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Why you should be doing cardio – Its effects on fat loss, muscle loss and sexual function

By October 22, 2012January 13th, 201728 Comments

Cardio has been given a bad rap for such a long time…

Stay away from that muscle-burning cardio bro – it will eat all your gaaaaainz…

It’s a highly prevalent concept that seems to have spread throughout the interwebz faster than you can say “Spank my a$$ and call me Charlie”.

Just so you know, I can say that phrase pretty darn quickly (yes, even with the dollar-signs).

Today I’d like to put cardio under the microscope

Is it really the big, bad, scary muscle-burner that it’s been made out to be, or does it actually benefit the average ‘unassisted’ trainer in not only their goals for perpetual leanness but also in other areas such as sexual health?

Let’s take a look…

Cardio and fat loss

There’s as much controversy surrounding cardio for fat-loss as there would be for Charlie Sheen applying for a pilot license.

I’ve gotta say, I frequently used cardio as one of the many tools in my ‘fat-burning arsenal’. That being said, I wouldn’t use cardio as a primary burner of fat, but rather as a strategic weapon coupled with a solid weight-training regimen and adherence to diet.

One thing you’ll notice with the introduction of additional cardio in your regimen, is that your fat-loss progress (whilst great at the beginning) will stall over time.

Unfortunately, fat oxidation slows down with a higher frequency of cardio sessions[1]. So you may experience some ‘new comer’ fat loss when you first start increasing cardio, then a significant slow-down as the weeks go by.

It’s a common problem, especially for those seeking single-digit body fat levels. There is a propensity to either a) lower calories even further or b) increase the number of cardio sessions. Both of these scenarios I’d consider ‘high-risk’ in terms of muscle loss (especially over the long term).

Those with a higher VO2 max burn more body fat than people with lower levels (even when doing low intensity activity).

High Intensity Interval Training (HIIT) and fat loss

Without a doubt, HIIT is a valuable addition to any training program especially in regards to weight loss. It releases fat from the fat cells (which is great when coupled with steady-state cardio). HIIT also improves endurance (meaning you can train longer), and even more importantly, it’s been found to increase your V02 max.[2]

Why is VO2 Max important? Those with a higher VO2 max burn more body fat than people with lower levels (even when doing low intensity activity).[3]

An important caveat…

One thing to keep in mind, is that HIIT significantly increases your heart rate and training intensity. Once you’re working out at over 75% of your capacity, your body tends to use glycogen as an energy source.

Wait a second — I thought that once glycogen stores are diminished the body can then use stored fat as fuel right?

Sorta. It can utilise fat, yes, but it can also dip into your muscle tissue if you aren’t careful (more on that shortly).

Relying on cardio alone for burning fat…

Taking the aforementioned potential for ‘muscle loss’ into account, I’d highly suggest that relying on cardio alone to burn body fat wouldn’t be the best idea. [4]

Another negative for those that are already considered ‘quite lean’, is that the more you try to ‘diet down’ and shed fat, the lower your metabolism will dip.

If you’re single-digit body fat as a man or under 15% as a female, you need to be especially careful on how much of a deficit your caloric intake is, and how much cardio you plan on doing.

This leads me to the next point…

Cardio and muscle loss

I myself, have used one of the many ‘fat-burning tools’ such as HIIT and steady-state cardio with great success when trying to shed body fat (with no visible evidence of muscle loss mind you).

Potentially, those that do experience muscle loss have ‘bounced’ straight from a ‘bulk’ or caloric surplus into an immediate deficit. Or, they have introduced far too much cardio into their regimen (see previous point).

It makes a lot of sense: If you reduce calories to the point at which you fall below your ‘maintenance’ into negative and combine that with cardio, there’s a high potential for muscle loss.

I think Lyle Macdonald said it best with this statement:

…I think that one of the reasons that cardio has gotten a bad rap in terms of muscle loss on a diet is that people jump from doing basically zero cardio to fairly large amounts often overnight; this is often accompanied by a massive drop in calories and I suspect that it is this combination that tends to cause muscle loss.

What about HIIT?

When you add High Intensity Interval Training (HIIT) into the mix, the chance of muscle loss becomes significantly greater.

