How Often Can You Go to CrossFit or HIIT Exercises

The Sprint That Fed the Tribe

Your ancestors tracked game for hours—sometimes days—at a conversational pace. Low heart rate. Fat-burning metabolism. Sustainable forever.

Then came the moment: The final chase. The spear throw. The takedown.

Thirty to ninety seconds of maximum effort. Complete glycogen depletion. Explosive power. Then it was over.

That brief, intense burst—the kill—happened once or twice a week when the hunt was successful. The rest was walking, tracking, and carrying meat back to camp.

High-intensity interval training (HIIT) recreates that ancestral sprint. And like the hunt, you don't do it every day.

This is the 20% in the 80/20 rule. Brief, intense, essential—but not the foundation.

Why High-Intensity Training Matters

HIIT triggers adaptations that low-intensity aerobic work can't:

Improves VO2 Max

VO2 max—your maximum oxygen utilization capacity—determines how hard you can push when it matters.

High-intensity intervals are the most effective way to improve VO2 max. You're training your cardiovascular system to deliver oxygen under maximum demand.

Triggers Hormonal Responses

Brief, intense exercise creates an adaptive stress response that releases:

• Growth hormone: Tissue repair, fat oxidation, muscle building
• Testosterone: Strength, recovery, libido, mood
• Catecholamines (epinephrine, norepinephrine): Metabolic boost, fat mobilization

The key: brief intensity. Prolonged high-intensity work elevates cortisol instead, which suppresses these beneficial hormones.

Builds Power and Speed

Explosive movements develop fast-twitch muscle fibers and neural efficiency.

This isn't about becoming an athlete. This is about maintaining the physical capacity to move explosively when needed—picking up a child, catching yourself from a fall, sprinting to your car in the rain.

Creates EPOC (Afterburn Effect)

Excess post-exercise oxygen consumption (EPOC) means your metabolism stays elevated for hours after intense training.

You continue burning calories at an elevated rate during recovery. This doesn't happen with steady-state cardio.

Time-Efficient

A complete HIIT session—warm-up, intervals, cool-down—takes 20-30 minutes total.

You get maximum cardiovascular and metabolic benefit in minimal time.

The Problem: HIIT Is Addictive

I get asked all the time by people who just started CrossFit or some other type of high-intensity training: "How often should I go?"

They love it. They're feeling great—except for the constant muscle soreness and the fact that it hurts to walk upstairs most days.

Here's the issue: HIIT is highly addictive.

Yes, that's right. An exercise that causes severe muscle fatigue, soreness, and an utter lack of desire to move for three days somehow makes you want to do it again immediately.

Why? Dopamine.

High-intensity training fires those "feel good" centers in your brain. People who drink the CrossFit Kool-Aid want to keep triggering that dopamine hit as often as possible.

The problem: Too much of a good thing becomes a bad thing.

Why You Can't Do HIIT Every Day

We have two primary metabolic systems: aerobic (burns fat) and anaerobic (burns sugar/glycogen).

HIIT is predominantly anaerobic. You're depleting glycogen stores and creating metabolic byproducts that require recovery time to clear.

When you do HIIT 5-6 days per week, several things happen:

Chronic Cortisol Elevation

Cortisol is your stress hormone. Brief spikes are beneficial—they trigger adaptation. Chronic elevation is destructive.

Frequent HIIT without adequate recovery keeps cortisol chronically elevated, which:

• Damages arterial walls
• Suppresses immune function
• Breaks down muscle tissue (catabolic)
• Promotes visceral fat storage (despite intense training)
• Tanks thyroid function
• Disrupts sleep
• Triggers adrenal exhaustion

You're working harder but getting worse results because your hormones are wrecked.

Incomplete Glycogen Replenishment

HIIT depletes muscle glycogen. Full replenishment takes 24-48 hours with adequate carbohydrate intake.

Training again before glycogen is restored means you're training depleted. Performance drops. Recovery worsens. Injury risk increases.

Accumulated Microtrauma

High-intensity movements under fatigue create small tissue damage. Normally, this damage triggers adaptation (you get stronger).

But damage without recovery accumulates into injury.

Chronic HIIT participants develop tendonitis, joint inflammation, muscle strains, and overuse injuries because they never allow tissue repair to complete.

Endocrine Disruption

Chronic high-intensity training without adequate recovery can trigger:

• Hypothalamic-pituitary-adrenal (HPA) axis dysfunction
• Suppressed testosterone production
• Thyroid hormone downregulation
• Menstrual irregularities in women
• Loss of libido
• Mood disorders

Training becomes counterproductive. You're breaking down faster than you're building back up.

The Ancestral Pattern: Balance Intensity with Volume

Your ancestors didn't sprint every day. They sprinted 1-2 times per week (when the hunt was successful). The rest was low-intensity tracking, walking, carrying.

This isn't arbitrary. This is what human physiology evolved for.

We're designed to do lots of low-intensity aerobic work with brief bursts of high-intensity effort scattered throughout the week.

Modern fitness inverted this: Most people do high-intensity all week long with maybe a day or two of "cardio" that's still too hard to build aerobic base.

The imbalance between aerobic and anaerobic metabolism is what causes most HIIT-related injuries and problems.

How Often Should You Do CrossFit or HIIT?

Maximum: 2-3 times per week.

That's it. Not 5-6 days. Not daily. Two to three high-intensity sessions per week is the upper limit for most people to recover adequately and continue adapting.

