via the production of joint movement or thestretching of a joint capsule has been proposed to be ca-pable of inhibiting pain.14

It has also been speculated that HVLA may havea therapeutic effect by reducing zygapophyseal joint ef-fusion and peri-articular oedema by improving thedrainage of flow within a joint, or by stretching of zyg-apophyseal joint capsules to improve joint range of mo-tion. It has been suggested that manipulative techniquesplay a role in descending pain control systems projectingfrom higher centres such as the dorsal periaqueductalgrey (dPAG) to the spinal cord.15 Manipulation inducedhypoalgesia and the improvement of proprioception and

motor control may play a role in the short and long-term relief of patients.14 These proposals, however,would not be relevant to hypoalgesia following HVLAin asymptomatic individuals.

MET has been advocated as a safer alternative toHVLA, particularly for the upper cervical spine.2,16,17

The origins of MET are claimed to extend back to thedays of A.T. Still,18 the technique was developed andpopularised by Mitchell2 and despite many texts advo-cating the use of MET it is surprising how limited the re-search is with regards to its effectiveness.4e6 Of the fewstudies published to date, most have examined the effectof MET for increasing flexibility and range of mo-tion.19e23 Only one study was found that examined theeffect of MET on spinal pain, and this study suggestedthat MET was effective for reducing pain and disabilityin patients with low back pain.4

Pressure algometry is a method of quantifying softtissue tenderness which has been proven to be very relia-ble.24e27 The PPT is defined as the least stimulus inten-sity at which an individual perceives pain; it is the pointwhere the sensation of pressure turns to one of pain.24

Sterling et al.26 found that the measurement of painthresholds with an electronic algometer was reliable be-tween weeks (1 week period) in both asymptomatic par-ticipants and in participants with chronic back pain.Nussbaum and Downes25 recommended that the mea-surements be taken by one examiner, because this wasmore reliable than from multiple examiners.

Significant regional differences in spinal PPT valueshave been reported, where the PPT increases in a caudaldirection. Cervical segments have been determined to bethe most sensitive to pressure, followed by the thoracicregion and the lumbar spine.28,29 Vanderweeen et al.24

suggested this pattern might be due to the higher noci-ceptor density in the cervical spine.

The suboccipital region is one zone of particular clin-ical importance when assessing and treating the cervicalspine.30 This triangular area inferior to the occipitalbone includes the posterior aspects of C1 and C2 verte-brae and four small muscles: rectus capitis posteriormajor, rectus capitis posterior minor (RCPMn), obli-quus capitis superior and obliquus capitis inferior.The suboccipital muscles have been suggested to actas a ‘kinesiological monitor’ for the sense of proprio-ception, as well as having an affect on movement ofthe head.30 The RCPMn has been described by McPart-land and Brodeur16 as containing a high density ofmuscle spindles and therefore dysfunction at this levelmay disrupt proprioception of the head and cervicalspine. Dysfunction of the suboccipital muscles hasbeen claimed to arise from any trauma that causessudden or extreme movement of the head, or simplyfrom chronic postural stresses, such as those occurringduring slouching and the typical ‘‘chin poking’’posture.16,31

44 L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

It has been proposed that the suboccipital muscles area causative factor in both cervicogenic neck pain andheadache and in addition may become atrophic furthercomplicating the pain syndrome.16,32e35 The RCPMnhas been found to be continuous with the posterior at-lanto-occiptal membrane, which is intimately relatedto the dura mater.16,32 This relationship is important asthe RCPMn prevents crimping of the dura at the occipi-toeatlantal junction when the head is extended. Chronicpostural stress has been proposed to cause hypertonicityof the suboccipital musculature, leading to tension beingtransmitted to the pain sensitive dura resulting in chronicheadaches.16,32 Hallgren et al.36 examined patients withchronic headaches and neck pain using MRI and foundthat some individuals exhibited replacement of suboccipi-tal skeletalmusclewith fatty tissue. Thismay result in a re-duction ofmuscle spindle and golgi tendon organ density,with a decrease in proprioceptive information transmit-ted to the central nervous system, which may result inpostural destabilisation. It may also be possible thatproprioceptive changes could lead to a reduction in themechano-receptive gating effect at cord level, and as a re-sult be a contributing factor to neck pain. While cervicalproprioception is recognised as an essential component inmaintaining balance, adequate treatment of the region isimperative, especially when treating the elderly commu-nity. Research investigating the suboccipital region andwhat effects manual treatment may have on a potentialproblematic area is therefore warranted.

