Chronic obstructive pulmonary disease (COPD) is a heterogeneous lung condition characterised by chronic respiratory symptoms and persistent, often progressive, airflow obstruction.¹ It is a leading cause of morbidity and mortality worldwide.¹ The original project identified tobacco smoking, household biomass fuel exposure and occupational dusts as the principal risk factors.

The burden of COPD extends beyond the airways. Muscle dysfunction may involve both respiratory and peripheral muscles, and hyperinflation with increased work of breathing appears to be the main contributor to respiratory muscle dysfunction.² Chest-wall mobility is reduced in COPD and correlates with lung function.³ These changes contribute to dyspnoea and exercise intolerance.

Pulmonary rehabilitation (PR) is the established non-pharmacological treatment. The American Thoracic Society recommends PR for adults with stable COPD as a strong recommendation based on moderate-quality evidence.⁴ PR relieves dyspnoea and fatigue and improves emotional function.⁵ Exercise training is its core component.⁶ Interventions directed at chest-wall stiffness and shortened accessory muscles are less well established.

Proprioceptive neuromuscular facilitation (PNF) uses proprioceptive input, resisted contraction and stretch to modify neuromuscular responses. Autogenic inhibition, reciprocal inhibition, stress relaxation and gate control have been proposed to explain its effect on range of motion (ROM),⁷ although their relative contribution is debated.⁸ In respiratory care, PNF has been applied as hold–relax stretching of accessory and chest muscles and as facilitatory manual stimuli to the thorax.

Several studies have examined PNF-type interventions in COPD,^9-14 and a systematic review was published in 2025.¹⁵ Techniques, doses and comparators differ widely, and within-group improvement is frequently reported as efficacy. An updated critical synthesis is therefore warranted.

2. Rationale and objective

The original project asked “to determine the effect of different PNF technique in COPD individuals” and concluded that PNF was beneficial. This review updates that work. It incorporates recent clinical trials and systematic-review evidence and emphasises the distinction between within-group improvement and comparative treatment effect.

The objective was to critically synthesise published evidence on respiratory PNF in adults with COPD for pulmonary function, exercise capacity, dyspnoea, thoracic mobility, respiratory mechanics and health status, and to identify clinical implications and research gaps.

3.1 Review design This is a critical narrative literature review. It is not a systematic review, was not registered, and does not follow PRISMA methodology. 3.2 Literature search Original project. The project searched PubMed and Google Scholar. The search date was not reported in the original project. Targeted literature update. A targeted update was performed on 2 October 2026 by online searching of PubMed-indexed records, PEDro records, Cochrane records, ClinicalTrials.gov and publisher websites. Scopus and Web of Science were not searched directly. Publications from 2021 to 2026 were prioritised. 3.3 Search strategy The original project used the terms PNF, proprioception neuromuscular facilitation, repeated stretching, hold relax, COPD and chronic obstructive pulmonary diseases, combined with AND and OR. It reported 60,729 retrieved records. That figure exceeds one of its component searches (2,166 records) and is internally inconsistent; it is reported here as stated and is not relied upon. No screening counts were reported. The update combined intervention terms (proprioceptive neuromuscular facilitation, PNF, respiratory PNF, chest PNF, PNF stretching, respiratory muscle stretching, chest mobility) with COPD terms and outcome terms. Record counts were not logged and are not reported. 3.4 Eligibility considerations The original project included studies of people with COPD that used PNF as part of the intervention, published from 2015, with English full text. The update retained the population and intervention criteria, removed the lower date limit, and added quasi-experimental designs. One further criterion was applied: study details had to be verifiable against the published report or its indexed abstract. 3.5 Study selection A. Original project (four studies). Wada et al.10 and Liu et al.11 were retained. Singh et al.16 and Siva Jyothi et al.17 were not carried forward, because their full texts could not be accessed and their details could not be verified. Singh et al. also studied chronic bronchitis without confirmed spirometric staging, and Siva Jyothi et al. appears under the same title in two journals. B. Targeted update (four studies). Putt et al.,9 Mistry and Kamble,12 Kumaresan et al.13 and Zakaria et al.14 C. Contextual evidence. One systematic review,15 one trial of chest wall mobilisation20 and current guidelines.1,4 Six primary studies were synthesised (Figure 1). Selection was performed by a single reviewer. 3.6 Data extraction Design, sample, severity, intervention, comparator, duration, outcomes and findings were extracted. Four reports were read in full.10-13 Putt et al. was extracted from its indexed abstract.9 Zakaria et al. was extracted from its abstract and trial-registry record.14 3.7 Critical appraisal Randomisation, allocation concealment, blinding, attrition, sample size, comparator, co-interventions and follow-up were considered qualitatively. No formal risk-of-bias score was assigned. The PEDro scores in the original project were not carried forward.

