Walking,
measured as exercise.

Why Borg and the talk test, not steps

Guidelines prescribe aerobic exercise by minutes, intensity and weekly frequency: at least 150–300 min/week of moderate or 75–150 min/week of vigorous activity (WHO 2020³; U.S. HHS 2018⁴; AHA⁵). The ESC 2020 guidelines frame prescription with FITT — frequency, intensity, time and type¹.

The ESC notes intensity “is also commonly monitored using the rate of perceived exertion scale (e.g. 12–14 on the Borg 6–20 scale) or ‘talk test’, e.g. ‘to be able to talk while exercising’”¹. The AHA describes moderate intensity the same way: you breathe harder “but you’ll still be able to talk”⁵. Borg’s scale⁶ and the talk test^8,9 are validated, free and need no device.

In honesty about steps: step counts do carry evidence — a meta-analysis of 15 cohorts found lower all-cause mortality with more daily steps, leveling off around 6,000–8,000 steps/day in adults ≥60 and 8,000–10,000 in adults <60¹⁴. But a step count says nothing about intensity, hills or how the walk felt, so it cannot dose exercise. And the EAPC position statement warns that Borg and the talk test are an adjunct to an objective intensity method (such as an exercise test) in people with cardiovascular disease². The app is for education and self-monitoring. Each person logs their own personal guidelines, agreed with their healthcare team. It does not replace medical evaluation.

Beta-blockers: why heart rate alone is not enough

Beta-blockers lower heart rate at rest and during exercise. The ESC states: “There are caveats to the use of HR for prescribing and evaluating exercise intensity in persons using beta-blockers. Ideally, the HR derived for training should only be used if functional capacity was determined (an exercise test was performed) while taking the medication”¹.

In coronary patients on beta-blockers, a dedicated equation predicted maximal heart rate as 164 − 0.7 × age, with a standard error of 18 beats/min (r² = 0.13)¹¹ — too imprecise for an individual target. The EAPC also notes that changes in beta-blocker dose complicate the target heart rate². That is why the app’s core intensity signals are Borg and the talk test, and heart rate is optional.

Training heart rate (Karvonen)

When a user has a watch or strap and a target from their clinician, the app shows time in zone. The heart-rate-reserve method was described by Karvonen et al. (1957)¹⁰ and is cited by the ESC¹:

The ESC adds that “the use of prediction equations for HRmax is not recommended” because of the large spread around the age line; a measured maximum from an exercise test is preferred¹. Without a clinician-set target, the zone card stays hidden.

Hills and stairs: more effort at the same speed

The ACSM walking equation has a vertical (grade) term, so the oxygen cost rises with slope even when speed does not¹²:

Worked example (our calculation): at 3.4 km/h (56.7 m/min), level ground ≈ 2.6 METs; at a 5% grade ≈ 4.1 METs.

Values copied from the 2024 Adult Compendium of Physical Activities (Herrmann, Willis, Ainsworth et al.)¹³.

The barometer: the phone’s barometer detects small pressure changes that track climbs and descents. Weather changes and phone position add drift, so the app reports elevation gain and the extra effort as estimates over a whole session, not step-by-step measurements.