I have been doing a little Tabata yesterday, and it was an interesting (…) experience. At the beginning things were alright – 8 swings in 20sec are manageable, and the 10sec break was fine – but as the rounds went on the 10sec seemed to get shorter and shorter. After round 8 (the original Tabata protocol) I needed to really force myself to go on, and after round 10 I was dead. And it was neither the muscles, nor any particular set that would be to blame. It just happens that this fatigue – if this is the right word – crept up on me round after round.

So this got me thinking about RLR’s and the VO2 max, or how to combine recovery periods and the level of effort to optimally programme a metcon.

The basis idea is really very simple: almost by definition, VO2max is the effort one can sustain for a long time (assuming one is constraint by the cardio-vascular system; so this is probably true for kettlebell swings, but probably not true for preacher curls).

In interval training, the effort is not continuos, but there are *load* periods and *recovery* periods, with a certain recovery-load-ratio (“RLR”). Assuming the effort during recovery is zero (which is not quite true, but probably close*), the

*Effective* (or *Average*) *VO2max* = *Peak VO2max x (1/(1+RLR))*

So for example if one is operating at 150% of VO2max for 20s, and is recovering for 10s (ie a RLR of 1:2 or 0.5) then the Average VO2max is 150% x 20s/(20s+10s) = 150% x (1/(1+0.5)) = 150% / 1.5 = 100%. What does this mean? Simply that if during the 20s intervals one indeed operates at 150% of VO2max than in average one just operates at the anaerobic threshold, meaning that one should be able to sustain this effort for a while.

So let’s have a look at what this simple calculation gives. In the following table I have looked at the effective VO2max across a number of RLR’s (note: 0.25 is 1:4, eg 5s recovery on 20s load). In the first table, I have kept the Effective VO2max at 100% – ie just at the threshold – and have computed how big the effort in the load period must be in order to achieve this number at a given RLR. Clearly, everything above RLR > 0.75 does not really make sense in practice as the intensity is just not achievable.

Peak VO2max | 125% | 150% | 175% | 200% | 300% | 400% |

RLR | 0.25 | 0.5 | 0.75 | 1 | 2 | 3 |

Eff. VO2max | 100% | 100% | 100% | 100% | 100% | 100% |

Note that the Tabata value of 0.5 (in red) seem like a nice spot to be – if one is operating at 150% of VO2max during the load period then the overall effort is just at the threshold. Incidentally, the original Tabata protocol suggests an effort at 170% of VO2max which brings the Effective VO2max to about 115%. Whilst 4minutes seems a short time, it is actually very long if one is incurring an oxygen debt at this level…

In the next table I have computed the effective VO2max across a number of RLR’s with the VO2max under load of 175% which I believe is about the maximum one can reasonably do. Looking at the numbers it seems clear that anything over RLR>1 leads to a very low Effective VO2max, ie there is virtually full recovery between the load periods, ie they are metabolically separated.

Peak VO2max | 175% | 175% | 175% | 175% | 175% | 175% |

RLR | 0.25 | 0.5 | 0.75 | 1 | 2 | 3 |

Eff. VO2max | 140% | 117% | 100% | 88% | 58% | 44% |

So what does this mean? Firstly – the following reasoning *only* applies to metcon’s, ie exercises designed to strengthen the cardio-vascular system. It in particular does not apply to strength training, where the key recovery is that of the working muscle, and not that of the cardio vascular system.

So for metcons to be metabolically linked it seems that RLR’s must be between 0-0.75, whereby the higher end of the range is only possible under very high efforts (>175% of VO2max). The Tabata value of 0.5 seems to be right in the middle, ie it seems to put just the right average stress on the cardio-vascular system, at a level of peak effort that is just about achievable.

**To be a bit more precise one would for example also need to take into account that even when resting the body needs oxygen, so rather than averaging say 150% and 0%, one would average something like 150% and 10%. I dont now what the resting VO2max percentage is though, but simply counting breath I’d say it is rather small comparatively, and can be ignored for this very simplistic analysis*

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