Summary of the clinimetric properties, target population and limitations of field-based functional exercise tests
| Exercise test | Measures | Validity | Reliability | Responsiveness | Target population | Strengths and limitations |
| Cycle ergometry (Wpeak) | Peak power, continuous SpO2, HR, breathlessness, leg effort, recovery | Predictor of prognosis [2, 3] (death, lung transplant) Positive (weak) correlation with HRQoL scales [4] | Reliable when familiarised with the test [5, 6] | Responsive to high physical activity and exercise training [7, 8] | Children (≥5 years) and adults covering the entire spectrum of lung disease severity | Not much space required Ability to test PwCF with CF-related pathogens Prognostic value of similar magnitude as V ʹO2peak Test can be done with supplemental oxygen Continuous monitoring of ECG and SpO2 |
| 6MWT [9] | Distance, continuous SpO2 [9], HR, breathlessness, leg effort, recovery | Able to discriminate between PwCF and healthy controls Lower exercise response compared to other field tests Moderate evidence for construct and content validity in adults and children with CF [10–12] | Reliable once learning effects are ruled out Test–retest reliability when two tests undertaken [13–19] | Most responsive in people with more severe lung disease; minimal clinically important difference: 33 m [10] | Lung transplant assessment People with advanced lung disease, including those prescribed some modulator medication Interim functional assessments in people with advanced lung disease or in those who are deconditioned [10, 20–23] | Volitional, not externally paced, constant workload Test can be done with supplemental oxygen Substantially less information about the cause of exercise intolerance compared to laboratory-based exercise tests Insufficient cardiorespiratory response and ceiling effect in children with normal lung function and fit adults with CF [22, 24–26] Requires 30 m floor Risk of transmission of pathogens while exercising on the hospital floor |
| MST-15 [27] | Level, HR, breathlessness, leg effort, recovery | Comparable V′O2peak, MSTD, HR and breathlessness compared to CPET (treadmill) [28] Moderate evidence for criterion, construct and content [25, 29, 30] | Reliable Inconclusive data on learning effect [9, 31, 32] Test–retest reliability [25, 33–35] | Responsive to hospital and home-based exercise therapy [25, 34, 36–38]; minimal clinically importance difference in children and adolescents with CF: 97 m [34] | Interim functional assessments (MST-25) [10] People with moderate and advanced lung disease | Requires space (≥15 m) In people with mild lung disease, 40% would complete all 15 levels of the MST [39] It is very challenging to conduct the test with supplemental oxygen Infection control guidelines may preclude conducting the test in certain individuals in the hospital setting |
| MST-25 [40] | Level, HR, breathlessness, leg effort, recovery | Strong correlation between MSTD and V ′O2peak in children with CF [35, 40] | Reliable Test–retest reliability [10] | Responsiveness unclear [39] | Physically fit people with mild-to-moderate lung disease | Requires space (≥15 m) Few published studies reported on the 25-level version of the MST It is very challenging to conduct the test with supplemental oxygen Infection control guidelines may preclude conducting the test in certain individuals in the hospital setting |
| 1-min STS | Repetitions, HR, breathlessness, leg effort, STS power index | Moderate-to-strong correlations with V ′O2peak and Wpeak in adults [41, 42] Moderate correlations with quadriceps muscle strength in adults with CF [43] Moderate correlations with 6MWT distance in children with CF [13] No correlation between 1-min STS and quadriceps strength and maximal mouth pressures in children [13] | Substantial learning effect (i.e. 18% improvement between first and second test) in adults with CF and children with CF (i.e. 3.1 (95% CI 1.3–4.9) repetitions) [13] Reliable once learning effects are ruled out [41] | Responsive to exercise-based pulmonary rehabilitation; estimated minimal important difference: five repetitions [42] | People with moderate-to-severe lung disease and lung transplant candidates Interim functional assessments [41–44] | Limited space requirements Test can be done with supplemental oxygen Continuous SpO2 measurement complicated due to motion artifacts Minimal evidence for use in children |
| Quadriceps muscle strength | Maximal voluntary strength | Able to discriminate between PwCF and healthy controls Correlation between quadriceps strength and 6MWT distance [45] | Reliable once learning effects are ruled out (less than 5 min) [46] | Responsive to strength training (e.g. [47]) | Interim functional assessments | Requires specific material (chairs with strain gauges) No accepted normative reference values for use in CF |
| Handgrip strength | Maximal voluntary strength | Able to discriminate between PwCF and healthy controls although generally less affected than other muscle groups Correlation between handgrip strength and FEV1 [45] | No specific assessment in PwCF | Responsive to high-intensity interval training (e.g. [48]) | Interim functional assessments | Easy to conduct, no specific training required Preserved handgrip strength may mask reduced quadriceps strength |
1-min STS: 1-min sit-to-stand; 6MWT: 6-min walk test; CF: cystic fibrosis; CPET: cardiopulmonary exercise test; FEV1: forced expiratory volume in 1 s; HR: heart rate; HRQoL: health-related quality of life; MST: modified shuttle test; MST-15: modified shuttle test 15-level; MST-25: modified shuttle test 25-level; MSTD: modified shuttle test distance; PwCF: people with cystic fibrosis; SpO2: oxygen saturation; STS: sit-to-stand; V ′O2peak: peak oxygen uptake; Wpeak: peak work rate.