REHIT Training: The 9 Minute Cardio for VO2max, Fat-Loss, and Fitness
REHIT (Reduced Exertion High-Intensity Interval Training) is made to deliver greater cardiovascular benefits through just 2-3 intense 10-20 second sprints within a brief 9-15 minute workout. This streamlined approach significantly increases VO2max, with the potential to enhance metabolic function and insulin sensitivity, presenting a high-ROI, time-efficient workout.
What is REHIT Training?
Reduced Exertion High-Intensity Interval Training (REHIT) is a streamlined version of traditional HIIT. It involves 2-3 very short and intense sprints, typically lasting for 10-20 seconds, with longer active recovery periods in between. The point of REHIT is extracting the most beneficial parts of HIIT within the shortest duration, lasting from 9-15 minutes for the total workout. (1)
REHIT has been shown to improve cardiovascular fitness, insulin sensitivity, and metabolic health. It minimizes the total effort, hence the name reduced exertion, while providing most of the benefits of traditional HIIT. The structure of REHIT allows for better recovery and less cumulative fatigue, as the ratio of work to rest is way lower, reducing the total strain on the body.
The data shows high-intensity interval cardio to be an effective tool to (2) (3) (4) (5)
- increase aerobic capacity
- increase VO2max levels
- improve cholesterol profile
- support heart function
- improve metabolic function
- stimulate EPOC effect aiding in fat loss
- deplete glycogen stores.
The structure of REHIT strips the ineffective parts of the poorly defined HIIT training, and incorporates the most important one, intensity. This makes REHIT highly effective, high ROI type of exercise.
What is reduced exertion high intensity interval training?
REHIT is a minimal-effort version of HIIT, designed to achieve maximum health benefits with shorter workout durations. It typically involves 2-3 sprints of 10-20 seconds each, interspersed with low-intensity recovery, all within a 9-15 minute session.
What is the difference between HIIT and REHIT?
HIIT is not specifically defined, leaving room for suboptimal intensities, more frequent intervals, and longer lasting sessions (<20 minutes). REHIT, in contrast, uses fewer (2-3) and shorter (10-20 seconds) sprints, requiring less time (9-15 minutes) and exertion, while still providing significant metabolic and cardiovascular benefits.
How to Increase VO2max
VO2max is the maximal oxygen uptake the body can effectively absorb, transport, and utilize to produce energy. Lab tests on a cycle ergometer are the most accurate way to track VO2max levels; alternatives include health and fitness trackers.
Higher VO2max levels translate to greater aerobic capacity, making the body more efficient at transporting oxygen. It is one of the strongest predictors of longevity, a key health marker. Engaging in high-intensity interval exercise is the most effective way of increasing VO2max values. (6) (7) (8)
Such stressor for the cardiorespiratory system can be stimulated by using one of three protocols:
Longer Intervals
Running for 3 minutes at the velocity of your VO2max at (speed 8/10) with 3 minutes of active recovery at 50% of that speed. 5 sets in total, 3 min. activity and 3 min. recovery.
Short Intervals
Cycling for 30 sec. intervals at a submaximal intensity (speed 9/10) with 30 sec. active recovery at 40-50% that speed. Repeat 10-20x cycles of 30s. on with 30s. recovery.
Short Sprints
After a proper 5-minute warm-up, perform 5 cycles of 10-second all-out sprint (speed 10/10) with a 2-minutes active recovery in zone 2 (light cardio, slow speed).
The third method, short sprints, is what REHIT favors. 10-20 seconds of all-out maximal effort sprints above 100% VO2max which sufficiently stimulates the lungs and the heart to work at their maximum.
Two studies using CAROL bike’s REHIT protocol showed
- 3x REHIT training weekly was superior to MICT (moderate intensity training) of 5×30 minutes. 1st group increased VO2max by 12.3%, almost double what the second MICT group had – 6.9%. (9)
- REHIT presents a minimal amount of exercise with a high ROI for metabolic health. It improved insulin sensitivity by 28% in males and increased VO2max peak by 15% (males) and 12% (females). (10)
What is the fastest way to increase VO2 max?
The fastest way to boost VO2 max is via high-intensity interval training (HIIT) or REHIT, which pushes the cardiovascular system to its limits, enhancing oxygen uptake efficiency.
