ORIGINAL CONTRIBUTION

Resting Electromyographic Activity of Deep Thoracic Transversospinalis Muscles Identified as Abnormal With Palpation

Gary Fryer, BSc (Osteopathy), PhD; Michael Bird, PhD; Barry Robbins, DO; Christian Fossum, DO (Norway); and Jane C. Johnson, MA

Context: In the 1940s, osteopathic researchers suggested that activity at each of the three intramuscular sites was evident paraspinal tissue abnormality was associated with sponta - (mean [SD] percent of MVIC: abnormal 7.83 [8.76]; normal 9.47 neous muscle activity, but few studies have since re-examined [8.45], 6.65 [7.39]). No statistically significant differences existed these reports. in the intramuscular EMG values between the two resting baseline periods ( P=.10). Objective: To determine whether abnormal motor activity plays a role in deep paraspinal tissues that appear abnormal Conclusion: The lack of statistically significant differences to palpation. between EMG activity at the abnormal and normal paraspinal sites suggests that factors other than muscle activity are respon - Methods: Using an observational study design, the PVG of sible for the apparent abnormality of these tissues to palpation. participants with thoracic pain were palpated by two exam - Investigation of these regions for increased tissue fluid and iners for consensus on the most marked level of tissue abnor - inflammatory mediators is recommended. mality. Dual fine-wire, intramuscular electrodes were inserted into the deep transversospinalis (multifidus, rotatores) mus - J Am Osteopath Assoc . 2010;110(2):61-68 cles at the abnormal level and at two normal sites (above and below the abnormal level). Surface electrodes were placed over the erector spinae muscles adjacent to each intramuscular esearchers in osteopathic medicine and other manual electrode site. Electromyography signals were recorded during Rmedicine disciplines have claimed that paraspinal tissue initial prone resting, three maximal voluntary isometric con - texture irregularity is an important clinical sign of functional tractions (MVIC), and a second prone resting. The area under disturbances to the spinal joints and tissues. 1-5 These functional the curve for a 2-second period was analyzed for each con - disturbances, termed somatic dysfunction in the osteopathic lit - dition, and values were normalized and reported as a per - erature, are identified primarily by the palpation of abnormal centage of MVIC. Data were analyzed using a 2-factor tissue texture, asymmetry, range-of-motion disturbance, and repeated-measures analysis of variance. tenderness. 2,3 Tissues in the paravertebral gutter (PVG) Results: Twenty-five participants with mean (SD) thoracic region—the longitudinal groove that lies between the verte - pain of 3.3 (1.9) on a 0 to 10 visual analog pain scale com - bral spinous processes and the bulk of the erector spinae pleted the study protocol. There were no statistically signifi - muscle group—are claimed to be of particular relevance to cant differences in normalized resting activity between the spinal assessment. 1-3,6 Irregularity of segmental tissue tex - three intramuscular sites ( P=.25) or between the three sur - ture in the PVG may include abnormal hardness, bogginess, face sites ( P=.33). Substantial variability in normalized resting or ropiness of the deep paraspinal tissues. 1-3,6 Increased motor activity of the deep paraspinal musculature, particularly the multifidus and rotatores muscles, has been cited as a possible etiologic process for paraspinal tissue irregularity associated From the A.T. Still Research Institute (Dr Fryer, Mr Fossum, and Ms Johnson) with somatic dysfunction. 1,2,6 and the Department of Neurobehavioral Sciences (Dr Robbins) at Kirksville Col - Although the clinical concept of somatic dysfunction has lege of Osteopathic Medicine-A.T. Still University in Missouri; and from the been central to osteopathic manipulative medicine for more Department of Exercise Science at Truman State University, also in Kirksville (Dr Bird). Dr Fryer is also affiliated with Osteopathic Medicine, School of than a century, objective evidence for the pathophysiology of Biomedical & Health Sciences at Victoria University in Melbourne, Australia. the proposed dysfunction and associated tissue texture abnor - This study was funded by the Strategic Research Fund (Grant # 501-281) mality is limited. Various models for the etiologic process of of the A.T. Still University of Health Sciences in Kirksville, Missouri. The authors have no conflicts of interest to declare. somatic dysfunction have attributed tissue texture abnormal - Address correspondence to Gary Fryer, BSc, PhD, Osteopathic Medicine ities to overactivity of segmental musculature, 7,8 tissue inflam - Unit, School of Biomedical & Health Sciences, Victoria University, PO Box mation, 8,9 segmental muscle atrophy, 9 or a combination of all 14428 MCMC, Melbourne, 8001, Australia. E-mail: [email protected] these factors. 9 As cited in the osteopathic medical literature, 10-12 many Submitted May 19, 2009; revision received October 6, 2009; accepted October researchers 13 -16 in the 1940s claimed evidence of increased 19, 2009.

