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Muscular load to the therapist's shoulder during three alternative techniques for trigger point therapy
ARTICLE IN PRESS Journal of Bodywork and Movement Therapies (2009) 13, 171–181
Journal of Bodywork and Movement Therapies www.intl.elsevierhealth.com/journals/jbmt
PILOT STUDY
Muscular load to the therapist’s shoulder during three alternative techniques for trigger point therapy Emily Kristen Smith, B. Physiotherapy [Hons]a,, Mary Magarey, Ph.D.a, Steve Argue, M. Physio, Manip Physiob, Shapour Jaberzadeh, Ph.D.c a
School of Health Sciences, Division of Health Sciences, University of South Australia, North Terrace, Adelaide 5000, South Australia b School of Physiotherapy, Division of Health Sciences, University of South Australia, North Terrace, Adelaide 5000, South Australia c School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Peninsula Campus Building B, Frankston, Victoria 3199, Australia Received 7 December 2006; received in revised form 1 July 2007; accepted 10 July 2007
KEYWORDS Trigger point therapy; Shoulder; Muscle load; Surface electromyography; Treatment tool
Summary Aim: To compare the muscular load (level of muscle activity) to the shoulder during alternative approaches to trigger point therapy (TPT). Method: Massage therapy students (n ¼ 7) applied a predetermined level of force to an artificial contact surface. Changes in five pairs of superficial shoulder muscles (indicated by surface electromyography) were recorded while the student performed the single-arm technique (SAT), the double-arm technique (DAT) and the treatment-tool technique (TTT) using TriggerMateTM, a new treatment tool. Results: For the contact arm, muscle activity was significantly decreased using the TTT compared to the SAT (po0.05) but was not significantly different between the TTT and DAT. For the non-contact arm, none of the test techniques led to significant differences in muscle activity. Conclusions: While there is evidence that the TTT decreases the muscular load to the shoulder of the contact arm, there is no indication of where this load is redistributed. & 2007 Elsevier Ltd. All rights reserved.
Corresponding author. Tel./fax:+61 8 8536 2923.
E-mail address: [email protected] (E.K. Smith). URL: http://www.triggermate.com (E.K. Smith). 1360-8592/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbmt.2007.07.004
ARTICLE IN PRESS 172
Introduction Work-related musculoskeletal disorders (WRMSDs) occur from exposure to risk factors in the work environment, which are major contributors to the injury, but are not the single cause (World Health Organization 1985, cited by Glover, 2002). Therapists who routinely use manual therapy techniques report three and a half times higher rates of injury to the wrist and hands than therapists who do not routinely use these techniques (Bork et al., 1996; Cromie et al., 2000). Trigger point therapy (TPT) is a manual therapy technique used in the treatment of myofascial trigger points (TrPs) and it has been identified by therapists as a factor involved in the development and exacerbation of WRMSDs (Snodgrass et al., 2003). The repetitive movements, production of large forces with the upper limbs and maintenance of awkward postures are risk factors for injury present in TPT (Cromie et al., 2000; Bork et al., 1996; Sjøgaard and Sjøgaard, 1998). Traditional methods use the fingers or thumbs to apply the treatment pressure. Therapists performing TPT have recognized the need to protect the hands, fingers and thumbs from excessive loading and as a result have developed techniques which use alternative body areas and a variety of manmade devices to apply TPT (Cantu and Grodin, 1992; Maher et al., 2002; Stanborough, 2004; Bork et al., 1996; Cromie et al., 2000). The level of activity in the muscles that act on the glenohumeral joint (muscular load) plus compression from external forces through the upper limb contribute to the total load at the glenohumeral joint. For this study, the load to shoulder was evaluated by determining the level of muscle activity (muscular load) elicited in the prime movers of the glenohumeral joint. One strategy to reduce the load to the wrists and hands during application of TPT is to use the elbow to apply the treatment pressure, thus providing an alternative contact surface through which forces can be transmitted. However, the load may be transferred to and adversely affect other areas of the upper limb, such as the shoulder complex, as considerable muscular stabilizing force at the shoulder is required to maintain the treatment position. Use of strategies to unload the contact arm may reduce the muscular load at the shoulder. Reinforced techniques, where the non-contact arm is used to share the load with the contact arm, are frequently used by therapists. Three treatment techniques were investigated in this study. Two traditional techniques were selected based on anecdotal evidence that they are both taught to manual therapists and used in the
E.K. Smith et al. clinical setting (Simons et al., 1999; Stanborough, 2004). The traditional techniques were the ‘single-arm technique’ (SAT) (Figure 1) where one arm only is used to apply the treatment pressure and the ‘double-arm technique’ (DAT) (Figure 2) where the contralateral ‘‘non-contact’’ arm reinforces the treatment pressure. For the DAT considerable force is applied through both wrists and hands at the end range of extension. The ‘treatment-tool technique’ (TTT) (Figure 3) was introduced as a variation of the DAT performed with the new treatment tool TriggerMateTM (Figure 4) (Developer: S. Argue, physiotherapist) to assist in the reinforcement of the treatment pressure in a manner which may allow the therapist to reinforce the treatment pressure with the wrists in a more neutral position and arms more supported against the trunk. This may be beneficial in further reducing the load to the shoulder muscles of the contact arm, relative to the DAT.
Figure 1 Single-arm technique (SAT).
Figure 2 Double-arm technique (DAT).
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy
Figure 3 Treatment-tool technique (TTT).
173 ment forces to be generated by the more superficial muscles (David et al., 2000) and it is likely that the prime movers of the glenohumeral joint (with their principal action occurring at this joint) would act isometrically in co-contraction to maintain the arm in the correct position. Significant changes in performance in these muscles may occur during the test techniques and therefore the comparative workload for the same muscles of both shoulders was compared to determine whether the muscular load is transferred between arms when reinforcing the technique. For this study, muscle activity was measured as an indication of muscular load to the shoulder. The aim was to compare the muscular activity in the shoulder of the therapist during three alternative approaches to TPT where the elbow is used to apply the treatment pressure. Relative muscle activity, as recorded via surface electromyography (sEMG), was investigated in the left and right PM, anterior, middle and posterior heads of deltoid (AD, MD and PD, respectively) and LD. Three questions were of interest: 1. What is the pattern of muscle activity (relative contribution of each muscle, for each arm) across the superficial shoulder muscles for each technique? 2. Does any technique produce consistently lower levels of muscle activity in the muscles under investigation? 3. Are there significant differences in muscle activity between the shoulders when comparing the reinforced techniques to the SAT ?
Figure 4 TriggerMateTM.
The relationship between a muscle’s activity and its force production remains controversial; however, during isometric contractions where the muscle force is gradually increased over 3–5 s, a near linear increase has been demonstrated (Tu ¨rker, 1993). Muscles of the shoulder that have significant and varying actions at the glenohumeral joint include the deltoid, pectoralis major (PM), latissimus dorsi (LD), teres major, biceps brachii, triceps brachii and the rotator cuff (supraspinatus, infraspinatus, subscapularis and teres minor) (Halder and An, 2000; Itoi et al., 2004). There is no evidence of which muscles are loaded during these test techniques; however, the rotator cuff is likely to stabilize the glenohumeral joint to allow move-
Methods This study, approved by the Human Research Ethics Committee of the University of South Australia, was a same-subject, repeated-measures design run over two separate sessions. The first session consisted of group training and the second was an individual testing session. All subjects gave informed consent prior to participation.
Subject details Volunteers studying a TPT elective module within the Diploma of Remedial Massage were recruited using convenience sampling methods from the Natural Health Academy of Australia (Adelaide). Subjects were excluded if they had a history of a significant neuromusculoskeletal disorder affecting the neck or upper limbs. A prospective power
ARTICLE IN PRESS 174 calculation was not possible due to the lack of literature on the techniques under investigation, and therefore as many subjects as possible were recruited and a post hoc power analysis performed.
