“They change people’s biomechanics in a way that can be unpredictable, and brings up the question of potential injury risk,” says Dr. Adam Tenforde, director of running medicine at Mass General Brigham’s National Running Center.

A matter of mechanics

The problem comes down to basic biomechanics, says Dr. Kenrick Dennis, a podiatrist in Houston who served as medical director for the Houston Marathon.

“If you are standing on that marshmallow, it allows your foot to torque in and out a little bit more, the leg rotates to follow it, and that rotation is translated through the ankle, the knee and the hip,” he says.

It takes a bit longer to sink into the cushiness and subconsciously find your balance before you push off again, similar to the extra effort required when walking on sand. The wobbliness, he says, plus the added height of max-cushion shoes, also increases the risk of twisting an ankle or falling.

Moreover, max-cushion shoes diminish proprioception (awareness of where you are in space), since you have less sensory feedback of where you are vis-à-vis the ground.

A number of civil lawsuits have been filed against shoe manufacturers by track stars, including an Olympian, who allege, among other things, that wearing high-stack shoes with carbon plates caused injuries that derailed their careers. Nike faces one such suit in California Northern District Court. Puma—the parent company as well as some of its divisions and partners—was named in three cases filed in Massachusetts Superior Court.

Nike declined to comment on pending litigation, but in court filings the company denies its product is “defective and unsafe for its intended purposes” and neither “caused injury and/or contributed to the risk of injury.” Puma said in a statement that it strongly denies its shoes cause injury. The company is further pursuing a countersuit against its three accusers in a German court.

While the suits focused on shoes that included a carbon plate, Tenforde says max-cushion shoes can modify biomechanics independent of that feature. Hoka didn’t respond to requests for comment about safety concerns.

Of course, back when barefoot running was the rage in the mid-2000s, alleged injuries caused by zero-stack, or “barely there,” shoes resulted in lawsuits against manufacturers.

“The pendulum has swung from the barefoot shoes to now having a marshmallow under your foot,” says Dennis, the Houston podiatrist.

Proponents of max-cushion shoes, particularly those with an embedded carbon plate, point to studies that suggest the shoes improve running economy and performance by 4% and 2%, respectively. A 2023 review published in Sports Biomechanics says that every world record from the marathon to 5 kilometers has been broken by athletes wearing these kinds of shoes. The comfort and springy design may allow athletes to tolerate higher training volumes or intensities.

“If a shoe makes running easier, you will run faster,” says Dr. Laurent Malisoux, a sport and physical-activity research leader at Luxembourg Institute of Health. “But people should remember that if they get an injury, it’s because they probably ran too much, too fast or too soon, not because of the shoe.”

Stressing the muscles

Nevertheless, concerns remain. A 2018 study published in Nature indicates max-cushion shoes actually increase the total load on muscles, bones and joints compared with more-moderately cushioned shoes in part because the foot is on the ground longer.

“You’re hitting the ground with the same magnitude of force,” says Dr. Daniel Lieberman, a Harvard evolutionary biologist whose research focuses on how modern footwear has altered human biomechanics. “But you’re spreading that force over a longer period of time.”

Your leg also appears to stiffen more when you land, intensifying the jolt, according to the authors of the Nature study. If there is a carbon plate in the shoe, it can help you spring back into the air a bit faster, but Lieberman says more research is needed to determine whether the total load is larger than in more moderately cushioned or minimalist shoes.

While max-cushion shoes may feel great initially, repetition of these minute wobbly, twisting moments plus the extra mechanical load on muscles, tendons, joints and bones could lead to injury in the long term, critics say. During a mile run, each foot will strike the ground on average about a thousand times. Running 20 miles a week adds up to a million foot strikes a year.

There is also the concern that the squishiness of max-cushion shoes and/or the location of the flex point, particularly if there is a carbon-fiber layer, may also shift where on your foot you land and push off. That might make you more vulnerable to foot fractures, according to a 2023 analysis of high-stack running shoes with carbon-fiber plates published in Sports Medicine, with Tenforde as the lead author.

Scott Christensen, lead endurance instructor for USA Track & Field, says while he appreciates the potential performance-enhancing qualities of bouncy foam and carbon springboards, “everything has a cost-benefit ratio to it.” One of the more counterintuitive costs, he says, is the shoes’ exceptional comfort. Runners don’t get as sore, which is the body’s way of saying: Hey! Back off before you do damage.