How quickly can you regain VO2 max?
VO2 max can begin improving within 2-4 weeks of consistent aerobic or interval training after a period of inactivity, depending on fitness level and training intensity.
Does zone 2 running increase VO2 max?
Yes, zone 2 running improves VO2 max by building aerobic capacity and mitochondrial efficiency, laying the foundation for higher-intensity performance. It trains the ability to burn fat for fuel; oxidizing fat requires more oxygen which stimulates the aerobic metabolism. Zone 2 also improves red blood cell function and capillary density which helps carry more oxygen.
How much can VO2 max be increased?
VO2 max can typically be increased by 10-20% with consistent and targeted training long term. In healthy adults, with consistent 4-week HIIT training twice weekly, VO2max can be increased by approximately 4-13%. However, it strongly depends on various factors like genetics, workout intensity, adherence, and fitness level.
Training Zones and Intervals
Understanding training zones is critical to optimizing cardio training to achieve a specific goal. Training zones present a range of intensity in which the body trains at, determined by the percentage of maximal heart rate (HRmax) or maximal oxygen uptake (VO2max).
| Zone 1 | Stimulates Recovery, Warm up | 50-60% HRmax |
|---|---|---|
| Zone 2 | Improves Endurance, Fat Burning | 60-75% HRmax |
| Zone 3 | Improves Aerobic Fitness | 70-85% HRmax |
| Zone 4 | Trains Lactate Threshold, Improves Speed Endurance | 80-95% HRmax |
| Zone 5 | Increases VO2max and Anaerobic Capacity | 90-100% HRmax |
The lower the zone, the lower the intensity, the more oxygen the body uses. In the first two zones (zone 1, 2) aerobic metabolism is stimulated, which is great for warm-up, recovery, and fat burning. Zone 3 is moderate intensity, training aerobic fitness, and zone 4 is more intense, training muscle endurance and lactate threshold. Zone 5 is the anaerobic zone trained at maximal intensity during the 2-3 sprints in the REHIT protocol.
What is zone 1, 2, 3 training?
Zone 1: Very light intensity (50-60% of max HR) for recovery and easy activity.
Zone 2: Low to moderate intensity (60-75% of max HR), ideal for building aerobic endurance.
Zone 3: Moderate to hard intensity (70-85% of max HR), improving cardiovascular endurance.
Which zone is best for training?
The “best” zone depends on your goals. Zone 2 is excellent for building aerobic endurance and fat metabolism, while higher zones (4 and 5) are better for improving anaerobic capacity and increasing VO2 max levels.
Is zone 2 or zone 5 better?
Zone 2 is better for long-term aerobic development and fat burning, while Zone 5 is ideal for maximizing VO2 max and anaerobic power. A balanced approach incorporating both zones often yields the best results.
The 9-Minute Cardio
The 9-Minute cardio protocol uses the short sprint method. The goal is to achieve two to three cycles of all-out sprinting for 10-20 seconds. The REHIT protocol alternates between high and low intensity for optimal recovery. Recovery, warm-up, and cool down are essential parts of the workout, done at 40% maximal speed, totaling 2 minutes each.
| Warm-up | 2 minutes | Low-intensity (40%) |
|---|---|---|
| Sprint 1 | 15-20 seconds | maximal intensity (100%) |
| Recovery | 2 minutes | low-intensity (40%) |
| Sprint 2 | 15-20 seconds | maximal intensity (100%) |
| Recovery | 2 minutes | low-intensity (40%) |
| Sprint 3 | 15-20 seconds | maximal intensity (100%) |
| Cool Down | 3 minutes | low-intensity (40%) |
The protocol uses a combination of zone 5 and zone 2 training. Zone 2 is the warm-up, cool down, and active recovery phase while zone 5 is the maximal, purely anaerobic, all-out sprints at 100% HRmax.
Assessing training zones (intensity) is key for being independent and training accurately. While the CAROL bike is designed to assist in this, not everyone can buy it. Understanding these zones enables one to do this regardless of the HIIT method used, not relying on specific equipment. However, for accurate tracking, you’d need a heart monitor or an accurate fitness tracker.
What is a REHIT training example?
A REHIT workout might include
- 2 minutes cooldown.
- 2 minutes warm-up (low-intensity cycling).
