Reliability and validity of heart rate variability threshold assessment during an incremental shuttle-walk test in middle-aged and older adults

Studies on the assessment of heart rate variability threshold (HRVT) duringwalking are scarce. We determined the reliability and validity of HRVTassessment during the incremental shuttle walk test (ISWT) in healthy subjects.Thirty-one participants aged 57 ± 9 years (17 females) performed 3 ISWTs. Duringthe 1st and 2nd ISWTs, instantaneous heart rate variability was calculated every30 s and HRVT was measured. Walking velocity at HRVT in these tests (WV-HRVT1and WV-HRVT2) was registered. During the 3rd ISWT, physiological responses wereassessed. The ventilatory equivalents were used to determine ventilatorythreshold (VT) and the WV at VT (WV-VT) was recorded. The difference betweenWV-HRVT1 and WV-HRVT2 was not statistically significant (median andinterquartile range = 4.8; 4.8 to 5.4 vs 4.8; 4.2 to 5.4 km/h);the correlation between WV-HRVT1 and WV-HRVT2 was significant (r = 0.84); theintraclass correlation coefficient was high (0.92; 0.82 to 0.96), and theagreement was acceptable (-0.08 km/h; -0.92 to 0.87). The difference betweenWV-VT and WV-HRVT2 was not statistically significant (4.8; 4.8 to 5.4vs 4.8; 4.2 to 5.4 km/h) and the agreement was acceptable(0.04 km/h; -1.28 to 1.36). HRVT assessment during walking is a reliable measureand permits the estimation of VT in adults. We suggest the use of the ISWT forthe assessment of exercise capacity in middle-aged and older adults.