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segmental muscle activity and segmental sympathetic motor individuals during different activities indicates that this method output at spinal levels associated with palpable lesions (ie, should be examined for reliability. More importantly, sub - somatic dysfunction). Denslow and Clough 13 used needle stantial electromagnetic noise contaminated the EMG record - electrodes to examine the electromyographic (EMG) activity at ings and particularly affected the resting conditions, during “lesioned” and normal segments, as identified by palpation, of which activity was low. When resting conditions were excluded the thoracic paraspinal muscles in 16 healthy participants. from the analysis, a statistically significant difference between They reported that spontaneous electrical activity occurred at the normal and abnormal sites still existed, 25 but these limita - lesioned segments but was rare at normal segments. 13 These tions cast doubt on the veracity of the findings. findings were also reported in participants with postural The present study re-examined the hypothesis of Fryer et abnormalities. 14 A few years later, Denslow 15 and Denslow al 22 that increased paraspinal EMG activity at rest is associated et al 16 reported that when graded pressure was applied to the with abnormal sites as determined by palpation. Sites that thoracic and lumbar spinous processes, reflex paraspinal EMG appeared abnormal to palpation in the PVG were chosen for activity occurred at lower pressures in segments palpated as the present study because practitioners in the field have claimed abnormal than in adjacent, normal segments. Although these tissue abnormality in this region may be indicative of seg - studies 13 -16 are regarded as landmark research in the osteo - mental dysfunction. 1-3,6 In addition, increased activity of the pathic medical profession, they are more than 50 years old multifidus and rotatores muscles has been proposed as the and are, by today’s standards, poorly described with insuffi - cause of this tissue abnormality, 1,2,6 and these muscles, as well cient data and sometimes no statistical analysis. 17,18 as the zygapophysial joint, are located within the thoracic Few researchers have since investigated paraspinal tissue PVG region. 26 Compared to previous studies, 13,22 the current texture abnormality for empirical characteristics. In 2004, Fryer study examined a larger cohort of symptomatic participants et al 19 reported that sites abnormal to palpation in the tho - using fine-wire intramuscular EMG procedures and used a reli - racic PVG were substantially more sensitive to pressure than able method for EMG normalization. The purpose of the pre - adjacent sites. One year later, the same researchers 20 mea - sent study was to determine whether abnormal motor activity sured the anteroposterior cross-sectional dimension (thick - plays a role in deep paraspinal tissues that appear abnormal ness) of the paraspinal muscle bulk directly underlying sites to palpation. in the thoracic PVG using diagnostic ultrasonography. Normal and abnormal palpated regions had similar mean dimensions, Methods suggesting that factors other than paraspinal muscle thick - Participants ness were responsible for the apparently abnormal tissue tex - Students and staff from two university campuses in Kirksville, ture. 20 Missouri, were recruited to participate in the present study Given that Denslow 15 and Denslow et al 16 are commonly through e-mails and posted flyers. Participants were included cited as evidence of the facilitated segment concept of somatic if they had current or frequent thoracic spinal pain during the dysfunction, 10 -12 it is surprising that few researchers have preceding 3 weeks, were aged 18 to 50 years, and had an iden - attempted to re-examine and expand on this body of work. tifiable paraspinal region that appeared abnormal to palpation There is little direct evidence to support the proposition that by the examiners. Participants were excluded if they had abnormal muscle contraction or spasm is associated with obvious spinal deformities or pathologic processes or any paraspinal regions identified as abnormal. A large volume of medical condition that precluded them from fine-wire EMG research demonstrates lumbar paraspinal motor changes asso - testing, such as abnormal blood pressure, current prescrip - ciated with low back pain (increased, decreased, or delayed tion anticoagulant, antiplatelet therapy, blood disorders, needle activity), but the relevance of these findings to the concept of phobia, postural hypotension, skin conditions (eg, sensitivity somatic dysfunction and palpation is tenuous. 17,21 to adhesives), or syncopal attacks. Participants were excluded In the only recent study comparing the EMG activity of if no focal tissue abnormality was detected with palpation. deep paraspinal muscle sites identified by palpation as All participants read an information sheet about the study abnormal or normal, Fryer et al 22 found statistically signifi - and signed a consent form before participation. The study cant increases in normalized EMG activity at abnormal sites was approved by the A.T. Still University’s Kirksville College under various resting and active conditions. The study, 22 how - of Osteopathic Medicine Institutional Review Board. ever, had a number of substantial limitations. It used a small Participants reported their present severity of thoracic cohort of healthy participants (N=12) who had a history of pain on a visual analog scale of 0 (no pain) to 10 (most pain thoracic discomfort but were not symptomatic at the time of experienced). They then removed clothing to expose their testing. The method of EMG normalization—essential for the back (women wore disposable gowns that opened at the back) comparison of sites within a muscle or between individ - and lay prone on an osteopathic manipulative treatment table uals 23,24 —was calculated using the peak amplitude recorded with their face at the midline face hole. Two researchers (G.F. in any activity; however, the great variation of amplitudes in and C.F. or B.R.) experienced in osteopathic manipulative

