You just finished a run and your smartwatch is screaming at you. It says your "cardio load" is unproductive or, worse, that you’re overreaching. It’s frustrating. You feel good, but the data says you're failing. Or maybe you feel like absolute garbage, yet the app tells you to push harder. This disconnect happens because most people don't actually know what is a good cardio load for their specific biology and goals.
It isn't a single number. It's a moving target.
If you're training for a marathon, a "good" load looks like a mountain range of stress. If you're just trying to not get winded walking up the stairs, that same load would probably land you in the physical therapy office. We have to stop looking at these metrics as "high scores" to beat. Instead, think of cardio load as a budget. You only have so much "stress currency" to spend before you go bankrupt.
The Science of Internal vs. External Strain
We need to get technical for a second, but I'll keep it simple. There are two ways to look at work. External load is what you actually did—you ran five miles at an eight-minute pace. Internal load is how your heart and lungs reacted to that effort.
That distinction matters.
If you’re stressed at work, haven't slept, and drank three cups of coffee, your internal load for that same five-mile run will be much higher than if you were well-rested. This is why "what is a good cardio load" is such a tricky question. A 400-load score on a Garmin or Polar device might be a standard Tuesday for a triathlete, but for a beginner, it represents a massive physiological shock.
According to the Bannister Impulse (TRIMP) model, which is the grandaddy of these calculations, your training impulse is a factor of duration and intensity (usually tracked via heart rate). Most modern apps use a version of this. They look at your heart rate zones and multiply the time spent in each.
Why the "Acute vs. Chronic" Ratio is the Only Number That Matters
Forget the daily score. It’s a distraction.
✨ Don't miss: Fruits that are good to lose weight: What you’re actually missing
The real magic is the Acute:Chronic Workload Ratio (ACWR). This concept was popularized by sports scientist Dr. Tim Gabbett. It compares what you’ve done in the last seven days (acute) to what you’ve done over the last 28 days (chronic).
If your acute load is way higher than your chronic average, you’re in the "danger zone."
Typically, a ratio between 0.8 and 1.3 is considered the "sweet spot."
If you go above 1.5? Your risk of injury spikes. It's like trying to overclock a computer without upgrading the cooling system. You'll smell smoke eventually. Honestly, most people get hurt because they see a "low" load score one day and decide to double their mileage the next. That’s a recipe for shin splints or worse.
Breaking Down the Numbers: What’s "Good" for You?
Let’s look at some real-world context.
For a general fitness enthusiast working out 3–4 times a week, a "good" cardio load usually keeps their weekly total consistent. You aren't looking for massive spikes. You want a steady baseline. If your device gives you a numerical score, look for a 10% weekly increase at most.
- The Weekend Warrior: You likely have a low chronic load during the week and a massive spike on Saturday. This is risky. A "good" load for you involves raising your weekday floor so the weekend doesn't break you.
- The Performance Athlete: You’re likely flirting with that 1.3 ratio constantly. For you, a "good" load includes planned "deload" weeks where you intentionally drop your load by 30-50% to let your tissues repair.
Heart Rate Variability (HRV) is the secret sauce here. If your cardio load is high but your HRV stays stable, you're adapting. You're getting stronger. If your load is high and your HRV crashes, your "good" load just became a "bad" one. You're overreaching.
The Trap of Over-Reliance on Wearables
I've seen people ignore literal chest pain because their watch told them their "Training Readiness" was high. Don't be that person.
🔗 Read more: Resistance Bands Workout: Why Your Gym Memberships Are Feeling Extra Expensive Lately
The algorithms used by companies like Garmin, Whoop, and Oura are based on population averages. They are smart, but they aren't in your body. They don't know if you have a cold or if you're grieving or if you just had a really salty dinner that's messing with your fluid retention.
A good cardio load is one that challenges your cardiovascular system without causing systemic fatigue that bleeds into your non-gym life. If you're too tired to play with your kids or focus at work, your cardio load is too high. Period. It doesn't matter what the "Optimal" zone on your app says.
