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May 18, 2009

A Burning Question About Lactic Acid

 

Q: What is lactic acid?  Why does it cause that “burn”?

A: The simplest answer is that lactic acid is a byproduct of anaerobic ATP production.  But let’s backtrack a little and review some exercise physiology to put that definition into context…

A cell can produce energy in one of two ways: with or without the presence of oxygen.  If there is an adequate supply of oxygen to your cells (regardless of your activity – sleeping, typing, walking, running, etc), then your cells are involved in aerobic energy production.  Your cells are actively utilizing fat stores, sugar stores, and oxygen to produce ATP (short for the molecule adenosine triphosphate).  Think of ATP as your cells’ battery power.

Example: You are attempting to lift a dumbbell into a bicep curl.  First, your body needs fat, sugar, and oxygen in order to produce ATP molecules.  The new ATP is used to drive the muscle contraction in the bicep muscle, allowing you to curl the weight.  Realistically, this occurs on a much grander scale, but you get the idea…

In aerobic energy systems, water and carbon dioxide are the byproducts of the chemical reaction that creates ATP.  Both compounds are easy for the body to utilize or eliminate, thus aerobic energy production does not lead to muscle fatigue.

On the other hand, sometimes your body is unable to extract enough oxygen from the blood to continue the high demand for ATP production.  Now you begin to exercise anaerobically, or without oxygen.  This is often the case during vigorous workouts, sprints, heavy weight lifting – basically whenever the intensity at which you are exercising exceeds the available oxygen.  This upper limit of sustainable aerobic exercise usually corresponds with a heart rate elevated above 50-85% of maximum heart rate, and is referred to as the anaerobic threshold (sometimes called the lactate threshold).

Continue reading “A Burning Question About Lactic Acid” »

April 29, 2009

Exercise Does More Than Burn Calories

In “The Only Math You Need to Know,” I talked about creating a daily calorie deficit.  Specifically, in order to lose 1 pound per week you need to create a deficit of 500 calories each day.  Exercise is really the most powerful tool to do this.  Working out expends energy and, in order to expend that energy, your body needs to burn calories (usually sugar and fat).  Could you lose weight simply by cutting 500 calories from your diet without working out?  Sure.  If you’re creating a deficit, you’ll lose weight – no matter how it’s done.

Changing Your Body

But weight loss is not about getting down to a certain clothing size or a number on the scale (although that’s often what goals are structured around unfortunately).  It’s really about restructuring your body – about building a system that not only works more efficiently, but processes food and burns calories in a way that keeps you from gaining the weight back.  Sure, you can lose weight through diet alone, but I guarantee you that weight will come back just as quickly as you lost it.  And often you end up worse off than you were before you started losing weight.  This is a vicious cycle that many people get caught up in – often termed “yo-yo dieting”.

The addition of exercise does more than increase your calorie deficit.  Exercise is the mechanism by which you can change your body.

Here’s how it works: There are three main components of exercise – strength, flexibility, and cardiovascular work.  Flexibility should always be a part of your exercise program, but for the purpose of this discussion I’m going to assume you include some stretching after your workouts and leave it at that.  Strength training and cardiovascular exercise are the two components I’ll focus on for weight loss.

The Cardio Component

Cardiovascular exercise is aerobic activity (think running, walking, jogging, cycling, swimming, skiing, hiking, etc).  People usually engage in these types of activities to burn calories and because they enjoy them.  But cardiovascular exercise can improve your health on so many other levels beyond weight loss.

Here are just a few of those benefits:

  1. Reduced blood pressure.
  2. Reduced total cholesterol.
  3. Reduced body fat.
  4. Reduced depression symptoms.
  5. Reduced resting heart rate.
  6. Reduced incidence of some cancers.
  7. Increased HDL cholesterol (the “good” kind).
  8. Increased heart function.
  9. Increased oxygen consumption & blood flow to active muscles.
  10. Increased utilization of fat.
  11. Prevention of type-II diabetes.

For weight loss, I would suggest 45-60 minutes of cardiovascular exercise 3-4 days per week.  Any activity that is sustained for this period of time and keeps your heart rate up around 65-80% of your maximum heart rate will help you burn calories and reap the benefits listed above.*

The Strength Component

I’ve written before about strength training (“4 Reasons Why You Should Be Strength Training”) and its significant benefits, both for weight loss and for restructuring your body.  Here’s a clip from that article:

Your muscles are what carry out many of the metabolic reactions that burn sugar and fat stores for energy.   Want to lose weight?  Increase the percentage of lean muscle mass you have on your body, and you’ll be burning more calories per day – even while you’re sleeping!

Increasing your muscle mass is accomplished with strength training.  By adding weight training and toning exercises to your routine, you’ll be burning calories while you build muscle.  And the more muscle you have, the more calories you’ll burn each day – which really means that as you lose weight and change your body, it will get progressively harder for you to gain that weight back! That is the key right there, and it’s the reason why so many people can’t successfully maintain their weight.  They haven’t fundamentally changed their body.

Putting It All Together

For weight loss, I would suggest 30-60 minutes of total body strength training 2-3 non-consecutive days per week.  Combined with your cardio work, your exercise schedule would look something like this:

Monday          50 minutes Cardio

Tuesday         40 minutes Strength Training

Wednesday     50 minutes Cardio

Thursday        40 minutes Strength Training

Friday             50 minutes Cardio

Saturday         60 minutes Cardio

Sunday           Rest

It’s important to allow yourself at least one day off each week, to let your body recover from the stress of exercise.  Strength training, especially, requires a recovery period, which is why I say schedule your weight training on non-consecutive days.  After these training sessions, your muscles need time to synthesize proteins and build strength back up, which typically takes about 48 hours.

Adding exercise to your weight loss program will not only help you in reaching your calorie deficit, it will improve your ability to utilize and burn fat and reduce your risk of many diseases.  You will be more successful in keeping the weight off – and let’s face it, you’re working hard to lose that weight!  Don’t set yourself up to fail by neglecting the most important part of weight loss – exercise.

*If you are just beginning an exercise program, are recovering from an injury or illness or are over 65, start with 20-30 minutes of cardio activity at an intensity of 40-65% maximum heart rate and gradually build up to higher levels.

For more on weight loss strategies: “10 Ways to Make Weight Loss Work for You.”

Resources:
Bryant, Cedric X., and Daniel J. Green, eds.  ACE Personal Trainer Manual, 3rd ed.  San Diego: American Council on Exercise, 2003.