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treatment or osteopathic manipulative therapy both palpated of approximately 5 cm free to allow slack for movement. The the deep tissues in the thoracic PVG region using deep, short skin was then abraded and swabbed with alcohol for attach - gliding movements of the fingertips. A consensus was reached ment of the adhesive dual surface electrodes (Ag/AgCl; between both examiners on the site with the most marked Noraxon, Scottsdale, Arizona), which were placed over the tissue texture abnormality (ie, hard, boggy, or ropy deep tis - erector spinae bulk just laterally to each electrode (approxi - sues). Because sites that appear abnormal to palpation tend to mately 4 cm from the midline). A surface reference electrode be more sensitive to pressure, 19 participants in the current was connected to the participant’s acromion process on the study verbally indicated when a site was tender to pressure, same side of the participant’s body as the other electrodes. thus reinforcing the examiners’ palpatory findings. In total, EMG activity was collected from each patient at When an abnormal-to-palpation (AbP) site was located six separate electrode sites: and agreed upon, the skin at this site was marked by impres - sion with light pressure from the end of a plastic tube. Sites two Ⅲ NP site above the AbP site (NP1) via intramuscular elec - spinal segments above and below the AbP site were palpated trode to ensure they were relatively normal to palpation (NP) and Ⅲ AbP site via intramuscular electrode reported by the participants as not sensitive to pressure. If any Ⅲ NP site below the AbP site (NP2) via intramuscular elec - of these sites were considered abnormal, then a different NP trode site was chosen instead—generally a spinal segment above Ⅲ erector spinae adjacent to NP1 (ES1) via surface electrode or below that site. The NP sites were marked with the plastic Ⅲ erector spinae adjacent to the AbP site (ESA) via surface tube in the same manner as the AbP site. These sites were electrode used for insertion of electrodes. Ⅲ erector spinae adjacent to NP2 (ES2) via surface electrode