Procedures Treatment tool TriggerMateTM is a treatment tool that can be used to assist application of the double-arm TPT technique (Figure 4). It consists of two hand grips connected by an adjustable rope loop. TriggerMateTM is designed to reinforce and stabilize the contact elbow pressure while allowing continuous patient–therapist contact during the application of treatment pressure (TTT). For this study, TriggerMateTM rope lengths were set to 75% of the subject’s forearm length measured to the nearest 0.5 cm. Forearm measures were taken at the start and conclusion of the training session for six subjects by the same investigator and the reliability of this measure calculated. Surface electromyography AMLAB, Associated Measurement LABoratory (AMLAB Technologies, Lewisham NSW) was used to detect, process and record integrated sEMG muscle activity in conjunction with AMLAB II software (AMLAB Technologies, Lewisham NSW). Surface electrodes ‘Duotrode’ bipolar surface electrodes (Ag–AgCl self-adhesive, pre-gelled active electrodes) (MyoTronics Inc., USA) were positioned parallel to muscle fibres according to a standard placement procedures (Cram et al., 1998). Electrodes were 12.5 mm in diameter and had a 19 mm interelectrode distance. A lip clip was used to ground the subjects (Tu ¨rker, 1993). Muscle activity Activity of the prime movers of the glenohumeral joint was evaluated: left and right PM, AD, MD, PD and LD (Itoi et al., 2004). The rotator cuff has an important stability function at the glenohumeral joint to allow movement forces to be generated by these more superficial muscles (David et al., 2000), yet the rotator cuff itself was not observed for this exploratory study. Subject training Subjects first attended a group training session (approximately 1 h) where they were trained by an experienced physiotherapist familiar with all three test techniques (Mr S. Argue). Subjects were given
E.K. Smith et al. supervised training until they reported confidence in performing the technique correctly and such performance confirmed by the experienced clinician. Correct posture and upper limb position was determined as the ability to maintain the correct level of force (to calibrated mechanical scales) for the 90 s test duration. Techniques were taught one at a time, from the simplest to the most complex: the SAT first, then the DAT followed by the TTT. Testing On a separate day, each subject participated in an individual testing session where the muscular load generated during the test techniques was assessed with sEMG. Each technique was performed against an artificial treatment surface that was height adjusted for the comfort of the individual to a level similar to that adopted in the clinical setting. The treatment surface was used to indicate the level of treatment pressure applied and promote a consistent force production within and between subjects. It consisted of calibrated mechanical scales and pressure-sensitive sensors (FSCAN Mobile pressure measurement system, Tekscan Inc., South Boston, Massachusetts). FSCAN sensors (disposable, Model #3000) were taped to 12 mm firm foam padding placed on the scales to improve subject comfort and provide a soft contact surface to reduce variability in FSCAN force output (Hsiao et al., 2002). FSCAN sensors were calibrated with a 20 kg weight (calibrated within 5%) once at the beginning of the test session for 2 min. This standard treatment surface was devised in an attempt to minimize variability in force application which may have otherwise been a confounding variable for muscle activity. Surface EMG muscle activity was sampled at 1000 Hz and amplified (3000 times) within a 10–500 Hz bandwidth (low pass filter 500 Hz, high pass filter 10 Hz). Due to the high common mode rejection ratio in this system (120 db), no notch filter (48–52 Hz) was used. In this system the raw sEMG signals were automatically smoothed, rectified and converted to their root mean square (RMS) values. Both raw and RMS EMG readings were presented on the computer screen. Surface electrodes were applied following standardized skin preparation procedures to enhance integrity at the skin–electrode interface and reduce impedance. Excessively hairy skin was shaved, the area cleansed with 70% isopropyl alcohol, gently abraded with fine-grain sandpaper and cleansed again with 70% isopropyl alcohol. Subjects were asked to inform the researchers when they experienced a light stinging sensation during the preparation procedure, to indicate the
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy skin impedance had been reduced below 10 MO (Bitter et al., 2006, in press, accepted for publication). A semi-conductive water based gel was used between the skin and electrode interface and the electrodes taped in position to further maintain the integrity of the skin–electrode interface. Three standard manual muscle tests (Kendall et al., 1993) were performed for each muscle in an attempt to elicit a maximal voluntary isometric contraction (MVIC) for normalization. Three 6-s contractions were performed with the middle 2 s recorded, and the highest of the three attempts taken as 100%MVIC. Twenty-second rest periods were allowed between attempts. A further 2-min rest period was allowed on completion of the manual muscle tests to control for fatigue. Techniques were tested in random order with 2-min rests between, and all test values were normalized to a %MVIC (Tu ¨rker, 1993). Subjects were allowed practice in each technique immediately prior to the test until they felt confident and were assessed by the investigator to be performing the technique correctly according to the same criteria used during the training session. Two minutes of rest were allowed to control for fatigue prior to testing. One test attempt only was allowed for each technique due to the high physical demands of the task. Subjects were asked to apply 20 kg of force to an artificial treatment surface continuously for 90 s. No feedback was supplied to the subject from the investigators during the test phase. A 2-min rest period was allowed before this procedure was repeated for the second and final test techniques. Order of testing was randomized between subjects. Surface EMG data were saved and archived in AMLAB software for later offline use and analysis. Ratio data, in the form of RMS muscle activity (mV) for each 10 s block were automatically calculated by the AMLAB II software and manually transcribed directly into Microsoft Excel 2003 (Microsoft Corporation) for storage. Every effort was made to reduce the impact of noise on the EMG data, including piloting of the study procedures, testing of the equipment and repositioning of affected electrodes. Despite these measures, visual inspection of the raw EMG waveforms during data collection revealed noise artefact that was not able to be resolved during data collection and therefore had to be addressed as part of the analysis procedure. Data corrupted by noise were identified and removed. Subjects were not withdrawn from the study on the basis of noise; however, data from the individual muscles in which noise was identified were removed from the study. Data were normalized
175 to a percentage of a MVIC (indicating 100% MVIC). Surface EMG data were transformed to their natural logarithm (LnEMG) to achieve a normal data distribution and allow comparisons of mean values to be justified (Portney and Watkins, 2000). LnEMG muscle activity for each TPT technique was compared between the ‘non-contact’ left arm and the ‘contact’ right arm.
Results Thirteen individuals expressed interest but three were unavailable to attend the training session. A further three did not participate in testing: one subject was unavailable and two did not meet the inclusion criteria. Subjects were excluded if they had any significant musculoskeletal injury in the previous 12 months to the upper limbs, neck or upper back or if they were not student massage therapists. Seven subjects (n ¼ 7) aged 30–53 years (mean 40.55, SD 8.99 years) participated in both the training and testing sessions. Six were female, one was male, all were right hand dominant and used their right arm as the contact arm. A retrospective power analysis was performed on the data demonstrating a minimum expected power of 99%. Despite efforts to reduce the effect of noise, raw EMG waveforms were observed to be corrupted by noise artifact and values over 200%MVIC removed. Data from the SAT and DAT only were considered for one subject as the EMG data for the TTT was irretrievable from AMLAB. Data on all three techniques were collected and analysed from all other subjects. The reliability for forearm measures used to adjust the TriggerMateTM rope length was calculated as good (ICC ¼ 0.81) (Portney and Watkins, 2000). Average muscle activity (%MVIC and LnEMG) for each muscle group is presented in Table 1 for the three test techniques. The relative contribution of each muscle to the muscle group was indicated by ranking its activity in relation to other muscles in that group for each technique (Table 2). Muscle activity patterns appear variable across subjects with few consistent patterns. For the contact arm during the SAT and DAT, posterior deltoid contributed the most and LD the least. Using the treatment tool, PM contributed the most and middle deltoid the least. For the noncontact arm, LD contributed the most to the SAT and middle deltoid contributed the least. PM was the largest contributor for the treatment-tool and double-arm methods. Middle and posterior deltoid were the least active muscles during the TTTs and DATs, respectively.
ARTICLE IN PRESS 176 Table 1
E.K. Smith et al. Mean muscle activity (%MVIC) and transformed mean muscle activity (LnEMG).
