One of the common training philosophies we see spoken about in 2022 is HIIT training. Many people have come out of lockdown and feel that they are overweight and unfit. Theoretically, interval training could be the quickest way to get there.
You can spend hours of your life on the internet researching the latest in HIIT workouts that will work your aerobic and anaerobic energy systems. However, finding the right workout that also allows you to progress as a rower can be a challenge.
In this article I want to put together a guide that will help you to be able to:
- Understand the science behind the energy needed for intervals.
- Discuss the different types of intervals.
- Show you how intervals can help you judge the efficiency of your training.
The Science of intervals
High-intensity-interval-training or HIIT for short is a training format that forces your body to go through a number of max-effort sprints. Between each sprint, you have a short time to recover and then you go at full effort again… and again… and again. People with a high level of maximal power will be able to use high amounts of energy phosphates at a quick rate.
Our bodies are able to hold on to roughly 25mmol/kg in dry muscle of ATP. ATP is Adenosine Triphosphate and is what your body uses for quick energy during max effort exercise. If you exercise at a maximal level, it will use up around 15mmol/kg in just 1 or 2 seconds. So really maximal effort is dictated by the efficiency in which Adenosine Triphosphate is hydrolysed and synthesised.
Roughly speaking you will use up around 45% of your ATP in a 30-second sprint. Somewhere between 10% and 30% will have been used in just the first 10 seconds. When we start to break down ATP during exercise, a number of metabolic systems jump into action to re-synthesize the ATP to try to maintain the highest rate that ATP can be used.
As we try to recover in between the intervals, our body attempts to fill back up our stores. The amount that your body is able to re-synthesize ATP, is very much a determining factor in its ability to perform at a high level on your next sprint interval.
The energy systems that are involved in this process are the Phosphocreatine (PCr), anaerobic glycolysis, and the aerobic systems.
PCr
In our muscles, we have around 80mmol/kg of PCr. That is three times the amount of ATP. PCr has a usage rate of 9mmol.kg/sec, this means that your PCr is used up in the first ten seconds of your first interval. However, this is the amazing bit. Your PCr system also has the quickest recovery rate. Approximately 85% of your PCr is back ready to use again after 2 minutes of rest. After 4 minutes, you have 90% back, and after 8 minutes 100%.
Aerobic Glycolysis
As we use up our PCr, our body switches to the next best option. Which are your aerobic glycolysis and glycogenolysis systems. Your glycolysis systems deals with the breakdown of glycolysis in your bloodstream. Your glycogenolysis system deals with the breakdown of glycogen in your cytoplasm. In your muscles, you keep a store of 400mmol/kg. This means that repeated sprints are probably not going to impact of its ability to provide ATP. Research shows that it is more likely that it will be your metabolic environment that will be impacted.
Types of Interval training
So how can we use HIIT to improve our aerobic capacity and muscular endurance? This table below shows us four of the most popular training systems. The aim of these systems is to improve on aerobic fitness.
| Training session | Protocol | Training intensity | Pre to post-training VO2 Max |
| 15/15 intervals | 15x15secs at 90-95% HRmax. 45 secs rest | High | 60.6 ml/kg/min to 64.4 ml/kg/min |
| PCr training | 6-12 rds of 30secs at 85-90% HRmax. 60sec rest | High | 55.5 ml/kg/min to 56.8 ml/kg/min |
| Anaerobic Glycolysis | Max intensity 30sec intervals. 4mins rest | High | 59.6 ml/kg/min to 60.8 ml/kg/min |
| Muscle buffer capacity | Repeat bouts (up to 6) of 30-60sec intervals with a 1:1 work-rest ratio. | Mod | 55.5 ml/kg/min to 60.4 ml/kg/min |
So what does it mean? These studies have used VO2 max as the premier determinant of training protocol performance. This makes complete sense to us seeing as it has such an important role in ATP re-synthesis.
Most RSA based studies have all used VO2 max as a major determinant of training protocols performance – no surprise given its role in ATP resynthesis and the contribution it makes as intervals extend. As with any training system it has to be tested over time. You cannot just jump into it and expect it to make an immediate impact.
How to start using intervals
If you are not used to HIIT it can have a significant impact on your body as a whole. Depending on the type of exercise you can have sore muscles and joints that can impact your overall training. For that reason, training should be slowly started. I would recommend that you do not do more than one session of HIIT per week to start off with. Then as your body gets used to it you can increase.
Do remember to take some baseline tests when you first get started. If you are doing it to help with your rowing I would recommend doing a 2km erg as a baseline. If you want to use the sprint intervals to help with your running then you will want to have 1km time trial as well as a 2km.
High-intensity interval training is a great training system to be used alongside other methodologies that challenge your physical abilities. Remember to do what is best for you and your body.
If you are looking to improve your power and strength then you should have a look at our article below:
If you are wanting to work on your endurance and stamina and learn a bit more about both, then check out this article:
