Intensity and Heart Rate Zones
Coach Kris Perry-Tedesco • November 1, 2024
The Three Energy Systems & The Balance of Bio Energenetics
Why do program 5 minute workouts vs. 30 minute workouts?
(and all the time domains in between)
Let’s break down the differences between these two CrossFit workouts by looking at the intensity, energy systems used, heart rate zones, and recovery needs:
1. Intensity and Heart Rate Zones
30-Minute CrossFit Workout at Average Zone 3:
Intensity: This workout would be a moderate-intensity session. Zone 3 (around 70–80% of max heart rate) represents a steady aerobic state.
Heart Rate: In Zone 3, your heart rate is elevated but stays within a manageable range, allowing you to sustain the activity for a longer period without burning out.
VS.
5-Minute CrossFit Workout at Average Zone 5:
Intensity: This workout is very high-intensity. Zone 5 (90–100% of max heart rate) pushes your heart rate to the max, close to its peak.
Heart Rate: In Zone 5, your heart is working at or near its capacity, delivering maximum oxygen to muscles.
It’s difficult to sustain Zone 5 for more than a few minutes without significant fatigue.
2. Energy Systems Used
30-Minute Workout (Zone 3):
Primary System:
The aerobic (oxidative) system dominates here, as it’s best for prolonged, lower-intensity exercise.
Support from Glycolytic System:
During intense parts of the workout (like short bursts within the workout), the glycolytic system may provide additional energy.
Benefits:
Builds endurance, improves cardiovascular health, and increases aerobic capacity.
VS.
5-Minute Workout (Zone 5):
Primary Systems:
The ATP-PC and glycolytic systems are the main sources of energy, providing quick ATP without oxygen for high-power output.
Limited Aerobic Contribution:
The aerobic system plays a minor role because there’s not enough time for it to be the primary energy provider.
Benefits:
Enhances power, speed, and anaerobic capacity, and boosts VO₂ max over time
3. Workout Goals and Training Effects
30-Minute Workout (Zone 3):
Goal: Build endurance and improve aerobic fitness.
Training Effect: Improves muscle stamina and efficiency in oxygen usage, which helps with longer WODs or endurance-based CrossFit events.
Recovery: Lower intensity means quicker recovery time, so you’re less likely to feel burned out the next day.
VS.
5-Minute Workout (Zone 5):
Goal: Boost anaerobic power, muscular strength, and explosive endurance.
Training Effect: Increases power output, speed, and lactate tolerance, which can improve performance in sprint-style WODs or competitions.
Recovery: Zone 5 intensity requires longer recovery, as it leads to higher muscle breakdown and increased lactic acid build-up.
4. Fatigue and Recovery Needs
30-Minute Workout (Zone 3):
Fatigue:
Moderate fatigue due to sustained effort, but manageable because it’s mostly aerobic.
Recovery Needs:
Generally shorter recovery, as Zone 3 intensity doesn’t cause as much muscle strain or lactic acid buildup as Zone 5.
VS.
5-Minute Workout (Zone 5):
Fatigue:
High fatigue due to intense effort, leading to “burnout” feeling in muscles and potential soreness.
Recovery Needs:
Requires more recovery time, potentially a day or two, due to the higher stress on muscles and cardiovascular system.
Summary
30-Minute, Zone 3 Workout: Steady aerobic effort, builds endurance, and has moderate fatigue/recovery needs.
5-Minute, Zone 5 Workout: High-intensity anaerobic effort, builds power and strength, and has significant fatigue/recovery needs.
Both workouts are valuable in CrossFit but serve different purposes:
One builds endurance, while the other enhances power and anaerobic capacity.
Let's dig a little deeper....
Bioenergetics is about how living cells manage energy, especially how they create and use it to keep the body functioning.
Think of it like a battery. Just as your phone or flashlight needs to be charged to work, your body needs energy to function. You get this energy from food, which your body converts into a molecule called ATP (adenosine triphosphate). ATP is like a tiny packet of energy that powers everything your cells need to do, like muscle movement, brain activity, and even breathing.
The balance of bioenergetics involves two main processes:
1. Energy Production
(Charging the Battery): Your body breaks down food (like sugars, fats, and proteins) in a process called cellular respiration. This happens in the mitochondria, the "powerhouses" of cells, where food is converted into ATP.
2. Energy Usage
(Using the Battery): When your body needs to do work—like contracting muscles when you walk or think—it "spends" ATP. This energy allows cells to do tasks, and then the ATP is depleted and needs to be replenished by breaking down more food.
The goal of bioenergetics is to keep these processes balanced so that your body has enough energy to function without running out. If your body produces too much ATP or too little, it can disrupt the balance and affect your health and energy levels.
Heart rate is closely tied to which energy system your body is using because different intensities and durations of exercise require different levels of oxygen and energy.
Here’s how heart rate connects to each energy system:
1. ATP-PC System
(Immediate Energy System):
Since this system is for very short, explosive bursts (like sprinting or lifting heavy weights), it doesn’t rely on oxygen and doesn’t demand much from the heart.
Heart rate may rise quickly at the start but won’t reach high levels because the activity is too brief for the aerobic system to kick in fully. So, you might feel a quick spike but not a sustained high heart rate.
2. Glycolytic System (Anaerobic System):
In this phase, your body still isn’t using oxygen fully, so the heart rate increases to deliver more oxygen to muscles in anticipation of greater demands.
As you push through moderate-duration, high-intensity exercise (like a 400-meter run), your heart rate climbs toward the upper end of your anaerobic zone (usually around 80–90% of your maximum heart rate) to help sustain this effort and deal with the buildup of lactic acid.
3. Oxidative System (Aerobic System):
For longer, lower-intensity activities, the oxidative system takes over, relying on oxygen to generate ATP. To provide enough oxygen, your heart rate will stay elevated but usually at a lower, steady rate compared to anaerobic activities.
For moderate aerobic activities, your heart rate may stay in the 60–80% range of your maximum heart rate. This lets you sustain the exercise for longer without fatiguing.
In essence:
Short sprints (ATP-PC): Short, quick heart rate rise but not sustained.
Moderate time/effort (Glycolytic): Higher heart rate (around 80–90%) to support anaerobic work.
Longer, steady activities (Oxidative): Moderate, steady heart rate (60–80%) for sustained aerobic energy.
The more intense the exercise, the higher your heart rate goes, reflecting the body’s need for faster energy replenishment and greater oxygen delivery to muscles.
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DISCLAIMER
This is not Legal, Medical, or Financial advice. Please consult a medical professional before starting any workout program, diet plan, or supplement protocol.
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