Patients with chronic respiratory diseases (CRDs) perceive various limitations of exercise capacity, which go far beyond (exertional) breathlessness. Peripheral muscle weakness and associated physical inactivity accelerate physical deconditioning and amplify exercise-induced breathlessness and peripheral muscle discomfort.1 The beneficial effects of exercise training (either as a standalone intervention or as part of a pulmonary rehabilitation (PR) program) have been well documented in patients with CRDs.2-4 Thus, exercise training has been established as a key component of non-pharmacological treatment options in CRDs.5,6 However, when it comes to practical recommendations on how to prescribe exercise training in patients with CRDs, there is only scarce information available in the international respiratory societies’ official statements and guidelines (Tables 1-2).5,7,8 This lack of information is even more noticeable regarding how exercise training should be adjusted and progressed during an ongoing exercise training program. Therefore, we collected the experiences of multiple international experts from the field of exercise training in CRDs on how they initially set and subsequently adjust exercise training workloads in patients with CRDs.

We initially developed a 64-item online survey to understand international expert practices on the delivery of exercise training in the setting of PR in patients with CRDs like chronic obstructive pulmonary disease, asthma, or interstitial lung disease. Peers checking for plausibility and consistency proofread the survey before its dissemination. The survey consisted of mixed open-ended questions and multiple-choice questions. Most of the questions afforded multiple answers – no question was mandatory to be addressed. The survey was built by using SurveyMonkey Software.

Thirty-five out of 45 invited experts from 21 countries across 5 continents (e-Figure 1) completed the survey (response rate: 78%). The professional background of the experts was multidisciplinary, consisting of physiotherapists (66%), pulmonologists (20%), and clinical exercise physiologists (14%). Most experts provide outpatient programs (71%) of 8 to 12 weeks, including 2 to 3 training sessions per week or inpatient exercise programs (37%) for 3 to 4 weeks applying 5-7 exercise sessions per week (e-Figures 2-4). All experts (100%) provide endurance training and 94% apply strength training. The online supplement includes all survey questions and the experts´ responses.

Tables 1-2 summarise the findings from the survey relevant to CET, IET and ST recommendations reported within international respiratory society statements, and guidelines as well as evidence from the literature.

Adjusting CET load during an ongoing training program

To advance the training load, 57% of experts initially increase the duration of exercise, aiming for a total CET duration of 30 to 40 minutes per session (71% of experts, e-Figure 21). As a second step, the intensity is increased. The rate of intensity progression is variable, as 71% increase the intensity depending on the patients´ symptoms (breathlessness and/or leg discomfort, e-Figure 25). Fig. 1 provides an overview on experts´ practices, when patients need to interrupt a CET session due to various reasons.

Fig. 1.

Summary of expert-based practices for prescribing and adjusting continuous and interval endurance training in patients with chronic respiratory diseases.

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Exercise prescription flowcharts

Exercise flowcharts were developed (Figs. 1 and 2) to facilitate tailoring of exercise training prescription to the individual patient's needs and capabilities. The expert practices on adjusting exercise training for the presented cases, were derived on the basis of the most prevalent responses to the survey questions (see online supplement).

Fig. 2.

Summary of expert-based practices for prescribing and adjusting strength training in patients with chronic respiratory diseases.

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We conducted a survey to capture the practices of international experts in delivering exercise training for patients with CRDs. Based on the expert clinical practice, exercise flowcharts were developed including suggestions on prescribing and adjusting continuous, interval, and strength training in patients with CRDs. International experts from 35 different centres across 21 countries completed the survey. This reflects the largest collection of multiple expertise within this field and provides an update and extension of previously published practical recommendations on exercise training in patients with COPD.13 Interestingly, there was considerable heterogeneity amongst experts on how they apply and adjust exercise training. This shows that there are several ways to reach the same aim for improving physical performance.

International guidelines and statements on PR provide recommendations on how exercise training in patients with CRDs should be prescribed (Tables 1–2). Our survey indicates that exercise training practices closely align with these guidelines. However, guidance on how to further adjust exercise training workload during an ongoing exercise training program and how to deal with situations when patients need to discontinue a session of exercise training due to various limitations, is scarce. Former surveys about exercise prescription also focussed more on exercise programme structures and modalities rather than on practical advice on tailoring exercise training workload.14,15 However, these aspects are highly relevant to the delivery of exercise training, and as such our flowcharts may provide further practical guidance on prescribing and adjusting exercise training according to the individual patient's needs and capabilities.

Endurance training (CET or IET) is consistently considered a fundamental component of exercise training in patients with CRDs.5,16-18 Most endurance training programmes are based on the CET method, in which exercise is performed at a constant intensity for an extended period without interruption. However, patients with severe CRDs are usually unable to sustain CET at relatively high intensities for an extended period due to increased respiratory distress.19,20 IET, which consists of repeated bouts of maximal/high-intensity exercise, alternated with short intervals of rest or low-intensity exercise, is a suitable alternative to CET.21 Several systematic reviews have consistently concluded that CET and IET demonstrate comparable efficacy in improving exercise capacity, exercise-induced dyspnoea sensations, muscle fiber structure and function, and quality of life.10,22 However, there is also some evidence, that especially patients with advanced CRDs perceive less dyspnoea during IET compared to CET.20,23 Underlying physiological reasons include a lower reliance on anaerobic glycolysis associated with lower ventilatory requirement and degrees of dynamic hyperinflation during IET.24,25 This explains the greater tolerance to IET compared to CET in patients with advanced CRDs. In our flowchart we presented practical indications from the experts´ experiences on when to consider IET instead of CET. Furthermore, practical cases are presented, that show how experts proceed, when patients need to interrupt CET or IET due to various reasons.

