My Honest Bas Rutten O2 Trainer Review 2025

When I first came across the Bas Rutten O2 Trainer, I was deep into a phase of leveling up my cardio and conditioning. I’m an avid runner, dabble in BJJ, and like pushing my limits, especially in terms of endurance. I’d seen Bas talking about the O2 Trainer with the kind of passion that makes you stop and think, “Okay, maybe there’s really something here.” After weeks of debating the price and reading a mountain of reviews, I finally pulled the trigger.

Now, after using the O2 Trainer almost daily for the past three months, I’ve got a lot to say. If you’re wondering whether it’s worth it, whether it works, or whether it’s just another overhyped fitness gadget, read on. This is my full, brutally honest take—from the highs to the lows, and everything in between.

First Impressions: A Weird Little Thing in a Fancy Box

When the O2 Trainer arrived, I was immediately impressed by the packaging. It looked clean, professional, and came with a full set of resistance caps ranging from level 15 (easiest) down to level 1 (most difficult). The device itself? Honestly, it looked a little odd—like a bulky blue mouthpiece you’d see in a dentist’s office. But it felt solid. The rubber was soft, slightly tacky in a good way, and it didn’t smell like cheap plastic or rubber (although I’ve heard some people report otherwise—maybe I got lucky).

Inside the box, I found QR codes to training videos, a carry case, and a guide on how to get started. Right away, I appreciated that it didn’t take batteries or require syncing with an app—just pop it in your mouth and breathe.

Getting Started: Confusion, Coughing, and a Lot of Spit

Let me be real with you: the first few sessions were rough. Like, what-the-hell-am-I-doing rough. I started with cap #6, which is a mid-range level, thinking I was in decent shape. Within 30 seconds, my lungs were screaming and I was drooling like a teething toddler.

Breathing through the device feels unnatural at first because you’re forced to slow down and use your diaphragm. For people like me, who thought they knew how to breathe properly already—this was a humbling moment. I was shocked to realize how shallow my normal breathing was.

The drooling? Yeah, it’s real. There’s no sugarcoating it. If you’re not okay with slobbering all over yourself, you’re going to hate this thing. I started keeping a towel on my lap. Not sexy, but necessary.

Using It Consistently: Building the Habit (And the Muscles You Didn’t Know You Had)

After the first week, things started to improve. My breathing became more rhythmic. My diaphragm and core felt sore, almost like I’d done ab workouts. I began to notice subtle changes—especially during my jiu-jitsu rolls and cardio sessions. I wasn’t gasping for air as quickly. My heart rate recovery improved. I could push harder during interval training and bounce back faster between rounds.

What surprised me the most was how using the O2 Trainer impacted muscles I didn’t expect. My back, neck, and even shoulders started feeling looser and more activated. Turns out, a lot of our tightness comes from dysfunctional breathing patterns. This device helped me unlock areas I hadn’t realized were holding me back.

Performance Gains: Real or Placebo?

This is where it gets tricky.

Did I become a superhuman endurance athlete overnight? No.

Did I experience some improvements in stamina, lung capacity, and recovery? Absolutely.

But let’s be honest—any focused breathwork practice, done consistently, is going to deliver results. Whether it’s the O2 Trainer, Wim Hof breathing, or box breathing, you’ll likely feel better over time.

So is the O2 Trainer magical? No. Is it a solid tool that helped me breathe deeper, recover faster, and become more mindful of my breath? Yes. And for me, that made it worth the investment.

The Pros: Why I Keep Using It

1. Compact and Simple

No batteries, no app, no fuss. You just stick it in and go. I used it while walking, doing chores, warming up, or even sitting at my desk.

2. Surprisingly Effective

It’s like resistance training for your lungs. After a month, I found myself breathing deeper even outside of workouts—whether I was climbing stairs or dealing with stress.

3. Scalable Difficulty

With 15 cap levels, you can truly tailor the resistance to your own fitness level. I moved from cap #6 to #4 in three months.

4. Time-Efficient

It only takes 4-8 minutes a day to use. You can knock out a full breath workout in less time than it takes to scroll through TikTok.

The Cons: What I Didn’t Like (And Still Don’t)

1. Price Point

Let’s not beat around the bush—this thing is overpriced. It’s mostly plastic and silicone. While the quality is decent, the price tag feels more about branding than materials.

2. Excessive Drooling

There’s no elegant way to describe this. You will drool. Maybe not everyone, but most of us. Some people adapt quickly, others never do. I didn’t mind it much, but it definitely makes public use awkward.

3. Missing or Mispacked Parts

I’ve seen multiple reports—and experienced this myself—of missing or duplicate resistance caps. That’s frustrating, especially when the default cap (#5 or #6) is often the one you start with. You’d think quality control would be better at this price.

4. Lack of Detailed Instructions

Yes, there are QR codes linking to videos, but the instructions feel vague. Should you do 2 minutes per exercise? 4? What if you’re already fit? It took some trial and error to build a routine that worked for me.

5. Not Ideal for All Activities

I wouldn’t recommend using it during high-intensity workouts or swimming. It messed with my breathing rhythm during pool laps and felt dangerous. This is more of a warm-up, cooldown, or stand-alone session tool.

Unexpected Benefits: Things I Didn’t Expect

Here’s where the O2 Trainer really surprised me:

• Cleared out mucus: The first two weeks were like a lung detox. I coughed up more gunk than I thought possible. I thought I was getting sick, but it was just clearing out.
• Mindfulness: Focusing on slow, resisted breathing had a meditative effect. It lowered my anxiety and helped with sleep.
• Posture: Strengthening my core and breathing muscles improved my posture. Subtle, but noticeable over time.

Who Should Buy the O2 Trainer?

You’ll probably love it if you are:

• An endurance athlete (runner, cyclist, fighter)
• Someone with asthma or shallow breathing habits
• Looking for a mental and physical edge
• Interested in breathing techniques or performance training
• Willing to be consistent with short daily routines

But skip it if you are:

• Expecting massive gains overnight
• Sensitive to drooling or dry mouth
• Already deep into breath training and looking for advanced tools
• Not into gadgets or forming new habits
• Hoping to use it during swimming or high-movement sports

Final Verdict: Worth It? Yes… But With a Few Asterisks

So, is the Bas Rutten O2 Trainer worth the hype?

In my opinion: yes—but only if you know what you’re getting into.

It’s not a miracle device. It’s not a shortcut. But it is an effective and simple way to improve your breathing, stamina, and recovery if you use it consistently. The design could be improved, the price could come down, and the learning curve is a little steep at first. But I can honestly say it’s become a part of my daily routine, and I feel better for it.

Would I buy it again? Probably. Would I recommend it to everyone? Not necessarily.

But if you’re the kind of person who geeks out over optimization, wants to push your cardio performance, and doesn’t mind some drool for the sake of progress—then yes, the O2 Trainer might just be your secret weapon.