Applied Exercise Physiology for FAT LOSS

Its 6:30 AM and  I’m just getting back from the gym. Every Wednesday I lead a 30-minute, high intensity, body weight/interval-style workout with another chiropractor. We call it “ChiroFit” (not to be confused with Cross-Fit).

Anyway, as I was working out in my “zone”, I noticed the usual suspects on the treadmill and elliptical trainer. They were on those machines before I started and still there after I left the gym 45 minutes later (my workout was 30 minutes with 15 minutes as a warm-up/cool-down)

The workouts we do are short and intense. The intensity is the key.  

Having worked out at this gym around the same people for almost 10 years, I can say that I don’t see much change in how they exercise and consequently, how they look.

I am assuming that they exercise to look and feel better, and while I can’t speak for the latter, the former speaks for itself.

In a nutshell, these people spend at least  30-60 minutes doing low intensity cardio  and then either no resistance training or 15 minutes of low intensity machines.

The research shows you can spend about half the time as these people do in the gym, while still maintaining (or building) a strong, fit, healthy body.

So what’s “the secret”?

It’s actually no secret. It’s physiology.

While genetics may play some role, I can assure you, that epigenetics (using diet and exercise) trumps.

It’s all about fibers.

Muscle fibers can be classified into two general categories:

  1. Slow- Type I

  2. Fast- Type II (sub-categorized into IIa and IIx)

The percentage of fiber types contained in skeletal muscles can be influenced by:

1. Genetics

2. Exercise habits

3. Hormones (also influenced by exercise and diet)

Slow (Type I) Fibers contain a large number of oxidative enzymes and mitochondria. They are  resistant  to fatigue, efficient at fat burning and adapt to endurance exercise (steady state, relatively low intensity and long duration).


Fast (Type II) Fibers have a limited capacity for aerobic metabolism. They are less resistant to fatigue but have a  large anaerobic capacity.

Athletes and  Muscle Fiber Types:

  • Distance runners have about 80% slow fibers and 20% fast fibers

  • Track sprinters have about  30% slow fibers and 70% fast fibers

  • Non-athletes have about 50% of slow and fast fibers, respectively

There are three main principles of training that help to explain the pattern of recruitment of muscle fiber types during exercise of progressively greater intensity and duration:

1. Overload-  Tissue will adapt systematically and progressively, based on the intensity, duration and frequency.

2. Specificity- Exercise training is specific to the muscles involved in that activity, the fiber type recruited, the principal energy system involved, the velocity of contraction and the type of contraction.

If an individual participates in slow endurance running that utilizes slow twitch fibers, there is little  or no training effect  in the fast twitch fibers located in that same muscle.

3. Reversibility- The fitness gains with training are quickly lost when training is stopped and overload is removed. This is much slower with resistance training than with endurance training.

Based on the principle of specificity, concurrent endurance and resistance training will have antagonistic effects. These effects can include:

1. Neural factors- impaired force production (the ability of muscles to optimally contract)

2. Depleted glycogen (stored energy in the liver and muscles)- affecting performance and the magnitude of adaptations

3. Over-training- over-stressing the body

4. Depressed protein synthesis (muscle growth and/or repair)- adversely affecting strength gains and lean body mass

Fast Twitch=Fat Burn

A workout that recruits mainly fast-twitch fibers is a more intense workout because it requires you to exert power and speed. As a result, it releases more fat-burning hormones during your workout and causes your body to continue burning fat for eight hours or more after your workout.

Workouts such as aerobics and general strength-training exercises that activate slow-twitch fibers only boost your metabolism for a short amount of time after your workout.

Interestingly, unlike the adverse effects that endurance training can have on fast twitch fibers and anaerobic adaptations, resistance training and High Intensity Interval Training enhance one’s aerobic conditioning and in a fraction of the time, i.e. You get a much higher return on your investment when you do 15-20 minutes of intense intervals or resistance training than you would get with 60 plus minutes of steady state cardio.

 Did someone say Anti-Aging?

Fast twitch fibers are primed for fat burning and increasing metabolism. They also restore and counter the  adverse age-related changes in body composition and metabolism.

Applying physiology to fat burning

1. Perform exercise that leads to Type II (fast) fiber  adaptations, e.g. resistance training and HIIT (High Intensity Interval Training)- “Chirofit” style

2. Limit steady state cardio, especially concurrently with weight training

3. Eat a modified Paleo diet. I say modified, because you need some healthy carbohydrates to replenish glycogen in order to increase fast twitch fiber adaptations

4. Get adequate rest

There are a lot of fad diets and exercise plans out there.

Forget the Phads- Follow the PHYSIOLOGY. It’s what works!

About the Author

Dr. Geoff LecovinNaturopathic Physician/Chiropractor/Acupuncturist/Certified Strength and Conditioning Specialist/Corrective Exercise Specialist/Performance Enhancement Specialist/Certified Sports Nutritionist/View all posts by Dr. Geoff Lecovin