Prolonged mean response time in older adults with cardiovascular risk compared to healthy older adults

BACKGROUND: During incremental exercise (Inc-Ex), the mean response time (MRT) of oxygen uptake (V̇O(2)) represents the time delay before changes in muscle V̇O(2) reflect at the mouth level. MRT calculation by linear regression or monoexponential (τ’) fitting of V̇O(2) data are known to be highly variable, and a combination of incremental and constant load exercise (CL-Ex) is more reproducible. METHODS: We evaluated MRT in older adults using linear regression and combination methods. We recruited 20 healthy adults (male: 9, 69.4 ± 6.8 years) and 10 cardiovascular risk subjects (male: 8, 73.0 ± 8.8 years). On day 1, they performed Inc-Ex using a 10W/min ramp protocol, for determination of the ventilatory anaerobic threshold (VAT) using the V-slope method. On day 2, they performed Inc-Ex to VAT exercise intensity and CL-Ex for 25min total. The MRT was calculated from the CL-Ex V̇O(2) average and the time at equivalent V̇O(2) in the Inc-Ex. We also assessed the amount of physical activity using the International Physical Activity Questionnaire short form (IPAQ-SF). RESULTS: The MRT of healthy participants and those at cardiovascular risk were 49.2 ± 36.3 vs. 83.6 ± 45.4s (p = 0.033). Total physical activity in the IPAQ-SF was inversely correlated with MRT. CONCLUSION: The MRT was significantly prolonged in cardiovascular risk participants compared to healthy participants, possibly related to the amount of daily physical activity. Individual MRT may be useful for adjustment of exercise intensity, but this should also be based on daily physical activity and individual condition during exercise.