Technique
Muscle
Mean muscle activity—%MVIC
N
Std. deviation
Mean LnEMG muscle activity
Std. deviation
Single arm
Contact arm Non-contact Both arms
27.774 12.689 20.232
63 63 126
15.541 5.583 13.878
3.167 2.455 2.811
0.572 0.412 0.612
Double arm
Contact arm Non-contact Both arms
18.960 12.970 15.965
63 63 126
19.289 4.066 14.205
2.547 2.516 2.531
0.881 0.308 0.658
Treatment tool
Contact arm Non-contact Both arms
9.960 13.737 11.849
54 54 108
6.745 5.668 6.485
2.108 2.530 2.319
0.623 0.441 0.578
Total
Contact arm Non-contact Both arms
19.345 13.102 16.223
180 180 360
16.662 5.121 12.699
2.632 2.499 2.565
0.827 0.388 0.648
The relative activity of each muscle and group muscle activity was then ranked according to technique (Tables 3 and 4) to determine if one test technique consistently produced lower muscle activity values for individual muscles. For the contact arm, the TTT consistently produced the lowest relative workload across all muscles except LD, which was least active for the DAT. All muscles generated the highest levels of activity during the SAT, where for the non-contact arm the lowest relative levels of activity were in PM, anterior and middle deltoid. LD and posterior deltoid were the least active muscles for the DATs and TTTs, respectively. Overall, for the contact arm the TTT produced the lowest muscle activity followed by the DAT. For the non-contact arm, the lowest levels of activity were produced during the SAT, then TTTs. Clustered linear regression was used to determine whether the differences in muscle activity (LnEMG) for each muscle group (contact arm and non-contact arm) were significantly different between the test techniques. The reinforced (treatment tool and double arm) techniques were compared to the SAT. The treatment-tool muscle activity was significantly different to the single-arm activity (p ¼ 0.004) comparing all muscles of both arms (Table 5). Double-arm muscle activity did not differ significantly from that of the SAT (p ¼ 0.159, Table 5). The analysis was repeated to compare the DATs and TTTs, but they did not differ significantly either (p40.05, data not presented). For the contact arm, the single-arm muscle activity was significantly different to that of the TTT (po0.001, Table 6). However, comparing the DATs and the SATs (p ¼ 0.057, Table 6), or the
treatment tool to the DATs (p ¼ 0.054, not presented) no significant differences were revealed (to the p ¼ 0.05 level). Comparing the muscle activity for the noncontact arm, no significant differences were revealed between any of the three techniques (SAT and DAT p ¼ 0.725, SAT and TTT p ¼ 0.650, Table 7. TTT and DAT p ¼ 0.93, data not presented).
Discussion The majority of previous studies on TPT have been concerned with evaluating the desired clinical outcome or effect of specific treatment techniques (Hou et al., 2002; Huguenin, 2004). TPT is performed in various clinical settings with conflicting evidence in relation to its effectiveness (Hou et al., 2002; Huguenin, 2004; Simons et al., 1999). The effect of performing these techniques on the treating therapist was the basis for this exploratory study. The techniques investigated (DATs, SATs and TTTs) are used as an alternative to traditional treatment methods to reduce the load to the joints of the digits, wrists and thumbs. Specifically, the reinforced DATs and TTTs are hypothesized to reduce the strain to the contact shoulder experienced during application of the SAT by redistributing the load over the larger area of both upper limbs. Using effective treatment pressures reported by Hou et al. (2002), it is possible that forces up to 17 kg/cm2 are transmitted through the joints of the wrists, hands and digits during traditional TPT treatment (estimated using a hypothetical area of
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy Table 2
177
Ranked LnEMG muscle activity across all muscles.
Single-arm technique Contact arm (a) Subject
PM
1 2 3 5 7 8 9 Mean
4 5 3 2 3 3 n/d 3.3
Non-contact arm (b) AD 2 2 1 3 2 2 4 2.3
MD 3 3 2 1 4 4 2 2.7
PD
LD
PM
n/d 4 4 n/d 5 5 3 4.2
1 1 n/d 4 1 1 1 1.5
5 4 4 2 3 4 3 3.6
AD 3 5 3 4 2 2 2 3.0
MD 1 1 1 1 1 5 1 1.6
PD 4 3 2 3 5 1 4 3.1
LD 2 2 5 5 4 3 5 3.7
Double-arm technique Contact arm (c) Subject
PM
1 2 3 5 7 8 9 Mean
4 5 3 2 5 3 n/d 3.7
Non-contact arm (d) AD 1 2 2 4 2 1 3 2.1
MD 3 1 1 1 3 4 2 2.1
PD
LD
PM
n/d 4 4 3 4 5 4 4.0
2 3 n/d n/d 1 2 1 1.8
4 5 3 4 3 4 3 3.7
AD 5 4 4 5 2 3 2 3.6
MD 3 3 2 2 5 5 1 3.0
PD 2 1 1 1 4 2 4 2.1
LD 1 2 5 3 1 1 5 2.6
Treatment-tool technique Contact arm (e)
Non-contact arm (f)
Subject
PM
AD
MD
PD
LD
PM
AD
MD
PD
LD
1 2 3 5 7 8 9 Mean
4 n/d 4 4 4 4 n/a 4.0
1 n/d 3 5 2 1 4 2.7
2 n/d 1 1 3 2 1 1.7
n/d n/d 2 3 5 5 2 3.4
3 n/d n/d 2 1 3 3 2.4
5 n/d 5 4 5 5 2 4.3
4 n/d 4 5 2 4 4 3.8
1 n/d 2 2 1 1 1 1.3
2 n/d 1 1 3 2 3 2.0
3 n/d 3 3 4 3 5 3.5
Muscle activity is ranked from lowest (1) to highest (5).Key: n/d—no data; mean—mean rank across all subjects; PM—pectoralis major; AD—anterior deltoid; MD—middle deltoid; PD—posterior deltoid; LD—latissimus dorsi.
force application of approximately 4 cm2). The findings from this study are specific to the application of the test techniques which require high levels of sustained pressure. Myers et al. (2005) defined categories of shoulder muscle activity as mild (o20%MVIC), moderate (20–50%MVIC) and moderate to marked (450% MVIC). The activities reported by Myers et al. (2005) were dynamic rather than sustained isometric, as in this study. However, despite the differences in mode of activity, for the purpose of comparison between techniques, similar classifications
were applied to muscle activity used in this study (Table 8). The muscle activity in the contact arm would therefore be classified as mild for the DATs and TTTs (17.3% and 10.2%) and moderate for the SATs (28.5%). For the non-contact arm, all techniques produced mild levels of activity (12.7%, 12.9%, 13.7% MVIC for the SATs, DATs and TTTs, respectively). The minimum level of EMG activity accepted by Myers et al. (2005) as an indication of a functionally active muscle was 10%. For the current study, every muscle group could be considered active for each technique, although
ARTICLE IN PRESS 178 Table 3
E.K. Smith et al. Ranked muscle activity (LnEMG) by muscle and technique. Contact arm
Pec major Ant delt Mid delt Post delt Lat dorsi
Non-contact arm
Single arm
Double arm
Tool
Single arm
Double arm
Tool
3 3 3 3 3
2 2 2 2 1
1 1 1 1 2
1 1 1 3 3
2 3 3 2 1
3 2 2 1 2
(3.33) (2.59) (3.08) (3.52) (1.47)
(2.84) (1.87) (1.59) (2.83) (1.09)
(2.56) (1.72) (1.01) (1.89) (1.22)
(2.53) (2.05) (0.45) (2.07) (2.52)
(2.68) (2.66) (2.20) (1.93) (2.02)
(3.15) (2.64) (0.48) (1.27) (2.48)
Muscle activity is ranked from lowest (1) to highest (3). Key: Pec major—pectoralis major; ant delt—anterior deltoid; mid delt—middle deltoid; post delt—posterior deltoid; lat dorsi—latissimus dorsi.
Muscle contributions
body); however, it was believed more appropriate to allow the participants an opportunity to choose a ‘‘position of comfort’’ to more closely simulate the clinical application of the techniques. Variation in activation patterns between clinicians is therefore also likely to be reflective of a multitude of individual factors, including the individual’s fine tuning of body positioning, injury avoidance strategies or muscle imbalance and compensatory activation. Other variables including level of clinical experience and pre-existing injury, which are also likely contributors to differing activation patterns, were screened for in both the selection and exclusion criteria. Differences in variation across the muscle set throughout a technique may be reflective of the technique itself (i.e. stable, controlled), and/or the strength, or fatigue resistance of the muscles involved.