Electromyography These sites are shown in the Figure. Disposable paired hook-wire electrodes (44 gauge, insulated Following electrode insertion, EMG activity was visually nickel alloy wire; VIASYS NeuroCare, Madison, Wisconsin) verified on the scope to ensure connectivity. Participants were used for intramuscular EMG data collection. Electrodes relaxed in the prone position for several minutes to establish were inserted using 30 mm (27 gauge) and 50 mm (25 gauge) resting baseline activity. hypodermic needles. At the terminal ends of the wires, 2 mm Electromyography data were collected during three of insulation were stripped, and 2 mm of one wire and 5 mm periods. First, baseline data were obtained as the patient rested of the second wire extended from the tip of the needle. During in the prone position (“pre-MVIC”). preliminary testing, we varied the site of needle insertion from Next, participants were asked to complete a maximal vol - a medial location close to the spinous process to more lateral untary isometric contraction (MVIC) task. To complete this locations using a more oblique direction of needle insertion to determine the approach that would most consistently locate the deepest muscle layer. Location of needle placement within the muscle was visualized using diagnostic ultrasonography (iU22; Philips, Amsterdam, The Netherlands). By using a medial insertion location 27 —approximately 2 cm lateral to the midline spinous process—and directing the needle posteriorly and slightly medi - ally, the needle was reliably inserted in the multi - fidus and rotatores muscles of the deep transver - sospinalis muscles. 28 These muscles cannot be distinguished by ultrasonography, making it likely that recordings include activity from both muscles. 29 The skin around the marked regions of each par - ticipant was swabbed with alcohol, and the surface electrode sites were abraded and swabbed. Dual fine- wire, intramuscular electrodes were inserted at the marked sites Figure. The six electrode sites used to collect electromygraphic activity until the needle met the resistance of the lamina. The needle from each patient. Dual fine-wire electrodes were inserted at the was then withdrawn, leaving the fine-wire electrode in situ. transversospinalis muscle site that was abnormal to palpation (center) Spring coil connector leads were attached to the free wires, and and normal sites above and below the abnormal site. Surface elec - the leads were taped to the participant’s back, keeping a loop trodes were placed adjacent to each intramuscular electrode site.

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task, participants remained in the prone position with their of 3.3 (1.9) based on a 0 (no pain) to 10 (worst pain) visual arms resting by their sides. They were then asked to lift their analog pain scale. Two participants had no thoracic symp - head and chest off the table as hard as possible for 3 seconds toms on the day of testing. Nine participants had thoracic against the resistance of the examiner, whose hands were on symptoms for less than 3 months, 3 participants had symptoms the participant’s upper thoracic region. 22 The resistance was not for longer than 3 months but less than 1 year, and 12 partici - quantified, but it matched the maximal force of the subject. Par - pants had symptoms for longer than 1 year. All but 1 partici - ticipants did this task three times with a 5-second rest between pant were right-hand dominant. The AbP site was commonly contractions. This task has previously been established as located in the mid-thoracic region (median level, 5.5; mode, 5; having excellent repeatability (G.F., unpublished data, May range, 3-9) and on the right side of the participant (18 right, 2008). 6 left). The levels were defined by the proximity to the spinal After the MVIC tasks, participants returned to a prone vertebra, as determined by palpation and counting of spinous resting position for a second (“post-MVIC”) baseline. Partici - processes and taking into account the obliquity of these pro - pants were allowed approximately 5 to 10 seconds rest after the cesses (“rule of threes”). MVIC. Electromyography levels were monitored to ensure that this baseline was stable and at a similar level to the first Normal vs Abnormal Sites baseline before recording to ensure that the participant had Raw EMG values (area under the curve, uV) are presented in completely relaxed. Table 1 . Normalized baseline values for resting periods 1 and 2 are presented in Table 2 . Considerable variation between indi - Data Collection and Statistical Analysis viduals is evident from the large standard deviations. There Electromyography data were collected using a TeleMyo 2400G2 were no statistically significant differences between AbP and NP wireless telemetry EMG system with pre-amplified leads sites for normalized values during either the first or second (Noraxon) and was processed using MyoResearch XP Master resting baseline periods for either the intramuscular sites

Edition software (Noraxon). Raw EMG data were pre-ampli - (F2,14 =1.53, P=.25; F2,16 =2.84, P=.09) or the surface electrode sites fied, band-pass filtered (10-1000 Hz), rectified, and smoothed (F2,17 =1.20, P=.33; F2,17 =0.79, P=.47). The raw EMG values of with a root mean squared (RMS) 20 millisecond window. the two baseline periods were not statistically significant for

