Muscle Energy Techniques in patients with COPD: a randomised controlled trial

Abstract Background Physiotherapy plays a major role in long-term management of COPD. The aim of this study was to evaluate the effects of a 4-week muscle energy technique programme on pulmonary function measures, functional endurance capacity, chest wall mobility and ADLs in patients with COPD. Method A parallel-group, randomised controlled trial was adopted. 108 participants with COPD were recruited and randomly assigned to the intervention or control group. The intervention group received MET interventions, three-times weekly for 4 consecutive weeks, while the control group continued with their standard medical treatment. The study is clinically registered (ClinicalTrials.gov Identifier: NCT04773860). Results Statistically significant improvements in pulmonary function (p < 0.001), chest measurements (p < 0.001) and ADLs (p < 0.001) were observed for participants in the intervention group when compared to baseline measures. Clinical but not statistically significant improvements in the 6MWT were also noted (p = 0.08), outcomes which were not observed in participants enrolled in the control group. Conclusions This study concludes that METs can be used as an adjunct with other non-pharmacological treatments for patients with COPD to help manage their shortness of breath, improve their respiratory function and hence, as a result, improve their activities of daily living.


Introduction
Chronic Obstructive Pulmonary Disease (COPD) is a progressive and irreversible respiratory condition characterised by expiratory flow limitation that is associated with an inflammatory reaction to noxious particles or gases [1].It encompasses a spectrum of diseases, with Emphysema at one end, and Chronic Bronchitis at the other [2].
Progressive expiratory flow limitation eventually causes air trapping and pulmonary hyperinflation, leading to musculoskeletal alterations as a method of compensation for these respiratory changes, including also ribcage position alteration [3].This may therefore result in the typical barrel-shaped chest seen in patients with COPD [3], forcing the diaphragm and intercostal muscles to operate at a mechanically disadvantageous position.The diaphragm shortens and flattens, diminishing its ability to generate an adequate contractile force [4] and increasing the work of breathing [5].As a result of this, the recruitment of the accessory muscles of respiration takes place as compensation [6].
Although the accessory muscles of respiration adapt to the increased workload, their dual function as muscles of the upper limb and neck movements become limited, thereby decreasing the range of motion in these joints [6].Moreover, shortening of these muscles may lead to the characteristic forward head posture [1], cervical and shoulder protraction [3], and increased thoracic kyphosis [6].Another resultant effect of these changes is shortness of breath during activities of daily living (ADLs), these including simple tasks such as going up and down the stairs and dressing up, requiring one to seek assistance [7].
Current research is focussing on the use of Muscle Energy Techniques (METs) in the management of such circumstances.Studies [8,9] show that following the application of METs, muscle lengthening is observed, resulting in an increased range of motion, hence contributing to decreased thoracic wall stiffness [10].These studies also report improvements in Forced Expiratory Volume in 1 s (FEV 1 ) [4], reduction in respiratory rate [1] and increase in oxygen saturation [3].METs have been recommended as safer methods for patients than high-velocity manipulations, most especially in the upper cervical region [4].This is because it only applies a resistance of 20% of the patient's maximal contraction.However, few studies focus on COPD, with the available studies having a small sample size [4], unclear risk of bias [9] or only addressing the immediate effect of these techniques [3].Together with these limitations, to the knowledge of the authors, no study looked at the effects of METs on ADL performance.
Seeing these reported benefits, the authors aimed at investigating the effects of such techniques in a group of patients with COPD, a study that foresees benefits being reported in such patients in all outcome measures.Through this study, the effects of a 4-week MET programme on improvements in chest wall mobility, pulmonary function, functional endurance capacity, and ADLs was evaluated.

Design
This study reports the outcomes of a parallel group randomised controlled trial.
Patients with a diagnosis of COPD were referred between the period May 2021 to February 2022 from the respiratory outpatient clinic at the local general hospital.Upon consent, following verbal and detailed written information about the procedures, the patients were assessed for the 4 outcome measures that were performed at baseline and at the end of the 4-week intervention by the researcher.
Patients were centrally randomised by the intermediary to either the intervention or the control group using block randomisations via a computerised random number generated.The allocation sequence was accessible for the intermediary only and concealed through sealed envelopes for patients and researchers, people who assessed and performed the intervention for the purpose of this study (Figure 1).Therefore this study was single-blinded.The PEDro scale ensured for reliability and validity of the study.

