Running every day might seem like a muscle-killer to most gym enthusiasts. But what happens when you actually put that theory to the test?
One fitness creator decided to find out by running daily for 30 days, using MRI scans and extensive lab testing to track every change in his body. The challenge? Preparing for an international race against elite athletes while potentially watching his hard-earned gains disappear.
In a recent YouTube video documenting his transformation, Jeremy Ethier took on what many lifters fear most: combining serious cardio with strength training. The results surprised even him.
His journey began with a simple question that turned into a 30-day experiment that would test not just his body, but everything he thought he knew about cardio and muscle preservation.
Jump to:
- Starting Point: Better Than Expected
- The Hyrox Challenge
- Zone Two Training and Recovery
- The Science Behind Cardio and Muscle Loss
- Building Elite Conditioning
- An Unexpected Benefit: Runner’s High
- Unexpected Strength Gains
- Race Day Preparation
- Final Testing Results
- Competition Day
- Key Takeaways for Combining Cardio and Strength
Starting Point: Better Than Expected
Before diving into daily running, Ethier underwent a comprehensive VO2 max test to establish his baseline cardiovascular fitness. For context, average gym-goers typically score in the mid-30s to 40s, while elite athletes like Cristiano Ronaldo reportedly hit 75.
So your VO2 peak was 58.3. It’s really good results.
That score placed him in the top 2% for his age group, despite not having run regularly before the test. However, deeper analysis revealed two critical weaknesses that would need addressing.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
His body had become extremely inefficient at burning fat for energy, instead relying heavily on limited carbohydrate stores that burn out quickly. Even more concerning, his lactate clearance was abysmal.
Pretty high. 10.5. That’s very high.
Twenty minutes after his test, his blood lactate levels remained dangerously elevated. When lactate accumulates and your body can’t clear it efficiently, hydrogen ions build up, creating painful muscle burning. In extreme cases, this leads to vomiting, nausea, or worse.
The Hyrox Challenge
Ethier wasn’t just training to run. He’d committed to competing in Hyrox, described as one of the toughest fitness races globally, representing Team Canada alongside fellow YouTuber Will Tennyson.
The format is brutal: run 1 kilometer, immediately transition to a demanding weights or cardio station, then repeat eight times. The final station—100 wall balls—is where competitors’ legs literally stop functioning.
Elite athletes complete the course in under 60 minutes. But Ethier faced an immediate problem that threatened to derail everything before it started.
Injury Strikes on Day One
After his very first run, sharp pain radiated through the outside of his foot with every step. An emergency visit to his physiotherapist, Rajan, confirmed he’d likely strained a joint or tendon along the bottom of his foot.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Best case scenario, it’ll probably get better in a couple weeks with a little bit of rest.
Two weeks of recovery meant only two weeks to actually train. His joints, tendons, and bones had never adapted to running’s repetitive impact. The realization hit hard.
I’m feeling really down right now. At this point, I’m honestly considering backing out from the event. This moment in time, I’m 50/50 about continuing.
Zone Two Training and Recovery
While his foot healed, Ethier swapped running for cycling and assault bike work—lower impact options that maintained cardiovascular progress without aggravating his injury.
His training plan incorporated zone two cardio—maintaining heart rate between 60-70% of maximum (120-140 beats per minute for him). This intensity level allows conversation without heavy breathing, though it requires 45-60 minutes to deliver full benefits.
Zone two training specifically addresses both problems identified in his initial testing: it trains the body to burn fat efficiently and improves lactate clearance.
But the burning question remained: would all this cardio destroy his muscle mass?
The Science Behind Cardio and Muscle Loss
To answer this scientifically, Ethier underwent full-body MRI scans on day one, measuring muscle thickness and cross-sectional area. After 30 days, follow-up scans would reveal exactly where any muscle loss occurred—if it happened at all.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Research provides encouraging news. A 2021 meta-analysis combining 27 studies found that beginners who paired cardio with strength training experienced essentially identical muscle growth compared to those doing weights alone.
However, trained individuals showed slightly negative effects. Not ideal for someone already lifting regularly.
Fortunately, researchers identified three crucial rules to prevent muscle loss when combining cardio and weights:
Rule One: Never Do Cardio Before Weights
Long or intense cardio sessions fatigue your nervous system and deplete energy reserves, compromising strength performance. Ethier scheduled all cardio after weights or later in the day.
Rule Two: Refuel Strategically
Beyond adequate protein intake, the extra cardio burned through significantly more carbohydrates than usual. Ethier consumed quick carbs like bananas and rice cakes pre-workout, then complex carbs including potatoes and rice immediately post-training.
Rule Three: Protect Leg Training Days
Long runs tax legs as intensely as heavy leg workouts. Since legs were already a weakness, Ethier needed them fresh for weighted training sessions—a challenge when running daily and practicing eight brutal Hyrox stations.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Building Elite Conditioning
Once his foot healed, Ethier implemented a comprehensive training protocol combining multiple approaches:
- Two weekly zone two sessions for aerobic base building
- Three high-intensity workouts using Norwegian training methods
- Regular Hyrox station practice with his physiotherapist Rajan
The Norwegian method has helped a country of just 5.5 million people produce countless world-class endurance athletes, including one holding the highest VO2 max ever recorded.
