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Hard Start vs. Normal Intervals vs. 30/15

In this Blog Post we want to look at different Intervals which target is to train the Vo2max capacity.

The goal of this article is to show how much time was spent in the targeted training zones and which workout is therefore the more efficient compared to others.

We as Athletes always want to get the most out of the time we train and therefore always look at how we can structure our workouts more efficiently. While all work Athletes put in, benefits them in a way, it is not always understood, what session is supposed to train what system or what goal a certain workout has.

All data is from one Athlete with a Vo2Max of around 59ml/kg/min. The different workouts were performed in a time span of around 2 weeks with appropriate rest in between the sessions. All workouts were done inside on the trainer.

Equipment used for all workouts:

Garmin HR Strap, Moxy Muscle Oxygen Sensor, Vo2Master Mask, Quark Powermeter, Wahoo Kickr,

We look at 3 different intervals and the training effect or better how much time the Athlete spent above the targeted 90% of Vo2Max in comparison to heartrate.

Workout 1: 5x6min @ 115% of FTP

Workout 2: 5x5min Hard Start @ 125% of FTP, Rest of Interval @ 115% of FTP

Workout 3: 3x7x30/15 @ 130% FTP

First, let's look at the workout with 5 Intervals with a length of 6min for each interval.

The Intervals are performed at 115% of the Athlete's FTP.

In the graph we have in red the HR and in blue the VO2 uptake in percent of the Athletes Vo2Max to determine, if the Athlete was able to reach 90% of it's Vo2 capacity. The dotted line is the 90% mark for both HR and Vo2. The green line shows the power of the workout.

After a warmup the Athlete jumped into the intervals. All intervals were performed at the planned power output and no alterations in the workout. Maybe as a site note: a fan was used during the session, but was placed behind the Athlete so the wind would not interfere with the mask.

The total time of the intervals would be 30min. So in theory we would hope to spend as much time as possible above 90% of the Athletes Vo2max during the 30min total time.

In reality the picture looks a little different as you can see on the data below.

Time spent above 90% of HR was 24.3min

Time spent above 90% of VO2 was 20,7min

Since we are looking at the VO2 Uptake and not so much the heart rate, the findings are that the Athlete spent around 69% of the workout above the 90% mark.

Not all Athletes have the access to a VO2 Mask and therefore the HR is often used as a factor to plan the workouts. Looking at the heart rate, in this case it would suggest that the Athlete spend quite some time more in the desired training zone. I think it is worth to mention, that in this case the heart rate is just in indicator where the Athlete approximately is. The longer the workout is, the higher the Athlete's HR will be and the data of HR and VO2 will match up more closely, but they are not 100% related as you can also see in the graphs.

Next we look at a hard start interval session with 5x5min.

The intervals are performed at 1.5min @ 125% and 3.5min @115% of the Athlete''s FTP.

A difference in this workout is that hard start of each interval is supposed to stress the pulmonary system a little more, so that the Athlete has to breath "faster" earlier. We maybe should not say faster since it is not really related to the speed of breathing but rather the uptake of Oxygen. But for an easier understanding lets use the term since under workload a faster or harder breathing brings a higher need of oxygen and therefore a higher oxygen uptake with it.

The rest of the intervals are performed at 115% of FTP just like in the first workout we looked at.

The total time of the intervals would be 25min. So in theory we would hope to spend as much time as possible above 90% of the Athletes Vo2max during the 25min total time.

In reality the picture looks again a little different as you can see on the data below.

Time spent above 90% of HR was 26.9min

Time spent above 90% of VO2 was 18.6min

Since we are looking at the VO2 Uptake and not so much the heart rate the findings are that the Athlete spent around 75% of the workout above the 90% mark.

Looking at the time spent above 90% of VO2max, the findings are that we can extend our time in the desired zone with hard start intervals by around, in this case, 6%.

The last interval is another well known workout among Athletes, 30/15, where the interval is performed at 130% of FTP with a short rest period in between. These workouts also come in different variations like 30/30 or 40/20. Ratio from work to rest periods are either 1:1 or 2:1.

In the first block of intervals, we can see a big difference to the other intervals we talked previously about. In the picture you can see that heart rate and also VO2 is very delayed due to the short bursts and rest periods between. It takes the HR and also the pulmonary system a while to catch up. Also good to see in the first set is, that the HR stayed lower compared to the other intervals, which is again mainly because of the short rest periods. Towards the end of the first block all systems caught up, with the HR still slightly underneath the 90% mark. Literature also recommends 90-95% of HR for VO2max training so we would be still a little further away if we would look at 95% instead of 90%. Where we see a bigger difference however is in the second and third block.

With the start of the second set of intervals, HR and VO2 uptake reacted a little faster, due to the stressed systems in the first set. In set 2 and 3 therefore we can see that the time spent in the targeted zones is quite a bit more than during the first set.

A summary of this workout looks like following:

The total time of the intervals would be 10.5min. So in theory we would like to spend as much time as possible above 90% of the Athlete's Vo2max during the 10.5min total time.

Time spent above 90% of HR was 4.63min

Time spent above 90% of VO2 was 7.51min

In this workout, the Athlete stayed therefore about 73% of the total interval duration above the desired 90% of VO2max.

Summary

While all workouts have their effect in a different way, the 3 different workouts show a different efficiency, when it comes to time spent in the desired zone.

Pointing out that this is the picture of just one Athlete and that it could look a little different for others. However, it gives us a good idea to understand the workouts better.

Another point is, that literature suggests, that you can use heart rate and/or Power to target your training, however knowing now that VO2 Uptake does not equal being above a certain heart rate, it is a good indicator, but not a true measurement. It takes time for HR and Oxygen uptake to respond to the workload and therefore it needs to be understood that short burst into high power zones may not have the targeted effect if the rest between is to big.

It is also to mention, that another effect of hard start intervals or Tabata Intervals is that a Athlete can improve its pulmonary function and work on its pulmonary limitation due to the fast increase of breathing rate. More to that maybe at a later time.

Knowing your individual zones and limiters is therefore another important step to train more efficient.

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