- 20 seconds all-out sprint.
- 3 minutes low-intensity recovery.
- Repeat for 2-3 sprints.
Why is cycling the best HIIT method?
Cycling minimizes joint impact, allows for controlled resistance adjustments, and enables maximal effort safely, making it ideal for high-intensity workouts.
How often can you do REHIT?
REHIT can be done 2-3 times per week (at maximum), allowing for recovery between sessions while still providing significant health benefits.
The Science on Carol Bike Cycling
The reason CAROL bike cycling and REHIT training are so popular is adaptability and time efficiency. The point is to extract the maximal benefit from an HIIT cardio, to improve heart health, metabolic function, and VO2max levels, per the least time invested.
It is a premium bike that provides premium experience at a premium price. The CAROL bike modifies the resistance based on your strength. It guides you with coaching and music via a monitor. It also recommends the type of cardio based on your HRV levels, which has its pros.
While doing REHIT on the CAROL bike is superior than monitoring yourself, one can still get most of the benefits just by assessing and training in these two zones: zone 2 and zone 5. Since zone 5 is all-out maximal sprints one can’t hold longer than 10-20 seconds, accurately determining recovery at zone 2 is key.
There’s strong scientific evidence emphasizing the benefits of REHIT training, such as:
- Increasing VO2max levels (11)
- Improving insulin sensitivity (12)
- Substantial EPOC effect and fat-loss (13)
- Metabolic function support (14)
Can 9 Minute REHIT Cardio Offset all the Sitting?
9 minutes of exercise weekly won’t undo the damage that sitting all day does. Period. Is incorporating REHIT once weekly superior to just living sedentary? Yes. Is it enough? No.
Increasing VO2max, depleting glycogen, training anaerobic power are just one piece of the puzzle of building healthy heart and a strong cardiorespiratory system REHIT assists with.
Movement matters. Neat activity, 10,000 steps daily, and low-intensity cardio are also fundamental steps to heart health, endurance, and longevity.
EPOC Effect
Excess Post-Exercise Oxygen Consumption (EPOC) refers to the elevated oxygen uptake after intense exercise, as the body recovers and “repays” the oxygen debt incurred during anaerobic activity. This process increases metabolic rate, leading to continued calorie burn post-workout.
High-intensity sprints, which push the body into an anaerobic state, require elevated oxygen levels for recovery. This heightened oxygen demand boosts energy expenditure as the body restores homeostasis.
Research from ACE Fitness demonstrates that a 15-minute REHIT session on a CAROL bike burns more calories than a 30-minute run. Short sprints significantly increase oxygen consumption and metabolic rate for up to three hours post-exercise, during which 60% of the total calories are burned. (15)
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Metabolic Function
High-intensity exercise is well-documented for enhancing metabolic health. HIIT improves insulin sensitivity, glucose tolerance, and muscle glucose uptake. (16) (3) Research indicates that the all-out sprints in short HIIT sessions deplete muscle glycogen, redirecting excess glucose to replenish glycogen stores rather than being stored as fat. This mechanism supports obesity and diabetes prevention. (17) (18)
- REHIT protocols, such as 10-minute sessions with two 10-20 second sprints, have shown a 28% improvement in insulin sensitivity. (19)
- Three weekly sessions on a CAROL bike reduced type 2 diabetes risk by 62% within eight weeks. These findings underscore HIIT’s efficiency in promoting glucose regulation. (20)
Enhanced glucose control through high-intensity training prevents metabolic dysfunctions that lead to fatigue and sugar overconsumption, mitigating risks of diabetes and obesity while optimizing muscle glucose utilization.
Lipid Profile
Cholesterol levels are key indicators of cardiometabolic health. Effective interventions focus on lowering LDL and triglycerides while increasing HDL cholesterol, and HIIT has shown notable efficacy in achieving these goals. (21)
An 8-week study on three weekly CAROL bike sessions demonstrated significant improvements: (22)
- 5% reduction in blood pressure
- 10% lower triglycerides
- 6% increase in HDL cholesterol
- 2% reduction in blood sugar
Compared to 30-minute moderate-intensity continuous training (MICT), HIIT proved more effective at improving cholesterol profiles and overall cardiometabolic health, emphasizing its efficiency for time-constrained individuals. (22)