Sample size
A total of 108 participants were enrolled in this study.This was calculated in advance using the equation from Gogtay [11].The total number of patients diagnosed with COPD and referred for Pulmonary Rehabilitation during the previous 3 years was the total population considered to identify the sample size used for this study.A significance level of 5%, alpha value of 0.8 and power of 0.8 was assumed, with a 10% expected drop-out rate to increase the degree of confidence in this study

Participants
All patients had to meet the following inclusion criteria which included a diagnosis of COPD by a medical consultant, had to be medically stable with no exacerbations within the previous 3 months, and had to be between the age range of 40 to 79 years of age.Participants who suffered from rheumatoid arthritis, musculoskeletal or neuromuscular pathologies, or cognitive disability that could affect comprehension or execution of the intervention protocol or outcome measurements were excluded.

Outcome measures
Four outcome measures were performed on all participants as indicated below: 1. Spirometry The patient was asked to breath out at maximal effort for 6 s so that FEV 1 is taken in the initial second of maximal expiration while FVC is taken throughout the whole duration of the test [12].The Spirometry machine used to carry out the outcome measure was the Spirometry PC software V2.2.4994.11.706 of Carefusion, by Micro Medical Limited.

6-Minute Walk Test (6MWT)
The 6MWT is a reliable, objective, and inexpensive outcome measure used to test submaximal exercise capacity and functional activity [13].It gives an indication of the individual's ability to carry out their ADLs and can be performed by patients suffering from severe COPD [13].The participants were asked to walk along a 30 m corridor and cover as much distance as possible in 6 min [13].The assessor used standardised verbal prompts to encourage the patient, while also recording oxygen saturation levels and dyspnoea scores using the Borg Dyspnoea Score every minute [14].

Chest measurements
Chest wall measurements were assessed using a tape measure, one of which is a valid, inexpensive, objective, and reproducible method [15].Measurements were taken at 2 points being at the 4 th vertebral level and 10 th vertebral level.

Manchester Respiratory Activities of Daily Living (MR-ADL)
Questionnaire MR-ADL is a repeatable and reliable physical disability scale for patients diagnosed with COPD [16].It is a self-completed scale and frequently takes around 10 min to complete.The MR-ADL questionnaire assesses functional ability in 4 different domains, that is in the kitchen, mobility, home duties and leisure activities [16].It provides information that is individualised to the patient and may be useful in designing care aimed at maintaining independent living at home [16].

Intervention
Participants in the experimental group received a 30-minute, one-to-one MET session for a duration of 4 weeks for 3 times a week, as per the Chaitow Protocol, with the aim of lengthening the accessory muscles of respiration, that is Upper Trapezius, the 3 parts of the Scalene muscle, Sternocleidomastoid, the Pectoralis Minor, Latissimus Dorsi and Serratus Anterior [17].The Chaitow protocol recommends that each muscle is individually stretched until no longer possible due to tightness and/or pain [17].A 7 s gentle isometric contraction is performed followed by 3 s of relaxation.The muscle was then taken to a new barrier through passive stretching for 30 s and the procedure was repeated twice and, bilaterally [17].This intervention was delivered in person by the main researcher at the department of Physiotherapy in Malta's general hospital.

Control group
The remaining 54 participants were asked to continue with their medical treatment as per the usual current procedure.All patients were then offered the possibility of receiving this treatment on completion of the intervention.

Data Analysis
Statistical analysis was performed using the Statistical Package of Social Science software, version 28.Upon ensuring all data was normally distributed, the One-way Analysis of Co-variance (ANCOVA) was computed to compare the intervention group with the control group at week 4.Moreover, the paired samples T-test was performed to assess each group separately at week 0 and week 4.