In Visual Impact Cardio, Rusty Moore explains:

…when you do intervals you typically spend a time near or above your lactate threshold level. If you do this type of training too often or for too long of periods, there is a strong chance you will lose muscle.

However, Human Growth Hormone (HGH) release is also increased during interval training. Why is that significant? Well, HGH stops cortisol from doing undesirable things to your body (cortisol is a hormone that causes fat gain and muscle breakdown).[5]

With that information on board, it’s easy to see that HIIT can be both beneficial and largely detrimental when not used correctly.

My take on it…

If you incorporate sprints/intervals into your training regimen on a bi-weekly basis and keep the duration short (under 10-15mins), the effects on muscle loss should be minimal. As for steady-state cardio, I’d suggest that the effects on muscle loss would be even less-so (as long as the intensity is low, and the number of sessions isn’t excessive).

For maximum effect, and if holding onto muscle is a concern, I’d limit your sessions of any form of intense cardio (be it steady state or HIIT) to twice a week.

When considering a fat-loss approach, careful monitoring of your caloric deficit is paramount in making sure you’re not exhausting your glycogen stores to the point where the body turns immediately to your muscle tissue. Secondly, I’d suggest using HIIT at the beginning of your cardio session, then finishing it off with 20-30 mins of steady state. The reason for this being that the HIIT will help release fat from the stores, and the steady-state will then help oxidise it.

Running, sprinting and other forms of cardio vascular exercise allow you to be able to dodge garbage in abandon warehouses (not recommended).

Cardio and its effects on sexual function

There’ve been plenty of studies in this area, but mainly on ‘physical’ exercise rather than cardiovascular exercise specifically [6].

From a ‘male only’ perspective, one specific study in the area of Erectile Disfunction (ED), did 5 randomized controlled studies (between 2004-2010) using the International Index of Erectile Function as measure of treatment outcome. A total of 385 subjects were involved and the results indicated a significant effect of aerobic training on erectile disfunction.[7]

…quitting drinking, smoking nor losing weight don’t improve sexual function quite the way cardio exercise does.

Similarly, a study by Doctors at the New England Research Institute on 600 middle-aged men found that those who hadn’t reported any problems with impotence were those who had exercised regularly.

How does it to relate to both men and women?

Cardio exercise increases blood flow and circulation. This is an undeniably important factor in regards to sexual health in both the guys AND gals.

Circulation can be hampered by obesity, smoking or heavy alcohol use, however quitting drinking, smoking nor losing weight don’t improve sexual function quite the way cardio exercise does.

My take on it…

Plain and simple — if you want to ‘keep it alive’ in the bedroom, you’d be doing the relationship with your better half a disservice by not incorporating some form of regular cardio vascular exercise into your lifestyle.

Speaking from my own experience, I’ve found that my sex-drive tends to ‘wane’ if I abstain from any form of moderate to high intensity cardio activity for extended periods of time (2 weeks or more).

The conclusion

As you can see, there are significant benefits to incorporating cardio into your lifestyle and very few negatives.

Yes the predominant negative of ‘muscle loss’ (for those that are aspiring to ‘build muscle’) needs to be taken into consideration, but also needn’t make you avoid cardio altogether. Using cardio strategically (without excess) will allow you to stay relatively lean year-round without the standard ‘mid winter bulk’ that sees most pile on muscle (if you’re lucky) coupled with a significant proportion of fat.

Being able to literally ‘see your junk’ without a mirror as well as being able ‘get it up’ throughout the entire year is a pretty decent incentive for a large proportion of the population :)

Key Points

  • When looking to lose fat, couple strategic cardio with a weight training regimen and solid nutrition (don’t rely on cardio alone in regards to fat loss).
  • Excess cardio is potentially detrimental to mass gains in a ‘muscle building’ phase (use it wisely and in smaller amounts).
  • HIIT specifically, can be detrimental to mass gains and assist in muscle catabolism when used in excess but can also blunt cortisol (take away: use in moderation 1-2 times a week tops at no more than 10-15mins a session).
  • Monitor your caloric intake when undertaking any form of cardio exercise – this will play a huge part in both fat-loss and muscle loss.
  • Cardio exercise improves sexual function by increasing blood flow and circulation (if you have trouble ‘getting it up’, consider incorporating more cardio into your regimen).

