Assessment of exercise capacity provides valuable information to guide exercise prescription. This includes subjective assessment of an individual’s exercise tolerance, and objective exercise test results, which can be used to calculate exercise intensity based on an equation or algorithm.

All assessments of exercise capacity have strengths and weaknesses in assisting exercise prescription, and many published studies have evaluated their validity in various clinical settings.

When deciding on the most appropriate exercise test, consider:

• The workload intensity achieved during the assessment and its implication for risk
• The clinical risk of patients you are likely to manage within your service
• Whether the assessment will also be used for research or to evaluate your service. If so, strict adherence to testing procedure guidelines will promote validity and reproducibility of outcomes

Exercise capacity can be assessed by the following tests depending on the facilities available and the level of medical support:

• Maximal test (exercise stress test; EST)
• Cardiopulmonary exercise test (CPET)
• Submaximal test (six-minute walk test; 6MWT)
• Submaximal treadmill test
• Incremental shuttle walk test (ISWT)

While some measure of exercise capacity should be included in all assessment processes, select the tests to be performed according to setting, expertise and desired outcomes.

TIP: Most submaximal, non-diagnostic tests are performed while the patient is taking their normal medication. HR-based calculations are complicated by medications that alter HR response during exercise (e.g., such as beta-blockers). Therefore, it is important to document all medications at the time of assessment and consider cardiac medications that impact on exercise response.

HR response may not be a reliable guide to exercise prescription so it is useful to also use the Rating of perceived exertion (RPE) - Borg scale.

Maximal tests are characterised by HRs greater than 85% of age-predicted values off medication (maximum HR = 206.9 - 0.67 x age) or a rating of perceived exertion >15 (6-20 Borg scale; RPE).

Maximal exercise testing allows for:

• More precise exercise prescription than submaximal testing and greater reproducibility for follow up assessment
• Identification of cardiovascular compromise at higher levels of exercise and provision of an individualised maximum HR on which submaximal prescription can be based
• Gradation of exercise until the patient experiences signs/symptoms of cardiovascular compromise or reaches volitional exhaustion, or some other limiting symptom

Exercise stress test (EST)

ESTs are symptom-limited tests performed with a 12-lead ECG used to diagnose exercise-induced myocardial ischaemia, arrhythmias or an abnormal blood pressure response (see image below).

Figure 1: Patient undergoing exercise stress test (EST)

Reproduced with permission from SA heart

Cardiopulmonary exercise test (CPET)

A CPET is similar to an EST, with the addition of ventilatory gas analysis to determine peak oxygen consumption (VO₂ peak). Oxygen consumption is determined by central (heart) and peripheral (muscle) factors that respectively influence the body’s capacity to pump and utilise oxygenated blood.

A CPET is commonly used to determine prognosis in patients with HF and to stratify patients for cardiac transplantation.

• A VO₂ peak <14 mL/kg/min (or <12 mL/kg/min  in those tolerating optimal beta-blockers) identifies patients with poor 1-year survival who are likely to benefit from cardiac transplantation
• In patients under 50 years of age, VO₂ peak <50% of the value predicted for age supports consideration for transplant listing
• If the CPET is deemed submaximal (respiratory exchange ratio <1.05), a ventilation equivalent of carbon dioxide (VE/VCO₂) slope of >35 may also help determine transplant listing

TIP: Maximal exercise tests have a substantial risk of adverse events, so they require a medically supported environment with 12-lead ECG and BP monitoring.

Submaximal exercise testing is used more commonly than maximal testing as it is easily administrated, less likely to cause adverse events and does not require medical supervision and ECG monitoring.

Submaximal tests are defined by an age-predicted HR <85% calculated by the Gelish formula (maximum HR = 206.9 - 0.67 x age) or a RPE <15 (Borg scale of 6-20).

Perceived exertion is particularly important for patients taking beta-blockers. HR, blood pressure (BP, oxygen saturation, RPE and any symptoms should be recorded. The test should be terminated if the patient's HR exceeds the pre-determined limit or if symptoms develop.

Which Borg Scale?

Rating of perceived exertion (RPE) is commonly used to monitor and prescribe exercise intensity.

The original Borg Scale ranged from 6-20 and was developed to correlate with HR.

The modified Borg Scale is a category ratio on a scale of 0-10.

Both scales are widely used and no guidelines exist recommending the use of one over the other. For more information see Borg's rating of perceived exertion.

The six-minute walk test (6MWT is a self-paced walking test well suited to a hospital or community setting. An abundance of resources relate to its use in many clinical settings, most of which are adapted from the European Respiratory Society/American Thoracic Society technical standard.[#holland-ae-spruit-ma-troosters-t-et-al.-2014]

For complete instructions on administration see:

• 6MWT instructions (for administration and standardised verbal instructions)
• 6MWT recording form (to record physiological data and distance).

The test is undertaken using strict guidelines to ensure standardisation. A 30-metre track is recommended where space is available and standardised instructions are given.

