HIIT - 21MINS OR 30MINS?

hi guys,
 
last week i did HIIT 4 times. i did 21mins 2mins jog 1 min sprint. I am now 4 weeks away from my holiday and i need this fat gone! Shall i up it to 30mins so do 3 extra sets or keep the same time of 21mins but make it harder?  how does it work? longer HIIT = more fat loss, or what?
 
help will be aprreciated thankyou

What else are you doing?
What's your diet like?
xx

Usually go for 20 mins.  Space the HIT out with the other training days though.

I'm not sure you could do proper HIIT for 30 minutes, that is pretty damn tough.

Are you going all out on the sprint ?

as above the longer you do it,the more it becomes just intervals and not HIIT.
HIIT is meant to be done almost all out for the sprint part,and i doubt anyone could do that for 1min.

^ Agreed, I work with a shorter sprint time so I can go all out, that obviously brings the jogging part down too (2:1). After 10 minutes I'm dying and I'm pretty fit.

Concerntrate on blitzing the sprint for a shorter time.

i read a study that said,you can only sprint fully for 8secs,which is probably correct when you think about usain bolt etc do about 9+ secs but that includes getting out of the blocks and slowing down over the line.
you can obviously run at 100% for a minute but not sprint the whole distance.

Exactly, thats why you have a 100m sprint.

Its not exactly a full sprint in HIIT so I would guess something like 20-30seconds is about right.

When you do it right though 5 minutes really does seem like about 15.

As above the longer you do it the less benefit your atr getting from the interval aspect of it.

Your options are:

Explore other interval lengths
Combine it with some extra activity
Make sure your diet is dialed in and the important one...
Start earlier next year!

cheers for the replys guys and ladies. What shall i do then i currently jog at 7kph for 2mins then do a minute on 11kph. Im panting hard after 21mins of it. What else do you suggest i do? how could i make it more effective?

Sprint harder for a shorter period.

If you're doing this on a tread, find out what sprint you can do for about 20 seconds. Then use the other 40 seconds as the jogging part. Its very very tough.

how many sets of this do i do? 20sec sprint 40sec jog

As much as you can handle. I'd imagine you won't get much past 15 minutes. The first time I did it I could only manage about 7-10. Build it up slowly, but you do know this will burn calories after you've finished ? On the treadmill it will show a low amount burned but you will continue to burn, so if you eat a low amount of calories too, you could shift a fair amount of weight.

ok, i see. Thanks for your help

also if you can only do 10mins,there is nothing stopping you jogging for another 10 or 20 mins to burn more cals.

Exactly, do as much 'proper' HIIT as you can, then do some normal cardio to take it to half hour or so.

I hate cardio btw, bike rides or long walks in the country don't make it seem as bad !