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What Are Intensity Mechanisms?

Every exercise produces fatigue, but not all fatigue feels the same. A heavy deadlift taxes your central nervous system through load. Twenty pull-ups burn out your pulling muscles through volume. A two-kilometer row wears you down through sustained duration. A set of box jumps demands explosive power.

These are intensity mechanisms: the physical pathway through which an exercise creates demand on the body. Limberjack tracks four of them:

Skill appears as a fifth tag on movements like jump rope that require significant coordination. It is a demand limiter, not a fatigue driver, so it does not accumulate the same way.

Understanding which mechanism a movement expresses helps you make better programming decisions before you've even picked up a pen.

The Four Mechanisms in Practice

Load

Load-driven exercises are prescribed near maximum effort for low reps. The stress comes from the weight, not the repetitions.

Examples: Barbell squat (3RM), barbell deadlift (5RM), barbell press (1RM)

Format pairing: For Load (1RM, 5RM). When you prescribe a barbell squat as "For Load," Limberjack infers the active mechanism as load.

Volume

Volume-driven exercises accumulate reps at moderate intensity. The stress builds through repetition, not near-maximal weight.

Examples: Pull-ups (21), thrusters @ 95lb (15), push-ups (50), air squats (100)

Format pairing: AMRAP, EMOM, For Time. A barbell squat at "95lb, 21 reps" is expressing volume, not load.

Duration

Duration-driven exercises sustain effort over time. The prescription is distance or time, not reps.

Examples: 400m run, 500m row, 1-mile assault bike, 200m swim

Format pairing: Any format with a distance or time prescription. Locomotion-pattern movements default to duration.

Power

Power-driven exercises demand speed and explosiveness under load, or short-duration maximal output.

Examples: Barbell snatch, clean and jerk, box jumps, kettlebell swings, thrusters (heavy)

Format pairing: Tabata intervals favor power expression. Plyometric movement patterns infer power regardless of format.

How Limberjack Detects Mechanisms

Limberjack uses a two-step process to identify which mechanism an exercise is currently expressing:

Step 1: Archetype tagging

Every movement archetype in the library is tagged with the mechanisms it can express. A barbell squat carries [load, volume] because it can serve either purpose depending on prescription. A 400m run carries [duration, volume].

Step 2: Context inference

The Recommendation Engine applies priority rules to determine the active mechanism given what you've selected:

1. For Load format + weight capability → always infers load
2. Tabata format → infers power if the archetype supports it, else volume
3. Locomotion movement pattern or distance capability → infers duration
4. Plyometric movement pattern → infers power
5. AMRAP, EMOM, or For Time + weight capability → infers volume (moderate weight, high reps)
6. Default → uses the archetype's primary listed mechanism

This inference runs at recommendation time, before you finalize your workout.

Accumulation warnings

As mechanisms accumulate across elements in your workout, the Recommendation Engine tracks overlap:

• Low (1 occurrence): No concern
• Medium (2 occurrences): Yellow badge: consider whether this is intentional
• High (3+ occurrences): Red badge: high overlap risk; priority score reduced

The mechanism summary bar at the top of the element list shows the current distribution across all candidates.

Practical Tips

When to stack mechanisms deliberately

Some workout intentions require mechanism concentration:

• Strength day: Stack load mechanisms: heavy barbell movements with low reps across the session. High load accumulation is the goal.
• Glycolytic conditioning: Stack volume mechanisms: repeated pulling, pushing, and squatting at moderate weight. This deliberately taxes the same demand pathway to create metabolic stress.
• Aerobic base: Stack duration mechanisms: run, row, bike in sequence to keep the stimulus aerobic and time-based.

When mixing mechanisms is a feature

Mixed-modal workouts benefit from mechanism variety because different pathways recover independently:

• A "For Time" workout with a 400m run (duration), 21 pull-ups (volume), and a heavy deadlift (load) spreads demand across all three systems. Each movement type recovers while the others are working.
• A pure-volume workout (thrusters + pull-ups + push-ups) may produce a similar intensity score but with concentrated shoulder and upper-body volume demand.

The distinction matters for weekly programming. You can schedule a high-volume day and a high-load day back-to-back because the fatigue pathways are different.

Reading the mechanism panel

In the Recommendation Modal, each element shows:

• Mechanism badge: The inferred active mechanism for that element given the current format
• Badge color: Green (safe), yellow (2 already present), red (3+ already present)
• Summary bar: Running counts across all displayed elements

The priority score for high-overlap elements is reduced by 0.4 points (high risk) or 0.2 points (medium risk), nudging the ranked list toward more varied selections.

The Jump Rope Example

Jump rope is a canonical example of mechanism ambiguity, and why context inference matters.

A jump rope set can express:

• Volume: 100 double-unders in a metcon
• Duration: 5 minutes of continuous jump rope for aerobic work
• Skill: a technique drill focused on timing and coordination

If you program jump rope in an AMRAP alongside thrusters and pull-ups, all three movements express volume in that context. The session has heavy upper-body volume demand from thrusters (push), pull-ups (pull), and jump rope (shoulder rotation). The muscle fatigue panel will flag upper-body stress; the mechanism panel will show three volume counts.

Replacing the jump rope with a 400m run shifts that third element from volume to duration, spreading the demand and giving your shoulders a relative break during the locomotion segment.

Interaction with Energy Systems and Stimulus Types

Mechanisms and energy systems overlap, but they are not the same dimension:

A workout can express a glycolytic energy system through either volume (many reps) or power (explosive bursts at submaximal weight). The energy system tells you which metabolic pathway is taxed; the mechanism tells you how the exercise creates that demand.

When you select a stimulus type in the Recommendation Modal, Limberjack uses it to set a mechanism target profile:

• Strength / Power Output → targets load and power mechanisms
• Anaerobic Capacity / Mixed Modal → targets volume and power
• Aerobic Capacity / Endurance → targets duration and volume

The workout generator then sorts candidate elements by how well their inferred mechanism matches the target profile.