For patients whose baseline 6MWT distance is >300m, a second test should be performed to account for a learning effect. For these individuals, walking distance is usually limited by walking speed rather than symptoms. For patients with more severe classes of heart disease, 6MWT results correlate well with VO2 peak, and only one 6MWT is recommended.[#adsett-j-mullins-r-hwang-r-et-al.-2011,#bellet-rn-francis-r-jacob-j-s-et-al.-2011]

Change in 6MWT distance can be measured in several ways. The most common include:

• Absolute change (post-program distance minus pre-program distance)
  The minimum important distance (MID) is 25m in patients with coronary artery disease (CAD) and 36m for patients with chronic HF.[#gremeaux-v-troisgros-o-benaim-s-et-al.-2011,#tager-t-hanholz-w-cebola-r-et-al.-2014]
   
• Percentage change
  This may be a more relevant measure for frail patients whose baseline distance is very short (e.g., <100m), and can be calculated as follows:
  % change = (post-program distance ‒ pre-program distance) ÷ pre-program distance x 100

The use of reference equations to adjust for variables such as height, weight, age and gender predict clinical progress no better than simply using 6MWT distance alone.[#frankenstein-l-zugck-c-nelles-m-et-al.-2008]

This incremental test is an externally paced test and involves walking between two markers 10 m apart. Auditory cues signal increased walking pace at each level (levels last 1 minute), until the patient reaches a predetermined criteria for test termination (85% max HR, Borg scale RPE = 15, failure to maintain walking pace on two consecutive lengths, development of symptoms).

The ISWT may be beneficial for less symptomatic patients who may reach a ceiling effect in a 6MWT.

In addition to measuring exercise capacity, more specific functional testing may be relevant for some individuals to assist exercise prescription and assessment of program outcomes. Some examples of commonly used functional tests include muscle strength testing, the timed up and go test, walk speed, tests for upper limb exercise capacity, step tests, balance and flexibility tests. More recently, combined measures such as the Short Physical Performance Battery and the Functional Difficulty Questionnaire have been validated in cardiac surgery patients.

Muscle strength may be included in the assessment to:

• Determine the appropriate load for resistance training
• Provide a global measure of muscle strength as a pre- and post-program outcome measure
• Assess strength deficits in specific muscles, thereby guiding exercise prescription

The 1RM method (i.e., the maximum weight lifted in one full range of motion) is often used to determine the appropriate intensity for resistance training. In patients with HF, however, it should be used cautiously as it can lead to Valsalva manoeuvre.

A graded approach such as 10-15 RM may be more appropriate,[#benton-mj.-2005] or more commonly, the Borg scale may be used. In the case of the latter, it is recommended that loads be progressively increased to a maximum RPE of 15.[#piepoli-mf-conraads-v-corra-u-et-al.-2011]

Muscle strength can be measured in several ways including:

• Isokinetic dynamometers – these provide accurate dynamic measures; however, they are rarely available in the clinical setting
• Hand-held dynamometers – these are simple and portable and provide useful quantitative data
• Manual muscle testing

Grip strength

Grip strength is measured quantitatively using a hand-held dynamometer (see example below).

Figure 3: Hydraulic hand dynamometer

Reproduced with permission from Optomo

Grip strength has demonstrated predictive validity, and low values are associated with falls, disability, impaired health-related quality of life, prolonged length of stay in hospital and increased mortality.[#chaudhry-s-mcavay-g-chen-s-et-al.-2013,#roberts-hc-denison-hj-martin-hj-et-al.-2011] Standardised procedures improve the validity and reliability of the assessment:

• Body position seated, shoulders adducted and neutrally rotated
• Testing upper arm by the side and elbow flexed at approximately 90°
• Forearm in neutral and wrist between 0-30° of extension
• Adjusted for hand size
• Recording which hand is dominant
• Using the maximum or the mean of three trials of grip strength in each hand

The following standard terminology/approach should be used when giving patients instructions: [#fess-ee.-1992]

• First state, ‘I want you to hold the handle like this and squeeze as hard as you can’
• Demonstrate the desired action and then pass the dynamometer to the participant
• Then, say the following: ‘Are you ready? Squeeze as hard as you can’
• As they squeeze, say: ‘Harder!…Harder!…Relax’

Assessment of other muscle groups

Assessment of other muscle groups, such as the quadriceps and hamstrings, may provide useful functional information. For patients with HF, local muscle strength has been found to correlate with patient outcome[#hulsmann-m-quittan-m-berger-r-et-al.-2004] VO2 peak,[#anker-s-swan-j-volterrani-m-et-al.-1997] and other parameters such as tumour necrosis factor alpha (TNFa).[#cicoira-m-bolger-a-doehner-w-et-al.-2001]

Quadriceps and hamstring strength may also be measured using a hand-held dynamometer (e.g., Lafayette Manual Muscle Test System – see below) using the protocol described by O'Shea et al. [#oshea-sd-taylor-nf-paratz-jd.-2007]

