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An interval training session is most often defined by the work time, the rest time, the number of cycles and the intensity of each work time (sometimes also the intensity of the “rest” time). This intensity can be expressed by a measure of external load (power, pace, time to cover a known distance), internal load (heart rate - expressed in beats per minute, or more sensibly, as a percentage of HRmax or as a percentage of HRR - the difference between maximum and resting heart rate), or a subjective measure of the severity of effort (RPE).
Norwegian researchers at Agder University set out to examine the external load (power), internal load (HR and lactate levels) and perceptual load (RPE) of three types of interval training sessions, varying the duration of work (4×16 min., 4×8 min. or 4×4 min.) with a 2-minute interval between repetitions, with each session performed:
(a) with the maximum, sustained effort of the entire session (isoverset),
(b) so that the entire session can be completed,
(c) so that the average power obtained during the next 4 repetitions is equal or slightly increasing.
Sixty-three trained cyclists were tested on bicycle ergometers, each performing all 3 types of intervals several times over a 12-week period. A total of more than 1,400 sessions were analyzed.
The table shows the average results of selected parameters for each type of intervals
Session | % power obtained in TT 40min | test % 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 each repetition of the trial, subjects also determined the subjective perceived exertion severity index (RPE) on the Borg scale from 6 to 20, and after each session also the perceived exertion index of the entire session on the Foster scale from 0 to 10. Despite performing each type of interval with the maximum maintainable exertion of the entire session, the RPE of the shortest 4x4minute intervals was determined significantly more often (4-6 times) at 19-20, and the sRPE at 9-10, than that of intervals of longer duration.
Figure 1
Obtained power (Power), heart rate (%HR Peak) and rate of perceived exertion (RPE) during successive repetitions of the three types of interval sessions. Power was significantly different between session types, but not between successive repetitions during a given session (which was one of the assumptions of the experiment). %HRmax and RPE were significantly different between session types - inversely proportional to the length of the intervals, and these rates increased gradually between successive repetitions during each session, regardless of the duration of the intervals.
It turns out that with intervals with maximum sustained effort, the subjective perceived heaviness of this effort, both ongoing (after each repetition) and the entire session, is inversely proportional to the duration of the intervals, i.e., paradoxically - the shorter the duration of individual repetitions and the entire session, the more tiring it seemed. Those planning the type of interval training should be aware of this phenomenon in the practical selection of exercises.
Source:
“How Does Interval Training Presc.ription Impact Physiological and Perceptual Responses?”
Stephen Seiler; Øystein Sylta - International Journal of Sports Physiology and Performance
DOI: 10.1123/ijspp.2016-0464