To date, no studies have examined the effect of HVLAmanipulation orMETon suboccipital tenderness. The lit-tle research into HVLA has focused on the mid to lowercervical spine, with emphasis on different techniquesapplied to this area and what effects they have had on de-creasing pain and increasing the range of motion.8,10,26,35

Similarly, MET is commonly advocated by authors ofmanual therapy for treatment of somatic dysfunctionand muscle pain, although limited research exists intothe effects of MET on pain and tenderness.4e6 Manualtechniques have been reported to lower spinal PPT inan asymptomatic population.9 The aim of this studywas to investigatewhetherHVLAmanipulation of the oc-cipitoeatlantal joint or an MET stretch to the suboccipi-tal region had an effect on PPTs in the suboccipitalmusculature within an asymptomatic population.

2. Methods

2.1. Participants

Ninety participants (29 males, 61 females, meanage¼ 23 years� 5) were recruited and randomly allo-cated into either a control group (n¼ 25) or experimen-tal groups which were divided into HVLA (n¼ 35) andMET (n¼ 30). All participants were recruited from the

student and teaching body at Victoria University. Partic-ipants were required to sign consent forms and provideinformation in a questionnaire regarding the presenceof cervical spine problems and other recurrent healthrisks. Participants were excluded if they had received up-per cervical spine manipulation in the previous threedays, had any cervical spine pathology, were long-termcortico-steroid users, or had vertebro-basilar insuffi-ciency, as these contraindicated the use of HVLA.1 Par-ticipants who experienced chronic headaches were alsoexcluded from the study. The Victoria University HumanResearch Ethics Committee granted ethics approval forthe study.

2.2. Measures

2.2.1. Pressure pain thresholdsThe PPTs were measured using a hand-held electronic

algometer (Somedic algometer II, Sweden) consisting ofa pressure transducer and an output screen that measuredand displayed the pressure and the rate of applied pres-sure. The algometer was calibrated before the testing be-gan. Participants were requested to lie prone on a benchwith their head in the face hole. The head end of the benchwas angled approximately 30� towards the floor to exposethe suboccipital region adequately and allow the re-searcher to palpate a tender point in the area betweenthe occiput and the C2 spinous process. A midline pointbetween the occiput and C2 was chosen as the locationfor PPT measurement as both are prominent landmarkstherefore enabling the procedure to be repeatable. Fur-thermore, it was considered an appropriate point of mea-surement as it lies in close proximity to the OA joint, thesuboccipital muscles span the region, and according topain maps by Dreyfuss et al.37 the site of measurement islocated within the C0eC1 zone of pain referral. The mea-surement procedure was based on the procedures used byFryer et al.9 The PPTwasmeasuredwith the transducer ofthe algometer positioned centrally and at 90� to the site tobe measured in the suboccipital region (Fig. 1). Pressurewas applied at 30 kPa/s. When the pressure being appliedchanged to a sensation of pain, the participants were in-structed to press a buttononan extendedhand-helddevicelinked to the algometer. As the button was depressed theon-screen counter froze and an audible beep alerted the re-searcher to arrest the force that was being applied. Thereading (when the button was pressed) was displayed onthe screen of the algometer and was recorded. ThreePPT measurements were performed with a 20-s break be-tween each to calculate the mean PPT score at three sepa-rate time intervals; an initial, at 5 min and at 30 min.

2.2.2. Pilot reliabilityTo assess the test-retest reliability of the examiner us-

ing the algometer, a pilot study was conducted prior tothe main study. Three measurements of PPT were

45L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

performed on 20 participants who were not involved inthe main study at the time intervals of interest (initial,5 min and 30 min). The average measure Intraclass Cor-relation Coefficient (ICC) was 0.96, indicating high re-peatability for the PPT measurement. The precision ofthe measurement procedure is estimated by the standarderror of measurement (SEM) of the mean differences be-tween intervals.38 The initial e 5 min mean differencewas 7 kPa (SEM¼ 9.64 kPa) and the initial e 30 minmean difference was 11 kPa (SEM¼ 11.60 kPa), so theabsolute error range of the measurement procedurewas considered to be 9.64 kPa and 11.60 kPa.

2.2.3. InterventionThe HVLA treatment group received two HVLA

thrusts, one delivered to both the right and left occipi-toeatlantal joints (C0/1).1 The participant lay supineon a bench and a registered osteopath contacted the pos-terior aspect of the occiput or the posterior arch of theatlas, positioned the head and neck using a small

Fig. 1. PPT measurement.