“As a coach, I want soreness,” Christensen says. “I depend on soreness in my athletes. Soreness is the governor of training.”

Making good choices

So, what is a person to do when confronted with a wall of shoes in a run shop or sporting-goods store? “The answer is there is no one answer,” Christensen says. People have different physiologies, exercise regimes and injury histories which might dictate not only level of cushioning, but also support, stability and heel-to-toe drop of the shoe.

Whether you’re a runner, walker or maybe someone whose job requires you to be on your feet all day, the best shoe is the shoe that fits. You may think you’re wearing the right size, but a 2018 study in the Journal of Foot and Ankle Research suggests as many as 72% of people wear shoes that don’t accommodate either the width or length of their feet. Your shoes shouldn’t hurt or feel uncomfortable either during or after physical activity.

And don’t pay attention only to the pillowy feel under your feet, Dennis says. Test your ability to maintain balance and coordination in the shoes by doing things like raising up on your toes and holding and then rocking back on your heels and holding, as well as doing quick turns and pivots. Notice any additional workload or twisting moments demanded of the joints and muscles in your legs and hips. Also listen to your footfall. It should be light and have a steady, crisp cadence—no clomping, scuffing or shuffling, as can happen when you have too much bulk under your feet.

Beyond that, Christensen’s advises training in more than one kind of shoe, varying amount of cushioning and stack height. The combination will vary stressors on your body and reduce the chance of repetitive foot strike and motion injuries.

Dr. Stéphane Bermon, director of the health and science department at World Athletics—the international governing body for track and field, cross-country running, road running, race walking, mountain running and ultra running—is also a proponent of the shoe-rotation strategy, but he cautions to introduce any new shoe “very, very progressively” to avoid injury. Maybe running or walking in a new kind of shoe once a week for one week and then twice a week the following week, and so on.

“In biomechanics, in human physiology, what kills you is routine,” Bermon says. “Whether it’s your bone, whether it’s your muscle, whether it’s your tendon, you have to challenge yourself every day with different things.” In shoes, just as in life, “There is nothing worse than monotony.”

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It wasn’t just the sun causing problems. “All it takes is one gust of wind and it’s on the side of a mountain,” he said. Behind the rugged peaks, drones lost their signal. 

Next to Bennett, another pilot prepared to launch a drone from Theiss UAV Solutions. After a prolonged wait to charge a drained battery, the aircraft took another 10 minutes to get airborne. Ukrainian soldiers can get a drone of about the same size off the ground in under a minute. 

Defense Secretary Pete Hegseth last year threw down the gauntlet with a directive to transform the Army into an AI-powered force equipped with drones and 3-D printers to quickly spin up weapons components, and directed the service to buy more software and startup tech. He instructed the Defense Department to stop looking for perfection in its tech, and buy off-the-shelf products that are good enough, stressing the urgency of modernizing. 

America’s investments in such weapons, some of which date to the Biden administration, have slowly begun to change the way it fights. In Iran, a war that has relied largely on older and expensive systems, the U.S. also used an unmanned boat made by defense startup Saronic to rescue a stranded helicopter crew. A drone modeled on Iran’s Shahed has been among the military’s most successful low-cost offensive weapons. The drone, called Lucas, costs $10,000 to $55,000 a unit thanks to an arrangement in which the Pentagon owns the design and farms out production to a group of manufacturers. 

Artificial-intelligence tools have also greatly accelerated intelligence analysis and target selection. The rapid evolution of the fighting in Ukraine shows how central such technologies will be to future wars. 

But America’s soldiers are still far from reaping the full benefits of cutting-edge autonomous weapons and AI systems, and haven’t been forced by necessity to quickly modernize as militaries like Ukraine’s have in the heat of conflict, current and former national-security officials said. Transforming a land-based fighting force with a history of slow technological adaptation into a nimble organization that makes the most of new innovations has been difficult.

A soldier enters a building during an assault exercise at Fort Irwin.

A soldier enters a building during an assault exercise at Fort Irwin.

Soldiers run into position during a combat training exercise.

Soldiers run into position during a combat training exercise.

