T Nation

High vs Low Intensity Cardio


Just wanting to voice my opinions on this oft contested issue. I have, and still do, employ both high intensity intervals and longer duration cardio to leanout. For me, both methods are effective, but for different reasons.

The benefits of either modality has already been covered ad nauseum on this site, but to refresh:


1) Burns little actual fat during performance, but through the compensatory effect of EPOC has you burning fat at an accelerated rate post workout.

2) Appears to stimulate hormones conducive to fat loss and muscle gain.

3) Increases fast twitch muscle fibres.

4) Rapidly increases conditioning levels.

LISS - Now remember low intensity doesn't qualify as jogging, and certainly not running, it's more of a brisk walk - non-panting.

1) Directly taps fat stores without influencing muscle glycogen levels.

2) Can be performed frequently.

3) Beneficial for recovery.

Here's the kicker, either method will fall flat if you don't eat correctly for them. LISS requires a glycogen depleted state to be useful. Conversely, HIIT will chew up your lean tissue like nobodies business in a similar state - you need to treat it like a weight session. Further, HIIT has a point of diminishing returns. Exceeding three sessions a week on a reduced calorie diet is a recipe for disaster.

Cheers J.


While you do have some good knowledge on either mode of energy systems work, I think you are making some absolute assumptions that are not valid accross the board.

A caloric deficit is a caloric deficit. Whether you are eating a Subway sandwich while doing an hour of low intensity incline walking, doing it on an empty stomach, or even fasted, you will have the same net cals for that 24 hour period. Unless you are sipping on maltodextrin or sucrose, most of the energy burned during the exercise will be endogenous.

Also, since you even stated yourself that low intensity cardio burns mostly fat, then whether in a deplete glycogen state or not would burn just as much fat, right? In actuality, a muscle will always burn some glycogen first, even when going low intensity. Your body doesn't know you only want to tap into fat stores or that you will be walking for a hour. It always goes through its energy protocol: glycogen and amino acids if need be, then fat. So, after several minutes (10-20 maybe?) you'd be more lipolytic.

Having said that, even when in a fasted state, again your body wants to initially burn glycogen (as its prgrammed to do so). So, initially you'd probably find cortisol levels and even glucagon levels rise in reaction to provide this energy, but after some time your body would turn to stored body fat (cortisol and subsequently glucagon react to any stress or exercise).

Also, as it has been alluded to, its almost impossible to be in a completely glycogen depleted state, as you should be re-feeding the muscle after intense exercise, thus allowing the body to re-up its stores of glycogen. Further, EPOC and general energy needs stimulate gluconeogenesis thus your body can re-up glycogen without even having a carb re-feed. Even while fasting at night, the body is at such a low metablic rate that it's likely going to burn body fat for fuel, not muscle glycogen.




this is the kind of response I was hoping for. I'm not looking for people to outright agree with me, more to flesh out the issue and provide some real world insight.

You mention that low intensity cardio, since it relies primarily on fat for fuel, should work independent of being in a fasted state. I've often wondered about this myself, yet the reality is it works well for me under those conditions.

Over the years I've gravitated towards a combined approach largely because it is very difficult to recover from excessive sprint sessions, assuming your weight training as well. If you were on higher calories that might offset the recovery issue, but the majority of people implementing them rarely are.

More to the point of the post, I've seen alot of people get extremely passionate about lauding the benefits of one system over the other - say the wrong thing in some circles is like picking a fight. I just don't think such rapant dogmatism has its place in trying to achieve the body composition you're after. But, proove me wrong, I'm prepared to listen.



The body is pretty smart; feed it fat it'll burn more triglycerides; feed it more carbs and it will burn more carbs.


For the amount of views this thread is getting I'm surprised more people aren't weighing into the debate. Surely there's people out there who have experimented with either modality. Post up your experiences.


I don't know the science behind it well,but I personally get leaner doing high intensity on an empty stomach while consuming more calories during the day as opposed to a lower calorie diet and walking briskly.Maybe it in my head,but HIT cardio gives me more energy during the day and I don't get the mental blah's like I do with low intensity cardio and lower calories.I'm doing the brisk walk and lower calorie(1600 cal)right now and Monday,I'm increasing my cals. and switching to morning sprints,I'm going insane.