Relative contribution of each superficial shoulder muscle, according to arm and technique There does not appear to be a consistent activation pattern in terms of the production of force by individual muscles for these techniques. This suggests great individual variability exists in the workload of the superficial muscles and may also reflect differences in skill level and experience, as muscle activation patterns are more variable during the learning of a motor skill (Shumway-Cook and Woollacott, 2001). However, even for totally consistent isometric activities, evidence exists of a wide variation in muscle recruitment strategies where continual substitution and variation in muscle activation occurs throughout the task duration (Scutter and Tu ¨rker, 1998). These alternating periods of rest and activation are thought to be one mechanism employed to prevent muscle fatigue and injury. Attempts were made to standardize the upper limb position during technique application (including plinth height, elbow position relative to the
Relative muscle activity in individual muscles Comparison of the techniques revealed that the muscles of the contact arm work at a higher level during the SATs than for the DATs and TTTs. This finding was expected since for the SAT only the contact arm is producing the treatment pressure yet for the reinforced techniques, the non-contact arm is assisting force application. Between the reinforced techniques, muscle activity for the TTT is comparatively less than for the DAT, although this was not significant. This change may be a reflection of difference in glenohumeral joint position during the TTT, where the humerus of the non-contact arm may be in a lesser degree of abduction and the forearm can be braced against the trunk. This could provide further stability to the glenohumeral joint from structures other than the muscles in comparison to the DAT. The finding of least muscle activity in the noncontact arm for the SAT was expected, as it was not used to apply the treatment pressure.
Table 4 Average activity (LnEMG) ranked for all muscles. Technique Single arm Double arm Tool Contact arm 3 (2.80) Non-contact arm 1 (1.92) Both arms 3 (2.36)
2 (2.04) 3 (2.29) 2 (2.17)
1 (1.68) 2 (2.00) 1 (1.84)
Muscle activity is ranked from lowest (1) to highest (3).
contact-arm muscle activity for the TTT is barely above this threshold.
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy Table 5
179
Clustered linear regression—both shoulders.
Linear regression Number of obs ¼ 360 F(2, 6) ¼ 19.07 Prob4F ¼ 0.0025 R2 ¼ 0.0948 Root MSE ¼ 0.61846
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
t
p4|t|
[95% Conf. interval]
Double arm vs. single arm Tool vs. single arm _Cons
0.279
0.173
1.61
0.159
0.705
0.145
0.491 2.810
0.109 0.148
4.48 18.88
0.004 0.000
0.760 2.446
0.223 3.175
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Table 6
Clustered linear regression—contact arm.
Linear regression Number of obs ¼ 180 F(2, 6) ¼ 48.29 Prob4F ¼ 0.0025 R2 ¼ 0.2726 Root MSE ¼ 0.70911
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
t
p4|t|
[95% Conf. interval]
Double arm vs. single arm Tool vs. single arm _Cons
0.620
0.620
2.35
0.057
1.267
0.026
1.059 3.167
0.133 0.205
7.96 15.39
0.000 0.000
1.385 2.663
0.733 3.670
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Table 7
Clustered linear regression—non-contact arm.
Linear regression Number of obs ¼ 180 F(2, 6) ¼ 0.12 Prob4F ¼ 0.8889 R2 ¼ 0.0072 Root MSE ¼ 0.38838
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
Double arm vs. single arm Tool vs. single arm _Cons
0.061
0.165
0.075 2.454
0.158 0.152
t
p4|t|
[95% Conf. interval]
0.37
0.725
0.344
0.466
0.48 16.11
0.650 0.000
0.312 2.081
0.464 2.827
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Changes in muscular load Compared to the SAT, muscle activity in the contact arm was reduced during the DATs and TTTs although
the reduction was significant only for the latter technique. This finding provides evidence that the TTT decreases the load to the shoulder; however, this load is not redistributed to the equivalent
ARTICLE IN PRESS 180 Table 8
E.K. Smith et al. Muscle activity by category. Muscle activity (%MVIC) Mild (o20%)
Contact arm Single arm Double arm Tool Noncontact arm Single arm Double arm Tool
Moderate (20–50%)
Moderatemarked (450%)
28.5 17.3 10.2
12.7 12.9 13.7
muscles of the non-contact arm. Bracing the upper limb against the trunk during the TTT may reduce the stability demands on the shoulder, thus decreasing overall load on the shoulder, as ‘total load’ is the sum of ‘treatment force’+‘stability force’. The amount of force applied through the noncontact arm during the DAT was not measured; therefore, the non-contact arm may not have been used effectively to assist application of the treatment pressure and thus contributed to the lack of difference between the SATs and DATs. The design of TriggerMateTM for this experiment incorporated a calibrated spring measure to determine that a minimum force was being applied through the device using both arms and therefore, the device was being used effectively.
of a treatment technique. Therefore, further research is required before a strong conclusion can be drawn on the usefulness of each technique for prevention WRMSD injury. However, while acknowledging these limitations to the study, for the healthy, novice massage therapist population, it was found that: 1. The contribution of each individual muscle tested was highly variable and inconsistent between subjects. 2. For the contact arm, the TTT produced the lowest amount of muscle activity across techniques. For the non-contact arm, the lowest levels of muscle activity were demonstrated in the SAT. 3. Reinforced techniques decreased the muscular load to the superficial shoulder muscles of the contact arm compared to the SAT to a similar extent; however, only the TTT significantly decreased the load compared to the SAT. Conflict of interest statement: Steve Argue is a qualified physiotherapist and the inventor of the TriggerMateTM tool. His involvement in the training and testing of participants was necessary as he is experienced in Trigger Point Therapy and the correct use of TriggerMateTM.
Acknowledgments The authors would like to express gratitude to the following people for their contributions to this study. Professor Adrian Estermann for his generous assistance in the statistical analyses of the surface EMG data. Dr. Sheila Scutter for her assistance in the interpretation of the surface EMG data.
Conclusions
References
The findings from this study apply to use of the test techniques in application of high levels of sustained pressure and interpreted within the context of evaluation of the prime movers of the shoulder only. The study involved a small sample size, but had sufficient statistical power for the results to be acceptable, although they cannot be extrapolated to the general population of manual therapists. Use of an artificial treatment surface may have altered the demands on the therapist in relation to the lack of normal interaction with a patient during application
Bitter, N., Clisby, E., Jones, MA., Magarey, ME., Jaberzadeh, S., Sandow, M., 2006. Relative contributions of infraspinatus and deltoid during external rotation in healthy shoulders. Journal of Shoulder and Elbow Surgery (December), in press, accepted for publication. Bork, B.E., Cook, T.M., Rosecrance, J.C., Engelhardt, K.A., Thomason, M.E.J., Wauford, I.J., Worley, R.K., 1996. Workrelated musculoskeletal disorders among physical therapists. Physical Therapy 76, 827–835. Cantu, R.I., Grodin, A.J., 1992. Myofascial Manipulation, Theory and Clinical Application. Aspen Publishers, Gaithsburg. Cram, J., Kasman, G.S., Holtz, J., 1998. Introduction to Surface Electromyography. Aspen Publishers, Gaithsburg.
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy Cromie, J.E., Robertson, V.J., Best, M.O., 2000. Work-related musculoskeletal disorders in physical therapists: prevalence, severity, risks and responses. Physical Therapy 80, 336–351. David, G., Magarey, M., Jones, M., Dvir, Z., Tu ¨rker, K., Sharpe, M., 2000. EMG and strength correlates of selected shoulder muscles during rotations of the glenohumeral joint. Clinical Biomechanics 15, 95–102. Glover, W., 2002. Work-related strain injuries in physiotherapists: prevalence and prevention of musculoskeletal disorders. Physiotherapy 88, 364–372. Halder, A.M., An, K.N., 2000. Anatomy and biomechanics of the shoulder. Orthopaedic Clinics of North America 31, 159–176. Hou, C., Tsai, L., Cheng, K., Chung, K., Hong, C., 2002. Immediate effects of various physical therapeutic modalities on cervical myofascial pain and trigger-point sensitivity. Archives of Physical Medicine and Rehabilitation 83, 1406–1414. Hsiao, H., Guan, J., Weatherly, M., 2002. Accuracy and precision of two in-shoe pressure measurement systems. Ergonomics 45 (8), 537–555. Huguenin, L.K., 2004. Myofascial trigger points: the current evidence. Physical Therapy in Sport 5, 2–12. Itoi, E., Morrey, B.F., An, K.N., 2004. In: Rockwood, C.A., Matsen, F.A. (Eds.), Biomechanics of the Shoulder in the Shoulder, third ed., vol. 1. MA Wirth & SB Lippitt. Saunders, Philadelphia. Kendall, F.P., McCreary, E.K., Provance, P.G., 1993. Muscles, Testing and Function: With Posture and Pain, fourth ed. Williams and Wilkins, Baltimore, Philadelphia.
