Button B;  Monash University, Melbourne, Australia,
Dharmakumara M; Wilson L; Parry N; Hartley F; Borg B; T Keating D

Canadian Respiratory Journal. 2026(1):e9062245, 2026.

BACKGROUND: The Alfred Step Test Exercise Protocol (A-STEP) and
feasibility study were previously published. The aim here was to determine
the validity of the A-STEP compared to cycle ergometry (CPET) in adults
with CF.

METHODS: The A-STEP and CPET were carried out in random order 2 weeks
apart. A wearable, portable metabolic system was used to measure
breath-by-breath and minute-by-minute sampling of O2, CO2, heart rate, and
VO2. The main outcome measures were VO2max and HRmax.

RESULTS: Seven stable-state adults (3 male) on CFTR modulator therapy
with a mean (SD) and range of age 38.2 (13.4) 26-64 years; height 169.9
(10.9) 149.7-185.3 cm; BMI 22.8 (2.10) 19.5-28 kg/m2; FEV1 79.4 (18.9)
38.0-106.0; and FVC 95.1 (16.7) 63.0-114.0 percent predicted (pp)
completed both A-STEP and CPET. The VO2Max had high correlation and good
agreement between the A-STEP 31.3 (5.9) and CPET 29.8 (6.2) mL/min/kg, r =
0.88. The HRMAX was strongly correlated with the A-STEP 174 (17) bpm and
95.7 (7.4) pp versus 168 (15) bpm and 92.4 (5.3) pp with r = 0.92 and
0.86, respectively. The SpO2Nadir for A-STEP was 91.0 (4.0) and CPET 92.0
(3.3), r = 0.82. The VO2 at the anaerobic threshold (VO2@AT) occurred
significantly earlier for the CPET at 1021 (260) versus A-STEP 1361 (234)
mL/minute, p < 0.05. The VEMax for CPET was 84.1 (18.8) and A-STEP 73.5
(15.8) L/minute, p < 0.05. The AWESCORE also ensured baseline stability.
The number of levels completed during the A-STEP was 10.7 (12.9) ranging
from 9 to 15.

CONCLUSION: The A-STEP may be a portable, valid surrogate to
cardiopulmonary exercise testing using cycle ergometry.