Gas exchange threshold to guide exercise training intensity of older individuals during cardiac rehabilitation

The gas exchange threshold (GET), which is determined during incremental exercise (Inc-Ex) testing, is often considered a safe training intensity for cardiac rehabilitation. However, there are only a limited number of reports on the actual implementation of this method. We assessed the applicability of GET-guided exercise using a constant load exercise (CL-Ex) protocol.We recruited 20 healthy older individuals (healthy, age: 69.4 ± 6.8 years) and 10 patients with cardiovascular diseases or risk factors (patient, age: 73.0 ± 8.8 years). On day 1, we determined the GET during symptomatic maximal Inc-Ex. On day 2, CL-Ex at work rate (watt: W) where the GET manifested during Inc-Ex (therefore, not corrected for the known oxygen response delay) was maintained for 20 minute. Arterialized blood lactate (BLa) levels were also determined.Oxygen uptake reached a steady state in all participants, with a mean respiratory exchange ratio of < 1.0. The mean BLa at the GET during Inc-Ex was 1.51 ± .29 mmol·l-1 in the healthy group and 1.78 ± .42 mmol·L-1 in the patient group, which was about .5 mmol·L-1 above the resting level. During CL-Ex, BLa increased significantly over the value at the GET (Inc-Ex). However, it reached a steady-state level of 2.65 ± 1.56 (healthy) and 2.53 ± 0.95 (patient) mmol·L-1. The %peak oxygen uptake, %peak heart rate, and %heart rate reserve during CL-Ex were 58.8 ± 11.5, 71.8 ± 10.3, and 44.9 ± 17.4, respectively. All participants could complete CL-Ex with mean perceived exertion ratings (Borg/20) of 11.8 ± 1.3 (healthy) and 12.2 ± 1.3 (patient). These heart rate-related indices and exertion ratings were all within the recommended international guidelines for cardiac rehabilitation.CL-Ex at the GET appears to be the optimal exercise intensity for cardiac rehabilitation.