181 Maher, C.G., Latimer, J., Starkey, I., 2002. An evaluation of Superthumb and the Kneeshaw device as manual therapy tools. Australian Journal of Physiotherapy 48, 25–30. Myers, J.B., Pasquale, M.R., Laudner, K.G., Sell, T.C., Bradley, J.P., Lephart, S.M., 2005. On-the-field resistance-tubing exercises for throwers: an electromyographic analysis. Journal of Athletic Training 40, 15–22. Portney, L.G., Watkins, M.P., 2000. Foundations of Clinical Research: Applications to Practice, second ed. Prentice-Hall, New Jersey. Simons, D.G., Travell, J.G., Simons, L.S., 1999. Travell and Simons Myofascial Pain and Dysfunction: the Trigger Point Manual, second ed., vol. 1. Williams and Wilkins, Baltimore. Shumway-Cook, A., Woollacott, M., 2001. Motor Control: Theory and Practical Applications, second ed. Lippincott Williams and Wilkins, Philadelphia. Sjøgaard, G., Sjøgaard, K., 1998. Muscle injury in repetitive motion disorders. Clinical Orthopaedics and Related Research 351, 21–31. Scutter, S.D., Tu ¨rker, K.S., 1998. Recruitment stability in motor units of human masseter. Muscle and Nerve 21, 1290–1298. Snodgrass, S.J., Rivett, D.A., Chiarelli, P., Bates, A.M., Rowe, L.J., 2003. Factors related to thumb pain in physiotherapists. Australian Journal of Physiotherapy 49, 243–250. Stanborough, M., 2004. Direct Release Myofascial Technique: An Illustrated Guide for Practitioners. Churchill Livingstone, Edinburgh. Tu ¨rker, K., 1993. Electromyography: some methodological problems and issues. Physical Therapy 73, 698–710.
Journal of Bodywork and Movement Therapies www.intl.elsevierhealth.com/journals/jbmt
PILOT STUDY
Muscular load to the therapist’s shoulder during three alternative techniques for trigger point therapy Emily Kristen Smith, B. Physiotherapy [Hons]a,, Mary Magarey, Ph.D.a, Steve Argue, M. Physio, Manip Physiob, Shapour Jaberzadeh, Ph.D.c a
School of Health Sciences, Division of Health Sciences, University of South Australia, North Terrace, Adelaide 5000, South Australia b School of Physiotherapy, Division of Health Sciences, University of South Australia, North Terrace, Adelaide 5000, South Australia c School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Peninsula Campus Building B, Frankston, Victoria 3199, Australia Received 7 December 2006; received in revised form 1 July 2007; accepted 10 July 2007
KEYWORDS Trigger point therapy; Shoulder; Muscle load; Surface electromyography; Treatment tool
Summary Aim: To compare the muscular load (level of muscle activity) to the shoulder during alternative approaches to trigger point therapy (TPT). Method: Massage therapy students (n ¼ 7) applied a predetermined level of force to an artificial contact surface. Changes in five pairs of superficial shoulder muscles (indicated by surface electromyography) were recorded while the student performed the single-arm technique (SAT), the double-arm technique (DAT) and the treatment-tool technique (TTT) using TriggerMateTM, a new treatment tool. Results: For the contact arm, muscle activity was significantly decreased using the TTT compared to the SAT (po0.05) but was not significantly different between the TTT and DAT. For the non-contact arm, none of the test techniques led to significant differences in muscle activity. Conclusions: While there is evidence that the TTT decreases the muscular load to the shoulder of the contact arm, there is no indication of where this load is redistributed. & 2007 Elsevier Ltd. All rights reserved.
Corresponding author. Tel./fax:+61 8 8536 2923.
E-mail address: [email protected] (E.K. Smith). URL: http://www.triggermate.com (E.K. Smith). 1360-8592/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbmt.2007.07.004
ARTICLE IN PRESS 172
Introduction Work-related musculoskeletal disorders (WRMSDs) occur from exposure to risk factors in the work environment, which are major contributors to the injury, but are not the single cause (World Health Organization 1985, cited by Glover, 2002). Therapists who routinely use manual therapy techniques report three and a half times higher rates of injury to the wrist and hands than therapists who do not routinely use these techniques (Bork et al., 1996; Cromie et al., 2000). Trigger point therapy (TPT) is a manual therapy technique used in the treatment of myofascial trigger points (TrPs) and it has been identified by therapists as a factor involved in the development and exacerbation of WRMSDs (Snodgrass et al., 2003). The repetitive movements, production of large forces with the upper limbs and maintenance of awkward postures are risk factors for injury present in TPT (Cromie et al., 2000; Bork et al., 1996; Sjøgaard and Sjøgaard, 1998). Traditional methods use the fingers or thumbs to apply the treatment pressure. Therapists performing TPT have recognized the need to protect the hands, fingers and thumbs from excessive loading and as a result have developed techniques which use alternative body areas and a variety of manmade devices to apply TPT (Cantu and Grodin, 1992; Maher et al., 2002; Stanborough, 2004; Bork et al., 1996; Cromie et al., 2000). The level of activity in the muscles that act on the glenohumeral joint (muscular load) plus compression from external forces through the upper limb contribute to the total load at the glenohumeral joint. For this study, the load to shoulder was evaluated by determining the level of muscle activity (muscular load) elicited in the prime movers of the glenohumeral joint. One strategy to reduce the load to the wrists and hands during application of TPT is to use the elbow to apply the treatment pressure, thus providing an alternative contact surface through which forces can be transmitted. However, the load may be transferred to and adversely affect other areas of the upper limb, such as the shoulder complex, as considerable muscular stabilizing force at the shoulder is required to maintain the treatment position. Use of strategies to unload the contact arm may reduce the muscular load at the shoulder. Reinforced techniques, where the non-contact arm is used to share the load with the contact arm, are frequently used by therapists. Three treatment techniques were investigated in this study. Two traditional techniques were selected based on anecdotal evidence that they are both taught to manual therapists and used in the
E.K. Smith et al. clinical setting (Simons et al., 1999; Stanborough, 2004). The traditional techniques were the ‘single-arm technique’ (SAT) (Figure 1) where one arm only is used to apply the treatment pressure and the ‘double-arm technique’ (DAT) (Figure 2) where the contralateral ‘‘non-contact’’ arm reinforces the treatment pressure. For the DAT considerable force is applied through both wrists and hands at the end range of extension. The ‘treatment-tool technique’ (TTT) (Figure 3) was introduced as a variation of the DAT performed with the new treatment tool TriggerMateTM (Figure 4) (Developer: S. Argue, physiotherapist) to assist in the reinforcement of the treatment pressure in a manner which may allow the therapist to reinforce the treatment pressure with the wrists in a more neutral position and arms more supported against the trunk. This may be beneficial in further reducing the load to the shoulder muscles of the contact arm, relative to the DAT.
Figure 1 Single-arm technique (SAT).
Figure 2 Double-arm technique (DAT).
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy
Figure 3 Treatment-tool technique (TTT).
173 ment forces to be generated by the more superficial muscles (David et al., 2000) and it is likely that the prime movers of the glenohumeral joint (with their principal action occurring at this joint) would act isometrically in co-contraction to maintain the arm in the correct position. Significant changes in performance in these muscles may occur during the test techniques and therefore the comparative workload for the same muscles of both shoulders was compared to determine whether the muscular load is transferred between arms when reinforcing the technique. For this study, muscle activity was measured as an indication of muscular load to the shoulder. The aim was to compare the muscular activity in the shoulder of the therapist during three alternative approaches to TPT where the elbow is used to apply the treatment pressure. Relative muscle activity, as recorded via surface electromyography (sEMG), was investigated in the left and right PM, anterior, middle and posterior heads of deltoid (AD, MD and PD, respectively) and LD. Three questions were of interest: 1. What is the pattern of muscle activity (relative contribution of each muscle, for each arm) across the superficial shoulder muscles for each technique? 2. Does any technique produce consistently lower levels of muscle activity in the muscles under investigation? 3. Are there significant differences in muscle activity between the shoulders when comparing the reinforced techniques to the SAT ?
