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Physiology Foundations: Feedforward Control and Anticipatory Regulation

Capítulo 8

Estimated reading time: 6 minutes

1) Feedforward control: anticipatory regulation that reduces predicted error

Feedforward control is a form of physiological regulation in which the body makes anticipatory adjustments based on a prediction of what will happen next, rather than waiting for a variable to drift away from its desired range. The goal is to reduce the size of the upcoming disturbance (and therefore reduce the error that would otherwise occur).

Key idea: feedforward uses cues (sensory information, learned associations, motor commands, context) to trigger responses before the regulated variable changes much. This is especially useful when disturbances are predictable or when feedback would be too slow to prevent a noticeable deviation.

How feedforward differs from feedback (without re-teaching feedback)

Timing: feedforward acts early (before the disturbance fully impacts the variable); feedback acts after a deviation is detected.
Information source: feedforward relies on predictive cues (e.g., sight/smell of food, intention to exercise); feedback relies on measurements of the variable itself (e.g., blood gases, plasma glucose).
Typical outcome: feedforward reduces the magnitude of the deviation; feedback corrects whatever deviation still occurs.

In real physiology, feedforward and feedback commonly operate together: the feedforward response blunts the disturbance, and feedback fine-tunes the response and prevents overshoot.

Schematic: prediction-based control (feedforward) working with feedback

Predicted disturbance cue (sensory/context/motor command)  Actual regulated variable (measured)  Disturbance happens (meal/exercise/etc. )
                |                                                     |                                   |
                v                                                     v                                   v
        Feedforward controller ------------------------------> Effectors -----------------------------> Variable
                |                                                     ^                                   |
                |                                                     |                                   |
                +--------------------- (works early) -----------------+                                   |
                                                                                                           |
                                   Feedback controller <---------------------- Sensors -------------------+
                                              (works after deviation is detected)

Interpretation: the feedforward pathway uses a cue to initiate an effector response early. The feedback pathway monitors the variable and adjusts output to match the actual need.

2) Paired examples: feedback-only vs feedforward-plus-feedback

Example pair A: Preparing for digestion and nutrient handling

Scenario	Feedback-only pattern	Feedforward-plus-feedback pattern (typical physiology)
Food is about to be eaten	Responses begin mainly after nutrients enter the gut and blood, once changes are measurable.	Cephalic phase responses begin with sight/smell/taste/thought of food: salivation, gastric secretions, and early insulin release. Feedback then adjusts based on actual absorbed nutrients.

Concrete cues and responses:

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Salivation: triggered by sensory cues and chewing, lubricating food and starting digestion before absorption changes anything measurable in blood.
Cephalic phase insulin release: early insulin secretion can begin before a significant rise in plasma glucose, helping limit the post-meal spike.

Step-by-step: how feedforward-plus-feedback plays out during a meal

Cue detection: visual/olfactory cues, taste, and oral mechanoreceptors signal “food incoming.”
Anticipatory output: salivary glands increase secretion; GI secretions and motility begin adjusting; pancreas releases some insulin early.
Disturbance arrives: nutrients enter the intestine and are absorbed.
Feedback refinement: actual plasma glucose and gut hormones drive additional insulin/glucagon adjustments to match the real load.
Stability check: if the meal is larger/smaller than predicted, feedback corrects the mismatch (preventing prolonged hyperglycemia or hypoglycemia).

Why feedforward helps here: waiting for blood glucose to rise before responding would allow a larger spike; anticipatory insulin and digestive preparation reduce the peak and smooth the trajectory.

Example pair B: Ventilation at the onset of exercise

Scenario	Feedback-only pattern	Feedforward-plus-feedback pattern (typical physiology)
Exercise begins abruptly	Ventilation increases mainly after CO₂ rises and pH falls enough to stimulate chemoreceptors.	Immediate rise in ventilation occurs at exercise onset from central command and mechanoreceptor input, before large blood gas changes occur; feedback then tracks CO₂/pH to fine-tune ventilation.

Step-by-step: exercise onset ventilation control

Cue detection: motor cortex “central command” and muscle/joint mechanoreceptors signal that exercise is starting.
Anticipatory output: respiratory centers increase drive; ventilation rises quickly.
Disturbance develops: metabolic CO₂ production increases; acid-base status begins to shift depending on intensity.
Feedback refinement: chemoreceptor input adjusts ventilation to match actual CO₂ production and pH changes.
Overshoot prevention: if the initial ventilatory jump is too large or too small, feedback corrects it.

Why feedforward helps here: blood gas-based feedback alone can be delayed relative to the sudden increase in metabolic demand; anticipatory ventilation reduces the transient mismatch between CO₂ production and elimination.

Important pattern across examples: prediction is imperfect

Feedforward depends on the accuracy of the cue-to-disturbance relationship. If the cue predicts the wrong magnitude (e.g., you see food but eat very little; you intend to exercise hard but stop quickly), the anticipatory response can be mismatched. This is why feedback is usually present: it corrects prediction error and stabilizes the outcome.

3) Application prompts: classify responses as feedback, feedforward, or mixed

Use this decision process for each prompt:

Step 1 (trigger): What started the response? A cue predicting change (feedforward) or a measured deviation in the variable (feedback)?
Step 2 (timing): Did the response begin before the variable changed much (feedforward) or after (feedback)?
Step 3 (purpose): Is the response mainly preventing a predicted error (feedforward) or correcting an existing error (feedback)?
Step 4 (combo check): Is there an early anticipatory phase plus later fine-tuning based on measurements (mixed)?

Prompt set A (everyday physiology)

You smell fresh bread and your mouth waters. Classify: feedback, feedforward, or mixed. Justify by identifying the trigger and what variable is being prepared for.
After a sugary drink, insulin secretion increases as blood glucose rises. Classify and justify based on whether the trigger is a cue or a measured change.
Before the first bite of a meal, insulin begins to rise slightly; after absorption, insulin rises further in proportion to the glucose increase. Classify and justify by separating early vs late phases.
You start jogging and your breathing rate increases immediately, even before you feel “out of breath.” Classify and justify using timing and trigger.
During sustained running, ventilation adjusts to keep arterial CO₂ close to normal despite changing intensity. Classify and justify by identifying what is being sensed and corrected.

Prompt set B (mixed and tricky cases)

You stand up quickly and your heart rate increases within seconds. Is this purely feedback, purely feedforward, or mixed? Justify by stating whether the initial trigger is a predicted change or a sensed change in pressure/flow.
Right before a race starts, you feel “amped,” and your heart rate and ventilation rise while you are still standing still. Classify and justify using the presence of a predictive cue (anticipation) versus a measured deviation.
You take a deep breath before submerging underwater. Classify and justify: what cue triggers the action, and is it preventing a predicted disturbance?
You begin to sweat after your core temperature has already risen during a hot day. Classify and justify based on whether the response begins after a measurable change.
On a hot day, you start drinking water because you see you will be outside for hours, before you feel thirsty. Classify and justify by identifying whether the trigger is prediction or sensed osmotic/volume change.

Answer format learners should use (template)

For each item, respond using this structure:

Classification: feedback / feedforward / mixed
Trigger: (cue predicting disturbance) or (sensed deviation in variable)
Timing evidence: before vs after the variable changes
What is being protected: name the regulated variable or performance goal
Why mixed (if applicable): early anticipatory phase + later corrective phase

Now answer the exercise about the content:

Which description best matches how feedforward and feedback commonly work together during a meal?

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Feedforward uses predictive cues to start responses early (e.g., cephalic phase salivation and insulin), while feedback monitors variables like plasma glucose to fine-tune output and correct any mismatch.