Training Analytics

The "Performance Athlete" Model

Most fitness apps track Gross Volume (Weight × Reps). While big numbers look good, they fail to account for the actual physiological cost of training. A 100kg Squat creates exponentially more fatigue than a 100kg Calf Raise.

Intrvl's core engine is built on four key pillars:

• Effective Volume: Only counting work that contributes to growth (excluding warm-ups).
• Systemic Strain: Measuring the actual physiological cost of every movement.
• Training Density: Analyzing work capacity per unit of time using passive timer logging.
• Muscle Hotspots: A granular heatmap of focus based on primary and secondary muscle roles.

The Workload Triad

To accurately measure progress, Intrvl classifies every set into one of three tiers. This classification ensures that your warm-ups don't skew your PRs and your failure sets get the credit they deserve.

Set Type	Fatigue Cost	Growth Stimulus	Analytics Logic
Warm-up	Zero	None	Excluded from Effective Volume and Strain Score.
Straight Set	1.0x	High	Standard contribution to all metrics.
Failure Set	1.5x - 2.0x	Very High	Significant multiplier applied to Strain Score.

Total System Mass (The Physics Layer)

Before calculating strain, Intrvl determines the actual load moved. This "Physics Layer" unifies weighted, bodyweight, and assisted exercises into a single standard.

Examples:

• Weighted Dip (+20kg): 80kg bodyweight + 20kg external = 100kg Load
• Standard Push-up: 80kg bodyweight × 0.65 leverage factor = 52kg Load
• Banded Pull-up (-15kg): 80kg bodyweight - 15kg assistance = 65kg Load

Systemic Strain (The Fatigue Layer)

Systemic Strain is Intrvl's proprietary metric for measuring session cost. It accounts for the fact that different muscle groups and intensities have different recovery requirements.

Size Factors

The Size Factor accounts for the CNS cost of moving large vs. small muscle groups. Intrvl defaults to these scientifically-aligned multipliers:

• Legs: 1.5x (Highest systemic cost)
• Back: 1.2x
• Chest: 1.0x (Standard baseline)
• Shoulders: 0.8x
• Arms/Core: 0.5x (Lowest systemic cost)

Muscle Hotspots

Intrvl maps your training focus using a Primary/Secondary distribution model. This creates a realistic "Heatmap" of where your strain is actually being absorbed.

• Primary Muscles: Absorb 100% of the exercise's Strain Score.
• Secondary Muscles: Absorb 50% (default) of the Strain Score.

Example (Back Squat):
Total Strain: 1,000 units.
• Quads (Primary): 1,000 points.
• Hamstrings (Secondary): 500 points.

Training Density

By leveraging the app's native timer, Intrvl calculates your work rate without any extra data entry. Training Density is a key indicator of cardiovascular efficiency and work capacity.

• Density Score: Effective Volume / Duration (expressed as kg/min).
• Rest Adherence: The percentage of sets where you followed your prescribed rest intervals.

Open the "Black Box"

We believe advanced athletes should control their data. Intrvl allows you to tune the physics engine and fatigue algorithms in the app's advanced settings.