Interval training is efficient for cardiovascular health
If you train at low intensity (where you can still talk almost normally) you need to do 6 two-hour sessions a week to get the same effect as by doing 3 one-hour sessions a week at high intensity – or as little as one session of 15 minutes a week if you do all-out exercise.
Now, nobody can do 15 minutes in a row of continuous exercise near their maximum heart rate! And if you have any concerns about your heart condition you shold definitely not try!
What we can do, however, is to alternate short intervals of high intensity exercise with lower intensity recovery intervals.
In this way, we can get a higher total time of exercise at high intensity than when we do continuous exercise.
Alternating periods of higher and lower intensity exercise is exactly what defines interval training. So, if you do a session of 4 x 5 intervals of 15 seconds at all-out intensity, you will have done 5 minutes total and it will have taken you 20 minutes if your lower intensity intervals are 45 seconds.
Using this logic you can consider that you have done the equivalent of 6 two-hour sessions of jogging if you do this interval session 3 times a week!
Of course you cannot translate exactly like this AND you would already have to be in great shape in order to do an interval session like that. HOWEVER, the point is that when you work at high intensities, there is a lot of time to save! And you actually work your cardio-vascular system in a way that forces healthy adaptations.
Now don’t go out there and blast away in your very first session.
Like with any other training, you need to respect the progression limits of your body or you will put yourself at risk of an injury. Gradually work your way up!
As always, you should consult with a physician before engaging in high intensity interval training to make sure you have no counter indications.
To improve your maximal aerobic effect – your VO2max – you will benefit from high intensity aerobic interval training. This is a way to work at high intensity without reaching exhaustion. High intensity in this type of training is around V02max with a heart rate of 20-40% of max heart rate. This intensity is crucial to improve VO2max. (It can be improved at lower intensities with endurance training as well but then you need to spend a lot more time on each session.)
A great protocol for training the cardio-vascular system and get a healthy heart consists of repetitions of a 3-minutes long hard interval followed by a 3-minutes easy. If you find it too hard to exercise at real high intensity, you can compensate by shortening the duration of the easy interval to 2 or even 1 minute as you work up your aerobic power.
This should be repeated for 4-8 times depending on your fitness level.
You can also work with shorter duration intervals but then the duration of the recovery intervals becomescrucial. If it is too long compared to the working interval you will never reach VO2max because you will always catch up during the recovery. If it is too short, you will be relying on the anaerobic energy systems and your session wil be training tolerance more so than aerobic power.
So if improved aerobic power is your goal and you want to do shorter intervals (shorter than 2 minutes) closer to all-out intensity, you should aim for a recovery interval that is about a third to half as long as the hard interval. That is, for instance [20 sec. hard, 10 sec. easy] or [90 sec. hard, 30 sec. easy].
Please consult with a good exercise physician to make sure you don’t have any counter-indications or seious heart problems for such training protocols. For most people, though interval training can only improve their cardio vascular health – which in turn helps prevent heart disease.