4.1 Overview of the evidence

Six primary studies were synthesised (Table 1): three parallel randomised trials,^10,11,14 one double-blind crossover trial⁹ and two single-group pre–post studies.^12,13 The 2025 systematic review was registered in PROSPERO, searched to 10 June 2024 and included eight studies.¹⁵

4.2 Characteristics of included studies

4.3 PNF intervention characteristics

Two forms of intervention carry the PNF label (Table 2). Hold–relax stretching was used in four studies.^9-11,14 Liu et al. stretched eight respiratory and accessory muscles using a 3-second isometric contraction followed by a 15-second stretch, repeated three times.¹¹ Wada et al. combined hold–relax with passive stretching and acknowledged that the two techniques cannot be separated.¹⁰ Facilitatory manual stimuli were used in two studies.^12,13 They require no voluntary contraction and rest on a different rationale.

4.4 Effects on pulmonary function

FEV1 and FVC. In Liu et al., FVC and FEV1 did not increase significantly, and the groups did not differ after training.¹¹ In Zakaria et al., FEV1 rose by about 7% with chest mobility exercises and about 4% with PNF. The between-group differences in FEV1 and FVC favoured chest mobility exercises.¹⁴ No study showed a between-group advantage of PNF.

FEV1/FVC. No retained study reported this ratio as an outcome.

Inspiratory capacity and inspiratory reserve volume. IC and IRV were significantly better in the PNF group than in the control group after training.¹¹ This is a single-trial finding.

PEFR. PEFR increased immediately after one session of intercostal stretch, from 179.23 to 194.82.¹² It increased from 165.42 to 226.67 L/min after five days of facilitatory techniques.¹³ Neither study had a comparator.

Vital capacity. In a double-blind crossover trial, hold–relax stretching of pectoralis major produced a significant effect on VC compared with sham.⁹

4.5 Effects on exercise capacity

Evidence is mixed. Six-minute walk performance was better in the PNF group than in controls in Liu et al.¹¹ In Wada et al., results were similar between groups (488.0 versus 454.0 m), although the authors described the 33.2 m difference as clinically significant.¹⁰ In Zakaria et al., the between-group difference was 30.3 m (95% CI 19 to 41.6) in favour of chest mobility exercises.¹⁴ Kumaresan et al. reported a pre–post gain of 52.33 m.¹³ The minimal important difference for 6MWD in chronic respiratory disease is 30 m.¹⁸ Statistical significance and clinical importance did not coincide across trials.

4.6 Effects on dyspnoea and respiratory symptoms

Dyspnoea VAS scores were significantly lower in the PNF group than in the control group after training.¹¹ In Wada et al., dyspnoea after the 6MWT was lower with respiratory muscle stretching (1.53 versus 2.78 Borg points, p < 0.001).¹⁰ Zakaria et al. concluded that chest mobility exercises may relieve exertional dyspnoea more effectively than PNF stretching.¹⁴ Dyspnoea was an outcome in the crossover trial, but its abstract reports significant effects only for VC and ROM.⁹

Respiratory rate. RR fell from 24.82 to 21.18 breaths per minute immediately after intercostal stretch.¹² This is a within-group finding. No retained study reported SpO2 as an outcome.

4.7 Effects on thoracic mobility and respiratory mechanics

Chest expansion. Chest expansion increased by about 1 cm at axillary, nipple and xiphisternal levels immediately after intercostal stretch.¹² This was a within-group finding. Chest expansion improved in both arms of the head-to-head trial.¹⁴

Neck and shoulder mobility. Head protraction and shoulder flexion ROM were better in the PNF group than in controls, whereas pectoralis minor length did not change.¹¹ Upper-limb ROM also improved against sham in the crossover trial.⁹

Thoracoabdominal kinematics. Chest-wall volume increased with respiratory muscle stretching compared with control (140 ± 170 versus −86 ± 240 mL, p < 0.001), mainly through abdominal volume; rib-cage volumes did not differ.¹⁰

Respiratory muscle function. Individual muscle activity did not fall, but inspiratory muscle activity per litre was lower with stretching (p = 0.03).¹⁰ No PNF study measured respiratory muscle strength.

