How rucking builds endurance, strength, and long-term fitness safely

Originally published on April 3, 2024

Rucking is one of the clearest ways to build aerobic fitness, posture, and load tolerance with a simple change: add weight to a walk. In Episode 266 of the WHOOP Podcast, Will Ahmed talks with Jason McCarthy, co-founder and CEO of GORUCK, about why rucking is growing, how military load carriage became a mainstream training tool, and what people should know before trying it. McCarthy served in Army Special Forces after 9/11, later built GORUCK from a go-bag idea into a global training business, and still frames rucking through performance, service, and durability. This article breaks down the physiology, the progression, and the WHOOP insights that make rucking useful across training and daily life.

To listen to Episode 266 of the WHOOP Podcast in full, head to the WHOOP Podcast on YouTube.

What is rucking, and why is it growing so quickly?

Rucking is walking with weight on your back, and its appeal comes from how easy it is to understand and scale. You do not need a technical skill, a specialized facility, or a long learning curve to start.

McCarthy defines it in the simplest possible terms, then makes clear that the range is wide. A light loaded walk and a heavy military-style effort both count. On the podcast, Will Ahmed cited WHOOP data showing that rucking was the 12th most popular logged activity in 2023 and one of the fastest-growing, with a 49% increase in logs from 2022 to 2023. WHOOP later revisited rucking as part of its coverage of summer fitness trends, which fits the same pattern McCarthy heard from the field: more people are trying it because it feels practical.

McCarthy also points to a daily-life reason for that growth. Rucking fits into tasks people already do, including walking the dog, carrying a child, or taking a call outside. He described using a rucksack during meetings so the session can double as work time and aerobic work.

In the conversation, McCarthy gives the clearest possible definition.

"Put weight on your back and carry it, go for a walk."

What you should take away

• Rucking is load carriage, usually by adding weight to a walk.
• Rucking can be scaled from very light loads to demanding performance work.
• WHOOP data cited in the episode showed a 49% increase in rucking logs from 2022 to 2023.
• Rucking fits daily life because it can happen during walks, meetings, and other routine movement.

If you want to hear McCarthy unpack why rucking is entering the mainstream, listen to the full episode on Spotify

Why can rucking improve fitness with less joint stress than running?

Once the basic definition is clear, the next question is why people choose rucking over other conditioning. McCarthy's answer is joint stress, durability, and a heart-rate profile that still gives you real aerobic work.

He contrasts rucking with running by focusing on force through the knees. In the episode, McCarthy says the force load from running reaches far higher levels than walking with weight. That helps explain why people who want conditioning, but want to avoid the repetitive pounding of frequent running, often find rucking easier to repeat week after week.

Will Ahmed added that McCarthy's own WHOOP rucking data showed 27% of time in zone 2 and 22% in zone 3. That is a useful mix for aerobic conditioning, especially for people who want steady work rather than repeated sprint efforts. McCarthy also argues that rucking helps posture by pulling the shoulders back and helps bone density because the body is moving under resistance. Questions of movement quality and durability also show up in Dr. Kelly Starrett's discussion of mobility and injury prevention.

McCarthy puts the joint-stress case in numerical terms.

"Every time you run, it's 8 times your body weight onto your knees. When you walk or ruck, it's 2.7."

What you should take away

• McCarthy argues that rucking can deliver conditioning with lower repetitive knee loading than running.
• WHOOP data cited in the episode showed one rucking profile spent 27% of time in zone 2 and 22% in zone 3.
• McCarthy links rucking to better posture because the load encourages the shoulders and spine into a more upright position.
• McCarthy also describes rucking as active resistance work that can support bone density.

If you want to hear McCarthy go deeper on joint stress and aerobic training, watch the full episode on YouTube.

How should beginners start rucking and progress safely?

That lower-impact case leads to the practical question of progression. McCarthy's main point is that rucking is a spectrum, and people get into trouble when they copy advanced standards before they have built the posture, feet, shoulders, and back to support them.

On the podcast, he describes loads as low as 10 pounds and as high as 125 pounds, with very different outcomes. That matters because the skill is not only aerobic. Load carriage also asks your upper back, trunk, hips, and feet to tolerate sustained work. McCarthy says he learned this the hard way. He came into Army training heavy from gym work, then found that a rucksack challenged him in ways barbell strength had not prepared him for.

For everyday training, his examples point toward a simple rule: start with a load you can carry upright while breathing and talking normally, then add distance, pace, or weight one step at a time. Recovery-guided progression shows up in other WHOOP reporting too, including Project PR, the eight-week study on Recovery-based training.

McCarthy uses a Special Forces benchmark to show what advanced load carriage looks like.

"Twelve miles with 45 pounds is kind of a standard. If you get more than 3 hours is the cutoff. If you don't make 3 hours, you fail. Under 2 hours is the goal."

What you should take away

• McCarthy describes rucking as a wide spectrum, from light loaded walks to very heavy efforts.
• Good rucking posture, trunk strength, foot tolerance, and shoulder tolerance all need time to build.
• Advanced military benchmarks are useful context, but they are not beginner starting points.
• Progressive loading works best when you add one variable at a time, such as distance, pace, or weight.

