Hyrox’s ‘hybrid athletes’ compete in fitness races that combine running, strength training and endurance.HYROX/Supplied
More than half a million people around the world will take part in a Hyrox competition this year, alternating eight kilometres of running with eight workout stations, including sled pulls, sandbag lunges and medicine ball tosses.
That combination of strength and endurance tasks may sound like a tough ask. But a new paper in the journal Medicine & Science in Sports & Exercise challenges the traditional view that strength and endurance interfere with each other. Instead, the authors argue that in some contexts, getting stronger can help build your endurance and vice versa – an assertion that Hyrox’s “hybrid athletes” would enthusiastically endorse.
The ‘interference effect’ theory
The idea that strength and endurance don’t mix is more than just locker-room lore. Studies in the early 2000s showed that the two types of workout produce different molecular signals, which can then block each other. The findings seemed to explain the cliché of the skinny endurance athlete and the easily winded bodybuilder.
But that picture is oversimplified, according to an international research team led by Carrie Ferguson and Harry Rossiter of Harbor-UCLA Medical Center in California that includes Canadian scientist Russ Hepple, now at the University of Florida.
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Studies frequently find that strength and endurance are inversely related: Those with the highest endurance tend to have the lowest strength; likewise the opposite. But these studies are typically limited to homogeneous groups, such as young sedentary people or older masters athletes.
If you pool all these studies together so that you’re comparing people of different ages and activity profiles, a different picture emerges. On this larger scale, the strongest people also tend to have the best endurance.
According to Ferguson and Rossiter, this pattern suggests that there are some common mechanisms that help people improve both parameters at once. One candidate is the mitochondria in muscle cells, which help provide fuel for sustained efforts but are also important for maintaining muscle mass. Endurance training, which triggers the growth of new mitochondria, may thus indirectly support increased strength.
Long-distance runners usually incorporate weights or plyometrics into their weekly training.OCTAVIO JONES/AFP/Getty Images
Combining strength and endurance workouts
In practice, a growing body of evidence suggests that strength training can enhance endurance in two key ways. One is that it increases efficiency, enabling you to burn less energy while running or cycling at a given pace. The other is that it enhances physiological durability, keeping your muscles functioning well even as you fatigue.
Those are the primary reasons top long-distance runners typically incorporate a few weekly weightlifting or plyometric sessions into their training routines. They’re seeking better endurance, not bigger muscles.
The picture is a little more complicated when it comes to the effects of endurance training on muscular strength and power. For the average person, there’s no negative effect on muscle-building, but for trained athletes there may be a slight negative result.
For explosive muscular power, which is the ability to rapidly exert force – leaping up onto a chair or hurling a baseball, for example – there’s stronger evidence that endurance training can interfere.
The solution, Ferguson and Rossiter suggest, is to do strength training first if you’re combining it with endurance practice in the same workout. Better yet, separate the sessions by at least six hours and refuel with carbohydrates and protein during the intervening time.
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There is, of course, one unavoidable source of interference between strength and endurance: You have finite time and energy, so you have to make choices about how to allocate your workouts. Those choices should reflect your goals: You can neither bench-press your way to a great marathon nor cycle your way to big biceps.
But most of us have goals that require a mix of both strength and endurance – if not competing in Hyrox, then being able to hoist ourselves out of a chair, climb stairs and walk down the street when we’re older. Training for both, the science now suggests, won’t compromise either one.
Alex Hutchinson is the author of The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.