A final thought

One important point that is outside of the realms of this post, is that for many, cardio exercise is a powerful ‘stress reliever’ and thus it’s inclusion in a training regimen outweighs any of the negative aspects. I would even go as far as to say a lot of folks prefer cardio over weight training as it’s easier to accomplish and requires little to zero equipment.

Different strokes for different folks and perhaps a topic for another post…


1. Am J Clin Nutr. “Lipid metabolism during endurance exercise” 2000 Aug;72(2 Suppl):558S-63S.
2. Tabata I, Nishimura K, Kouzaki M, et al. “Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max”. Med Sci Sports Exerc 28 (10): 1327–30. 1996.
3. Am J Phys Med Rehabil. “Long-term Lifestyle Intervention with Optimized High-Intensity Interval Training Improves Body Composition, Cardiometabolic Risk, and Exercise Parameters in Patients with Abdominal Obesity.” 2012 Nov;91(11):941-50.
4. Wolfe, R. R. “Fat metabolism in exercise”. Adv. Exp. Med. Biol. 441: 147-56. 1998.
5. J Clin Endocrinol Metab. “Effects of cortisol and growth hormone on lipolysis in human adipose tissue.” 2000 Feb;85(2):799-803.
6. J Sex Med. “Exercise is associated with better erectile function in men under 40 as evaluated by the International Index of Erectile Function.” 2012 Feb;9(2):524-30
7. Ethiop J Health Sci. “Effects of Aerobic Exercise in the Management of Erectile Dysfunction: A Meta Analysis Study on Randomized Controlled Trials” 2011 November

Over to you…

What are your thoughts on cardio? Do you use it regularly or avoid it? Comment below.

Clint Nielsen

Author Clint Nielsen

Clint is a dad and husband trying to stay in shape. He's also a highly opinionated fitness enthusiast and author of Reveal The Steel. Follow him on: Instagram, Twitter, Facebook and Google+

More posts by Clint Nielsen

Join the discussion 28 Comments

  • Drew says:

    i was looking for an answer to my workout question about cardio. thank you for posting this

  • Jay says:

    Great post Clint.

    I remember when I was doing my first cut, I would kill myself doing cardio(HIIT and steady state)and lost a lot of strength and muscle. It sucked really bad and fat lost came to a halt because I was eating wayyy too little( 1500-1600 cals 50-100g of carbs) It was a miserable experience and I definatly learned from it.

    Thanks Clint and great work.

    • Clint says:

      Cheers Jay,
      I’ve been in the same boat with ‘cardio overload’ in the past. As with everything, there are ‘good ways’ and ‘bad ways’ to approach things depending on the specific goal at the time.

      • Jay says:

        Yeah I agree. This was during my phase 3 VIMB. For some odd reason I developed a fear of carbs and did insane amounts of cardio hopeing to lose fat and paid the price, but yea its about balance and like you said, approach cardio in a good way. I prefer the cardio you have outlined in Reveal the Steel; works wonders and very effective (on stage1 at the moment)

  • Clint,

    Great post. I do quite a bit of cardio, but I try to avoid too much HIIT especially on consecutive days. I think 15 minutes of HIIT followed by 30 minutes of steady state a couple of times per week is a good formula for fat loss and muscle preservation.


    • Clint says:

      Certainly – as your goals change, you can always incorporate further stints of steady-state to bring down body fat levels. It’s a case of trial-and-error here however (especially in regards to caloric reduction).

      • I also have to be careful with the blend of cardio I do. I’ve found that cycling it makes it work for me. I think the breaks give me time to recover and adapt. Having said that, it’s only really the hard stuff I cycle, I tend to keep a fairly steady state of steady state (sorry, couldn’t resist it!) cardio going on most of the time. Much of it accidental, like cycling to work, running with clients and going biking on the weekeneds. It’s no surprise really that I need to cycle my HIIT style stuff, as it’s always on top of that background…

        Keep up the good work

  • Gordon says:

    interesting post. I am currently on stage one in your program and incorporate two days of cardio. One day, I am doing Rusty’s pyramid training for 33min (start slow and increase speed every minute and once you reached a top, you decrease it again minute by minute) and on the other day, I am skipping (interval) for 15-20min followed by 15min steady. Do you think this could be too much?