Two-second periods from each of the electrodes at pre- either the intramuscular sites ( F1,14 =3.18, P=.10) or the surface MVIC baseline, during MVIC, and at post-MVIC baseline sites ( F1,18 =1.53, P=.76). Results from the nonparametric were processed, and the area under the curve (uV) was cal - Friedman tests were consistent with the results of the ANOVA. culated for each period. Data from each measurement of MVIC and the two baseline periods were analyzed for reliability Repeatability using intraclass correlation coefficients (ICC). Baseline EMG For the two baseline periods for the intramuscular (intraclass scores were normalized to the highest MVIC value obtained correlation coefficient [ICC] range, 0.55-0.94) and surface sites from the three MVICs. Normalized baseline scores from the (ICC range, 0.35-0.69), repeatability varied considerably. How - three intramuscular sites were analyzed for differences using ever, repeatability was excellent for the MVIC tasks for all a 2-factor repeated-measures analysis of variance (ANOVA) to intramuscular (ICC range, 0.96-0.99) and surface electrode examine the effect of site and to determine whether differ - sites (ICC range, 0.91-0.95) ( Table 3 ). ences existed between the two baseline periods. Power anal - ysis indicated that 25 participants would provide 80% power Comment (␣=.05) to detect an anticipated medium to large effect size Several individuals 1,2,6 have claimed that increased motor between abnormal and normal sites. Data were also analyzed activity of the deep paraspinal musculature is present in using nonparametric Friedman tests. paraspinal regions that appear abnormal to palpation, but the evidence supporting this claim rests within a body of research Results that lacks validation by subsequent studies. 17,21 In contrast to Participants a previous study, 22 the current study found no evidence of Twenty-seven participants were recruited for the study. Three distinguishing EMG activity in the deep thoracic paraspinal participants were excluded—1 had no evident focal tissue musculature at sites identified as abnormal to palpation under change or tenderness, 1 was insufficiently symptomatic, and resting conditions compared to sites identified as normal. 1 had poor EMG recordings from several abnormal and normal Given the limitations of the previous study 22 and the more sites (either no signal or contamination by artefact). The robust methodology of the present one, it appears likely that remaining 24 participants (mean age [SD], 23.8 [8.2] years; abnormal motor activity in the deep musculature is not a mean [SD] BMI, 24.8 [4.5]; 10 men, 14 women) were included factor in the apparent abnormal tissue texture of these in the study. paraspinal regions. Participants had a current mean (SD) thoracic pain level The findings of the present study, which examined mul -