Figure 4 TriggerMateTM.
The relationship between a muscle’s activity and its force production remains controversial; however, during isometric contractions where the muscle force is gradually increased over 3–5 s, a near linear increase has been demonstrated (Tu ¨rker, 1993). Muscles of the shoulder that have significant and varying actions at the glenohumeral joint include the deltoid, pectoralis major (PM), latissimus dorsi (LD), teres major, biceps brachii, triceps brachii and the rotator cuff (supraspinatus, infraspinatus, subscapularis and teres minor) (Halder and An, 2000; Itoi et al., 2004). There is no evidence of which muscles are loaded during these test techniques; however, the rotator cuff is likely to stabilize the glenohumeral joint to allow move-
Methods This study, approved by the Human Research Ethics Committee of the University of South Australia, was a same-subject, repeated-measures design run over two separate sessions. The first session consisted of group training and the second was an individual testing session. All subjects gave informed consent prior to participation.
Subject details Volunteers studying a TPT elective module within the Diploma of Remedial Massage were recruited using convenience sampling methods from the Natural Health Academy of Australia (Adelaide). Subjects were excluded if they had a history of a significant neuromusculoskeletal disorder affecting the neck or upper limbs. A prospective power
ARTICLE IN PRESS 174 calculation was not possible due to the lack of literature on the techniques under investigation, and therefore as many subjects as possible were recruited and a post hoc power analysis performed.
Procedures Treatment tool TriggerMateTM is a treatment tool that can be used to assist application of the double-arm TPT technique (Figure 4). It consists of two hand grips connected by an adjustable rope loop. TriggerMateTM is designed to reinforce and stabilize the contact elbow pressure while allowing continuous patient–therapist contact during the application of treatment pressure (TTT). For this study, TriggerMateTM rope lengths were set to 75% of the subject’s forearm length measured to the nearest 0.5 cm. Forearm measures were taken at the start and conclusion of the training session for six subjects by the same investigator and the reliability of this measure calculated. Surface electromyography AMLAB, Associated Measurement LABoratory (AMLAB Technologies, Lewisham NSW) was used to detect, process and record integrated sEMG muscle activity in conjunction with AMLAB II software (AMLAB Technologies, Lewisham NSW). Surface electrodes ‘Duotrode’ bipolar surface electrodes (Ag–AgCl self-adhesive, pre-gelled active electrodes) (MyoTronics Inc., USA) were positioned parallel to muscle fibres according to a standard placement procedures (Cram et al., 1998). Electrodes were 12.5 mm in diameter and had a 19 mm interelectrode distance. A lip clip was used to ground the subjects (Tu ¨rker, 1993). Muscle activity Activity of the prime movers of the glenohumeral joint was evaluated: left and right PM, AD, MD, PD and LD (Itoi et al., 2004). The rotator cuff has an important stability function at the glenohumeral joint to allow movement forces to be generated by these more superficial muscles (David et al., 2000), yet the rotator cuff itself was not observed for this exploratory study. Subject training Subjects first attended a group training session (approximately 1 h) where they were trained by an experienced physiotherapist familiar with all three test techniques (Mr S. Argue). Subjects were given
E.K. Smith et al. supervised training until they reported confidence in performing the technique correctly and such performance confirmed by the experienced clinician. Correct posture and upper limb position was determined as the ability to maintain the correct level of force (to calibrated mechanical scales) for the 90 s test duration. Techniques were taught one at a time, from the simplest to the most complex: the SAT first, then the DAT followed by the TTT. Testing On a separate day, each subject participated in an individual testing session where the muscular load generated during the test techniques was assessed with sEMG. Each technique was performed against an artificial treatment surface that was height adjusted for the comfort of the individual to a level similar to that adopted in the clinical setting. The treatment surface was used to indicate the level of treatment pressure applied and promote a consistent force production within and between subjects. It consisted of calibrated mechanical scales and pressure-sensitive sensors (FSCAN Mobile pressure measurement system, Tekscan Inc., South Boston, Massachusetts). FSCAN sensors (disposable, Model #3000) were taped to 12 mm firm foam padding placed on the scales to improve subject comfort and provide a soft contact surface to reduce variability in FSCAN force output (Hsiao et al., 2002). FSCAN sensors were calibrated with a 20 kg weight (calibrated within 5%) once at the beginning of the test session for 2 min. This standard treatment surface was devised in an attempt to minimize variability in force application which may have otherwise been a confounding variable for muscle activity. Surface EMG muscle activity was sampled at 1000 Hz and amplified (3000 times) within a 10–500 Hz bandwidth (low pass filter 500 Hz, high pass filter 10 Hz). Due to the high common mode rejection ratio in this system (120 db), no notch filter (48–52 Hz) was used. In this system the raw sEMG signals were automatically smoothed, rectified and converted to their root mean square (RMS) values. Both raw and RMS EMG readings were presented on the computer screen. Surface electrodes were applied following standardized skin preparation procedures to enhance integrity at the skin–electrode interface and reduce impedance. Excessively hairy skin was shaved, the area cleansed with 70% isopropyl alcohol, gently abraded with fine-grain sandpaper and cleansed again with 70% isopropyl alcohol. Subjects were asked to inform the researchers when they experienced a light stinging sensation during the preparation procedure, to indicate the
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy skin impedance had been reduced below 10 MO (Bitter et al., 2006, in press, accepted for publication). A semi-conductive water based gel was used between the skin and electrode interface and the electrodes taped in position to further maintain the integrity of the skin–electrode interface. Three standard manual muscle tests (Kendall et al., 1993) were performed for each muscle in an attempt to elicit a maximal voluntary isometric contraction (MVIC) for normalization. Three 6-s contractions were performed with the middle 2 s recorded, and the highest of the three attempts taken as 100%MVIC. Twenty-second rest periods were allowed between attempts. A further 2-min rest period was allowed on completion of the manual muscle tests to control for fatigue. Techniques were tested in random order with 2-min rests between, and all test values were normalized to a %MVIC (Tu ¨rker, 1993). Subjects were allowed practice in each technique immediately prior to the test until they felt confident and were assessed by the investigator to be performing the technique correctly according to the same criteria used during the training session. Two minutes of rest were allowed to control for fatigue prior to testing. One test attempt only was allowed for each technique due to the high physical demands of the task. Subjects were asked to apply 20 kg of force to an artificial treatment surface continuously for 90 s. No feedback was supplied to the subject from the investigators during the test phase. A 2-min rest period was allowed before this procedure was repeated for the second and final test techniques. Order of testing was randomized between subjects. Surface EMG data were saved and archived in AMLAB software for later offline use and analysis. Ratio data, in the form of RMS muscle activity (mV) for each 10 s block were automatically calculated by the AMLAB II software and manually transcribed directly into Microsoft Excel 2003 (Microsoft Corporation) for storage. Every effort was made to reduce the impact of noise on the EMG data, including piloting of the study procedures, testing of the equipment and repositioning of affected electrodes. Despite these measures, visual inspection of the raw EMG waveforms during data collection revealed noise artefact that was not able to be resolved during data collection and therefore had to be addressed as part of the analysis procedure. Data corrupted by noise were identified and removed. Subjects were not withdrawn from the study on the basis of noise; however, data from the individual muscles in which noise was identified were removed from the study. Data were normalized
175 to a percentage of a MVIC (indicating 100% MVIC). Surface EMG data were transformed to their natural logarithm (LnEMG) to achieve a normal data distribution and allow comparisons of mean values to be justified (Portney and Watkins, 2000). LnEMG muscle activity for each TPT technique was compared between the ‘non-contact’ left arm and the ‘contact’ right arm.