4.8 Effects on quality of life

The COPD Assessment Test (CAT) was the only health-status instrument identified. CAT scores were significantly lower in the PNF group than in controls after training.¹¹ CAT improved in both arms of the head-to-head trial.¹⁴ The most reliable estimate of the minimum important difference of the CAT is 2 points.¹⁹ Magnitudes in Liu et al. were presented graphically and could not be compared with this threshold. The systematic review reported that improvements in the impact of disease on quality of life did not differ significantly between PNF and comparator groups.¹⁵

4.9 Comparative evidence

Only one trial compared PNF with another chest-wall intervention, and PNF was not superior.¹⁴ Chest wall mobilisation is a related but distinct intervention. In severe COPD, additional chest wall mobilisation produced significantly greater improvements in respiratory muscle strength and thoracic excursion.²⁰ Breathing exercises may improve exercise tolerance in selected individuals, but the data do not suggest a widespread role in comprehensive management.²¹ Inspiratory muscle training improves inspiratory muscle strength, exercise capacity and quality of life and decreases dyspnoea.²² No study compared PNF with a comprehensive PR programme.

Figure Legends

Figure 1. Evidence identification and synthesis framework. Record counts are not shown because they were not logged. This is not a PRISMA flow diagram.

Figure 2. Proposed physiological pathway of respiratory PNF. All links are hypothesised and have not been demonstrated as causal.

Figure 3. Proposed clinical integration framework. The framework reflects clinical reasoning and has not been validated.

Tables

Table 1. Characteristics of included primary studies

Table 2. PNF intervention characteristics

Table 3. Outcome-specific evidence

Table 4. Respiratory PNF in relation to conventional pulmonary rehabilitation

Table 5. Overall evidence summary

Figures

Figure 1. Evidence identification and synthesis framework.

Figure 2. Proposed physiological pathway of respiratory PNF.

Figure 3. Proposed clinical integration framework.

No new datasets were generated for this literature review.

