Interval Training · Performance Science · 2026
Stop using timers. Start using
VT1 / VT2
BIOFEEDBACK
RULE
@drdragutin
01 / 07
The Foundation
VT1 & VT2
Explained
Ventilatory thresholds are the non-invasive equivalents of blood lactate testing — detectable through breathing pattern in real time, no lab required.
VT1
First ventilatory threshold — corresponds to LT1. Breathing deepens but sentences still possible.
VT2
Second ventilatory threshold — corresponds to LT2. Breathing labored. Words only. Last stable zone.
Key fact
HR at VT2 can vary 20–30 bpm between athletes of same age — formulas are guesswork
Used for
Zone personalization · Recovery timing · Interval programming
@drdragutin02 / 07
The Biofeedback Rule
The Rule
Above VT2
Wait for VT1
Not a Timer
Effort intensity: above VT2
Recovery trigger: HR returns to VT1 level
Next rep starts: when HR = VT1 · Not before
Why VT2
Above VT2 — every rep creates the adaptation stimulus needed for LT2 development
Why VT1
VT1 return — ensures oxidative system has cleared enough metabolic byproducts for a quality next rep
Result
Every rep is high quality · Every recovery is earned · No guessing
@drdragutin03 / 07
The Key Difference
Program
vs Protocol
| Variable | Program | Protocol |
| Recovery | Fixed timer | VT1 HR return |
| Effort | Estimated pace | Above VT2 |
| Adaptation | Inconsistent | Guaranteed stimulus |
| Quality | Drops with fatigue | Every rep high quality |
| Basis | Assumption | Physiology |
@drdragutin04 / 07
Field Application
How to Find
VT1 & VT2
No lab equipment needed. Use the Talk Test during a progressive warm-up.
VT1 Test
Increase pace gradually. VT1 = last intensity where full sentences are comfortable. Mark the HR.
VT2 Test
Continue increasing. VT2 = first intensity where only single words are possible. Mark the HR.
Use these
VT1 HR = recovery target · VT2 HR = minimum effort threshold
Retest
Every 4–6 weeks — thresholds shift as fitness improves
@drdragutin05 / 07
Protocols Using the Biofeedback Rule
In Practice
Every protocol below uses the VT1/VT2 Biofeedback Rule — not fixed rest timers.
P-01
4 × 400m above VT2 — rest until HR = VT1
P-02
8 × 800m above VT2 — VT1 HR governs recovery duration
P-03
Sprint repeats 10–30 sec — 90 sec minimum or until VT1
P-04
2×300 + 2×400 + 1×600m — full VT1 recovery between each
Key rule
Never start next rep before HR returns to VT1
@drdragutin06 / 07
Next Step
STOP
GUESSING.
START USING
PHYSIOLOGY.
Free LT1/LT2 Protocol Cards with the complete VT1/VT2 Biofeedback Rule — available at drdragutin.com
drdragutin.com/resources.html
Free Protocol Cards · Link in Bio
@drdragutin07 / 07