Results Thirteen individuals expressed interest but three were unavailable to attend the training session. A further three did not participate in testing: one subject was unavailable and two did not meet the inclusion criteria. Subjects were excluded if they had any significant musculoskeletal injury in the previous 12 months to the upper limbs, neck or upper back or if they were not student massage therapists. Seven subjects (n ¼ 7) aged 30–53 years (mean 40.55, SD 8.99 years) participated in both the training and testing sessions. Six were female, one was male, all were right hand dominant and used their right arm as the contact arm. A retrospective power analysis was performed on the data demonstrating a minimum expected power of 99%. Despite efforts to reduce the effect of noise, raw EMG waveforms were observed to be corrupted by noise artifact and values over 200%MVIC removed. Data from the SAT and DAT only were considered for one subject as the EMG data for the TTT was irretrievable from AMLAB. Data on all three techniques were collected and analysed from all other subjects. The reliability for forearm measures used to adjust the TriggerMateTM rope length was calculated as good (ICC ¼ 0.81) (Portney and Watkins, 2000). Average muscle activity (%MVIC and LnEMG) for each muscle group is presented in Table 1 for the three test techniques. The relative contribution of each muscle to the muscle group was indicated by ranking its activity in relation to other muscles in that group for each technique (Table 2). Muscle activity patterns appear variable across subjects with few consistent patterns. For the contact arm during the SAT and DAT, posterior deltoid contributed the most and LD the least. Using the treatment tool, PM contributed the most and middle deltoid the least. For the noncontact arm, LD contributed the most to the SAT and middle deltoid contributed the least. PM was the largest contributor for the treatment-tool and double-arm methods. Middle and posterior deltoid were the least active muscles during the TTTs and DATs, respectively.
ARTICLE IN PRESS 176 Table 1
E.K. Smith et al. Mean muscle activity (%MVIC) and transformed mean muscle activity (LnEMG).
Technique
Muscle
Mean muscle activity—%MVIC
N
Std. deviation
Mean LnEMG muscle activity
Std. deviation
Single arm
Contact arm Non-contact Both arms
27.774 12.689 20.232
63 63 126
15.541 5.583 13.878
3.167 2.455 2.811
0.572 0.412 0.612
Double arm
Contact arm Non-contact Both arms
18.960 12.970 15.965
63 63 126
19.289 4.066 14.205
2.547 2.516 2.531
0.881 0.308 0.658
Treatment tool
Contact arm Non-contact Both arms
9.960 13.737 11.849
54 54 108
6.745 5.668 6.485
2.108 2.530 2.319
0.623 0.441 0.578
Total
Contact arm Non-contact Both arms
19.345 13.102 16.223
180 180 360
16.662 5.121 12.699
2.632 2.499 2.565
0.827 0.388 0.648
The relative activity of each muscle and group muscle activity was then ranked according to technique (Tables 3 and 4) to determine if one test technique consistently produced lower muscle activity values for individual muscles. For the contact arm, the TTT consistently produced the lowest relative workload across all muscles except LD, which was least active for the DAT. All muscles generated the highest levels of activity during the SAT, where for the non-contact arm the lowest relative levels of activity were in PM, anterior and middle deltoid. LD and posterior deltoid were the least active muscles for the DATs and TTTs, respectively. Overall, for the contact arm the TTT produced the lowest muscle activity followed by the DAT. For the non-contact arm, the lowest levels of activity were produced during the SAT, then TTTs. Clustered linear regression was used to determine whether the differences in muscle activity (LnEMG) for each muscle group (contact arm and non-contact arm) were significantly different between the test techniques. The reinforced (treatment tool and double arm) techniques were compared to the SAT. The treatment-tool muscle activity was significantly different to the single-arm activity (p ¼ 0.004) comparing all muscles of both arms (Table 5). Double-arm muscle activity did not differ significantly from that of the SAT (p ¼ 0.159, Table 5). The analysis was repeated to compare the DATs and TTTs, but they did not differ significantly either (p40.05, data not presented). For the contact arm, the single-arm muscle activity was significantly different to that of the TTT (po0.001, Table 6). However, comparing the DATs and the SATs (p ¼ 0.057, Table 6), or the
treatment tool to the DATs (p ¼ 0.054, not presented) no significant differences were revealed (to the p ¼ 0.05 level). Comparing the muscle activity for the noncontact arm, no significant differences were revealed between any of the three techniques (SAT and DAT p ¼ 0.725, SAT and TTT p ¼ 0.650, Table 7. TTT and DAT p ¼ 0.93, data not presented).
Discussion The majority of previous studies on TPT have been concerned with evaluating the desired clinical outcome or effect of specific treatment techniques (Hou et al., 2002; Huguenin, 2004). TPT is performed in various clinical settings with conflicting evidence in relation to its effectiveness (Hou et al., 2002; Huguenin, 2004; Simons et al., 1999). The effect of performing these techniques on the treating therapist was the basis for this exploratory study. The techniques investigated (DATs, SATs and TTTs) are used as an alternative to traditional treatment methods to reduce the load to the joints of the digits, wrists and thumbs. Specifically, the reinforced DATs and TTTs are hypothesized to reduce the strain to the contact shoulder experienced during application of the SAT by redistributing the load over the larger area of both upper limbs. Using effective treatment pressures reported by Hou et al. (2002), it is possible that forces up to 17 kg/cm2 are transmitted through the joints of the wrists, hands and digits during traditional TPT treatment (estimated using a hypothetical area of
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy Table 2
177
Ranked LnEMG muscle activity across all muscles.
Single-arm technique Contact arm (a) Subject
PM
1 2 3 5 7 8 9 Mean
4 5 3 2 3 3 n/d 3.3
Non-contact arm (b) AD 2 2 1 3 2 2 4 2.3
MD 3 3 2 1 4 4 2 2.7
PD
LD
PM
n/d 4 4 n/d 5 5 3 4.2
1 1 n/d 4 1 1 1 1.5
5 4 4 2 3 4 3 3.6
AD 3 5 3 4 2 2 2 3.0
MD 1 1 1 1 1 5 1 1.6
PD 4 3 2 3 5 1 4 3.1
LD 2 2 5 5 4 3 5 3.7
Double-arm technique Contact arm (c) Subject
PM
1 2 3 5 7 8 9 Mean
4 5 3 2 5 3 n/d 3.7
Non-contact arm (d) AD 1 2 2 4 2 1 3 2.1
MD 3 1 1 1 3 4 2 2.1
PD
LD
PM
n/d 4 4 3 4 5 4 4.0
2 3 n/d n/d 1 2 1 1.8
4 5 3 4 3 4 3 3.7
AD 5 4 4 5 2 3 2 3.6
MD 3 3 2 2 5 5 1 3.0
PD 2 1 1 1 4 2 4 2.1
LD 1 2 5 3 1 1 5 2.6
Treatment-tool technique Contact arm (e)
Non-contact arm (f)
Subject
PM
AD
MD
PD
LD
PM
AD
MD
PD
LD
1 2 3 5 7 8 9 Mean
4 n/d 4 4 4 4 n/a 4.0
1 n/d 3 5 2 1 4 2.7
2 n/d 1 1 3 2 1 1.7
n/d n/d 2 3 5 5 2 3.4
3 n/d n/d 2 1 3 3 2.4
5 n/d 5 4 5 5 2 4.3
4 n/d 4 5 2 4 4 3.8
1 n/d 2 2 1 1 1 1.3
2 n/d 1 1 3 2 3 2.0
3 n/d 3 3 4 3 5 3.5
Muscle activity is ranked from lowest (1) to highest (5).Key: n/d—no data; mean—mean rank across all subjects; PM—pectoralis major; AD—anterior deltoid; MD—middle deltoid; PD—posterior deltoid; LD—latissimus dorsi.
