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

By October 22, 2012 28 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+

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