At the end of the day, no matter if you are learning from the guru's here, your gym teacher, or Richard Simmons, there is no absolute, except the you need a caloric deficit to trim fat and a surplus to gain muscle/weight (I am talking "natural" state here). Besides that, there are only rules of thumb and guidelines to finding what works best for each of us. I love how Lowery clarified that there is only evidence, not proof, when it comes to fitness.

You may have found what you do works great for you, but your original post was more of a summary in general, applicable to everyone, when it cannot be applied wholesale.

Back to specifics, I have also done fasted AM cardio vs. lifting plus cardio in the afternoon. I noted no real difference in results, except that it was easier to push myself on both the weights and the cardio later in the day as I had plenty of energy stores to deplete and little chance of going hypoglycemic (which I have to be careful of).

Those of us who are predisposed to hypoglycemia can induce it (sometimes severely) doing cardio/lifting on an empty stomach and/or fasted. Hypoglycemics tend to have an over-reaction of cortisol (due to stress or hunger), so we can get severely catabolic quickly and do more harm than good.

Therefore, I can only tolerate about 30 minutes of cardio or even intense lifting on an empty stomach/fasted state. I'm more recently finding that if I just reduce the carbs in my peri-workout (pre and post) shakes, still using them religiously, and cut cals through out the rest of the day, I'm able to stay more energized for my workout. This allows me to look more forward to the workout, burn more cals because I feel good, push myself in strength movements, and protect my LBM. If I can achieve a 500-800 cal deficit/day by doing things this way, it will lead to the same bodyfat losses as if I had done this fasted.

Having said all that, I lift intensly 3/week (EDT kicks ass!!), I do incline walking fasted 2/week, and I throw in another cardio session just randomly (i.g. splitting wood). Some days I do a fasted and an afternoon cardio session, but always low intensity. I too used to work in more HIIT but found I just had no recovery ability to hit the weights with and soon burned out.

So, that's my situation, since you wanted a more personal take on the subject.

Client-wise, as long as they lift at least twice per week and do cardio 3-4 days per week, it doesn't matter when they do it, they always improve their body comp.



I think it also has to do with how much fat your carrying. Chris Aceto wrote in one of his nutritional books that "Men who were over 20% bodyfat and women who were over 30% BF needed long slow distance training." The theory he proposes is that their bodies have become so efficient at storing fat, the ability to burn fat has diminished. The 30-60 minute aerobic training sessions were neeeded to re-stimulate the bodies fat burning capabilities. I dont know that there are specific studies to back his hypothesis, but it sounded good!



Strange as it may seem your training approach is very similar to my own: Three whole body wokouts a week using varying rep schemes, 2-3 treadmill incline walks, then occasionally I'll throw in a day of sprints or bodyweight gpp.

Much like yourself - and I think this may be a key concern with HIIT - it becomes very difficult to adequately recover from intense weight training as well as high intensity ESW.

Cheers J.


I agree. Too much HIIT cardio on top of high intensity weight training spells certain overtraining for me. I was surprised about the low intensity definition though. I always thought by doing 45minute easy runs I WAS performing low intensity cardio!?!?!

What would 30-60minute running be considered? I find it is the single fastest weight loss method there is.


When one mixes days of high intensity and low intensity(longer duration) how do you know how much each one is contributing to you r final fat loss? What if the low intensity wasn't necessary at all?


I agree. Too much HIIT cardio on top of high intensity weight training spells certain overtraining for me. I was surprised about the low intensity definition though. I always thought by doing 45minute easy runs I WAS performing low intensity cardio!?!?!

What would 30-60minute running be considered? I find it is the single fastest weight loss method there is. [/quote]

Running doesn't really qualify as low intensity cardio, I think Dr. Lowery likes to refer to it as 'non-panting'. If you perform in a sport where it's necessary for you to run for this long that's fine. However, if your goals are cosmetic, it would not be ideal.

A general rule of thumb in performing cardio for fat loss is: short and hard or long and slow, but never long and hard (sorry if that all sounds a bit euphemistic). Thirty minutes of higher intensity work is my upper limit and even then I'd use an interval protocol.



I see what you are trying to say - and I think a lot of people on this board would agree with you - that; lower intensity cardio is just a means of creating a calorie deficit ergo just adjust your diet. There is a great logic to this idea, however, if you are a lean individual who is training intensely and on lowered calories as well it may not be practical.

That said, Cosgrove and Berardi offer some especially intelligent commentary on the necessity of low intensity cardio, so clearly the idea should be considered.



Fasted LIT training feels horrible so I don't do it - especially not first thing in the morning. To do it slowly enough also equates to using up damn all calories. I'ld be surprised if you notch up more than a few hundred in an hour. At 3,500 kcal per pound bodyfat, that's probably 20 hrs of LIT to lose one pound of BF - and that's assuming you're working solely off of bodyfat which isn't the case.

A few HIIT sessions during the week will do wonders, especially if they're performed at around 6 or 7 in the evening - then their metabolic boosting effect will be strongest during the hours where your metabolism would normally be winding down. Doing any form of cardio at this time would be better than fasted walking first thing in the morning for this reason.

The whole premise of LIT training is that the intensity is low enough for your energy needs to be completely met by bodyfat oxidation. However, consider that bodyfat stores are used constantly to provide a low speed energy source, not just when exercising. It is still used when your working at high intensities (although the energy it provides is now a smaller percentage of the total energy you're burning) and when you're preparing your meals in the evening for the next day (which is low intensity activity - does that count as LIT? :wink: ), it's used to replenish glycogen stores after exercise and is almost the exclusive energy source used to fuel metabolic processes while you're asleep.

The only time I can think of that fasted low intensity training might be beneficial is when your BF levels are very low, and your natural leptin production is largely suppressed (as well as other hormonal changes which occur as you go to low levels of bodyfat, such as lower testosterone levels, which increasingly instruct the body to catabolise muscle and eventually to even take visceral fat stores) that the idea of burning bodyfat directly becomes more attractive. However I personally believe that this still underestimates the effect of body homeostasis - i.e. your body is a very dynamic system which constantly changes carbs to fats and fats to glucose and amino's to muscle and muscle to glucose and ammonia (obviously this is a very simplified summary) etc. In other words, just because you burn bodyfat directly that doesn't mean anything - if your body's hormones dictate it, you will just replenish your adipose tissues again (I think - can't stand over that at the moment).

Anyway, to summarise, the key is to maximise your energy output for the day. Be well fed when exercising to ensure high energy levels - be less well fed (basically protein only) when hitting the hay. Exercise in the early evenings to maintain evening energy levels.


The key word here is "weight loss". You need to be concerned with over-all body comp, not just weight loss. Ideally, we want to reduce bodyfat and protect LBM. Maybe you understand this but just didn't put it correctly, but I thought I should mention it.

As for running for 45 minutes, if you can "run" for that long, first of all this NOT high intensity. Why? Because high intensity is really anaerobic. I don't know of any human being that can be anaerobic (or at least pushing hard, with near maximal heart rate) and sustain it for 45 minutes. So, this is where relativity comes in. Your personal low-intensity is much more intense than someone else's, plus you may have the conditioning, genetics, etc. to be able to perform this.

Remember, you don't have to always separate your cardio into either completely low-intensity or completely high intensity. Relatively speaking, that 45 minutes for you is low to medium intensity and burns a crap load of calories. As long as you are treating it like a moderate intensity lifting session (i.e. proper peri-workout nutrition) I agree that brisk running is one of the best body comp changers there is (lots of microtrauma) and EPOC.

Just be sure you are eating enough cals to support your lean body mass. The calculator that CT used in his second or third to last article is a good one to approximate that. BE CAREFUL: if you are under-eating (i.e. eating below your BMR) AND running you will likely lose LBM.

So, I say keep it up as long as your nutrition can protect your muscle mass.



In a nut-shell: ALL exercise contributes to your body comp!!

The more complicated answer: unless you where hooked up to tons of monitors in a lab, and they were collecting ALL your waste products and measuring your every microgram of food and water, no one could tell you this. But, rest assured you don't even need to know this to have success.

All you have to do is start out with a moderate routine (lifting 3-4 times per week) plus 2-3 cardio sessions, working out 6 days per week, once per day at the start, taking the 7th day off. If this isn't working after a week or two (you must accurately track weight, BF, and circumference to know) then go back and re-visit what you are doing. The article series Berardi just wrote explained this to a "T" (no pun intended).

You don't have to make it so hard on yourself - just start a reasonable routine and eval your progress at regular intervals.

Metabolically, your LBM (lean body mass) has a certain calorie requirement (called your BMR, basal metabolic rate). If you approx. eat this number of calories, and then use exercise to create a deficit, you will have a negative energy expenditure. Point being that you don't need to know what exercise is burning what/when. All you need to have is a moderate caloric deficit to lose fat.

You don't need to attack fat stores directly to get your body to burn them. If you simply provide less energy that is needed in a given period of time (usually 24 hours) your body has no choice but to turn to stored bodyfat for fuel.

[advanced trainees: yes, this is an over-simplistic approach for concept illustration. While it does work, there are infinite ways to tweak the variables (e.g. jack up protein, cut carbs, etc).]



I think everyone is confusing the purpose of cardio, coming from cardiovascular meaning it improves the efficiency of the CV system (heart and lungs).
And this helps to better deliver nutrients throughout the body.
There are in fact numerous fuel sources while doing cardio, so whose to say that bodyfat is being burned.

The reality is we're capable of burning fat anytime we're in an aerobic state, so right now we're aerobic. Assuming we're eating properly allowing the correct hormonal environment then fat release can occur throughout the day.

I just always tell people look at the body of a marathon runner and that of a sprinter. Marathon people will do tons and tons of cardio, and while usually small, they're not all that lean, because they've exercised away a lot muscle.

While cardio is important part of the puzzle, it shouldn't be looked at as a means to a lean body.


I think this is a damn good summary of many ideas we are discussing!

I'm in the same camp of thinking, just saying it differently. Your take on directly attacking fat stores is what I just posted about. You can attack all the stored fat you wish, but you still have to eat and live 23.5 or 23 hours after that - what are you eating and doing then? If you are eating too much or the wrong foods, your body will just re-up the fat your just burned. So, there is little use in directly attacking anything - although you can directly attack your LBM by not eating properly. So, I'll stand over that statement you made! :wink: Indeed your body does aim for homeostasis and in fact, when hypocaloric, it will tend to tighten its hold on stored fat as a protective/survival reaction.

Also, you are the second person who referenced doing mid-PM exercise (what ever it may be) in that it may be the most beneficial from a metabolic standpoint because we are in essence manipulating the metabolism to stay elevated, increase, or at least not decrease as our normal rhythms usually dictate. Therefore, sessions later in the day indeed burn the same cals as if it was done in the AM, but we might just burn additional cals compared to AM exercise. This seems like its worth looking into in depth. Anyone with any sources of evidence? I would think LL or JB would have at least considered this, if not studied it?!



People also forget that cardiovascular exercise burns calories. None the less, great point that any aerobic state burns fat (i.e. almost all day).

Not so fast however; marathoners are not only very small because they burn off what they eat and then some, but to be good at their sport they have to have a low body weight. Less weight, faster times. I have clients that were/are mediocre marathoners but look like sprinters because they eat quite a bit and weight train. They might do some long distance sprints for wind like 400m repeats (long for a non-sprinter), but they don't follow a rigourous sprint program to achieve their shape. They would probably never be amateur-elite though because they are simply too heavy.

What about those who want to get lean and don't have the facilities to sprint (treadmill sprinting is dangerous) or due to injury they cannot take the stress of sprinting (which is enormous)? Sprinting can really change your body comp for the better in a hurry, but its just not as easy as saying low-intensity equals little muscle and lean and high-intensity equals muscle and lean.

Further, most of the sprinters people are familiar with are gifted genetically, not just with speed but with body fat levels and metabolism. I know quite a few guys with decent 40-yard times who worked out just as hard as sprinters, ate about the same cals, yet had twice the BF% (yes, okay, I was one of them!).

Not to mention, I don't think many elite BB use HIIT or 100m sprints to lean out for a show. Sure they use drugs, but they also understand the simple metabolic equation of eat a bit less, exercise more (usually low-intensity) and you get lean beef.

TopSirloin (working on being lean beef...)


I would highly recommend the use of the indoor rower - you can do any kind of workout you want. LIT or balls to the wall anaerobic work - you control the output with none of the stress.

100m sprints = 250m sprints on the erg

400m sprints = 1K sprints on the erg

the computer on the erg will give you the time, the average split, and the power output for each rep, as well as the average total power output. Which is key for measuring progress. Another advantage is that the parameters can be controlled, not like in an outdoor track where you have to do deal with weather, wind, track condition, etc.

anyway, both eat up a ton of calories and both beat the living shit out of your legs. However, your joints don't take the beating they would on the track.

The only problem with a rowing machine is the (relatively) high barrier to entry - you have to take about 1-2 weeks to really get the technique down, and most people don't have the patience for it.