Intensity Distribution: The 80/20 Rule
You can't talk about cardio load without talking about intensity. A common mistake is doing everything at a "medium" intensity. This is the "black hole" of training. It's hard enough to tire you out, but not hard enough to trigger major aerobic adaptations.
Top-tier athletes, from Kenyan marathoners to Norwegian triathletes (look up the "Norwegian Method" utilized by the Ingebrigtsen brothers), spend about 80% of their time in Zone 2. This is low-intensity, conversational cardio. It builds the mitochondrial density you need to handle a high cardio load later.
The other 20%? That's high-intensity intervals.
When you ask what is a good cardio load, you should be asking how that load is distributed. If your load score is 500 for the week, but it all came from "moderate" slogs, you're likely plateauing. If that 500 comes from a mix of easy base miles and one or two sharp interval sessions, you're going to see your fitness (VO2 Max) actually climb.
The Role of Recovery in Load Calculation
Recovery isn't "not working." It's an active physiological process.
💡 You might also like: Core Fitness Adjustable Dumbbell Weight Set: Why These Specific Weights Are Still Topping the Charts
Your cardio load doesn't actually make you fit. The recovery from the load makes you fit. When you stress the heart and the vascular system, you create micro-damage and metabolic waste. Your body then over-compensates by making the heart stronger and the blood vessels more efficient.
If you don't provide the recovery window, you're just stacking stress on top of stress.
- Sleep: The most potent recovery tool. Eight hours is the gold standard for a reason.
- Nutrition: If you're running a high cardio load on a caloric deficit, your "good" load will turn into "Relative Energy Deficiency in Sport" (RED-S) real fast.
- Hydration: Blood volume drops when you're dehydrated, making your heart work harder for the same output. This artificially inflates your cardio load score.
Real Signs Your Cardio Load is "Good"
Forget the watch for a second. Use your "biological dashboard."
- Resting Heart Rate (RHR): Is it stable or slightly trending down over months? That’s a sign of a good load. If it jumps by 5–10 beats per minute and stays there, you’re overdoing it.
- Sleep Quality: Are you falling asleep easily? High cardio load often causes "tired but wired" syndrome where your cortisol is too high to let you sleep.
- Appetite: A healthy training load usually stimulates a healthy appetite. If the thought of food makes you nauseous, you’ve pushed too far.
- Mood: Are you irritable? Overtraining syndrome often looks a lot like clinical depression.
How to Adjust When the Load is Too High
It happens to everyone. You get ambitious, the weather is nice, and you overcook it.
The first thing to go should be intensity, not volume. Drop the sprints. Keep the movement. Gentle walking or "Zone 1" cycling can actually help clear out the metabolic gunk and reset your nervous system. This is called active recovery.
Also, look at your life stress.
The body doesn't distinguish between "boss yelled at me" stress and "I ran a 10k" stress. It all goes into the same bucket. If life gets hectic, your "good" cardio load must decrease to compensate. This is what experts call "Autoregulation." It’s the ability to pivot based on how you actually feel.
Actionable Steps to Optimize Your Training
Stop chasing the highest number possible. It's a trap. Instead, follow these steps to find a load that actually builds health rather than destroying it.
- Establish a Baseline: Track your normal activity for three weeks without changing anything. This average is your "Chronic Load."
- The 10% Rule: Never increase your weekly cardio load by more than 10% over the previous week. This is the safest way to avoid the "boom and bust" cycle.
- Prioritize Zone 2: Make sure at least 70-80% of your cardio load comes from efforts where you can still speak in full sentences.
- Monitor HRV Trends: Use a wearable to track Heart Rate Variability, but look at the 7-day trend, not the daily fluctuation. If the trend is down, pull back on the load.
- Conduct a "Talk Test": During your workouts, literally speak out loud. If you're gasping, your internal load is higher than you think.
- Schedule Deloads: Every 4th or 5th week, cut your volume by 30%. Your body will use this time to solidify the gains from the previous three weeks.
A good cardio load is ultimately the one that allows you to show up again tomorrow. Fitness is built through consistency over years, not through a handful of "epic" weeks that end in burnout. Pay attention to the data, but listen to your breath and your joints first. They rarely lie.