## 4 Discussion  
The purpose of this study was to elucidate whether exercise testing with ACE can be substituted for that of CE in the assessment of exercise capacity. Therefore, we tried to clarify whether the correlations between HR and VO\({}_{\text{2}}\) during exercise testing were different depending on the exercise modalities, i.e., ACE and CE. Our main findings were that the correlations between HR and VO\({}_{\text{2}}\) during the submaximal exercise testing were different depending on exercise modalities both in collegiate rowers and collegiate cyclists and that their VO\({}_{\text{2 max}}\) estimated from exercise testing with ACE was significantly lower than that with CE. As we have mentioned, it is sometimes difficult for people with disabilities or with orthopedic problems in their lower limbs to perform exercise testing with the lower extremities. For example, in a study which examined the feasibility of exercise testing in patients prior to total hip or knee arthroplasty, approximately 40% of them could not perform exercise testing with CE [26]. Therefore, if the exercise testing with ACE can substitute for that of CE, people with disabilities or with orthopedic problems in their lower limbs will benefit from exercise testing with ACE in assessing preoperative cardiopulmonary function. Exercise testing with ACE may also be useful for this population in evaluating the cardiopulmonary fitness for the purpose of understanding postoperative rehabilitation effects. The above was the reason it was necessary to verify whether exercise testing with ACE can be a substitute for exercise testing with CE. So far, some studies tried to compare the physiological responses during exercise testing between ACE and CE or treadmill walking and reported that peak VO\({}_{\text{2}}\) obtained by exercise testing with ACE was lower than that with CE or treadmill [12; 13; 14]. However, the subjects in these studies may simply have not reached the maximum cardiopulmonary loading during the exercise test with ACE due to muscle fatigue of the upper limbs [13]. In addition, HR at the end of the exercise testing with ACE was lower than that obtained with CE or treadmill, while RPE was similar or higher [12; 13]. Therefore, if the peak VO\({}_{\text{2}}\) at the maximum cardiopulmonary load can be predicted by exercise testing with ACE, exercise testing with ACE can be useful option, instead of that of CE, to evaluate cardiopulmonary fitness. From the above background, we tried to determine the correlation between HR and VO\({}_{\text{2}}\) during exercise testing for each exercise modality, ACE and CE, and estimated the VO\({}_{\text{2 max}}\) as the VO\({}_{\text{2}}\) corresponding to age-predicted maximal HR using the correlation formula. Contrary to our expectations, however, the correlations between HR and VO\({}_{\text{2}}\) were different depending on the exercise modalities, and VO\({}_{\text{2}}\) corresponding to the same HR was constantly smaller during the exercise testing with ACE than that during the exercise testing with CE. These results suggest that VO\({}_{\text{2 max}}\) may be underestimated in the case of using exercise testing with ACE compared to that of CE. Cardiopulmonary exercise testing is used in various clinical settings. For instance, such exercise testing is used as one of the measures for detecting coronary artery disease. In this case, exercise testing with ACE will be a useful option for people with injuries or disabilities in their lower limbs because it is enough to meet the purpose as long as the subject can reach an exercise load that causes any symptoms or abnormal findings to be displayed on an electrocardiogram.