Exercise Intensity Calculator 2

Powered by Snergy · Karvonen Method

Exercise Intensity Calculator

Find your personal heart rate zones, measure how hard you trained, and get the right nutrition to recover faster.

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Profile Zones Session Results Products

Your Profile

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We use the Karvonen method — a sports-science formula that personalises your training zones based on your actual heart rate range, not generic age charts. Enter your details below.

Age
Used to estimate your max heart rate automatically.
Resting HR
Measure it first thing in the morning, before getting out of bed.
Max HR
The highest your heart can beat. Auto-filled — override if you know your tested value.

15 – 80 years

Best measured on waking.

Auto-estimated. Override if known.

💡

Measure your resting HR for 3 mornings and use the average for more accurate zones. Most adults sit between 60–80 bpm. Fit athletes are usually 40–55 bpm.

✅ Age 30 · HRmax 190 · HRrest 65 bpm

Your Heart Rate Zones

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Your zones are calculated using Heart Rate Reserve — the gap between your resting and max HR. This makes them unique to you, not just your age group.

Formula: Target HR = (HRmax − HRrest) × % + HRrest

What Each Zone Trains

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How Long Did You Spend in Each Zone?

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Drag the sliders to match your session. If you have a fitness tracker (Garmin, Apple Watch, Whoop), check your app for exact zone times. Otherwise, estimate based on feel:

Z1 – Recovery
Warm-up, cool-down, rest periods
Z2 – Easy Aerobic
Comfortable pace, can hold a conversation
Z3 – Moderate
Breathing hard, short sentences only
Z4 – Hard
Can't talk, interval training territory
Z5 – Max Effort
All-out sprint, sustainable only for seconds

Minutes per zone

Total: 50 min

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Your Intensity Score

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The Intensity Score measures true session intensity — not just time spent. Harder zones count more because they demand more from your body. Max possible score is 480 (60 min entirely in Z5).

Intensity Score
0
out of 480
Weighted intensity load. Higher = harder session.
Intensity %
0%
of max session
How intense this session was vs. an all-out effort.
Intensity Minutes
0
weighted minutes
Easy = 1×, hard = 2×. Good for tracking weekly load.
Strain Index
0
total body stress
Higher value = more recovery time needed.
RestEasyModerateHardPeak
⬤ Calculating…

Aerobic vs Anaerobic Split

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Z1–Z3 = Aerobic (fat-burning, oxygen-based). Z4–Z5 = Anaerobic (glucose-burning, higher intensity). Endurance athletes aim for 80–90% aerobic; power athletes may go 50% anaerobic in hard sessions.

Aerobic · Z1–Z3
0%
of session
Builds endurance, burns fat, improves cardiac health.
Anaerobic · Z4–Z5
0%
of session
Boosts speed, power, and VO₂ max. Needs longer recovery.
Enter zone times to see your recovery recommendation.

Zone Distribution

Total: 0 min

How It's Calculated

Karvonen Formula

Target HR =
(HRmax − HRrest)
× Intensity% + HRrest

Personalises zone boundaries using your heart rate reserve, not just age.

Intensity Score

Score =
(Z2×1)+(Z3×2)
+(Z4×4)+(Z5×8)

Each zone is weighted by its metabolic cost. Max = 480 pts.

HRmax Estimate

HRmax =
208 − (0.7 × Age)

Tanaka Formula — more accurate than 220−age, especially over 40.

✅ Showing recommendations for —

Your Recovery Stack

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Different intensities deplete different fuel sources. We've matched products from Steadfast Nutrition's range to exactly what your body needs right now — nothing more, nothing less.

Calculating…

Matching products to your session intensity.

Full Range

The Complete Product Catalog

Every Steadfast Nutrition product — with macros, serving sizes, and direct shop links.

Reference Table
# Product Category Protein Carbs Fat Kcal Serving Ratio

Steadfast Nutrition — Exercise Intensity Calculator · Karvonen HR Reserve Method