The protocol: push maximally hard for four minutes, recover for three minutes, repeat four times total. Brutal, but effective.
Honestly, I’m shocked. You did pretty well. I’m really surprised in like one week. That was crazy.
An Unexpected Benefit: Runner’s High
Beyond physical adaptations, Ethier discovered something that shifted his entire perspective on cardio.
Something about like pushing yourself with cardio, it just gives you a high that you can’t replace with weights. I now know what people mean about the runner’s high. Feels incredible.
During moderate to high-intensity cardio, your body releases anandamide—often called the “bliss molecule.” This compound attaches to the same brain receptors that respond to THC in cannabis.
After 20-40 minutes of sustained cardio, enough anandamide accumulates to produce effects chemically similar to getting high. Weight training doesn’t trigger this response because the work occurs in short bursts with rest periods, preventing sustained effort required for anandamide release.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
This natural high became one of Ethier’s biggest training motivators.
Unexpected Strength Gains
Three weeks into the experiment, something remarkable happened.
I actually managed to set a PR today. That was a volume PR, so like most reps I’ve done at that weight, which is totally unexpected given all the extra cardio that I’m doing.
How is setting personal records possible while running daily? The answer lies in lactate management.
Lactate also accumulates during higher-rep strength training. Those accompanying hydrogen ions create the burning sensation when pushing close to failure. Cardio—especially high-intensity work—trains muscles to clear lactate more efficiently.
Simultaneously, cardiovascular training increases cellular energy production capacity. This helps muscles work harder, recover faster between sets, and ultimately perform better during workouts.
Recent studies suggest cardio may actually enhance rather than hinder muscle gains when properly programmed.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Race Day Preparation
One week before competition, Ethier shifted focus from conditioning to strategy. He consulted Cole Learn, a professional Canadian Hyrox competitor with over 20 race completions and multiple records.
The biggest thing for HYROX is maintaining your heart rate off of the start. If your heart rate is too high, your muscles are not going to work the way they should.
Learn’s counterintuitive advice for the rowing station: treat it as recovery rather than an opportunity to gain time. Going too hard would spike heart rate and deplete energy for subsequent stations.
Just before departing for London, complications arose. Will Tennyson withdrew due to scheduling conflicts, leaving Ethier without a partner. Fortunately, race organizers allowed his best friend Jeff—who’d competed in Hyrox four times—to join Team Canada.
Final Testing Results
Days before flying out, Ethier retested his VO2 max to measure improvement.
Your VO2 peak was 61.32 ml per kg per minute. So, you did great job. 61 is in the 99th percentile. You did excellent.
He’d improved from 58.3 to 61.32—jumping into the 99th percentile. Even more promising, his fat-burning efficiency had dramatically improved, addressing one of his initial weaknesses.
The MRI scan results? Zero muscle loss in both upper and lower body. He didn’t gain muscle, but he didn’t lose any either—exactly what the research predicted when following proper protocols.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
His DEXA scan showed body fat dropped 1%, despite eating more calories than ever while losing weight—a testament to dramatically increased activity levels.
Competition Day
Upon arriving at the stadium and seeing competitors from all 16 countries, intimidation set in. Team Korea included winners from Physical 100, a show featuring the fittest people from each country. Team France brought a Hyrox champion.
Starting the race and watching numerous teams sprint ahead triggered panic.
I honestly thought like that’s it. We are about to get crushed. I am going to get completely embarrassed.
But Ethier stuck to his race strategy, maintaining controlled pacing despite every instinct screaming to speed up. The discipline paid off as Team Canada steadily moved up in rankings.
With South Korea taking first and France securing second, only one podium position remained. Two countries battled for bronze as Ethier’s lungs and legs begged him to stop.
The lesson from 30 days of training crystallized in that moment: when everything tells you to quit, keep going.
If you want something simple that actually works, this is one of the most effective tools I’ve used to build strength, conditioning, and endurance without needing a full gym setup.
- Full-body training with one weight using swings, squats, and presses
- Solid cast iron build that feels stable and lasts for years
- Comfortable grip that makes high-rep workouts easier to handle
Team Canada crossed the finish line in third place, claiming the final podium spot.
Key Takeaways for Combining Cardio and Strength
Ethier’s 30-day experiment provides actionable insights for anyone worried about losing muscle while improving cardiovascular fitness:
- Timing matters: Schedule intense cardio after weights or later in the day
- Fuel appropriately: Dramatically increase carbohydrate intake to match increased activity
- Protect strength training: Manage cardio volume around leg days to ensure adequate recovery
- Progressive adaptation: Build up gradually to allow joints and connective tissue to adapt
- Mix intensity levels: Combine zone two work with high-intensity intervals for complete development
The myth that cardio inevitably destroys muscle gains doesn’t hold up when proper protocols are followed. MRI scans confirmed zero muscle loss despite daily running for 30 days, while VO2 max improved significantly and body composition leaned out.
Perhaps more importantly, Ethier discovered that cardiovascular training offers benefits extending beyond physical performance—the mental clarity, runner’s high, and confidence gained from pushing through discomfort proved just as valuable as any physiological adaptation.
