Short-term HIT and MIT are equally effective in improving aerobic fitness, but HIT increases experience of negative emotions and exertion in sedentary middle-age men. This may limit the adherence to this time-effective training mode, even though displeasure lessens over time and suggests similar mental adaptations to both MIT and HIT.

In conclusion, HIT was more effective short-term strategy to increase R-R interval variability than aerobic training, most probably by inducing larger increases in cardiac vagal activity. The acute autonomic responses to the single HIT session were not modified by short-term training.