Figure 4: Lafayette Manual Muscle Testing System

Reproduced with permission from Lafayette Instrument

The 'timed up and go' (TUGT is a valid and reliable measure of basic functional mobility, used particularly in the frail elderly and in those with neuromuscular impairment. The test requires minimal equipment and is quick and simple to administer in a variety of settings. Whilst not sensitive to mild levels of balance dysfunction, it has demonstrated benefit in frail, older patients participating in an exercise program aimed at improving gait.[#shimada-h-uchiyama-y-kakurai-s.-2003]

Test procedure

• Sit the participant in a chair with arms, of standard height (44-47 cm)
• Give no physical assistance but allow the participant to use their usual indoor walking aid
• With their back against the back of the chair, on the command ‘Go’ the participant stands up, walks at a comfortable and safe pace to a floor marker 3m away, returns to the chair and sits down again
• Using a stopwatch, measure the time from the command ‘Go’ to when the participant’s back reaches the back of the chair after sitting down
• Perform two tests to account for a learning effect.

Table 1: In a sample of community-dwelling older adults, normative data was recorded as follows:[#steffan-t-hacker-t-mollinger-l.-2002]

Table 2: Normative scores for community-dwelling independent women were:[#isles-rc-choy-nl-steer-m-et-al.-2004]

Walk speed is a validated and reliable measure of the timing and spatial aspects of walking. Slow walking speed is strongly associated with frailty[#fried-lp-tangen-cm-walston-j-et-al.-2001] and more recently has been shown to be a predictor of hospital admission for patients with HF.[#chaudhry-s-mcavay-g-chen-s-et-al.-2013] The test can be conducted over 4m, 6m or 10m with markers placed 8m, 10m or 14m apart respectively.

Test procedure

• The participant commences in the standing position and uses their usual gait aid
• Place markers are positioned at each end of the track as well as 2 m in from each end
• Give the standard instruction: ‘Walk at your comfortable speed to the other marker without stopping or talking until you reach the other end.’
• Walk beside the participant and, as their first foot crosses the 2m mark of the track, start the stopwatch and commence counting strides
• Stop the stopwatch and stride-counting when their first foot crosses the mark 2m from the end of the track. Data are therefore collected over the central section of the walkway, avoiding acceleration and deceleration periods

The test can be modified to measure ‘fast’, or maximum gait speed, by changing the instructions to ‘walk as fast and as safely as you can’.[#steffan-t-hacker-t-mollinger-l.-2002]

For a 14m track with measurement over the central 10m:

Table 3: Normative data for walk speed

Various studies have reported slightly different normative data; Steffan et al.reported:[#steffan-t-hacker-t-mollinger-l.-2002]

These tests are frequently used in patients with chronic respiratory disease. However, they are yet to be validated for patients with cardiac conditions. Upper limb exercise capacity can be measured in a number of ways:

• Upper limb ergometry
• Unsupported upper limb exercise test (UULEX)
• Grocery shelving task
• 6-minute pegboard and ring test (6PBRT)

Step tests are a quick and transportable and require little or no equipment. In appropriately selected individuals they provide useful information regarding cardiorespiratory fitness.

Due to the risk of falls, however, step testing is not recommended for those with impaired balance, osteoporosis, lower limb musculoskeletal limitations or extreme deconditioning.

Numerous step tests have been described for use in the clinical setting, without consensus regarding the most appropriate test to use in patients with cardiac disease. It is important to consider balance and lower limb limitations prior to commencing the assessment.

Avoid using step tests that use high step heights (e.g., Harvard Step Test).

Balance disturbances may be identified by specific balance testing or indirectly, using other functional tests such as the TUGT. Indirect measures are less accurate, giving only a global view of balance rather than identifying specific deficits.

For some individuals, decreased joint range of motion or muscle length may contribute to impairments of balance or function. Specific testing of these parameters may be appropriate for these patients.

The SPPB is an objective tool which uses three tasks (standing balance, walking speed, and chair stand) for measuring lower extremity physical performance. The timed result for each test is rescaled according to predefined cut-points for obtaining a score ranging from 0 (worst performance) to 12 (best performance). The MCID for adult cardiac surgery patients is 0.44 - 1.34 points out of a total 12 points [#katijjahbe-ma-granger-cl-denehy-l-et-al]. A limitation of this tool is that it does not capture upper limb and thorax function.

The Functional Disability Questionnaire (FDQ) evaluates functional recovery of the upper limbs and the thoracic cage following cardiac surgery. Participants are asked to rate the difficulty that they experience when completing specific tasks by placing a mark along a 10cm line ranging from “no difficulty” to “maximum difficulty”.  The original version (FDQ) included 13 questions whilst the shortened version (FDQs-10) includes 10 item items.  The FDQ is valid, reliable and responsive tool for use with cardiac surgery patients in both the short term (4 weeks post-operatively) and long term (3 months post-operatively [#sturgess-tr-denehy-l-tully-ea-et-al]). The MID for the FDQ is 16.35cm out of 130cm and 4-10 out of 100 cm for the FDQ-s -10 [#katijjahbe-ma-denehy-l-granger-cl-et-al].