Results
The results are based on outcomes from 108 patients recruited in this study.Demographic information of the participants is presented in Table 1.
A 4-week MET intervention resulted in statistically significant improvements in pulmonary function measures for participants in the intervention group (Figure 2 and 3) when compared to the baseline measure (Table 2) and when compared to the control group (Table 4).An improvement of 6.48% in FEV 1 values (p < 0.001), 9.83% in FVC values (p < 0.001) and 8.76% in the FEV 1 /FVC ratio (p < 0.001) value, when compared to week 0 was observed in participants enrolled in the intervention group.Such differences were not observed in participants recruited in the control group, where the FEV 1 measures decreased by 0.08% (p ¼ 0.84), FVC by 0.84% (p ¼ 0.27) and a statistically significant decline of 0.85% was observed in FEV 1 /FVC (p ¼ 0.03) following 4 weeks (Table 3).This resulted in a difference of 5.15% in FEV 1 values (p ¼ 0.003), 10.15% in FVC values (p < 0.001) and 12.33% in FEV 1 /FVC ratio values (p < 0.001) when compared to the control group at the 4 th -week time point, values which were not statistically significantly different at baseline.
Although statistically significant improvements were not obtained in the 6MWT, a 4-week MET programme also resulted in the intervention group gaining improvements in this functional measure.The mean difference in 6MWD was that of 26.77 m (p ¼ 0.08) when compared to baseline measures (Table 2), whilst a 36.32 m mean difference (p ¼ 0.053) was observed when compared to the control group at the 4 th week (Table 4), once again a value which was not statistically significantly different at baseline.This 4-week MET intervention also resulted in significant improvements in chest measurements (Figures 4 and 5).When compared to baseline (Table 2), a statistically significant increase in chest measurements at both T4 and T10 vertebral levels was noted for participants in the intervention group at both maximal inspiration and expiration (T4 inspiration À 4.51 cm increase, p < 0.001, T10 inspiration À 4.34 cm increase, p < 0.001, T4 expiration À 5.83 cm decrease, p < 0.001 and T10 expiration À 5.04 cm decrease, p < 0.001).Little to no change was however observed within the control group (T4 inspiration À 0.03 cm increase, p ¼ 0.6, T10 inspiration À 0.02 cm increase, p ¼ 0.99, T4 expiration À 0.02 cm decrease, p ¼ 0.66 and T10 expiration -no change, p ¼ 0.93) (Table 3).The changes observed in participants recruited in the intervention group at the 4 th week resulted in statistically significant differences when compared with the control group (Table 4) both at T4 and T10 vertebral level on maximal inspiration (T4 À 5.14 cm increase, p ¼ 0.002, and T10 À 5.97 cm increase, p ¼ 0.013) and at T4 vertebral level on maximal expiration (T4 À 5.06 cm decrease, p ¼ 0.002), a trend which was though not observed at the level of T10 on maximal expiration (p ¼ 0.19).
When analysing for changes in ADL performance, a 4week MET intervention also resulted in the intervention group having statistically significant improvements as reported through the MR-ADL questionnaire (Figure 6).Statistically significant improvements were observed from baseline to the 4 th week time point for the intervention group (0.69 increase, p < 0.001) (Table 2), improvements which were not noted for the control group, where a slight decrease of 0.05 (p ¼ 0.42) took place after 4 weeks (Table 3).These improvements for the intervention group were statistically significantly different when compared with the control group [(p ¼ 0.002) Table 4].The improvements observed in the intervention group were greater than the minimal important difference of 0.5 set for this tool [16].

