What Zone 2 is and why it matters for rucking
Zone 2 is a moderate aerobic intensity that is often estimated at 60 to 70% of heart rate reserve (HRR). Many people can speak in full sentences at this effort, which makes the talk test a useful check beside heart-rate data.
A pack can raise heart rate at the same walking speed. That may bring a walk into the estimated range without increasing to a jogging pace. The response varies by person and conditions.
How the calculator works
The HR target uses the Karvonen method: Target HR = ((HRmax - HRrest) × intensity) + HRrest. We default HRmax to the Tanaka formula (208 - 0.7 × age), derived from a 2001 meta-analysis of 351 studies and cross-validated in 514 healthy adults. It is an estimate of HRmax, not a measured maximum.
When you add body weight and ruck weight, the calculator works backward from the Pandolf load-carriage equation at the midpoint of your Zone 2 HR band to estimate a walking pace range on flat pavement. Compare the estimate with heart rate, perceived effort, and the talk test. Terrain, heat, and fitness can shift it.
Why pace alone is limited
Simpson et al. 2010 (PMID 20962921) measured participants carrying a fixed 20 kg pack. Raising speed from 6.4 to 7.4 km/h increased mean heart rate by about 20 BPM. The study did not measure the effect of adding that pack at an unchanged pace. Looney et al. 2021 (PMID 33652153) found heart rate reserve more useful than percentage of VO2max for prescribing intensity under heavy load. Pace alone therefore cannot describe loaded effort.
Zone 2 by age
Below is a quick lookup table for Zone 2 heart rate ranges by age, using an example resting heart rate of 65 BPM. Use the calculator above with your own resting HR. This table is a formula reference, not a measured training zone.
| Age | HRmax (Tanaka) | Zone 2 low (60% HRR) | Zone 2 high (70% HRR) |
|---|---|---|---|
| 25 | 191 BPM | 141 BPM | 153 BPM |
| 30 | 187 BPM | 138 BPM | 150 BPM |
| 35 | 184 BPM | 136 BPM | 148 BPM |
| 40 | 180 BPM | 134 BPM | 146 BPM |
| 45 | 177 BPM | 132 BPM | 143 BPM |
| 50 | 173 BPM | 130 BPM | 141 BPM |
| 55 | 170 BPM | 128 BPM | 139 BPM |
| 60 | 166 BPM | 126 BPM | 136 BPM |
| 65 | 163 BPM | 124 BPM | 134 BPM |
| 70 | 159 BPM | 121 BPM | 131 BPM |
In this example, the range changes with age because the formula estimates a lower HRmax. Resting heart rate also changes the output, which is why the calculator asks for it.
Using the talk test
The talk test is a field check, not an exact zone diagnosis. Full sentences usually suggest a moderate effort; speech reduced to short phrases suggests a harder one. Use that signal beside heart rate and perceived effort. There is no need to add pack weight just because conversation feels easy; pace can change first if you intentionally want a harder session.
Accounting for cardiac drift
Heart rate can rise during a longer session even when pace and load stay constant. Heat and fluid loss can contribute to this cardiac drift (Coyle and Gonzalez-Alonso 2001). A rising heart rate may call for a slower pace. Stop and seek medical help for chest pain, faintness, or unusual shortness of breath rather than treating those symptoms as routine drift.
Where this tool fits in your training
Use it to plan moderate, conversational rucks. Event pace and interval sessions have different targets. For body-weight goals, remember that training intensity is only one part of total energy balance.
Frequently asked questions
What is Zone 2 heart rate, and why does it matter for rucking?
Zone 2 is a moderate aerobic intensity often estimated at 60 to 70 percent of heart rate reserve. A pack can raise heart rate at a walking pace, so rucking may reach that range without increasing to a jogging pace. The calculated band is an estimate, and medicines or health conditions can change the response.
Is the Karvonen method more accurate than 220 minus age?
The Karvonen method includes resting heart rate, while 220 minus age does not. This calculator pairs it with the Tanaka HRmax formula, 208 minus 0.7 times age, derived from a meta-analysis of 351 studies and cross-validated in 514 healthy adults. Both methods still estimate an individual range rather than measure it.
Why does my heart rate jump when I add a ruck?
Loaded walking can change heart rate, but this tool does not assign one fixed increase to a given pack. Simpson et al. 2010 found a roughly 20-beat rise when participants carrying a fixed 20 kg pack increased speed from 6.4 to 7.4 km/h. It did not isolate the effect of adding the pack at the same pace.
Should I trust heart rate or pace when rucking in Zone 2?
Use heart rate together with perceived effort and the talk test. The tool estimates the pace band by working backward from the Pandolf equation, and the result can shift with terrain, heat, sleep, caffeine, hydration, medicines, and sensor error. Treat it as a starting estimate rather than a required pace.
Can I do Zone 2 without a heart rate monitor?
The talk test is a useful field check: a moderate aerobic effort usually allows full sentences, while short phrases suggest a higher intensity. A chest strap is generally more responsive than an optical wrist sensor, but neither turns an estimated zone into a clinical measurement.