Startups’ emerging new tech, most of which has never been to war, has at times proven to be too brittle in real-world applications, soldiers said. The Army is also in the throes of upgrading battlefield connectivity and communications, steps that are key to being able to fully capitalize on next-generation weaponry.

The military has held at least five press calls in recent weeks to talk about its modernization efforts. “There is a recognition that the battlefield is changing before our eyes,” Col. Gregory Merkl told reporters on one such call. “We are absolutely dedicated to transformation.”

Fort Irwin

Project Convergence brought 9,700 infantry soldiers to the desert for a 10-day, round-the-clock mock fight against an Army unit called Blackhorse, which stood in for China’s People’s Liberation Army. Media briefing materials billed the three-day July trip as a glimpse “inside the U.S. Army’s AI-enabled battlefield” and an opportunity for its leadership to demonstrate the use of AI apps, a data integration program, aerial and ground drones and sensor-loaded headsets in battle. 

In some of the moments meant to spotlight advanced technology on the battlefield, newly procured drones and developmental communication systems failed to perform as intended. 

Soldiers flew drones during limited windows and for half the maximum flight time to conserve battery and avoid losing them, and without full autonomy or any AI to assist. Chinese consumer drones could do the manual job a decade ago.

The battle offered the familiar scene of legacy warfare: green-suited soldiers kicking in doors, screaming above gunfire, weighed down with weapons from the last century. 

An Army spokesman for Project Convergence said the event was designed to allow for specific units to experiment with drones during pockets of fighting and learn about the tech, not to flood the airspace with autonomous weapons. The event was a way to “fact-check all the vendors that are coming to us” about the veracity of sales pitches from a crop of defense technology firms, said Alex Miller, chief technology officer to the Army’s chief of staff. 

Morning light filters through smoke and dust above the mock village at Fort Irwin.

Morning light filters through smoke and dust above the mock village at Fort Irwin.

The Army found during the exercise that the augmented-reality headsets referenced in its media invitation to Fort Irwin showed some deficiencies and the service is uncertain if it would move forward with them, a senior defense official at the training event said. Three companies have won contracts each worth more than $100 million to build the headsets.

While much of the tech there had already been awarded sizable Army contracts, officials and soldiers involved described it as experimental rather than essential new weaponry. 

“You take a piece of electronics and lay it out on a hot rock in 109 degree temperatures and try and make it work,” said Lt. Gen. Michael McCurry, one of the senior Army leaders running the event. “We’re seeing some of that.”

An Anduril spokesman said its drone overheated and that it had previously been tested in hot and cold temperatures. Following soldiers’ feedback, the company has prioritized making upgrades to improve the drone’s performance in extreme environments, he said. 

Theiss UAV Solutions founder Shawn Theiss said his drone typically launches within three minutes and that he received mostly positive feedback from soldiers at the exercise. Delays sometimes happen if soldiers aren’t trained, or if the communications parts, made by a separate company, have glitches, he said. The Theiss UAV drones there were more than three years old and batteries may not have been at peak performance, which can affect the launch, he said.

Some defense officials said the efforts would bear fruit longer term despite near-term stumbles.

Modernizing the military

Congress has long hammered the Army about modernizing its fighting. Congressional probes and government oversight reports have found that the Army has wasted billions of taxpayer dollars on fumbled new weapons programs, and suffered from inadequate training and failures in cybersecurity and data management. 

The Ukraine war brought the inadequacies into focus, bringing fully autonomous warfare to the battlefield with a tech proficiency that at times humbled the U.S. During battlefield drills held in Germany earlier this year, Ukraine’s drone operators took out a U.S. armored brigade. 

“The tech is moving so quickly that the U.S. military bureaucracy cannot keep up,” said Jonathan Rue, a former deputy assistant secretary of defense who played a key role in getting new technology into the Army, and is now a partner at firm MVP Ventures.

A soldier launches a drone.

A soldier launches a drone.

One soldier coordinates with another while operating a drone controller.

One soldier coordinates with another while operating a drone controller.

The last major Army transformation came about in the 1980s, when the service pivoted from Vietnam and built the force it would use in the Gulf War. It retrained, reorganized and brought in armored fighting vehicles, attack helicopters and modern air defense systems. 

The struggle now is to transform what recently ousted Army Sec. Dan Driscoll has called a “calcified bureaucracy” in preparation for a technologically sophisticated adversary—China. Driscoll departed in September, following disagreements with Hegseth. 