5.1 Principal findings People with COPD improve over time when given PNF. The evidence does not show that PNF is superior to an active comparator. The most consistent comparative finding is lower dyspnoea when stretching is added to aerobic training.10,11 The original project’s conclusion of “strong evidence” is not supported. 5.2 Interpretation of pulmonary function outcomes No controlled finding supports an effect of PNF on FEV1 or FVC. This is physiologically expected, because PNF acts on the chest wall and not on airway or parenchymal pathology. The original project stated that FVC and FEV1 improved in Liu et al.; the published trial reports no significant change.11 Gains in PEFR came from uncontrolled designs and an effort-dependent measure.12,13 The between-group gain in IC is consistent with improved operating volumes, but it rests on one trial that did not measure hyperinflation directly.11 The VC effect against sham is the only blinded finding, from ten completers over two days.9 5.3 Interpretation of functional exercise outcomes Walk-distance findings conflict. One trial found a significant between-group difference.11 Another found a non-significant difference that exceeded the 30 m threshold.10,18 A third found a significant 30.3 m difference against PNF.14 The 52 m gain after five days13 is likely to include a learning effect, since two tests are recommended at each assessment.18 5.4 Interpretation of dyspnoea and quality-of-life outcomes Dyspnoea was lower with added stretching in both add-on trials, using different scales.10,11 Participants could not be blinded, and dyspnoea is self-reported. Quality-of-life evidence is confined to the CAT in one comparative trial.11 5.5 Potential physiological mechanisms Established. Hyperinflation and increased work of breathing impair respiratory muscle function in COPD,2 and chest-wall mobility correlates with lung function.3 Proposed. Hold–relax stretching may lengthen shortened accessory muscles, reduce chest-wall stiffness and permit greater thoracic excursion.7,8 Facilitatory stimuli may alter breathing pattern through proprioceptive input.12,13 Greater abdominal contribution and lower muscle activity per litre after stretching10 are consistent with these proposals (Figure 2). None of these mechanisms has been demonstrated directly in the respiratory muscles of people with COPD. 5.6 PNF as an adjunct to pulmonary rehabilitation Both trials with between-group benefit delivered stretching alongside supervised aerobic training.10,11 The effect may therefore depend on that context. The evidence supports PNF only as a possible complement. It does not support replacing any component of PR. 5.7 Clinical applicability All participants were clinically stable. Two studies enrolled only men.13,14 Severity ranged from GOLD 1–212,13 to moderate-to-severe.10,11 Generalisation to very severe disease and the post-exacerbation period is not supported. 5.8 Safety and feasibility The four reports read in full did not report adverse events systematically.10-13 Wada et al. recorded two withdrawals after hospitalisation for non-respiratory diseases.10 Absence of reporting is not evidence of safety. Completion was 28 of 3010 and 55 of 6011 in the add-on trials, and 10 of 14 in the crossover trial.9 5.9 Limitations of current evidence Randomisation and concealment: three parallel trials were randomised; concealment was reported in two.10,11 Blinding: the crossover trial was double blind;9 assessor blinding was explicit in one parallel trial.10 Attrition and analysis: both add-on trials analysed completers only.10,11 Sample size: 10 to 65; calculations were reported in two trials.10,11 Comparators: two studies had none.12,13 Intervention standardisation: technique, muscle, hold time and dose all differed. Follow-up: none after treatment; three interventions lasted one week or less.12-14 Limitations of this review: This narrative review was restricted to English-language publications and was conducted by a single reviewer. The evidence base was updated using recently available literature; however, record counts from the updated search were not logged. Full-text reports were available for most included studies, while two studies were assessed using indexed abstracts, with additional trial-registry information available for one study. These limitations may have affected the completeness and reproducibility of the literature identification process. 5.10 Research gaps The following remain after the update: adequately powered multicentre trials; standardised protocols and dose; follow-up beyond the intervention; adherence and adverse-event reporting; interpretation against minimal important differences; stratification by GOLD grade; very severe disease and women; home-based and tele-rehabilitation delivery; cost-effectiveness; comparison with complete PR; and exacerbation and hospitalisation outcomes. 5.11 Future research directions Add-on trials should compare PR plus PNF with PR alone, with concealed allocation, blinded assessors and intention-to-treat analysis. Hold–relax stretching and facilitatory stimuli should be compared directly. Operating lung volumes and respiratory muscle strength should be measured. 6. Clinical implications Respiratory PNF may be considered for stable patients with reduced thoracic expansion or shortened accessory muscles who are already undertaking exercise training. A proposed framework is shown in Figure 3. Assessment should document dyspnoea, SpO2, respiratory rate, chest expansion, exercise capacity and, where available, pulmonary function. Technique should match the impairment. Chest mobility exercises are a supported alternative.14 The literature does not establish a dose, and none is recommended here. Response should be monitored and the technique modified if the target impairment does not improve.

Limited evidence suggests that PNF-type stretching added to aerobic training may reduce dyspnoea, and one trial suggests benefit for inspiratory capacity, health status and walk distance. The evidence does not establish an effect on FEV1 or FVC, superiority over chest mobility exercises, or any long-term benefit. Respiratory PNF should currently be viewed as an investigational adjunct to, and not a replacement for, pulmonary rehabilitation. Adequately powered trials with standardised protocols and follow-up are required.

Table 1. Characteristics of included primary studies

Table 2. PNF intervention characteristics

Table 3. Outcome-specific evidence

Table 4. Respiratory PNF in relation to conventional         pulmonary rehabilitation

Table 5. Overall evidence summary

Ethical approval

The authors state that ethical clearance for the original academic project. No approval number is recorded in the project file. This manuscript is a review of published literature; no participants were recruited and no primary data were collected.

Funding

No external funding was received for this work.

Conflict of interest

The authors declare no conflicts of interest.

Author contributions

Stelvin Alisha D’Almeida: conceptualisation; investigation (original literature search and data extraction); writing - original draft. Farseen Mohammed P: methodology; investigation (literature update); critical appraisal; writing - review and editing; visualisation. Both authors approved the final manuscript.

Acknowledgements

None.

Declaration of generative AI use

Grammarly-AI Writing Assistant and QuillBot AI paraphrasing tools are used for rephrasing sentences from existing literature and improving English language skills in written text.