Effects of two endurance training protocols (High Intensity Interval Training = HIIT versus Polarized Training = POL) on endurance capacity, heart rate at rest and heart rate variability (HRV) in young sport students

The goal of the present study was the analysis of the effects of two endurance training interventions (HIIT versus POL) over a period of 5 weeks on 16/17 year old sport major students. The study was integrated in regular P.E. lessons. In addition to the training load, daily changes of easily measurable cardiologic parameters were monitored in order to assess their validity in predicting endurance performance.The students conducted 12 training sessions in two groups. With pre- and post-tests the endurance capacity was determined via Luc Léger’s shuttle run test.Heart rate parameters were measured within a time period of one week prior to and after the intervention. Running performance improved in the HIIT group significantly by 6.5% (p < 0.05), but remained constant in the POL group (+2,4%). Those students who improved their endurance performance by at least 5% simultaneously had a significantly (p < 0.05) increased HRV (rMSSD +11%). Participants who could not improve their persormance by 5% showed a significantly (p < 0.05) decreased HRV (rMSSD –8%).The HIIT group improved their endurance capacity with only 47% of training time compared to the POL group. HRV was, in contrast to resting heart rate, a valid predictor of endurance capacity.