Discussion
Following 4 weeks of MET interventions, statistically significant improvements were observed in pulmonary function parameters (p < 0.001), chest measurements (p < 0.001) and ADLs (p < 0.001) when compared to baseline, for participants enrolled into the intervention group.Clinically significant but not statistically significant improvements were also observed in the 6MWT for this same group of participants (p ¼ 0.08).Such improvements were not observed for participants enrolled in the control group, where little to no change was noted following the 4-week intervention.These improvements also led to statistically significant differences when comparing outcomes between the intervention and control group at the 4 th week time point.One of the possible reasons for the significant improvements in lung function measures relates to the effects of METs on chest wall mechanics and the thoracic spine.significant improvements in pulmonary function scores.After just one single MET session, Yilmaz Yelvar et al.
[3] reported an improvement of 4% and 2% in FEV 1 and FVC measurements respectively.On the other hand, a 4-week intervention resulted in mean average increase of 6.48% for FEV 1 and 9.83% for FVC when compared to baseline.The improvements in these results therefore show that MET interventions carried out over a longer period might possibly result in more pronounced improvements in lung function measures.This could be attributed to an increased effect on muscle flexibility, allowing the muscle attached to one joint or a series of joints to lengthen and move through its range of motion as a result of longer duration interventions [20,21].
An increase in muscle flexibility results in a decrease in chest wall rigidity and the return of the accessory muscles of respiration closer to the optimal length, leading to improvements in mechanical efficiency [1].Such adaptations were also reported in an exploratory study performed by Morais et al. [5] where improvements in respiratory muscle strength, and neck and shoulder mobility led to an increased length in the pectoralis muscle and improvements in respiratory function.These authors continue to report that an improvement in head protraction angle led to the increased flexibility of the neck and shoulders and greater shoulder flexion angles, resulting in greater elevation of the upper limbs [5].These observations resulted in improvements in pulmonary function measures [5] suggesting that adaptive changes in the posture and mobility of a patient with COPD correlated with improvements in the patient's lung function [6].
A 4-week MET intervention also resulted in improvements in functional endurance capacity, improvements which could have occurred as a result of an alleviation in dyspnoea, which takes place as a result of relaxation of the accessory muscles of respiration.This leads to a reduction in the rate of firing of the muscle spindle when in the lengthened phase [22,23].This factor has been correlated by Wada et al. [24] with a reduction in dyspnoea sensation allowing patients to walk for longer distances and for a longer period when performing 6MWT [24].This though cannot be confirmed in our study, as dyspnoea scores were not recorded.
Wada et al. [24] reported that twice weekly sessions of hold-relax and passive stretching exercises for 12 weeks, resulted in their intervention group gaining 15 m in walking distance when compared to baseline, a difference that did not reach clinical significance, findings which relate to those obtained in our study.Although Wada et al. [24] carried out a longer duration programme, this did not translate into greater improvements in outcomes especially the walking distance.This therefore might confirm that the protocol of 4weeks of contract-relax METs, delivered 3 times weekly on alternate days carried out in our study was enough to provide the targeted outcomes, and recommendations set by Chaitow and Franke [17] of getting greater and longer improvements as a result of increase muscle viscoelasticity with that time period being adequate.The effects of such an intervention, as has been reported through the pulmonary function tests, have resulted in significant gains in the chest wall mechanics, but were not enough to target decreased lower limb endurance experienced by these patients, muscles which might require specific attention.
Even though the total distance gained by the intervention group was 26.77 m in the 4 th week when compared to baseline and 36.32 m when compared to the control group, both results were over the threshold for clinical significance [25].As stated by Holland et al. [26], patients suffering from COPD are expected to reach the minimal important difference of 25 m after any intervention.
Despite not having the right target to lead to improvements in walking distance, the MET interventions did influence chest wall mechanics.It is well known that chest wall dynamic hyperinflation and distortion of the ribcage due to airway obstruction cause a mechanical disadvantage to the respiratory muscles, dyspnoea and chest wall rigidity [22,27,28].Low-intensity prolonged fatiguing exercises such as respiration result in reduced relaxation of the muscle fibres due to a decrease in cross-bridge detachment rate, which therefore results in decreased lengthening of the muscle [29].Muscle stiffness could therefore be higher following prolonged tasks due to the muscle failing to relax [30].
Chest measurements were performed at both maximal inspiration and expiration to analyse the different breathing muscles recruited during the 2 stages of breathing [31].As was observed in our study, the assessment of chest measurements during inspiration and expiration confirmed statistically significant improvements in chest mobility, a gain which leads to several benefits, since changes in chest wall mechanics have an influence on pulmonary function measures and walking distance, as has been reported previously.This was confirmed by Kaneko et al. [32] who reported that any reduction in chest measurements correlated with lower lung function measures as interpreted through FEV 1 and FVC measures.Moreover, a decrease in exercise tolerance when compared to healthy individuals was observed by Kaneko et al. [32] due to decreased exertion contraction of the diaphragm and in the intercostal muscles.
These changes in muscle lengthening were also reported in another study by Rekha et al. [10] where a 4-week holdrelax intervention resulted in statistically significant (p ¼ 0.001) results in all 3 chest measurements when comparing pre-intervention and post-intervention measurements at axillary level, 4 th intercostal space and xiphisternal level.Lengthening of the accessory muscles and soft tissues around the chest wall was observed to assist in efficient muscle contraction and chest mobility [10].Muscle stretching promotes an increase in sarcomere number necessary when the muscle is not capable of lengthening by itself, thereby requiring an external force to increase its flexibility [29].With longer durations as in our intervention, that being three time weekly for 4 weeks, plastic and viscoelastic changes in myofascial connective tissue were observed to take place [33].Anand, Narwal and Sindhwani [33] observed statistically significant (p ¼ 0.001) improvements in chest measurements following a 3-day MET intervention.On comparing our study with that of Anand, Narwal and Sindhwani [33] greater results are observed following a longer and more frequent intervention.This further proves that the duration and frequency of stretching affects the extensibility of the muscle [33] leading to greater improvements in chest excursion measurements.
Significant improvements in the performance of ADLs also were noted, changes which could have resulted as a result of lower dyspnoea scores, lower metabolic load and improved pulmonary function measures [34].ADL performance may have improved following a possible increase in the length of accessory muscles of respiration, allowing for these muscles to act as both muscles of respiration, together with their primary role of muscles involved in upper limb movement.To the author's knowledge, this is the only study that investigated the effects of MET interventions on ADLs.Current research [34,35] is focussing more on the effects of strength training on respiratory or lower limb muscles through pulmonary rehabilitation rather than stretching exercises in the performance of ADLs in patients with COPD.Therefore, comparison of outcomes obtained through this study in relation of changes in ADL performance as a result of the MET intervention cannot be compared to other studies since these are lacking.