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of the different methodologies used, they Table 1 do not invalidate the earlier studies either. Electromyographic Activity of Deep Thoracic Transversospinalis Muscles: Further studies re-examining Denslow’s Raw Electromyography Values* for Baseline and MVIC, mean (SD) investigation of the erector spinae mus - cles may be warranted. Resting Baseline, Resting Baseline, Despite these differences, the present Site Pre-MVIC MVIC Post-MVIC study has a number of methodologic Ⅲ Intramuscular Electrode advantages over earlier studies. 13,14 We ▫ NP1 31.28 (54.07) 330.28 (336.93) 39.27 (50.35) used a greater number of participants ▫ AbP 23.88 (21.39) 390.02 (295.99) 30.32 (33.04) (25, as opposed to 17 or 16), all our par - ▫ NP2 27.71 (25.58) 420.64 (238.91) 33.08 (29.19) ticipants had a history of thoracic symp - Ⅲ Surface Electrode toms with only two nonsymptomatic ▫ ES1 10.05 (9.54) 174.36 (178.20) 8.49 (5.95) participants on the day of testing, and ▫ ESA 9.62 (7.41) 217.78 (223.90) 10.51 (9.48) our methods were consistent for each ▫ ES2 8.70 (7.68) 166.59 (165.74) 8.41 (6.75) participant. We also used modern EMG * Electromyography values were calculated as the area under the curve. equipment with fine-wire electrodes that probably caused less tissue disruption Abbreviations: AbP, abnormal-to-palpation; ES1, erector spinae muscles adjacent to NP1; ES2, erector spinae muscles adjacent to NP2; ESA, erector spinae muscles adjacent to AbP; MVIC, mean voluntary and discomfort than the thicker concentric isometric contractions; NP1, normal to palpation, above AbP site; NP2, normal to palpation, below needle electrodes used in earlier AbP site. studies. 13,14 Compared with the previous study by Fryer et al, 22 the present study is also more rigorous given its greater number of participants, Table 2 established means of EMG normalization, and lack of electro - Electromyographic Activity of Deep Thoracic magnetic noise in recordings during rest. 25 Transversospinalis Muscles: Normalized Electromyography Denslow and colleagues 13,14 indicated the activity in Values (Percent of MVIC) for Resting Baseline, mean (SD) lesioned areas varied in degree during each experiment, from occasional quiet periods to activity of single motor units, with Site Pre-MVIC Post-MVIC activity fading in and out and sometimes cessation of muscle Ⅲ Intramuscular Electrode activity from changes in participant position. The EMG trac - ▫ NP1 11.28 (9.02) 11.93 (7.28) ings published in these early studies showed EMG activity ▫ AbP 7.30 (8.00) 11.48 (12.05) in the lesioned areas well above baseline levels. However, ▫ NP2 6.54 (6.71) 7.41 (8.05) electrode placement, depth, and proximity to motor units Ⅲ Surface Electrode affect the amplitude of an intramuscular EMG signal, a problem ▫ ES1 10.58 (11.93) 8.42 (6.29) solved by EMG normalization. 23,24 In the present study, rather ▫ ESA 8.42 (8.23) 7.58 (6.10) ▫ ES2 7.47 (5.65) 7.68 (6.41) than determining the presence of activity by visual inspec - tion of EMG tracings, activity was calculated over a repre - sentative 2-second period, normalized against maximal activity, Abbreviations: AbP, abnormal-to-palpation; ES1, erector spinae muscles and analyzed with appropriate statistical methods. Results adjacent to NP1; ES2, erector spinae muscles adjacent to NP2; ESA, erector spinae muscles adjacent to AbP; MVIC, mean voluntary isometric contractions; from the ANOVA used on our non-normalized data were not NP1, normal to palpation, above AbP site; NP2, normal to palpation, below statistically significant, and, because comparison of nonnor - AbP site. malized data is not considered valid, this was not reported in the results. tifidus and rotatores activity associated with locations in the Normalization is more empirical than the visual inter - thoracic PVG identified as abnormal, do not preclude the pos- pretation of EMG tracings. Furthermore, Denslow and Has - sibility of abnormal activity in other muscles. For example, sett 14 reported no clear demarcation between a lesioned area earlier studies by Denslow and colleagues13,14 examined the and normal area and that if spontaneous activity was seen in more lateral erector spinae muscles, but they did not describe a control area close to a lesioned segment, the electrode was their precise needle placement, location, or depth. Although we moved to a quieter area. This methodology clearly introduced measured the activity of the erector spinae immediately lateral examiner bias in the selection of control sites, a flaw which did to the PVG sites, we used surface electrodes, which are more not occur in the present study. susceptible to crosstalk than the needle electrodes used by Denslow and Hassett 14 also reported that when sponta - Denslow and colleagues.13,14 Thus, while the results of the neous activity was not present in lesioned areas, stimuli (eg, present study do not concur with these early reports as a result slight movement of electrodes, pin pricks or pin scratches,

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sitive to motion artifact than the concen - Table 3 tric needle electrodes used by Denslow Intraclass Correlation Coefficients (ICCs) for Electromyographic Activity of Deep and colleagues, but despite the improved Thoracic Transversospinalis Muscles During Resting Baseline* and MVIC sensitivity, it does not seem likely that the earlier experiments can be repro - Resting Baseline* MVIC duced using modern electrodes. 95% Confidence 95% Confidence In the present study, substantial vari - Site ICC Interval ICC Interval ability in the resting EMG values was seen, as evidenced by large standard Ⅲ Intramuscular Electrode deviations in the EMG data and variable ▫ NP1 0.94 0.86-0.98 0.99 0.97-1.00 ▫ AbP ˇ0.55 0.19-0.78 0.96 0.91-0.98 reliability of the baseline measures. Indi - ▫ NP2 0.61 0.23-0.83 0.97 0.93-0.99 vidual variability of multifidus activa - Ⅲ Surface Electrode tion has been noted in the few studies ▫ ES1 0.46 0.03-0.74 0.91 0.83-0.96 that have examined the thoracic muscu - ▫ ESA 0.35 -0.06-0.66 0.91 0.82-0.96 lature 22,29,31 and may be characteristic of ▫ ES2 0.69 0.36-0.87 0.95 0.90-0.98 deep muscles that function as stabilizers rather than prime movers. Variable base -