Fig. 2. Experimental technique (HVLA).

amount of rotation and side-bending leverage, anda thrust was delivered to the joint, as described by Gib-bons and Tehan1 (Fig. 2).

Those participants allocated to the MET treatmentgroup received an MET stretch to the suboccipital andtrapezius muscles on both the left and right sides. Thepractitioner made contact with the base of the occiputusing one hand, while the other hand stabilised theshoulder. The head and neck were positioned in flexionand slight lateral bending to the opposite side until theparticipant reported a stretching sensation in the suboc-cipital region. The participant was instructed to gentlypush their head back against the practitioners’ resistancefor 3e5 s, followed by a period of approximately 5 s ofrelaxation.39 The practitioner repeated this procedure,so that three applications of ‘contractionerelaxation’were performed on the muscles of each side (Fig. 3).

A modified, sham ‘‘functional technique’’ was utilisedas a control treatment. Pain thresholds may be influ-enced by the expectation of a treatment effect and so

Fig. 3. Experimental technique (MET).

Fig. 4. Control.

46 L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

the sham treatment was designed to control for a placeboeffect. Participants were informed that they were to betreated with an osteopathic functional technique whichinvolved subtle positioning of the upper neck, whichwas held for 30 s, but no ‘position of ease’2 or barrierwas engaged, in order to keep the technique inert(Fig. 4).

2.3. Procedure

Three researchers were involved in the study: Re-searcher 1 explained the testing procedure and recordedthe pressure values, whilst Researcher 2 used the algo-meter to measure the PPTs, and Researcher 3 (a regis-tered osteopath) performed the treatment. Researchers1 and 2 were blinded to the group allocation of partici-pants during the testing procedure.

Participants entered a testing room and the initial PPTwas recorded as described earlier. The participants weredirected to another room where they were randomly allo-cated into the treatment or control group via a lotterydraw procedure by Researcher 3. After receiving the allo-cated treatment intervention, the participants were askedto return to the original testing room and the PPT mea-surements were recorded again by Researchers 1 and 2.The participants were asked to return to the room30 min later for a third measurement of PPT.

2.4. Statistical analysis

Data was collated inMicrosoft Excel and analysed us-ing the statistical package SPSS Version 11. The pre-,post-5 and post-30 mean PPT measurements were ana-lysed for differences over time and between groups witha SPANOVA. Paired t-tests and repeated measuresANOVA were used for further analysis of within-groupchanges. Thewithin-group effect size (Cohen’s d ) was cal-culated for each pair and can be interpreted as small(d¼ 0.2), medium (d¼ 0.5) or large (d¼ 0.8).40 Statisticalsignificance was set at alpha 0.05.

3. Results

Mean PPT values are shown in Table 1. A relativelylarge mean difference in PPT occurred between the ini-tial and 5 min interval for both the MET (42.03 kPa,SD¼ 62.37) and HVLA groups (39.37 kPa,

Table 1

Mean (SD) PPT values (kPa)

Initial PPT

measurements

Post-PPT

measurements

(5 min)

Post-PPT

measurements

(30 min)

HVLA 358.69 (132.12) 398.06 (133.51) 374.58 (127.50)

MET 340.63 (166.94) 382.s67 (158.29) 370.63 (182.17)

Control 352.56 (155.76) 368.44 (208.16) 368.68 (192.62)

SD¼ 76.07), but the standard deviations were also large(Table 2). A smaller mean change was noted for the con-trol group (15.88 kPa, SD¼ 83.62) over this time period.A modest mean change occurred between the initial to30 min post treatment interval in the MET group(30 kPa, SD¼ 69.53), but smaller changes were observedwithin the HVLA (15.89 kPa, SD¼ 83.62) and controlgroups (16.12 kPa, SD¼ 62.49) (Fig. 5).