If you want to hear McCarthy unpack how load, pace, and standards change the challenge, listen to the full episode on Spotify.

What does rucking build besides cardio and strength?

Once load and pacing are in place, the next layer is what rucking builds mentally and socially. McCarthy ties rucking to confidence, humility, and community, all of which came from his military background long before GORUCK became a business.

One of the hardest stories in the episode is his description of Robin Sage, the final phase of Special Forces qualification. After parachuting in with roughly 125 pounds of load, McCarthy says he had to carry that ruck for 18 hours. His description matters because it separates discomfort from quitting. The physical stress was extreme, but the deeper test was whether he would keep moving when he was tired enough to rationalize stopping.

McCarthy also argues that rucking creates social structure. He compares fitness groups to the supper clubs and bowling leagues people once used to stay connected. That is part of the appeal of GORUCK clubs, and part of the reason he links business back to service, including support for groups such as the Green Beret Foundation. For a related WHOOP conversation about lower-stress training days and nervous-system management, see Episode 41 with Jordan Shallow.

McCarthy sums up the mental side in a short line.

"Confidence is earned."

What you should take away

• McCarthy frames hard rucking as a mental test as much as a physical one.
• Load carriage can build confidence because the effort has to be completed, not imagined.
• McCarthy sees group fitness as a modern way to create connection and accountability.
• Rucking communities can serve both performance goals and a broader service mindset.

For McCarthy's full take on grit, service, and rucking culture, watch the full episode on YouTube.

What can WHOOP show you about rucking recovery and daily habits?

That broader effect is exactly where WHOOP becomes useful. McCarthy says the biggest value for him has not been proving he can train hard. It has been seeing how sleep, alcohol, screens, and daily choices change recovery.

He had worn WHOOP for about three months when he recorded the episode, and he said his Sleep scores were usually between 94 and 100 unless travel disrupted them. Recovery was the harder puzzle. McCarthy explains that years of military and endurance-style stress taught him how to keep performing while run down, but WHOOP pushed him to look at the cost of that habit. He specifically called out alcohol and screen time in bed as behaviors that become harder to dismiss when the next day's metrics reflect the drop.

That same logic sits behind Episode 51 on what WHOOP measures and other Recovery-based stories across the Locker. It also matches the idea that training data can support better pacing, rather than only confirm hard work after the fact.

McCarthy's clearest line on the value of wearable data is also the most practical.

"You can't argue with the data."

What you should take away

• McCarthy says WHOOP became most useful when it showed the cost of habits outside training.
• McCarthy reported Sleep scores between 94 and 100 on many nights when travel did not interfere.
• WHOOP made alcohol use and screen time before bed harder for McCarthy to rationalize away.
• Recovery data is most helpful when it changes the next decision, not when it only confirms effort after the fact.

The bottom line

• Rucking is a loaded walk, and its simplicity is part of why it is growing quickly.
• WHOOP data cited in the episode showed rucking logs increased 49% from 2022 to 2023.
• McCarthy argues that rucking can provide strong aerobic work while placing less repetitive force through the knees than running.
• McCarthy links rucking to posture, bone density, and zone 2 to zone 3 conditioning.
• Rucking works across a wide range of loads, which makes progression more important than copying advanced military standards.
• McCarthy's Special Forces background shaped his view that load carriage builds confidence because hard effort has to be carried through in real time.
• McCarthy uses WHOOP mainly to evaluate sleep, Recovery, alcohol effects, and the daily habits that shape readiness.
• McCarthy's central message is that data becomes useful when it changes behavior, especially around recovery.

Frequently asked questions about things discussed in this episode

How does WHOOP measure rucking?

WHOOP measures rucking as an activity session with heart rate, duration, Strain, and time in heart rate zones, so you can see whether a loaded walk stayed easy or became a harder conditioning effort.

What does WHOOP do for zone 2 training during rucking?

WHOOP shows how much of a rucking session landed in zone 2, which helps you check whether your pace and load matched your aerobic goal.

How does WHOOP help with recovery when you ruck often?

WHOOP uses signals such as Sleep, heart rate variability, and resting heart rate to generate Recovery, which helps you decide whether to keep the load high or back off.

What does WHOOP show about alcohol and rucking recovery?

WHOOP can make the next-day cost of alcohol visible through lower Recovery and worse sleep signals, which McCarthy said changed behavior for people around him.

How does WHOOP help you judge whether rucking is affecting sleep?

WHOOP quantifies Sleep performance and consistency, so you can tell whether added load is supported by good sleep or carried into the next day.

What does WHOOP measure outside workouts that still matters for rucking?

WHOOP captures strain from daily life and behavior patterns, which matters because stress, travel, late screens, and long days can affect readiness before the next loaded walk.

For rucking, WHOOP is most useful when it shows whether the extra load is building capacity or quietly carrying into the next day as lower Recovery.