Best Workouts for VO2max Improvement
 

Sprint intervals (SIT), high intensity intervals (HIIT), or endurance training (ET). Which is more effective at increasing VO2max?

Well, according to this paper, it depends. See this graph:

https://cimg4.ibsrv.net/gimg/bikefor...e7a252a1f3.png
Mølmen, K.S., Almquist, N.W. & Skattebo, Ø. Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports Med (2024). https://doi.org/10.1007/s40279-024-02120-2; Figure 7

Some interesting stuff from that graph:

Sprint intervals (SIT) showed the biggest early gains, but at 5 weeks, gains from SIT flatten out and HIIT is showing bigger gains. Gains at 5 weeks from SIT and endurance (ET) are about the same.

HIIT shows bigger gains that ET, but the advantage diminishes as training progresses, and by 14 weeks the difference is within the margin of error. Although HIIT didn't go beyond 14 weeks, it's possible that ET gains eventually overtake HIIT's.

So, takeaways?

• If you need a quick bump in VO2max, SIT may be your friend. With a big caveat, as the short-term benefits from SIT and HIIT seem to be pretty close.
• HIIT looks most effective during the first several weeks of training, while after 15 weeks, HIIT and ET seem to be roughly just as good.
• If you've been training for many months, you might benefit by doing HIIT/SIT more sparingly while increasing your endurance volume.

Some other things from the paper:

• Training frequency matters, with the biggest gains seen at 6 sessions per week.
• Women saw larger gains (~13%) than men (~10%)
• Participants under 35 saw greater gains (~12%) than older participants (~8%)

This paper was recently reviewed by Empirical Cycling, if anyone wants to hear a pretty good discussion. Looking at it now, I wonder if the HIT and SIT categories contained significant amounts of data from studies that used only high intensity training or too much of it. That would make fitness asymptote quickly!

Interested, do you have a link to the discussion?

It was actually a different, but similar, meta-analysis they were discussing. Still highly worthwhile.

https://www.empiricalcycling.com/pod...chives/03-2024

I may be missing something here. What's the difference between SIT and HIIT? Is it even possible to do HIIT without sprinting?

From a quick reading, it seems like the difference is whether the experimenters are using instrumentation as the differentiator. HIIT is "intensity below or above the second ventilatory threshold/4 mmol/L blood lactate concentration/87% of HRmax/87% of V˙O2max/75% of Wmax," while SIT is "maximal or near-maximal efforts..." So a lab session with blood draws for lactate measurements or O2/CO2 measurements, or an outside ride with a power meter, is HIIT. If a rider goes out and does the same intervals and reports max or near max effort (RPE?), this is SIT.

It sounds to me like a distinction without a difference, and makes me wonder about the differences in the outcomes. Wouldn't it be reasonable to conclude giving athletes free (expensive) lab time motivates them to stick with the program longer, and to exert themselves more during training?

I agree this is ambiguously written, but it's pretty clear, at least to me, that HIT is defined as the threshold–VO2max band, and SIT is max effort, 30/30-type, stuff with a top duration of 90s: kind of an intuitive way to divide the range.

i'm very much of the school that I'd rather do 3-5min maximal effort repeats for vo2 work vs 30/30s. Back when I did TR, I was given 30/30 type stuff at 120% over and off for under and it did jack squat for me. I'll do 30/30s full gas (generally 5min intervals), but those are intended to be anaerobic work and not vo2 related aerobic work. If I want to do vo2 work I'll go as hard as I can for those 3-5mins, which for me can be 110-115%

I think I know what you mean here, but "maximal" is used in two ways: One is the hardest you can go for a given work interval, rest interval, and number of reps, and the other is your hardest possible effort, period, theoretically as in 30/30s etc.

yeah, the way I describe vo2 it's that it should be "all out yet paced" so I go into it knowing what my typical power is at the intended time interval, so I am to be around that, but I also (at least at first) try to go harder than my prior best power.

so, in the recent buildup to CX season I did a block in which I did 4min vo2 efforts, each week I set a 4min PR, so went from 360 then 361 (huge I know lol) to 365. at the same time, though, I can't maintain the same power across all efforts, so in that last workout my last interval was 338w. even 30/30s are somewhat bound by some guardrails too, so I know my 1min max is 500w so I'll try to hit around 500w or a bit more on the overs.

That's interesting. I generally think of the original Tabata workout as HIT: that's 8 sets of 20 secs on/10 secs off at 170% of VO2Max power. I guess they'd classify that as SIT. My VO2Max power generally is in the ballpark of 120ish % of FTP, so 87% of VO2Max would be just a few percent above FTP, so I'd think of that as a threshold workout. (I'm not clear on what they count as Wmax.)

Gains per unit time was highest for SIT, then HIT, then ET -- but, of course, you couldn't do as many hours of SIT as you could of ET.