Learn how to utilize fat as fuel, improve efficiency and better gauge intensity by training in the right zones.
When you think of an easy run, thoughts of runners cruising down the sidewalk, rocking out to the beat in their headphones at a comfortable clip probably come to mind. Unknowingly, however, most runners don’t really run all that easy on their easy runs. After a few warmup miles, many runners start to feel good and begin pushing the pace without even realizing it. What started out as an easy run may end up being a push to simply get it over with as quickly as possible.
To help runners and other endurance athletes keep their easy runs easy and their hard workouts at the correct intensity, more and more coaches are relying on heart-rate training. Trapper Steinle, personal trainer, endurance coach and metabolic technician at Lifetime Fitness in Centennial, Colorado, encourages this type of training. He emphasizes that structured workouts in specific heart-rate zones will help increase an athlete’s metabolic efficiency, a fancy term meaning the body’s ability to burn fat as fuel.
During exercise, the body utilizes two primary sources of fuel, namely carbohydrates and fats. Unlike carbohydrates, which are limited and break down rather quickly, fat breaks down slower in the body and releases more energy. Plus, the amount of fat athletes can store is virtually limitless, even in the most slender of individuals. By teaching the body to burn more fat than carbohydrates, endurance athletes will be more efficient over longer distances. This translates to faster times and better performances. For many runners, it also means easy — but tedious — training.
To determine an athlete’s metabolic efficiency and identify their target heart-rate training zones, Steinle uses treadmill and bike tests. Athletes wear a heart-rate monitor, along with a mask that measures expired CO2 and O2. After a warmup, the athletes run or bike at an increasing level of effort until near exhaustion. The machine calculates ventilatory data and correlates metabolic efficiency with different heart-rate values.
Analyzing this data typically confirms the biggest problem for many athletes: they aren’t extremely efficient at utilizing fat as a fuel. When runners continually push their body hard in training, they teach their bodies to rely more on carbohydrates as fuel. This isn’t a desired adaptation according to Nicole Clark, personal trainer and triathlon coach in Westminster, Colo., who identifies training too hard as one of the biggest mistakes an athlete can make.
“Athletes are often feeling great in the beginning of their training block,” Clark says, “and it is easy to push too hard on light days, which can lead to injury, illness or overtraining.” To combat this problem, Clark advises all endurance athletes to train with a heart-rate monitor to gauge intensity.
Feel the Beat
Heart-rate training is hardly a new concept to endurance athletes. The usefulness of heart-rate data, however, has been questionable.
In the past, runners have ended their runs and stared at maximum and average heart rate values following a training session, not knowing exactly what to do with this information. Fortunately, the paradigm of heart-rate training has shifted in recent years, making it easier to understand what effort levels you should be running at for a given workout. Rather than focusing on one to two specific heart-rate values, “zone” training clumps values into five broader ranges, described below.
Although metabolic testing isn’t required to follow heart-rate based training, it is the most accurate way to determine your training zones as well as where you need the most work. If you can’t spring for testing, you can estimate your values by finding out your max heart rate and using the following percentages determine your own training zones.
— 50-60% of max heart rate. This zone corresponds to an athlete’s aerobic base and is typically reserved for a warmup and cooldown.
— 60-70% of max heart rate. This is an aerobic zone where an athlete can run comfortably and utilize fat as a primary fuel source.
— 70-80% of max heart rate. This is the last aerobic zone before crossing the anaerobic threshold. Training in this zone is challenging but sustainable for most athletes.
— 80-90% of max heart rate. This is an anaerobic zone which by definition implies the absence of O2 resulting in a negligible amount of fat metabolism. Therefore, our bodies are primarily using carbohydrates as a fuel source. Athletes in Zone 4 may mutter only a few words at a time.
— 90-100% of max heart rate. This is the top of the heart rate chain and leaves you gasping for air after only 10 to 20 seconds of work.
Burning Fat As Fuel
Heart rate zones are going to differ for each athlete depending on training, age and genetics. The goal of heart-rate training is to improve your body’s ability to burn fat as fuel, sparing carbohydrates for when you really need them, such as later in a long race.
According to Steinle, most athletes are doing far too much work at the high end of the spectrum. This not only affects your performance, but also your cravings and nutrition. If you’re utilizing a lot of carbohydrates during exercise, you’re likely going to crave more sugars throughout the day. To satisfy those cravings, endurance athletes typically chow down on pasta, rice, and other dense carbohydrates. Steinle indicates this might not be the best way to go.
“Your metabolism is influenced by more than just your training,” he says. “Nutrition plays the biggest role. If you’re eating a lot of breads, sugars, and refined carbohydrates, that’s what your body will burn.” In addition to proper training, feeding your body with lean proteins, healthy fats, and whole grains, you can teach your body to burn fat at a greater rate and preserve carbohydrates.
To maximize your metabolism, Steinle says to focus your training on three main types of workouts.
Base Building Runs: To increase your fat metabolism and spare carbohydrate usage, incorporate base-building runs into your training schedule. For this type of training, stick mainly in Zones 1, 2, and the bottom of 3 with easy runs and comfortable long runs to help build up your aerobic base and tap into your fat metabolism.
Threshold Workouts: These workouts are at the top of Zone 3 and are designed to increase your anaerobic threshold. This fairly intense pace should be one you can hold for 30 to 40 minutes, such as a tempo run. Breathing should be audible and it should be difficult to have a conversation. By getting comfortable at this pace, you’ll push your anaerobic threshold higher and improve your ability to burn fat at a higher heart rate.
Interval Workouts: Interval workouts will improve your anaerobic threshold as well as your heart rate recovery. These workouts, which consist of brief periods of intense running followed by a recovery interval should oscillate between Zones 4 and 2. By pushing yourself past your anaerobic threshold, your body will adapt to harder efforts while also improving your ability to recover back down to Zone 2.