Limitations
This study does have some limitations which need to be considered.The evaluation of lung volumes and chest measurements using an optoelectronic plethysmography (OEP) would have provided more information on the effects of the MET interventions, however, this was not available for use during the time of this study as such equipment is not available.Therefore, tape measures were used as it is a practical and cheap measurement with high reliability in patients with COPD [15,28,33,36].In the systematic review by Tukanova et al. [36] observed that the OEP was more accurate when compared to other systems, with the tape measure being next in accuracy.Therefore, the implementation of the type of measuring device should be considered regarding their practical use [36].The researcher performed both the assessments and the intervention.Therefore, some element of bias might have been present.Dyspnoea measures were also not assessed for, resulting in lack of information on the effects of METs on dyspnoea scores.

Conclusion
Following a 4-week MET intervention period on patients suffering from COPD, statistically significant improvements resulted within the pulmonary function measures, chest expansion and ADL performance, and improvement in walking distance.All these outcome measurements provide evidence that this technique can be an effective treatment which can be used as an adjunct with other non-pharmacological Physiotherapeutic treatments offered to these patients.

Figure 3 .
Figure 3. Graph showing FEV 1 /FVC measures in the intervention group and control group.

Figure 4 .
Figure 4. Graph showing CE at T4 (inspiration) measures in the intervention group and control group.

Figure 5 .
Figure 5. Graph showing CE at T4 (expiration) measures in the intervention group and control group.

Figure 6 .
Figure 6.Graph showing the MR-ADL in the intervention group and control group.
Abbreviations: FEV 1 : forced expiratory volume in 1 s; FVC: forced vital capacity; FEV 1 /FVC: ratio of forced expiratory volume in 1 s to the forced vital capacity; 6MWT : 6 min walk test; CE-T4 Insp : Chest excursion at T4 during inspiration; CE-T10 Exp : chest excursion at T4 during expiration; CE-T10 Insp:chest excursion at T10 during inspiration; CE-T10 Exp -:chest excursion at T10 during expiration; MR-ADL: manchester respiratory activities of daily living; SD : standard deviation.Figure 2. Graph showing FEV 1 measures in the intervention group and control group.
¼ 0.04).The difference in duration between the study of Yilmaz Yelvar et al. [3] and our study brings out the possible benefits of a longer intervention time.Four weeks of 3 times weekly interventions resulted in greater and more statistically Clarke et al. [6] well

Table 2 .
Comparison of pulmonary function, 6MWD, chest excursion and MR-ADL in pre-test and post-test of the intervention group (n ¼ 54).

Table 4 .
Comparison of the control group and intervention group after a 4week programme (n ¼ 108).

Table 3 .
Comparison of pulmonary function, 6MWD, chest excursion and MR-ADL in pre-test and post-test of the control group (n ¼ 54).