Studies have shown, that endurance training combined with strength training results in significantly greater improvements in muscle strength, muscle hypertrophy, and quality of life compared to endurance training alone in patients with COPD.11,12,26,27 Therefore, when patients with COPD have the capacity to perform a combined endurance and strength training program, this may provide the optimal exercise prescription.

One of the most important considerations concerning strength training is intensity. The general use of the term `intensity´ in the strength training literature, including the ACSM statement,28 refers to the load used (i.e. the fraction of 1 repetition maximum, %1RM). However, the expression of %1RM only represents the training load given as a fraction of maximal effort. The %1RM does not explicitly imply how hard an individual is working during a set of strength exercises. Therefore, Fisher and colleagues proposed that `intensity´ in its truest sense is the level of a subject´s effort applied to a given load.29 The inability to perform additional concentric contractions at a given load without significant changes in posture or movement speed was defined as `momentary muscular failure´.29 It has been shown that training to `momentary muscular failure´, maximizes muscle fibre recruitment (especially to the higher threshold fast-twitch muscle fibres), and increases the secretion of growth-promoting hormones compared to not reaching `momentary muscular failure´.30 Both are important factors for the capability of producing the greatest increases in muscle strength and hypertrophy.

To date, many studies have investigated the benefits of strength training and the different approaches to determine the optimal strength training intensity/load. Several systematic reviews have consistently concluded that muscle hypertrophy can be equally achieved across a wide spectrum of loads (30%1RM to 90%1RM).29,31,32 This evidence suggests that reaching `momentary muscular failure´ at the end of a strength training set (i.e. within a range of 8 to 15 repetitions) is the most important aspect for maximizing muscle hypertrophy. Therefore, it is not necessary to perform a 1RM effort for prescribing strength training intensity at a certain fraction of 1RM, because the fraction of 1RM alone is not relevant for improving muscle hypertrophy.29 Instead, it is the effort that a subject perceives as strenuous.

We are aware that the requirements for exercise training programmes in patients with CRDs vary widely across the world within different healthcare systems and local infrastructure. However, different types of exercise training apparatus (e.g. regular strength training machines, free weights, elastic tubes, etc.) can potentially increase exercise performance, when appropriate exercise training principles and intensity progression to reach `momentary muscular failure´ are applied.33,34 Recent studies have shown that an exercise training program using minimal equipment can be equally effective in increasing muscle strength and exercise performance compared to using sophisticated exercise apparatus.33,34 Therefore, what is much more relevant is how adequately patients exercise and not what kind of apparatus they use. Hence, our flowchart suggestions are also transferable to different exercise training settings.

Some limitations need also to be addressed. First, there is no direct proof of the benefits of the training recommendations included in our flowcharts. A clinical validation is needed. However, we suggest that the meaningful benefits shown in numerous exercise training studies might also apply to our expert-based recommendations since there is a substantial overlap in several basic training principles between the experts´ practices and scientific evidence.

Second, there was no official panel discussion involving all experts like a Delphi consensus process. Third, we did not ask for safety issues related to the experts´ experiences with exercise training. However, exercise training is usually accepted as a safe intervention for patients with CRDs following a baseline patient assessment to rule out any contraindications for physical exercise.5 Fourth, we provided general recommendations for a range of CRDs and did not take disease-specific considerations into account (i.e. an interval warm-up phase of 10-15 minutes in patients with asthma to prevent exercise-induced bronchoconstriction during a subsequent endurance training).35

Finally, the current flowcharts do not take into account non-invasive ventilation during exercise training,36 or other types of lower-limb muscle training, such as neuromuscular electrical stimulation,37 single-leg cycling,38 and whole-body vibration.39

A strength of this survey is the large collection and consolidation of international experts´ experiences for adjusting exercise training in patients with CRDs during an ongoing training program.

During the process of this survey, we have also identified important questions for future research like what patient/modality combinations are the best to safely achieve the largest training effects? What are the underlying changes in exercise performance, including intramuscular changes40 and oxygen uptake kinetics.41 Furthermore, is there a valid approach to optimise walking speed during ground-based walking training? Future studies should include a larger number of rehabilitation experts and should collect more data with a more detailed description of the expert responses, in order to standardize procedures at a world level in the area of exercise training in CRDs.

In conclusion, based on these experts´ experiences, exercise prescription flowcharts were developed. These flowcharts are meant to guide healthcare professionals in prescribing and adjusting continuous, interval, and strength training in patients with chronic respiratory diseases.

This study did not receive any funding.