Pulmonary rehabilitation: how to assess exercise capacity and peripheral muscle strength

There is also a short quiz at the end of the module to test your knowledge.

The guidance in this learning resource is aligned with the London Pulmonary Rehabilitation Competency Framework, which was developed to support the development of a consistent approach to documenting, evidencing and developing workforce competency in pulmonary rehabilitation services. Assessing exercise capacity and peripheral muscle strength using validated outcome measures are associated with Competency 8: Objective Assessment, as set out in the framework.

Find out more about the Competency Framework, individual competency records and other learning resources here.

Performed correctly, the 6MWT and ISWT are relatively safe tests for most patients attending pulmonary rehabilitation. However, there are some conditions which mean a patient should not take a field walking test:

Additionally, there are a number of relative contraindications for the tests. Patients with these conditions should be referred to a senior clinician for an assessment or decision regarding suitability to conduct the tests before they are undertaken:

With correct screening for the above conditions and appropriate monitoring during the tests, research suggests that very few patients who undertake either the 6MWT or ISWT will experience any long-term complications from the test itself.  

However, it should be noted that maintaining oxygen saturation monitoring during the tests is extremely important and the assessor should stop the test if the patient desaturates below 80%, or reports symptoms that make continuing with the test intolerable. Both of these are acceptable endpoints for the tests and should be recorded as such.

The 6 Minute Walk Test (6MWT) is a self-paced test where patients are asked to walk as far as possible in 6 minutes along a flat 30 metre track. The patient should aim to walk as far as possible in 6 minutes and should not run or jog. They are permitted to slow down, or stop and rest as necessary, but should resume walking when they are able and the timer should not be stopped during any periods the patient is paused.

Environmental factors or changes in methodology can have a significant impact on 6MWT results. In particular, the following factors should be kept consistent between tests and occasions to ensure valid comparable results:

There is evidence of a significant learning effect for the 6MWT, and therefore the test should be repeated twice (after an interval of 30 minutes) and the best distance recorded. Standardised instructions and phrases of encouragement should also be used to avoid influencing the test results.

Potential adjustments for comorbidities

For patients who need to hold anything in their hands during the test (such as a walking stick or supplemental oxygen), pulse oximeters should be positioned in such a way as to minimise interference - if possible by placing on the hand not in use.

For patients with poor peripheral circulation, you may need to use an ear probe oximeter.

The Incremental Shuttle Walk Test (ISWT) is a maximal and progressive walking test which gets harder as the test progresses.  The patient is asked to walk progressively faster on a 10 metre track in time to a set of beeps played on a pre-recorded audio track.  Access to the ISWT may be obtained from the University Hospitals of Leicester NHS Trust.

Initially, the speed is very slow, with the speed increasing every minute. The speed at which the patient should walk is directed by an audio signal. A triple bleep indicates the start of the test and whenever the walking speed is increased.   The patient continues to walk until they are either too breathless, or they can no longer keep up with the beeps (defined as the patient being 0.5 metres away from the cone when the bleep sounds on a second successive 10 metre length). The total number of completed 10 metre lengths (shuttles) should be noted.

Environmental factors or changes in methodology can have a significant impact on ISWT results. In particular, the following factors should be kept consistent between tests to ensure valid comparable results: 

Similarly to the 6MWT, there is evidence of a significant learning effect for the ISWT and therefore the test should be repeated twice (after an interval of 30 minutes) and the best distance (number of completed shuttles x 10 metres) recorded. Only standardised instructions from the prerecorded audio are used.  No additional encouragement is given by the instructor, with the exception of advising the patient of the need to increase their walking speed.

Potential adjustments for comorbidities

Because the test is dependent on being able to listen to both prerecorded instructions and regular beeps, it may not be possible to conduct this test for patients with significant hearing impairments. The 6MWT may be easier to perform in these circumstances.

For patients who need to hold anything in their hands during the test (such as a walking stick or supplemental oxygen), pulse oximeters should be positioned in such a way as to minimise interference - if possible by placing on the hand not in use.

For patients with poor peripheral circulation, you may need to use an ear probe oximeter.

Although assessing peripheral muscle strength (specifically lower-limb muscle strength) is outlined as necessary in the British Thoracic Society guidelines, there is no preference for a particular type of testing in the current guidance. Therefore, a variety of different approaches to measurement are possible.

Peripheral muscle strength tests, when performed carefully, help to guide accurate exercise prescription. However, these tests are contraindicated when a vigorous muscle contraction could cause further injury. Patients with these conditions should not perform tests of muscle strength: 

Some patients may also have comorbidities which limit their ability to exercise. In all cases clinical judgement should be exercised. Patients with the following conditions should be referred to a senior clinician for advice before testing:

Patients with these conditions (or other illnesses affecting their ability to exercise) are also likely to need specific modifications to their exercise prescription to allow them to complete the programme. 

There are two primary methods of testing muscle strength: 

Isometric and isotonic exercise methods can both be used as valid measures of quadriceps strength. Choosing between the two may come down to two considerations:

The rest of this section will explain how to use different techniques for measuring quadriceps strength.

There is no current international consensus on isometric testing approaches for pulmonary rehabilitation. You can find general guidance on isometric testing and common types of isometric testing (such as hand-held dynanometry) on Physiopedia.

Isotonic muscle testing uses equipment such as resistance machines or leg weights to test the maximum dynamic output of a muscle. A range of commercial gym equipment (such as leg extension machines or leg presses) may be used, as well as ankle weights or other free weights.

As with other tests, it is essential that the equipment used remains consistent between tests to allow for comparisons to be made. It is particularly important to be consistent in how the equipment is set up (e.g. consistent range of motion for resistance machines where the seat, lever or other parts of the equipment may be adjusted). Make sure that the patient can complete the full range of motion for an exercise without restriction; for tests such as the seated leg extension using ankle weight shown in the video in this module, you may need to adjust the height of the chair for taller patients to ensure the floor does not limit the range of motion.

The primary output of muscle strength testing is a 1 Repetition Maximum (1RM) - the greatest weight for which a single repetition can be achieved by the patient. You may choose to either test a true 1RM or use submaximal loads to estimate a 1RM. Your choice will depend on the equipment available to you and the experience of the patient; sub-maximal testing may be safer for patients who are less familiar with resistance training.

Watch the video below to find out more about warming up for isotonic muscle strength testing and conducting these types of tests.

Use of 1 rep maximum and calculations to estimate 1 rep maximum from sub-maximal work 

 The strength-building elements of most exercise prescriptions use percentages of a one-rep maximum (1RM) to guide training load. For example, the prescription may call for 5 repetitions of a dumbbell shoulder press at 70% of 1RM. 

1RM is used to indicate the maximum load that could be safely lifted for a single repetition. Isometric exercises can often be performed as 1RM.  

However, for isotonic exercises it is generally likely to be easier and safer to conduct a sub-maximal test, where the patient lifts a lighter load for as many repetitions as they can, and then estimate their 1RM using a calculation based on the load and repetitions achieved. 

The two main calculations used for this estimation are the Brzycki and Epley formulas: 

Brzycki formula 

Estimated 1RM = Weight lifted / (1.0278 – (0.0278 x number of repetitions))  

 
Epley Formula  

Estimated 1RM = (0.033 x number of repetitions x weight) + weight 

You can also use an online calculator to perform the calculations. 

Note that the two formulas give slightly different results; if you are using more than ten repetitions to estimate the 1RM, the Epley formula will return a slightly higher estimate. For this reason, it is important that the same calculation is always used when comparing scores for an individual patient. 

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