Response

Dear Editor in Chief, We would like to thank Dr. Stöhr and colleagues (1) for their comments about the accuracy and generalizability of our study (2). Below, I provide a point-by-point response to the issues raised in their letter. 1. V˙O2max significantly improved for the following reasons: (i) Initially, the subjects were sedentary and had low aerobic capacities. Before the experiment, subjects reporting any participation in outdoor recreational activities were precluded. The initial training status affects the training effectiveness in aerobic fitness; the worse the initial state, the greater the improvement (3). (ii) The definition of HIIT differs between the meta-analysis Dr. Stöhr mentioned (4) and our study. The meta-analysis included sprint interval training characterized by effort at intensities equal to or greater than V˙O2max (5). However, HIIT is generally performed at an intensity that elicits 80% of V˙O2max. The newest meta-analysis suggests a long-interval, high-volume, and moderate- to long-term training intervention as the optimal protocol to ensure improvement in V˙O2max; this corresponds to our HIIT protocol (6). We previously reported that the same training program in patients with heart failure induced a mean increase in V˙O2max of 8.9 mL·min−1·kg−1) (56%) (7). Therefore, further research is required for clarifying the distinct effects of various training protocols on aerobic fitness. 2. Strain measurements vary with age, sex, race, and echocardiographic vendors. Strain values obtained with the ACUSON SC2000 were significantly lower than those obtained with Vivid E9 (8). Nevertheless, our results were confirmed using the same system, software, and machine from the same vendor for follow-up. Accordingly, the machine-specific normal values should be addressed in future studies. The incidence of racial/ethnic differences is important. Asians have reduced longitudinal systolic and diastolic mitral annular velocities, greater E/Ea, markedly smaller volumes, and lower LV mass (9). Although many publications have identified the normal range, studies performed in white populations may not be generalizable to Asian populations. 3. To ensure a similar energy expenditure among training groups, each subject used an HR monitor to obtain the assigned target HR (HRtarget), determined using the percentage of HR reserve, equivalent to the percentage of V˙O2 reserve. The exercise intensity for reaching the HRtarget was ensured by continuously adjusting the ergometer work rate throughout the training period. 4. We used the constant absolute intensity because of the influence of the altered loading state by the elevated V˙O2max after training. We interpreted the training effects by comparing the relative change obtained from stress echocardiography before and after the intervention. How could the exercise responses be interpreted and compared if the absolute workload was not matched? The practical guideline for the implementation of stress echocardiography was published and recommended using an absolute intensity (25 W for 2 min), ensuring less breathlessness, and detecting HR of <110 to 120 bpm to acquire better-quality images (10). However, increased variability of LV mechanics during the test was noted in the present study (2). It was observed to the lower variability in LV mechanics during exercise reported by Dr. Stöht (11). A more accurate test protocol for investigating LV function is valuable in clinical settings. Accordingly, our future study will consider using the protocol of stress echocardiography reported by Dr. Stöhr (11). Jong-Shyan Wang Graduate Institute of Rehabilitation Science and Healthy Aging Research Center Chang Gung University Tao-Yuan, TAIWAN