Daniel Goure, a former military analyst with the Lexington Institute who has held numerous war college teaching positions and roles in the Defense Department, said the Army’s history of modernization efforts are “almost unblemished by success.” He blames a tradition of risk aversion and a hierarchical organization.

Still, upgrades like the Army’s Next-Generation Command and Control system, used for AI-enabled planning and logistics, are a start. The system, with a $4 billion price tag in this year’s budget, allows troops to move faster and in a more dispersed fashion over longer stretches of battlefield, which is essential in modern conflicts, Army officials say. 

Starlink connectivity has meant that for the first time in his 19-year Army career, Lt. Col. Shawn Scott can radio a soldier sitting in an air-conditioned operations center at another end of the base, without cumbersome transmission poles. And new data-sharing technology has cut by two-thirds the time it takes Scott to plan and communicate missions.

The next step is bolstering the reliability of communications and data integration systems so AI-powered weaponry can actually help human fighters out in remote and austere conditions.

Capt. Alex Bayer reviews information on a tablet during a training exercise.

Capt. Alex Bayer reviews information on a tablet during a training exercise.

Soldiers maintain a defensive position at Fort Irwin.

Soldiers maintain a defensive position at Fort Irwin.

The Fort Irwin fighting climaxed with a predawn attack on a fabricated city, Razish, a relic of training for the wars in Iraq and Afghanistan. Stryker armored combat vehicles rolled down the hills. Smoke trucks attempted to obfuscate the view. Mortar rounds exploded and soldiers moved from one building to the next, firing blank bullets and pausing for the occasional smoke break.

A swarm of five small drones was forced to turn back as three Black Hawk helicopters carrying senior Army officials flew into the same airspace, squandering a rare high-tech moment they had come to see.

“It’d be a very dangerous time for us just to hand over everything to technology,” said Brig. Gen. Daniel Hibner, commander of the Army’s Joint Modernization Command. “It’s very much still a human endeavor.”

A soldier looks out at the terrain during combat training.

When the White House forced Anthropic to shut off all access to two of its models due to security concerns, Amodei dispatched his chief compute officer to negotiate with the Trump administration after his own efforts fell short. Brown, a Republican, ended the two-and-a-half-week June standoff by assuring Commerce Department, Pentagon and White House officials that Anthropic understood their security fears and had upgraded its safeguards. 

The 6-foot-6 executive posed for a photo last week at a White House summit feting America’s advances in AI, posing shoulder to shoulder with technology CEOs and a president that has previously lambasted Anthropic as “woke.” 

His friendlier relationship with the administration was seen by some observers as one factor helping Amodei secure his first lengthy face-to-face meeting with Trump, a late September dinner at the White House after which he earned praise from the president. Amodei also attended last week’s lunch, making Anthropic one of two companies with a pair of executives in attendance. 

Brown at the White House for a lunch with technology leaders and President Trump. Andrew Leyden/ZUMA Press

Brown at the White House for a lunch with technology leaders and President Trump. Andrew Leyden/ZUMA Press

Brown bought a house in Washington earlier this year with his wife, a startup co-founder and former venture investor named Michelle Valentine. The couple has said in private conversations that they are allies of the Republican party and want to establish relationships in Washington, people familiar with the matter said.

Brown has supported the aggressive U.S. build-out of data centers and nuclear energy projects, a White House priority but an undertaking increasingly unpopular among Americans. Anthropic continues to need more computing power as it amasses users and models advance.

Brown said at a G-20 tech summit last month that he “really loved” a post by Trump on Truth Social that said communities that don’t embrace data centers risk becoming “backwards and poor.”

“He was pointing out that the data centers are just an enormous source of prosperity,” Brown said of the post.

“He is increasingly playing the dual role of founder and diplomat,” said Joseph Hoefer, chief AI officer at lobbying firm Monument Advocacy, which represents tech companies but not Anthropic.

His intense negotiating style masks his soft side as a father to a one-year old son, people who work with Brown say. When a colleague introduced him to their three-year-old, Brown put the boy on his shoulders and walked him around the room. 

The ‘awkward kid’

Brown grew up in the San Francisco Bay Area, then studied engineering at the Massachusetts Institute of Technology. He worked for a host of startups and participated in startup incubator Y Combinator. A self-described “awkward kid,” Brown has said he briefly worked on a group dating app called Grouper to help people like him “talk to girls.”