Analysis with SPANOVA revealed a significant dif-ference over time for the entire cohort (F2,174¼ 8.80,P< 0.01), but there was no significant difference be-tween the treatment groups (F2,87¼ 0.08, P¼ 0.93).Post-hoc analysis of within-group PPT changes using re-peated measures ANOVA for each group revealed sig-nificant differences in the MET and HVLA groups(F2,58¼ 5.89, P¼ 0.01 and F2,68¼ 4.86, P¼ 0.01, re-spectively), but not the control group (F2,48¼ 0.73,P¼ 0.49). Further analysis of the time period usingpaired t-tests revealed a significant increase in both theHVLA (P< 0.01) and MET groups (P< 0.01), but notthe control (P¼ 0.35). A significant change was alsofound for the MET group at 30 min (P< 0.03), butnot for the HVLA (P¼ 0.29) or control group(P¼ 0.21). Medium within-group effect sizes were calcu-lated for the HVLA group at 5 min (d¼ 0.52) and in theMET group at both the 5 and 30 min intervals (d¼ 0.67

Table 2

Mean differences (SD), P values (t-tests) and effect sizes (Cohen’s d )

Mean differences

(SD)

P

value

Effect

size (d )

preHVLA-HVLA-5 �39.37 (76.07) <0.01* 0.52a

preHVLA-HVLA-30 �15.89 (87.50) 0.29 0.18

preMET-MET-5 �42.03 (62.37) <0.01* 0.67a

preMET-MET-30 �30.00 (69.53) <0.03* 0.43a

preControl-Control-5 �15.88 (83.62) 0.35 0.19

preControl-Control-30 �16.12 (62.49) 0.21 0.26

*Significant at P� 0.05.a Indicates medium effect size.

0

20

40

60

80

100

120

140

MET HVLA ControlGroup

PPT

(kPa

)

Mean Difference - 5 minutes Mean Difference - 30 minutes

Fig. 5. Mean PPT changes.

47L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

and d¼ 0.43, respectively). The effect sizes were small atboth intervals for the control group (d¼ 0.19 andd¼ 0.26) and in the HVLA group at 30 min (d¼ 0.18).

The composition of the three treatment groups wassimilar with regards to the maleefemale ratio (MET¼8:22, HVLA¼ 13:22 and control¼ 8:17). No significantdifference was calculated between the ages of participantswithin the groups (F2,87¼ 0.07, P¼ 0.94) or between thepre-treatment PPT values (F2,87¼ 0.12, P¼ 0.89).

4. Discussion

Manipulation of the occipitoeatlantal joint andMET to the cervical spine and cervical musculatureare commonly advocated techniques in the osteopathicfield.1e3,10 In the present study, modest mean PPT in-creases following the MET and HVLA interventionswere noted (42.03 & 39.37 kPa, respectively), whereasonly a small increase occurred in the control group(15.88 kPa). However, these differences were not signif-icant when analysed using a SPANOVA. On furtheranalysis, using the less robust paired t-tests, the increasesfollowing HVLA and MET were significant at 5 min(P< 0.01), but were not significant in the control group(P¼ 0.35). Medium effect sizes were also calculated forHVLA and MET treatment groups (d¼ 0.52 andd¼ 0.67) at this interval. Despite the significant t-tests,it cannot be concluded that HVLA or MET had a hypo-algesic effect on suboccipital tenderness, because of thenon-significant SPANOVA. These findings, however,suggest that HVLA and MET may have some effect,and further research using a symptomatic populationis recommended.

The trends observed following the treatment inter-ventions appeared to be short lived. At the 30 min retest,the PPT was not significantly different from the initialmeasure for the HVLA group (P¼ 0.29). The relativelylarge standard deviation (SD� 87.5) may be a contribut-ing factor as to why a significant difference was notfound at 30 min when compared to the baseline. A sig-nificant pre-post change and a medium effect size werecalculated in the MET group at 30 min, but this increasewas smaller than the change at 5 min post treatment.

All of the participants had some degree of osteopathiceducation and it was possible that some participants wereaware of the sham nature of the control group. The con-trol treatment was a modified functional technique wherenomotion barriers were engaged, and, given the leveragesare normally very subtle, the researchers believe it is un-likely that participants would have been aware of thesham, but no follow up study was conducted to determinethis. The smallmean changes of the control groups (15.88,16.12, and 0.24 kPa, respectively) and the respective smalleffect sizes suggest little placebo effect.

The results from the present study differ from previ-ous research by Fryer et al.9 who found that HVLA

and mobilisation had a significant improvement onPPTs in the thoracic spine of asymptomatic participants.Other studies have reported improvements in PPT fol-lowing mid to lower cervical spine manipulation ina symptomatic population.8,10 The results of the presentstudy show similar trends to that of Terret et al.7 whoobserved a progressive elevation in pain tolerance fol-lowing thoracic spinal manipulation, and noted a distinctincrease at 2 min which lasted for at least 10 min post-manipulation. In the present study, a ‘peak’ cannot beidentified because PPT measurements were only re-corded at 5 and 30 min post-manipulation.

