why must cardio be at least 30 min?

[spatts]

I do agility drills, sprints, resistance sprints, hills, sprints with sled....something....at least 3 times a week. More if I can handle it.

 

[SofaGeorge]

I'm a "cardio is useless" proponent. I haven't met one person yet who has said, "I lost so much weight on the treadmill I had to stop."

I train cardio via boxing, kickboxing, and sprints... and I run... but for me this is endurance training and speed training. The cardio to burn bodyfat thing doesn't seem to add up to the reality I see in the gym.

 

[Zander1983]

Sofa, I gather you're quite lean?

You've got a lot of good training behind you and where cardio is concerned I think you're on the money.

Whether it be cardio or weights, I think its all about intensity.

 

[FatRat]

Yer, assuming that you are doing cardio for fat loss, you need to burn blood sugars and move to using stored body fat as energy before it is doing much good. I seem to remember that it took around 15 mins to do this, so I guess you would want to be doing at least 30 mins in order to actually burn any amount of fat. The times when this doesn’t apply is AM cardio on an empty stomach, or after your weights session. On both occasions, your blood sugar is already low so you are straight into burning body fat for energy.

I cant see why this principal would differ for HIIT training, since you still need to burn off the sugars before you are going to dip into the body’s fat stores. One explanation for success with HIIT over shorter durations is that fat burning does not stop when the cardio session stops, and perhaps the higher intensity of HIIT leads to a lengthened period of fat burning post workout, or generally raises metabolism? Also, I would expect that the high intensity of high might burn blood sugar faster, so shortening the initial 15 mins period…

 

[endpoint]

I cant see why this principal would differ for HIIT training, since you still need to burn off the sugars before you are going to dip into the body’s fat stores. One explanation for success with HIIT over shorter durations is that fat burning does not stop when the cardio session stops, and perhaps the higher intensity of HIIT leads to a lengthened period of fat burning post workout, or generally raises metabolism? Also, I would expect that the high intensity of high might burn blood sugar faster, so shortening the initial 15 mins period…

HIIT uses different energy systems

 

[circusgirl]

it's coz cardio like the bike or treadmill is so damn boring, if you don't froce yourself to stay at least N minutes, you'd never do any....

 

[spatts]

HIIT uses different energy systems

Yep, sprinting is fueled differently.

The rest of his paragraph is dead-on though, WRT prolonged metabolic increase and fat burning.

 

[FatRat]

Ok, different energy systems:

Muscles contract using ATP for energy, and there are three sources of high-energy phosphate to keep the ATP pool filled:

· Creatine phosphate
· Glycolysis of glycogen
· Cellular respiration in the mitochondria of the fibers.

Since during HIIT we are talking about short duration activity, the source is going to be the first two.

Can anyone explain how fat burning comes into this equation?

 

[spatts]

Elevated metabolism,anabolism, it's not fuel by fatty acids, etc...not sure what you're asking.

 

[FatRat]

As I posted above, I can see increased metabolic rate etc. being a factor with HIIT, i'm just trying to understand how the different energy sources burn fat in a different way.

This explains why duration is not so important with HIIT as it is not during the session that fat burning occurs, unlike more traditional cardio, but the ongoing effect on metabolism that it produces.

Cool, i think i get it