How HIIT Evaluator Measures Progress and Workout Quality

The principle behind HIIT Evaluator is simple: meaningful training progress should be measured against your own past performance rather than against other people. That idea is introduced in Compare Yourself to Yourself. Turning it into a practical evaluation system, however, requires a reliable way to measure both long-term change and the quality of an individual workout.

To support this approach, HIIT Evaluator uses two core metrics: PCS, the Progress Comparison Score, and SQS, the Session Quality Score. PCS is designed to measure long-term progress, while SQS evaluates the quality of an individual workout. Although they serve different purposes, both are grounded in the user's own training history.

After the first training session is completed, Day 1 becomes the user's personal baseline. This baseline does not represent excellence, an average fitness level, or a target that every user is expected to reach. It simply records the user's actual starting point under a defined training protocol.

Within the PCS framework, the Day 1 baseline is assigned a score of 60. This number has no special meaning in itself. It is not a passing grade, nor is it intended to represent average performance. Its purpose is to provide a fixed reference point for future comparisons.

Every later workout is evaluated relative to this personal baseline. As training capacity improves, PCS rises above 60. If performance declines relative to the baseline, PCS falls below 60. The score therefore reflects change rather than ranking.

As a result, the same PCS score can represent very different things for different individuals. Two users may both achieve a PCS of 75, yet arrive there through entirely different training journeys. The score does not claim that their fitness levels are equal. It indicates that each has improved relative to their own starting point.

PCS answers the long-term question of how today's version of a user has changed compared with Day 1. Long-term progress alone, however, does not tell us whether a particular workout was well executed. A second measurement is therefore needed to evaluate the quality of the individual session. This is the role of SQS.

SQS is not intended to measure progress. Instead, it evaluates whether a workout achieved its intended training quality. To do this, several characteristics of the heart-rate curve are converted into scoring dimensions.

Peak Score, or PS, represents training intensity. It uses an age-adjusted theoretical maximum heart rate as a reference point and maps the intensity reached during the workout into a standardized scoring system. Workouts that reach more effective intensity levels receive higher scores.

Peak Width Score, or PWS, represents workout cycle structure. It evaluates the timing and rhythm of the workout and whether the observed heart-rate pattern aligns with the expected structure of effective HIIT training.

Intensity and cycle timing alone are not enough. The shape and consistency of the heart-rate waveform also contain useful information about workout quality. For this reason, HIIT Evaluator also considers PS Ratio and PWS Ratio.

PS Ratio is primarily used to identify abnormal or low-quality heart-rate patterns. Its purpose is not simply to reward a visually ideal waveform. Instead, it helps penalize patterns that deviate significantly from the intended training model, including insufficient peaks, inadequate recovery, or distorted heart-rate curves.

PWS Ratio uses a segmented scoring approach. Rather than encouraging users to pursue one supposedly perfect value, different score ranges are assigned to different intervals. The goal is to recognize effective training while discouraging users from optimizing a single measurement at the expense of overall workout quality.

By combining PCS and SQS, HIIT Evaluator can distinguish between two different questions. PCS shows whether the user is changing over time relative to a personal baseline. SQS shows whether an individual workout displayed the intensity, structure, and heart-rate response expected from a meaningful HIIT session.

The detailed metrics make the evaluation possible, but the purpose of the system remains simple. It is not designed to rank users against one another. It is designed to make personal change visible, while also providing enough information to judge whether each training session achieved its intended quality.

Once progress and workout quality can be observed consistently, the next question is how the training protocol should respond. That is the subject of Make Small Adjustments.