Elite athletes might handle more, but they're genetic outliers with recovery protocols (massage, ice baths, professional nutrition, 9+ hours sleep) that most people don't have.

For normal humans with jobs, families, and life stress: 2-3 days maximum.

What About the Rest of the Week?

Low-intensity aerobic work.

Heart rate training at conversational pace—walking, easy cycling, swimming, hiking—for 30-60 minutes, 4-6 days per week.

This builds your aerobic base (the 80%), supports recovery, manages cortisol, improves fat oxidation, and allows your body to repair tissue damage from HIIT sessions.

You need both systems. But the ratio matters.

Signs You're Doing Too Much HIIT

If you're experiencing any of these symptoms, take a few days off from high-intensity work and focus on low-intensity movement:

• Lack of progress toward goals (despite training hard)
• Persistent muscle soreness (never fully recovering between sessions)
• Injuries (tendonitis, joint pain, muscle strains)
• Fatigue (physical and mental exhaustion)
• Brain fog (difficulty focusing, poor memory)
• Restlessness (wired but tired)
• Elevated resting heart rate (sympathetic nervous system stuck "on")
• Sleep disruption (trouble falling asleep despite being exhausted)
• Mood changes (irritability, anxiety, depression)
• Immune suppression (frequent colds, slow healing)
• Loss of motivation (training feels like a chore)

These are signs your sympathetic nervous system is stuck in fight-or-flight mode. Your body is pumping out excess cortisol, adrenaline, and noradrenaline constantly.

When your body is in this state of hormonal chaos, it's exceedingly hard to lose weight, build muscle, or feel good—despite training intensely.

How to Program HIIT Properly

Frequency

Week 1-4 (Building Base): 1x per week HIIT, 4-5 days low-intensity aerobic

Week 5-12 (Established Base): 2x per week HIIT, 4-5 days low-intensity aerobic

Advanced (6+ months consistent training): 3x per week HIIT maximum, 3-4 days low-intensity aerobic

Structure

A proper HIIT session:

• Warm-up: 5-10 minutes easy movement
• Intervals: 6-10 rounds of 20-45 seconds max effort, 90-120 seconds full recovery
• Cool-down: 5-10 minutes easy movement
• Total time: 20-30 minutes

If your "HIIT" session lasts 60-90 minutes, it's not HIIT. It's chronic moderate cardio disguised as high-intensity, which is the worst of both worlds.

Recovery Days

After a HIIT session:

• Next day: Low-intensity aerobic (walking, easy cycling) or complete rest
• 48 hours minimum: Before next HIIT session
• Sleep: 7-9 hours in dark room, no screens 1 hour before bed
• Nutrition: Adequate protein (3-7 oz per meal), carbohydrates for glycogen replenishment, anti-inflammatory whole foods

CrossFit-Specific Considerations

First, let me say: I'm a fan of CrossFit and other forms of HIIT when done properly.

CrossFit has an amazing capability to train the human body to accomplish impressive physical and athletic feats. The community is strong. The programming can be excellent.

But you need to be diligent about the box you choose.

What to Look For

• Proper scaling and modification: Not just weight variance, but movement substitutions for different skill levels
• Quality coaching: Instructors who prioritize mechanics over speed
• On-ramp programs: Structured introduction teaching movements, culture, and how to scale
• Recovery emphasis: Programming includes deload weeks, mobility work, and rest days
• Injury prevention focus: Not just "finish the workout or die" mentality

Talk with coaches and members. Watch the WODs. Take advantage of on-ramp programs before committing long-term.

The Addiction Factor

CrossFit's biggest strength is also its biggest risk: It's highly engaging and community-driven.

That dopamine hit from completing a brutal WOD alongside friends is powerful. You want to come back every day.

Resist this urge. Your body needs recovery more than it needs another workout.

Go to class 2-3 times per week. Fill the other days with aerobic base training, mobility work, and rest.

The Complete Picture

HIIT is the 20%. It's essential. It triggers hormonal responses, builds power, improves VO2 max, and maintains explosive capacity.

But it only works when supported by the 80%—low-intensity aerobic work that builds cardiovascular base, manages cortisol, improves fat oxidation, and allows recovery.

Add in strength training (carrying the meat back to camp) and recovery practices (tribal rest around the fire), and you have a complete ancestral movement framework.

For the complete 80/20 framework and how all these pieces fit together, see this comprehensive guide.

But you don't need the whole framework to benefit from this piece.

The Formula: Training = Work + Rest

If you work too much OR don't rest enough, you're overtraining.

Overtraining leads to injuries, fatigue, hormonal imbalances, and potentially the start of autoimmune disorders.

This happens when you train only one side of your metabolism (anaerobic HIIT) without balancing it with aerobic work and adequate recovery.

Yes, you can do too many days of CrossFit or HIIT.

If you're experiencing symptoms of stress and fatigue, take a few days off from high-intensity activities. Go for a walk. Let your body recover.

Then come back stronger.

For comprehensive stress management strategies that support training recovery, visit the Regulate Your System pillar page.

For nutrition strategies that support intense training and recovery, visit the Fuel Your Body pillar page.

Ready to optimize your health and performance? Dr. JJ Gregor uses Applied Kinesiology and functional health approaches to help patients achieve their wellness goals at his Frisco, Texas practice. Schedule a consultation to discover how personalized exercise programming, stress management, and recovery strategies can support your overall health.