I'm really interested in HIIT, and I'm trying to add muscle mass for a few months (about 8 or so or more).

I've read that HIIT raises growth hormones, so I thought it would be a good idea to do it after my lifting (I'm working to GAIN not MAINTAIN).

Should I do that, or will the HIIT take away the possible gains I will make? I don't want to slow my gains, but I don't want to get fat either.

HIIT works on the same principals as weights EPOC, so doing both together IMO is a bit pointless.
you could do it on non weight days.

HIIT should be on non-weight lifting days but its not bad to do it after you weight lift.

Like I just started doing HIIT and it feels really good. Theres many benifits to HIIT. See my gym is 40 minutes away so going to the gym 5 days in a row is alot of gas and time that my parents don't have. So thats why I do HIIT on the days I weight lift; after I weight lift though.

If you do HIIT after weightlifting do HIIT on something that won't put alot of pressure on the knees and joints. Especially if its on a day you squatted. I do my HIIT on a cross-trainer.

I did all my weight lifting, core work, and HIIT yesterday and this morning my legs are not sore. So you should be fine.

About the growth, HIIT does raises growth hormones so you should definetely do it. However, HIIT also raises your metabolism so on the day you do HIIT just eat a little more calories that day.

Good article on HIIT: TeenBodybuilding.com - Justin Palermo - High Intensity Interval Training!

if you have to do cardio after weights you would be better of doing ss-cardio at a low to moderate pace.
if your weight sessions last 45min to an hour,doing HIIT after that will use up muscle,and as both HIIT and weights use EPOC whats the point.

Do you mean that it will use energy that would normally be used by the muscles, or are you saying muscle breakdown of already gained muscle??

The reason I pimped that text, is because muscle breakdown is my greatest fear when I'm doing cardio...

Hows it going to burn muscle? If you have good post-nutrition you should be fine. Or you could have a wheyprotien shake after you weight lift and then another one after the HIIT.

your body releases cortisol after approx 45mins, cortisol uses muscle as energy so to carry on doing an anearobic exercise like HIIT will hinder your gains,but if you do an aerobic exercise "low intensity" you will be using fat and not muscle.
if you can chug down a protein shake before you do HIIT and not puke it up you have a stronger stomache than me or your not doing proper HIIT

as soon as you lift a weight your muscles start to breakdown its called protein synthesis,yes cortisol will use up energy that shoud be used by your muscles.

The major catabolic effects of cortisol involve its facilitating the conversion of protein in muscles and connective tissue into glucose and glycogen (cortisol may increase liver glycogen). Gluconeogenesis involves both the increased degradation of protein already formed and the decreased synthesis of new protein. Cortisol can also decrease the utilization of glucose by cells by directly inhibiting glucose transport into the cells (1).

So, when i start cutting, would it be good to lift heavy for 15 minutes, then do HITT for 30?

if you like,but why would you want to do that ,if your going on a defecit you will lose weight anyway so just lift heavy to maintane what muscle you already have,do your cardio on a sepperate day,or cardio AM weights PM.

So it would be OK to maintain monday, wednesday, friday and do HIIT on tuesday and thursday?

I'm a big fan of running...i love to do it, i love the adrenaline rush. But i've had to stay away from it for bulking..so...i've kind of missed it.

just do heavy basic compound exercises m,w,f, and if you want to do HIIT tu,th,thats
there is no point in doing loads of isos like curls etc,you are not going to gain any muscle you just need to let your body know that it needs to hold onto some muscle by lifting heavy.
when i say heavy i mean whats heavy for you.

Good point about the cortisol, you won this argument.

I'd still rather chug the protein shake though.

Well, school is comming back up in 2 months, and I'd like to lose some extra fat and gain some extra muscle. This month (June) was all about lifting and gaining. I've added like 3cm or so on my arms (probably not a lot, but I'm only 15).

And I think I will go through July with gaining muscle as well. But then on August, I want to focus all on losing fat (10 pounds is my goal, but I should lose more than that(I'm 165 now)).

buzz, you said simple compound movements, like the bench press, military press, dead lift, etc.? What would you suggest for set to rep ratio? 3x5??

Do you think it would make any real difference if I was to HIIT Mon, Wed, Fri and maintain Tues, Thurs?

Sorry for asking so many questions, it's just that I've worked my ass off for the last 6 months trying to build some muscle and I don't want to lose it.
If I get too annoying, please let me know, I've been known to do that

So, are you saying there are no significant ' cortisol related ' issues that trigger the use muscle / protein as an energy source during ' aerobic ' cardio of say 45 minutes or so ? Would this be the same is you ran ' aerobically ' for say 1 hour ? At what point does cortisol become an significant issue during ' aerobic ' cardio in your view ?

In other words, doing aerobic exercise for 45 minutes provides a lower risk of using muscle / protein as energy, as compared to HIIT, because " HIIT will hinder your gains........doing an anearobic exercise like HIIT......uses muscle as energy so to carry on "

HIIT cardio ............ increased risk of muscle loss

Aerobic cardio ........ lower risk of muscle loss

Is that it ?