194 High-Intensity Interval Training can have Negative Effects on Cardiovascular Risk Factors and ECG Parameters in a Young Healthy Population

Abstract

Low-volume – high intensity exercise has been shown to potentially be a time-efficient way to produce beneficial effects of exercise. Studies however have often demonstrated this in groups with existing pathophysiology and the relative benefits of high-intensity versus more usual moderate intensity interventions or resistance training remains unclear, as well as the durations required. Using a cross-sectional and an interventional approach we assessed relationships between exercise and cardiovascular risk factors within a young healthy population. 136 individuals had key measures of common cardiovascular risk including blood pressure, cholesterol and a 12-lead ECG taken, as well as completing a detailed exercise diary detailing volumes and intensity of exercise participation. A sub-set of 22 subjects participated in a six-week high-intensity exercise training programme comprising three sessions per week performing 10 sprints at 90–100% heart rate reserve (as assessed from measures of maximal heart rate reassessed every two weeks). All procedures were approved by the University of Leeds ethics committee. Weekly volume of exercise participated in did not significantly correlate with systolic blood pressure or total cholesterol, however intensity of exercise over the preceding 3 months did correlate significantly but positively with systolic pressure (p = 0.0164, regression coefficient 0.268 from Pearson correlation), a surprising potentially negative effect. Resistance training participation showed no correlation with blood pressure in terms of volume or intensity. Total volume of exercise participated in correlated with HDL cholesterol (r = 0.2, p = 0.03), but not intensity. With respect to ECG parameters volume of exercise showed no correlation with Tpeak-Tend but intensity of exercise correlated with the amplitude of T-wave alternans (r = 0.35, p -1 , p = 0.01; paired t-test) but not systolic blood pressure and had no effect on HDL cholesterol. The interval training protocol however also lead to a significant increase in the amplitude of T wave alternans (from 3.9 ± 1.4 µV to 7.62 ± 4.22 µV, p = 0.01) as well as increased T and R wave amplitudes in only six weeks. The data show the diverse possible impacts of exercise intensity versus volume. Volume and duration of training appears to be necessary for beneficial effects on HDL cholesterol. In contrast high intensity training offers potentially no benefit and possibly even negative effects. The ability of such a short intense protocol to effect notable cardiac electrical changes presumably mapping to structural remodelling and changes in cardiac repolarisation stability raises questions with regards to the use of, and effectively monitoring the safety of participation in intense exercise training programmes.