It may appear from the present study that MET haslittle effect on pain levels, but in the clinical setting mosttreatments are applied more than once and to symptom-atic patients. Wilson et al.4 used multiple applications ofMET over eight weeks for patients suffering with acutelow back pain, whereby application of MET in combi-nation with neuromuscular re-education and resistancetraining was more effective than the re-education andtraining alone for reducing pain levels. Although thepresent study is useful for examining and comparingthe effects of individual techniques, it does not accu-rately represent treatment in a clinical setting, and fur-ther research is recommended using a symptomaticpopulation and including multiple treatments.

The dPAG has been proposed in the descending con-trol of nociception.41 Manipulative techniques may pro-vide an adequate stimulus to activate descending paincontrol systems projecting from the dPAG to the spinalcord. A strong correlation was reported between hypo-algesia and sympatho-excitation (r¼ 0.82) followingspinal manipulation, suggesting the dPAG had been ac-tivated.15 In addition, Sterling et al.42 proposed that ma-nipulation of the cervical spine had a hypoalgesic effectspecific to mechanical nociception, an excitatory effecton sympathetic nervous system activity and also aneffect on motor activity. A central structure may beresponsible for the initial effects of HVLA. Anotherstudy found that plasma ß-endorphins were released fol-lowing spinal manipulation; heart rate, blood pressureand anxiety levels were monitored and controlled toestablish that the release of endorphins was not stressinduced.43 Recent studies have examined mobilisationof the knee in both humans and animals and demon-strated widespread hypoalgesia, further suggesting theinvolvement of central mechanisms.44,45 In the animalmodel, knee mobilisation of an experimentally inducedhyperalgesic joint has produced hypoalgesia which re-mained unaffected by spinal blockade of GABA andopioid receptors, supporting the role of descending in-hibitory centres that use serotonin and noradrenaline.46

The reliability pilot study demonstrated that the PPTmeasurement procedure appeared to be highly repeatable(ICC¼ 0.96), which was similar to a previous study thatused the same algometer (ICC¼ 0.93).9 However, there

48 L. Hamilton et al. / International Journal of Osteopathic Medicine 10 (2007) 42e49

were some large variations between the PPT measure-ments and this resulted in relatively large standard devia-tions. Reliability was improved in an earlier study whenthe first of the three measurements was excluded for esti-mating the average PPT.25 There was little change inmean differences between time intervals in the pilot studywhen the first value was removed, and therefore was notemployed in the present study.

Pain is a subjective experience and therefore difficult tomeasure. Studies which assessed pain using PPT have re-ported large amounts of variability in the measurements(SD between 95.22 kPa and 150 kPa).9,28 The use of algo-metry has been supported for research purposes, butsuch variability on consecutive measurements has led tocaution being advised when interpreting individual PPTsin a clinical setting.27 The participants in this study hadnine measurements (three readings on three occasions) ofPPT in the same location of their suboccipital region.Rest periods of 20 s occurred between each PPT readingtoprevent irritationof the tested region.One study demon-strated that changes inPPT sensitivity donot occur follow-ing repeated application of an algometer; however, thismay have been dependant upon the length of the rest pe-riod.25The20-sbreak in this studyappeared tohavea smallbut non-significant effect on subsequent PPT recordings,given the general trend of decrease in PPT readings 1e3.Due to the subjectivity of pain, studies using PPT are likelyto report relatively large standard deviations, and onlytreatments producing large effects are likely to yield statis-tically significant treatment results under robust analysis.

Given the increases in PPT were modest, further studiesshould examine PPTs in individuals with neck pain, becausethe changes may be more dramatic or long lasting in theseparticipants. In addition, research into other osteopathictechniques, such as counterstrain, articulation, functionaland cranial techniques may establish the most efficaciousprescription for treating suboccipital tenderness.

5. Conclusion

This is the first study examining HVLA and MET tothe occipitoeatlantal region and the effects on subocci-pital PPTs. Neither technique significantly increased thesuboccipital PPT in this asymptomatic population.Greater mean increases in PPT following HVLA manip-ulation and MET, compared to the control group, sug-gest that HVLA and MET may be effective techniquesin a symptomatic population, and further studies arerecommended to investigate this.

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