The shorter, the (seemingly) harder

trening interwalowy

A High Intensity Interval Training is commonly used in resistance sport. Understanding of loads arising from various reports of this type of training is a key to designing single sessions and create training plans. A high intensity interval training session is most often defined by working time, rest time, number of cycles and intensity of each working time (sometimes this includes “rest” time intensity). This intensity can be expressed in terms of external load (power, pace, distance time), internal load (pulse – expressed in beats per minute, or more reasonably – in HRmax percents or HRR percents – a difference between maximum pulse and rest pulse) or subjective rate of perceived exertion (RPE).

Norwegian scientists from the University of Agder decided to study the external load (power), internal load (HR and lactate level) and perceptive (RPE) of three types of high intensity interval training session. They differed in terms of working time (4×16 min., 4×8  min. or 4×4 min.) with a 2-minute break between repetitions, assuming that each session involves the following:

  1. a) maximum and keepable entire session effort,
  2. b) it is possible to finish the entire session,
  3. c) make sure the average power during subsequent 4 repetitions is equal or slightly rising.

Studies adopting a bicycle simulator involved 63 well-trained cyclists who performed all 3 types of intervals for several times within 12 weeks. In total 1400 sessions were subject to analysis.

The table below shows average results of specific parameters for particular types of intervals.


Session % of power in TT 40min % HRmax Lactate (mMol.L)
4 x 16 min. 95 89 4,7
4 x 8 min. 106 91 9,2
4 x 4 min. 117 94 12,7


After every repetition, the participants specified their subjective rate of perceived exertion (RPE) in the Borg’s scale from 6 to 20, and after every session the entire session exertion rate in Foster’s scale from 0 to 10. In spite of doing every type of intervals with maximum keepable entire session exertion, RPE of shortest intervals 4×4 minutes was much more frequently (4-6 times) defined to be 19-20, and sRPE – 9-10, when compared to longer intervals.

Fig. 1
Power, pulse frequency (%HR Peak) and Rate of Perceived Exertion (RPE) during subsequent repetitions of three types of interval sessions. The power differed substantially between types of session but not between further repetitions during a specific session (which was one of the assumptions). %HRmax and RPE differed substantially between types of session – inversely proportional to interval duration and these rates grew gradually between subsequent repetitions during particular sessions, regardless of interval durations.

It turns out that for intervals with maximum keepable exertion, subjective exertion hardness, ongoing (after every repetition) and entire session’s, is inversely proportional to interval duration, that is paradoxically – the shorter the single repetitions and entire session, the more tiring it seems. Persons who plan high intensity interval trainings must be aware of this in the process of choosing exercises.


“How Does Interval Training Prescription Impact Physiological and Perceptual Responses?”
Stephen Seiler; Øystein Sylta
International Journal of Sports Physiology and Performance
DOI: 10.1123/ijspp.2016-0464

Developed by Mariusz Goliński
Rehasport Clinic Motor Skills Trainer