# Study 000B Abstract

## Title

Adaptive Efficiency And Internal Cost Under Specialization: A Flagship Companion Study Following Study 000A

## Abstract

This flagship companion study was conducted after `Study 000A` to determine whether later running specialization in the high-resolution window coincided with adaptive efficiency, persistent unexplained HR burden, or both. Using bundled QC-pass running rows and the unified daily timeline, run-level efficiency metrics, next-day recovery measures, and a simple descriptive heart-rate residual model were evaluated.

Across the first and last 30 QC-pass runs, running share of 28-day activity increased from `15.26%` to `56.40%`. Speed-per-heart-rate efficiency improved by `13.41%`, while power-per-heart-rate efficiency improved by only `2.82%`. Next-day resting heart rate and next-day sleep score moved in a favorable direction. However, the simple speed-plus-power HR model showed that mean residual burden shifted upward rather than disappearing, from `-1.60` bpm to `3.09` bpm.

These results support a mixed interpretation. Specialization coincided with better adaptive efficiency and more favorable background recovery markers, but it did not eliminate session-level unexplained HR burden. As a result, `Study 000B` strengthens the broader program by showing that later adaptation in this system was not reducible either to pure hidden cost or to pure efficiency gain.