* Resting baseline values include pre-MVIC and post-MVIC values. line activity at many tested sites resulted in relatively high normalized resting Abbreviations : AbP, abnormal-to-palpation; ES1, erector spinae muscles adjacent to NP1; ES2, erector spinae muscles adjacent to NP2; ESA, erector spinae muscles adjacent to AbP; MVIC, mean voluntary activity values. These results may involve isometric contractions; NP1, normal to palpation, above AbP site; NP2, normal to palpation, below crosstalk from other muscle groups or AbP site. reflect a lack of complete relaxation in participants with thoracic pain. Regard - cubes of ice) were applied to the skin near electrodes in the less of the cause, regions that appeared abnormal to palpation lesioned and normal areas. There were no details of how often did not have a greater amount of rest activity. these stimuli were applied. The present study recorded activity Caution is required before concluding that abnormal over a much shorter time and may have missed transient EMG activity is not present in abnormal-to-palpation sites. episodes of spontaneous activity, but if motor activity has a role The regions in the present study required deep palpation, and in the alteration of tissue texture, then more consistent activity despite every attempt to direct the needle to the exact region than irregular and transient bursts of EMG should be observ - that was palpated, we cannot be certain that the EMG record - able. The inconsistent nature of these bursts and the subjective ings came from the tissues identified with deep palpation. nature of their recording and interpretation raise doubts about Studies from the 1990s and later 32-34 have reported sponta - the reproducibility of Denslow and Hassett’s findings. Many neous electrical activity in the loci of myofascial trigger points years after the original 1941 study, 13 Denslow 30 reported that (palpable bands or nodules in skeletal muscle that refer pain abnormal spontaneous activity was not consistently detected on manual compression), using a special recording and needle during subsequent attempts to repeat his original findings insertion technique. 33 Perhaps the palpable abnormalities in the and that activity was often eliminated when the participant was PVG represent trigger points in the transversospinalis mus - comfortably supported with pillows. culature. No study has investigated paraspinal regions using In further studies, Denslow 15 and Denslow et al 16 applied the method described by Hong and Simons, 35 so myofascial graded pressure to thoracic and lumbar spinous processes trigger points remain a possible cause of paraspinal tissue and reported that reflex activity from paraspinal muscles at irregularity and tenderness. lesioned segments occurred at lower pressures than sur - Inflammation and increased tissue fluid in deep rounding normal areas. Reflex activity spread from pressure paraspinal tissues may have a role in producing tenderness and stimulation of high threshold segments (where greater pressure abnormal texture to palpation, and future studies in this area was needed to evoke reflex muscle activity) to low threshold may yield rewarding results. Investigation of tissue fluid and segments (which were typically palpated as lesioned). Fur - inflammation in these deep locations would be challenging, but ther, pressure was reported to frequently produce pain and modern imaging techniques, such as magnetic resonance posttraumatic soreness at low threshold segments. In the pre - imaging, may aid these types of investigations. 36,37 Exploring sent study, similar measures were attempted, but the appli - these regions using measurement of intramuscular pressure cation of pressure on the spinous processes using an elec - with specialized probes may also be feasible. 38,39 Shah et al 40,41 tronic algometer inevitably produced contaminating motion developed a technique for measuring the local biochemical artifact in the EMG recording, so these data were not ana - milieu of skeletal muscle to determine the presence of inflam - lyzed or reported. The fine-wire electrodes may be more sen - matory mediators in trapezius muscle trigger points, and this

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technique may also be appropriate for investigation of the 17. Fryer G, Morris T, Gibbons P. Paraspinal muscles and intervertebral dys - paraspinal muscles. function: part 1 [review]. J Manipulative Physiol Ther . 2004;27(4):267-274. 18. Lederman E. Facilitated segments: a critical review. Br Osteopath J . Conclusion 2000;22:7-10. No differences in resting EMG activity were found in the deep 19. Fryer G, Morris T, Gibbons P. The relationship between palpation of tho - paraspinal muscles underlying sites in the thoracic PVG that racic paraspinal tissues and pressure sensitivity measured by a digital algometer. were identified with palpation as either normal or abnormal. J Osteopath Med . 2004;7(2):64-69. The results of this study do not support previous EMG inves - 20. Fryer G, Morris T, Gibbons P. The relationship between palpation of tho - racic tissues and deep paraspinal muscle thickness. 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68 • JAOA • Vol 110 • No 2 • February 2010 Fryer et al • Original contribution