  • Adrian says:

    Hi Clint,
    Thanks for the article. A quick (hopefully not stupid) question : Is walking considered steady state cardio? I often will walk on the treadmill (coz I’m spent) and then sprint for 30 secs when completing the 10-15mins cardio at the end of your program. cheers.

    • Clint says:

      Stupid questions are only the ones that are never asked ;)

      I’d classify walking as a form of steady-state cardio (in this case low intensity). Obviously there are varying degrees of walking from low > med > high intensity (walking as quickly as you possibly can).

  • Jason says:

    Great article. Its always hard to say a certain training method is good or bad without knowing a persons goals.

    For example, a shot putter wont have much use for cardio work, whereas a football player would train with a delicate balance between strength & cardio training.

    If you are talking purely for weight loss, I usually recommend people build muscle first, befor using any cardio. Then, after say 6-8 weeks, that extra muscle will burn more fat when you do start doing cardio.

    • Clint says:

      Absolutely – being ‘goal’ orientated at all times will help you get to where you want to be a lot quicker. It can be easy to become complacent and step into the gym without any idea what you’re trying to achieve. Do you want to lose fat? Do you want to build strength/muscle?

      Sort that out first, then you’ll have a better understanding of when and how you need to incorporate your cardio sessions.

  • Great article Clint. This reminds me that I should be doing more cardio. It always seems to be that part of my workout that gets left behind. Probably because I hate doing it. Looking forward to trying out your reveal the steel techniques.

    • Clint says:

      I’m hearing you Darren :)

      I’ve tried to incorporate cardio into RTS in a way that is a lot less monotonous and allows for plenty of lifestyle variation.

      Looking forward to your thoughts on the book and most importantly the training aspects.

  • Great article. I try to do HIIT a least once or twice a week and long slow cardio 2 to 3 times a week. I tend to bounce between 9% and 11% body fat. I can’t wait for all the holiday parties to be over so I can stop being exposed to so much junk food. January I want to get down to 7% body fat.

  • Hi Clint, very nice article, but include three things that are important to many: what and how much to drink when doing the HIIT + steady state cardio (assuming 45-50 minutes total), and what to eat (or drink) before and afterwards, and if it’s the best to do it the same day one trains with weights or better do it different days.

  • nhessler says:

    I think these are all great points. I do think you missed one form of cardio though, and that is metabolic conditioning (i.e. crossfit style workouts). I think adding these a couple times a week can do wonders for fat-loss while maintaining muscle mass.

    In the end though Diet is king IMO.

    • FromEnglandWithLove says:

      you would call crossfit cardio?….’facepalm’

      • nhessler says:

        pleas read my post again and not that I said metabolic conditioning is a form of cardio. your ability to suck oxygen during metabolic condition definitely plays a factor in how well you do and how well you can keep up your pace over time. it also hase muscle strength and muscle endurance factors as well, but there is a cardio factor to almost any metabolic conditioning you do.

  • Nestor says:

    Hi Clint, when is the best time to do cardio, Before or after weight training?

  • Анна says:

    Cardio exercises have never been my favorite. But after I’ve started taking Navy Seal Formula by Military Grade I was getting extreme results especially in this kind of trainings. My endurance has increased and my workouts have improved. I’ve been taking a lot of supplements, but this one is really doing it for me and my lifestyle.

  • Catha Finley says:

    I’ve been overweight for 10 years and tried so many things. Different things work for different people and I was lucky enough to find one that worked for me. I lost 24 pounds in one month without exercise and it’s been a life changer. I’m a little embarrased to post my before and after photos here but if anyone actually cares to hear what I’ve been doing then I’d be happy to help in any way. Just shoot me an email at and I’ll show you my before and after photos, and tell you about how things are going for me with the stuff I’ve tried. I wish someone would have helped me out when I was struggling to find a solution so if I can help you then it would make my day

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