Training according to heart rate zones is a myth that has been disproven in the literature...if it was true, HIIT would have little/no effect on fat loss. Overall caloric expenditure is what effects total fat loss, either through diet, exercise, EPOC, or any combination of them.

You have said ...

" ss-cardio below 70% hr will not utilise sugars/carbs "

" 60% to 70% zone doesnt use carbs read below recovery zone "

.....I'm getting a bit confused as to what you're trying to say. I'm sure it's just me.

My understanding is that even when you're sitting doing nothing ( i.e rest ) your muscles burn both types of fuel at the same time - both fat & sugar. And if I recall correctly, that while at rest the bulk of this fuel is made up of fat - comprising about 70% or so - with carbs / sugar making up the bulk of the remaining 30%.

You say low MHR " doesn't use carbs " & " will not utilise sugars/carbs " - I assume you mean a ' lower percentage ' of carbs and NOT virtually ' 0 ' carbs at sub 60% MHR ?

You aren't suggesting that at these lower MHR we are using virtually 100% fat and virtually 0% carbs below 60% are you ? Because that's what your comments appear to be suggesting - at least to me.

What would say your best guess be of the % of energy that comes from fat at - for example - say 55 % of MHR ? Something close to 50%, 60%, 75%, 90% or 100% from fat ?


btw - could you please paste in the link where you got all your ' heart rate zone ' descriptions - thnks.

No sure the point of this....we all have said we agree that weight training may result in higher levels of cortisol.

You have said it is best not to do HIIT after weight training - but it is better to do HIIT on it's own - due to the higher cortisol levels associated with some weight training - that IS your argument isn't it ?

When you say " your body releases cortisol because its run out of glucose/glycogen/sugars/etc " I assume you aren't saying 45 minutes to 1 hour of anaerobic weight training causes your body to ' run out ' of these carb based energy sources - thus stimulating the release of cortisol ?

Again, assuming adequate daily ' pre & post ' fuelling ' before training, most average gym rats have enough glycogen / glucose in their muscles, liver and blood to supply about 1,800 calories of carb based energy alone for weight training - in addition to any fuel for training that comes from fat.

Let's say the average gym rat does weights for 1 hour. You can't go at 95%+ MHR for a solid hour so lifting weights so your fuel consumption isn't coming 100% from glycogen / glucose but rather from both fat and glycogen. So, I don't think a complete depletion of glycogen / glucose stores is what would trigger cortisol and thus muscle to be sourced as fuel during 1 hour of weight training.

However, it sounds like your are saying that weight training for 1 hour followed by 30 minutes of HIIT will cause you to " run out of glucose/glycogen/sugars/etc " at some point during your HIIT - causing your HIIT session to then draw on muscle for fuel. Is that it ? So, assuming you only burn 80% of your total workout calories in 90 minutes from carb-based calories, are you saying you think it is possible to burn 2,300+-/ calories doing weight training and HIIT within 90 minutes ? Doesn't that seem like a lot ?

HIIT is not the sole domain of metered distance sprints ( i.e 100m 200m sprints ) alone. But a function of a combination of high intensity heart rates / and varying time durations during work intervals and varying durations and intensities of rest intervals. Look at the landmark Tremblay study on the effect of HIIT & fat loss for example.

i know heartrate training on its own is a myth ie, if i trained in the fatburn zone 60%hr i would burn fat during exercise,but the total cals would be minimal,so what i ate later in the day would most likely negate the exercise.

that was not my point or what i am trying to say,you can use your heartrate to figure out if your using carbs or not,ie 60% your not in the carb burning zone,so if you do an intense weights session,which will use EPOC afterwards,then droping down to 60% heartrate afterwards for 30mins cardio,is safer for retaining muscle than doing another anearobic exercise like HIIT.

That's what you're misunderstanding, Buzz: you can't use "zones" like that. HR reserve, estimated max HR, etc, etc, are all estimated levels based on general population scores. The only way to truly know your Max HR (and base numbers of of that) is with stress tests. And even if you get that, claiming that you're using carbs at this % of your Max HR or fat at that % of your Max HR doesn't work, either: your body uses all energy symptoms (phosphogens/creatine phosphate, aerobic & anaerobic glycolysis/lactic acid, oxidative/lipolysis) at all times. It is never just one (physiology doesn't work that way). What happens is, depending on intensity of work (and hence the speed at which energy is needed), one/more system will be supplying a greater % of energy than the other systems, but never to the exclusion of the others, which means that no one substrate will be used at the exclusion of any other. That means whether you are laying on the couch asleep or running a 100 meter sprint, you are using carbs, fats, and even a small percentage of proteins for energy. You can't determine what is being used by your HR: it's far more complicated than that.

Also, you don't use EPOC after weight training, you cause EPOC from weight training.

BIP
i understand what your saying,and i know you dont stop using carbs altogether,but if your at a heartrate of 60% you will be using minimal carbs compared to mhr of 95%.
so as the op asked should he do HIIT after weights,i said no if he had to do cardio after weights (i prefer non weight days) to do ss-cardio at a low mhr,that way there is less chance of wasting muscle.

Also, you don't use EPOC after weight training, you cause EPOC from weight training.
i know this i just worded it wrong.

Although at a HIIT session of 30 minutes, assuming you can sustain a work interval of 95% MHR for 1 minute ( assuming a 2 minute recovery ) - you may only be at a sustained 95% MHR for 10 minutes or so. So, you're not maximizing the burning of carbs during the entire session. But I suspect you're right , even though you may only be burning 30% - 40 % of total fuel from carbs at 60% MHR, you could be burning twice that proportion ( or more ) at 95% MHR.

Again,if you pre-fuel properly and all your glycogen stores a ' topped up ' before you train, I don't think 1 hour of weight training along with a post workout of 30 minutes of HIIT is going to exhaust your carb based stores so that such an occurrence ( i.e exhausting your carb stores ) is going to result in an enhanced chance of " wasting muscle ".

Properly fueled, as in small meal an hour before HIIT with carbs and protein?
I thought you were supposed to take carbs and protein after HIIT.

Actually, when I said " pre-fuel properly and all your glycogen stores are ' topped up ' before you train " by " pre-fuel properly " I really meant making sure all your glycogen stores were topped up prior to any exercise due to proper daily/weekly nutrition - and not so much due to immediate pre-exercise nutrition.

Given it can take just under 24 hours or so to replentish significantly depleted glycogen stores, you want to make sure you engage ' all day fueling ' all week long to allow yourself enough time to refuel properly over the course of a week. By that I mean, simply eat a clean diet every day, eating meals / snacks every 2.5 - 3 hours ( if you can ) with the bulk of your calories coming from carbs ( i.e to help replace glycogen ). Doing this ' all day fueling ' on a daily basis each week will help ensure you have enough time to create the adequate glycogen stores you need as the primary fuel for anaerobic workouts like weight training and HIIT cardio. That would also include meals / snacks that make up your pre and post workout nutrition.