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For the guys versed in endurance training, it is now clear that low intensity steady state cardio brings one key adaptation that HIIT is not able to : an increase in the heart stroke volume (also sometimes called eccentric hypertrophy or cardiac output training but cardiac output being stroke volume x heart rate, I find stroke volume to be more precise)

Apparently, this adaptation can only be triggered when doing low intensity (so the heart has the time to undergo full dilatation) for a prolonged continued period (1x60 min will trigger the adaptation, 3x20min will not or to a lesser extent AFAIK).

I am wondering if interval type training with clever effort/recovery management could still bring similar adaptations? Any reference would be appreciated.

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The notion that low-intensity stead-state endurance work is required to elicit an increase in stroke volume is an outdated one, an assumption made from early observations that stroke volume appeared to ‘plateau’ at around 40% of VO₂max. However, a large body of research has since demonstrated that no such plateau exists, especially amongst elite-level athletes, and that stroke volume increases progressively to VO₂max in both trained and untrained subjects. The former observation is believed to be the consequence of “enhanced diastolic filling, enhanced contractility, larger blood volume, and decreased cardiac afterload.” It has further been demonstrated that training-induced increases in maximal cardiac output is partly due to an attenuation of the decrease in stroke volume as exercise intensity is increased. Thus, the original assumptions as to why high-intensity training might not stimulate increases in stroke volume do not hold true, and we might expect, therefore, that training modalities like high-intensity interval training (HIIT) should increase stroke volume similarly effectively to the way they increase VO₂max.

Whilst the existing body of research is not as comprehensive or conclusive as it is regarding the relationship between exercise intensity and changes induced in VO₂max, this is nevertheless precisely what we are seeing from recent studies. In work-matched comparisons, maximum stroke volume has been shown to increase more or similarly following HIIT relative to low-intensity steady-state exercise, while conversely it has been shown to increase more or similarly in response to moderate-intensity continuous training (MICT) than with low‐volume sprint interval training (SIT) or HIIT. That is, high-intensity training modalities are at least as effective in increasing stroke volume when total work is considered, and similarly effective even when the workload is considerably smaller. These observations are now encouraging elite sports teams to adopt high-intensity intervals in their training for the very purpose of increasing stroke volume.

It is clear, therefore, that SIT and HIIT can induce increases in maximum stroke volume similarly to low- and moderate-intensity steady-state endurance work, and may even be superior.

I hope that helps.

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  • 2
    This is fantastic, and just what I was looking for. – Dave Liepmann Aug 25 at 7:17
  • Thank you, @DaveLiepmann. I just realised that I had written “low-intensity steady-state” in one place when I had meant “high intensity”. I trust that you and others had recognised and forgiven the error, which is now corrected, of course. – POD Aug 25 at 8:01

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