# Methodology: Norwegian 4x4 heart-rate ramp analysis

Dataset version: `2026-07-16-v1`  
Analysis version: `1.0.0`

## Scope

This is an observational N=1 field analysis of one participant's running workouts. It is not a clinical study or controlled experiment and does not test whether Norwegian 4x4 training improves VO2 max.

## Qualification rules

A main-analysis session must contain heart-rate samples, a valid lower and upper target, total duration between 30 and 55 minutes, all four hard phases, reconstructed hard intervals between 3 and 5 minutes, at least 80% sensor coverage in every hard interval, and at least one interval that sustainably reaches the lower target. Exact duplicate sample traces are removed. Short, partial, unusually long, missing-sample, low-response, and structurally implausible records remain excluded from headline averages.

## Interval reconstruction

The sample export leaves `phase_kind` and `interval_id` blank. The retained `phase_sequence` is consistent across full sessions: 1 warmup, 2/4/6/8 hard intervals, 3/5/7 recoveries, and 9 cooldown. Hard boundaries therefore use phases 2, 4, 6, and 8. This reconstruction is disclosed because stored interval totals are incomplete and sometimes conflict with sample-derived durations.

## Ramp rule

Ramp time is the elapsed time from the first valid sample in a hard interval to the first sample at or above that workout's lower target that remains at or above the threshold for at least 10 seconds, with no gap longer than 10 seconds. A single noisy sample does not count. If the rule is never met, ramp time is null and the interval is reported as not sustainably reaching target.

## Time in target

Each sample is time-weighted until the next sample. Gaps longer than 10 seconds are missing, not assigned to a zone. Below, inside, and above use each workout's own stored lower and upper target. Time at or above the lower target equals inside plus above; it is not the same as time inside the target range.

## Privacy

Public files use new sequential session identifiers, relative workout/interval seconds, and relative workout sequence. Exact dates, times of day, UUIDs, HealthKit identifiers, device identifiers, GPS, routes, and exact source identifiers are not published.