force application of approximately 4 cm2). The findings from this study are specific to the application of the test techniques which require high levels of sustained pressure. Myers et al. (2005) defined categories of shoulder muscle activity as mild (o20%MVIC), moderate (20–50%MVIC) and moderate to marked (450% MVIC). The activities reported by Myers et al. (2005) were dynamic rather than sustained isometric, as in this study. However, despite the differences in mode of activity, for the purpose of comparison between techniques, similar classifications
were applied to muscle activity used in this study (Table 8). The muscle activity in the contact arm would therefore be classified as mild for the DATs and TTTs (17.3% and 10.2%) and moderate for the SATs (28.5%). For the non-contact arm, all techniques produced mild levels of activity (12.7%, 12.9%, 13.7% MVIC for the SATs, DATs and TTTs, respectively). The minimum level of EMG activity accepted by Myers et al. (2005) as an indication of a functionally active muscle was 10%. For the current study, every muscle group could be considered active for each technique, although
ARTICLE IN PRESS 178 Table 3
E.K. Smith et al. Ranked muscle activity (LnEMG) by muscle and technique. Contact arm
Pec major Ant delt Mid delt Post delt Lat dorsi
Non-contact arm
Single arm
Double arm
Tool
Single arm
Double arm
Tool
3 3 3 3 3
2 2 2 2 1
1 1 1 1 2
1 1 1 3 3
2 3 3 2 1
3 2 2 1 2
(3.33) (2.59) (3.08) (3.52) (1.47)
(2.84) (1.87) (1.59) (2.83) (1.09)
(2.56) (1.72) (1.01) (1.89) (1.22)
(2.53) (2.05) (0.45) (2.07) (2.52)
(2.68) (2.66) (2.20) (1.93) (2.02)
(3.15) (2.64) (0.48) (1.27) (2.48)
Muscle activity is ranked from lowest (1) to highest (3). Key: Pec major—pectoralis major; ant delt—anterior deltoid; mid delt—middle deltoid; post delt—posterior deltoid; lat dorsi—latissimus dorsi.
Muscle contributions
body); however, it was believed more appropriate to allow the participants an opportunity to choose a ‘‘position of comfort’’ to more closely simulate the clinical application of the techniques. Variation in activation patterns between clinicians is therefore also likely to be reflective of a multitude of individual factors, including the individual’s fine tuning of body positioning, injury avoidance strategies or muscle imbalance and compensatory activation. Other variables including level of clinical experience and pre-existing injury, which are also likely contributors to differing activation patterns, were screened for in both the selection and exclusion criteria. Differences in variation across the muscle set throughout a technique may be reflective of the technique itself (i.e. stable, controlled), and/or the strength, or fatigue resistance of the muscles involved.
Relative contribution of each superficial shoulder muscle, according to arm and technique There does not appear to be a consistent activation pattern in terms of the production of force by individual muscles for these techniques. This suggests great individual variability exists in the workload of the superficial muscles and may also reflect differences in skill level and experience, as muscle activation patterns are more variable during the learning of a motor skill (Shumway-Cook and Woollacott, 2001). However, even for totally consistent isometric activities, evidence exists of a wide variation in muscle recruitment strategies where continual substitution and variation in muscle activation occurs throughout the task duration (Scutter and Tu ¨rker, 1998). These alternating periods of rest and activation are thought to be one mechanism employed to prevent muscle fatigue and injury. Attempts were made to standardize the upper limb position during technique application (including plinth height, elbow position relative to the
Relative muscle activity in individual muscles Comparison of the techniques revealed that the muscles of the contact arm work at a higher level during the SATs than for the DATs and TTTs. This finding was expected since for the SAT only the contact arm is producing the treatment pressure yet for the reinforced techniques, the non-contact arm is assisting force application. Between the reinforced techniques, muscle activity for the TTT is comparatively less than for the DAT, although this was not significant. This change may be a reflection of difference in glenohumeral joint position during the TTT, where the humerus of the non-contact arm may be in a lesser degree of abduction and the forearm can be braced against the trunk. This could provide further stability to the glenohumeral joint from structures other than the muscles in comparison to the DAT. The finding of least muscle activity in the noncontact arm for the SAT was expected, as it was not used to apply the treatment pressure.
Table 4 Average activity (LnEMG) ranked for all muscles. Technique Single arm Double arm Tool Contact arm 3 (2.80) Non-contact arm 1 (1.92) Both arms 3 (2.36)
2 (2.04) 3 (2.29) 2 (2.17)
1 (1.68) 2 (2.00) 1 (1.84)
Muscle activity is ranked from lowest (1) to highest (3).
contact-arm muscle activity for the TTT is barely above this threshold.
ARTICLE IN PRESS Muscular load to shoulder in trigger point therapy Table 5
179
Clustered linear regression—both shoulders.
Linear regression Number of obs ¼ 360 F(2, 6) ¼ 19.07 Prob4F ¼ 0.0025 R2 ¼ 0.0948 Root MSE ¼ 0.61846
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
t
p4|t|
[95% Conf. interval]
Double arm vs. single arm Tool vs. single arm _Cons
0.279
0.173
1.61
0.159
0.705
0.145
0.491 2.810
0.109 0.148
4.48 18.88
0.004 0.000
0.760 2.446
0.223 3.175
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Table 6
Clustered linear regression—contact arm.
Linear regression Number of obs ¼ 180 F(2, 6) ¼ 48.29 Prob4F ¼ 0.0025 R2 ¼ 0.2726 Root MSE ¼ 0.70911
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
t
p4|t|
[95% Conf. interval]
Double arm vs. single arm Tool vs. single arm _Cons
0.620
0.620
2.35
0.057
1.267
0.026
1.059 3.167
0.133 0.205
7.96 15.39
0.000 0.000
1.385 2.663
0.733 3.670
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Table 7
Clustered linear regression—non-contact arm.
Linear regression Number of obs ¼ 180 F(2, 6) ¼ 0.12 Prob4F ¼ 0.8889 R2 ¼ 0.0072 Root MSE ¼ 0.38838
Number of clusters (subject) ¼ 7 LnEMG (techniques compared)
Coef.
Robust std. err.
Double arm vs. single arm Tool vs. single arm _Cons
0.061
0.165
0.075 2.454
0.158 0.152
t
p4|t|
[95% Conf. interval]
0.37
0.725
0.344
0.466
0.48 16.11
0.650 0.000
0.312 2.081
0.464 2.827
Bold text indicates the meaningful value from the clustered linear regression analysis (significance p ¼ .05).
Changes in muscular load Compared to the SAT, muscle activity in the contact arm was reduced during the DATs and TTTs although
the reduction was significant only for the latter technique. This finding provides evidence that the TTT decreases the load to the shoulder; however, this load is not redistributed to the equivalent
ARTICLE IN PRESS 180 Table 8
E.K. Smith et al. Muscle activity by category. Muscle activity (%MVIC) Mild (o20%)
Contact arm Single arm Double arm Tool Noncontact arm Single arm Double arm Tool
Moderate (20–50%)
Moderatemarked (450%)
28.5 17.3 10.2
12.7 12.9 13.7
muscles of the non-contact arm. Bracing the upper limb against the trunk during the TTT may reduce the stability demands on the shoulder, thus decreasing overall load on the shoulder, as ‘total load’ is the sum of ‘treatment force’+‘stability force’. The amount of force applied through the noncontact arm during the DAT was not measured; therefore, the non-contact arm may not have been used effectively to assist application of the treatment pressure and thus contributed to the lack of difference between the SATs and DATs. The design of TriggerMateTM for this experiment incorporated a calibrated spring measure to determine that a minimum force was being applied through the device using both arms and therefore, the device was being used effectively.
of a treatment technique. Therefore, further research is required before a strong conclusion can be drawn on the usefulness of each technique for prevention WRMSD injury. However, while acknowledging these limitations to the study, for the healthy, novice massage therapist population, it was found that: 1. The contribution of each individual muscle tested was highly variable and inconsistent between subjects. 2. For the contact arm, the TTT produced the lowest amount of muscle activity across techniques. For the non-contact arm, the lowest levels of muscle activity were demonstrated in the SAT. 3. Reinforced techniques decreased the muscular load to the superficial shoulder muscles of the contact arm compared to the SAT to a similar extent; however, only the TTT significantly decreased the load compared to the SAT. Conflict of interest statement: Steve Argue is a qualified physiotherapist and the inventor of the TriggerMateTM tool. His involvement in the training and testing of participants was necessary as he is experienced in Trigger Point Therapy and the correct use of TriggerMateTM.
Acknowledgments The authors would like to express gratitude to the following people for their contributions to this study. Professor Adrian Estermann for his generous assistance in the statistical analyses of the surface EMG data. Dr. Sheila Scutter for her assistance in the interpretation of the surface EMG data.
Conclusions
References
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