Monitoring exercise intensity in diabetes: applicability of "heart rate-index" to estimate oxygen consumption during aerobic and resistance training

PURPOSE: Accurate quantification and monitoring of exercise "dose", described by oxygen consumption (VO2), is necessary for exercise prescription and individualization. However, due to the complexity and elevated cost of direct, gold-standard methods, this is rarely done outside research laboratories. Heart rate-index (HRindex) is a new simple method to estimate VO2 in healthy and clinical populations. We tested the performance of HRindex to estimate VO2 in diabetic patients during aerobic (AT) and isotonic training (IT). METHODS: Data from 12 males (age: 64 ± 5 years; BMI: 26 ± 12) with type 2 diabetes were analysed. VO2 and heart rate were measured during one AT and one IT session. Furthermore, VO2 was indirectly estimated based on HRindex. Then, the correspondence between measured and estimated VO2 was evaluated by two-way RM-ANOVA, correlation and Bland-Altman analysis. RESULTS: Estimated average VO2 values during AT (1292 ± 366 ml/min) were not different from (p = 0.243) and highly correlated with (r = 0.87, p < 0.001) the measured values (1369 ± 417 ml/min), with a small bias and imprecision. Conversely during IT, HRindex overestimated VO2 compared to the actual measures (1048 ± 404 vs 667 ± 230 ml/min, p ≤ 0.001) and only a moderate correlation was found between values (r = 0.43, p ≤ 0.001), with a large bias and imprecision. CONCLUSION: VO2 of aerobic exercises can be accurately estimated in diabetes patients using HRindex. During isotonic exercise, this method is not recommended for monitoring metabolic intensity due to large overestimation and imprecision. In aerobic exercise, HRindex offers a simple and valid alternative to the direct VO2 determination and may favour the applicability of time-resolved measures of exercise "dose".