Brown began learning about AI through online courses and math textbooks after reading “Superintelligence” by Nick Bostrom, a popular book in AI circles exploring what it says are existential dangers for humans from the creation of machines that are smarter than humans.

He offered to mop the floors at OpenAI to get his foot in the door. Shortly afterward, OpenAI co-founder Greg Brockman, with whom he had become friendly, hired Brown as one of the startup’s first 20 employees.

There, Brown met Musk, the lab’s main funder at the time. During one of Musk’s visits in 2016, Brown watched in panic as Musk savaged a demonstration from a legendary researcher. But when it was Brown’s turn to show off his work, Musk said he liked Brown’s tool that let an AI play the videogame StarCraft, according to people familiar with the matter. 

The encounter would end up paving the way to a pivotal computing deal between the two men’s companies a decade later.

Brown was laid off from OpenAI, then briefly joined Google’s DeepMind lab. Amodei brought him back to OpenAI in 2018, and he led engineering work on GPT-3. The breakthrough model demonstrated one of the central tenets underpinning the AI boom: that capabilities would increase when models were trained on more data. 

He joined Amodei and five other OpenAI leaders to create Anthropic at the start of 2021.

Brown’s main job in the early days of the company was securing the chips and computing power needed to train and run Anthropic’s models. While OpenAI had primarily relied on Nvidia chips through its partnership with Microsoft, Brown and Anthropic’s co-founders sought to work with other companies to make the company less dependent on a single supplier.

Brown with Elon Musk and Jensen Huang during a launch event for America.gov. Kylie Cooper/Reuters

When the early 2023 launch of Anthropic’s Claude models to compete with ChatGPT increased the need for computing power, Brown orchestrated deals with Google and Amazon.

Winning over Elon

As Anthropic leapt ahead in the AI race and its models gained traction with businesses, the company’s computing capacity wasn’t able to keep up and customers faced usage limits and outages.

Brown turned to Musk, whose SpaceX had excess capacity at its massive data center complexes after acquiring xAI. It was a tender time: Musk had spent months railing against Anthropic after it cut off xAI’s access to Claude Code, calling it “smug, sanctimonious and hypocritical” on X and giving it the nickname “Misanthropic.” 

But Brown saw that Musk and Anthropic ultimately had an opportunity to help each other. He drove to SpaceX’s offices in Hawthorne, Calif., in late March and told Musk that Anthropic wasn’t as “woke” as he thought, while acknowledging that some of its past models had been, according to people familiar with the matter. 

In early May, Anthropic and SpaceX announced that Anthropic would rent SpaceX’s compute for $1.25 billion a month. To keep up with competitors, Anthropic has also signed agreements worth tens of billions of dollars with Advanced Micro Devices and a trio of smaller companies in recent weeks.

Amodei sent Brown to put that diplomatic dexterity to work in Washington. 

The company clashed with the Defense Department earlier this year about the right guardrails for AI models when they are used by the military. The Pentagon’s designation of Anthropic as a security risk is still in place. 

Brown has regular conversations with Emil Michael, undersecretary of defense for research and engineering, but the Pentagon has barred all usage of Anthropic’s tools and told contractors to stop using them, a move that has been upheld in one court and struck down in another.  

Brown taking charge of the June model shutdown in Washington allowed Amodei to focus on customer relationships and other CEO responsibilities, a person familiar with the matter said. During that time, Brown and Amodei spoke daily on the phone, the person said. 

In recent weeks Brown has held regular discussions with Commerce Secretary Howard Lutnick and Michael Kratsios, head of the White House Office of Science and Technology Policy, about Anthropic’s models and AI safety. 

During last month’s G-20, Brown was seen talking casually with Lutnick and officials from other countries at the Carolina Inn on the University of North Carolina’s campus, with some in the group smoking cigars. 

On stage at the event, Lutnick asked Brown what the future holds for AI. Brown said he expects major progress on curing cancer and benefiting the economy in the next five years, echoing claims from Amodei.  

“Looking back we’ll be like, ‘Wow, back in 2026 we thought stuff was going fast and we thought we were seeing this, but actually we underestimated how impactful this would be and what the progress would be,’” Brown said.