By Mike Croskery, M.Sc. HK (Biomechanics) - Clinical Exercise Physiologist
You've just crushed your aerobic workout, breathing hard, legs burning. "That fat is going to be burned up like crazy!" you think. However, what you might not realize is that you could have just sabotaged your fat-burning efforts due to the high lactic acid levels generated by your intense workout.
This post will examine the crucial connection between lactic acid and fat burning, and how managing lactic acid can enhance your body's capacity to utilize fat stores for energy.
What is Lactic Acid?
Lactic acid is a natural byproduct of rapidly burning carbohydrates to provide energy, especially during high-intensity workouts. Its accumulation in your system manifests as muscle weakness and that familiar "burning" sensation either during, near the end, or immediately after your exercise session. If levels become too high, it can also lead to unpleasant symptoms like nausea, dizziness, and headaches.
The Problem: When Lactic Acid Hinders Fat Burning
The core issue with lactic acid arises when your primary goal is to utilize your body's fat stores through aerobic exercise. Your body is remarkably efficient at finding the most readily available energy source. Since lactic acid (derived from carbohydrates) is a readily available and quickly metabolized form of energy, your body will prioritize using it over the longer, more complex process of metabolizing fat.
When you produce a lot of lactic acid by:
- Exercising at a very high intensity (e.g., 85% - 100% of your maximum heart rate).
- Significantly increasing the energy demand on your muscles in a short period (e.g., rapidly increasing resistance on a stationary bike or suddenly running much faster).
...your body effectively "switches off" fat burning. Instead of fat, it predominantly uses lactic acid and other carbohydrates as its primary energy source to power the exercise. So, does lactic acid burn fat? No, high levels actually indicate your body is prioritizing carbohydrates over fat for fuel.
Optimizing Your Workout for Efficient Fat Loss
So, how do you structure your workouts to optimize fat reduction efficiently?
1. The Importance of a Proper Warm-Up
A proper warm-up, performed at approximately 50% - 55% of your maximum heart rate for 10 to 15 minutes, will help to contribute to lower levels of lactic acid when you begin your main workout. This prepares your body to burn fat more effectively.
2. Finding Your Fat-Burning Zone
The intensity for optimal fat-burning aerobic work should generally be at approximately 60% to 70% of your maximum heart rate. Exercising at this lower to moderate intensity helps to:
- Maximize fat loss.
- Maintain lactic acid levels at a low enough level to avoid interfering with the fat-burning process.
3. Post-Workout Strategies
A cool-down portion of 5-10 minutes at 50% of your maximum heart rate after aerobic exercise can also help reduce the rise in lactic acid following the session.
Since a significant portion of your fat-burning effects often occurs after the exercise session (your metabolic rate can stay elevated for several hours), avoid doing any weight training or other high-intensity exercise for 3 to 4 hours following your fat-burning workout. These types of exercise can produce high levels of lactic acid, potentially hindering the post-exercise fat-burning effect.
Key Takeaways for Efficient Fat Burning
Optimizing your exercise routine for body fat reduction can sometimes feel like a tricky process. However, understanding the role of lactic acid and fat burning is key. Being physically active several times a week for at least 25 to 30 minutes per session, with appropriate intensity management, is a large part of the process towards proper and long-term body fat reduction.