Running versus riding, head to head
Researchers from RPTU University Kaiserslautern-Landau in Germany put together randomised controlled trials comparing running-only training with cycling-only (or mixed) training. Their meta-analysis, published in Frontiers in Sports and Active Living, included 7 studies lasting four to ten weeks.
Participants ranged from untrained young adults to competitive college and cross-country runners. The team looked at three outcomes:
- VO2max tested on a treadmill
- VO2max tested on a bike ergometer
- Running time trials over 1 mile, 3k and 5k
What the researchers found
In short: no statistically significant differences. Both sports produced broadly similar improvements.
Bike-tested VO2max: runners improved about as much as cyclists, with a small, non-significant trend in favour of cycling.
Treadmill-tested VO2max: the mirror image, a small trend in favour of running.
Running performance: practically identical, with an effect size of 0,02, which is about as close to zero as science gets.
In one 9-week trial, for example, VO2max measured on the bike rose by 15% in the cycling group and 8,7% in the running group. In an 8-week trial, the gains on the bike test were 7,7% and 6,8%.
Before you read this as proof that the two sports are interchangeable, the authors urge caution. The studies were small, most used training protocols from the 1970s to 1990s, and several carried a high risk of bias. Crucially for us, none of them tested trained cyclists. As the researchers put it, non-significant findings “should not be interpreted as evidence of equivalence.”
Why the engine transfers but the frame does not
To make sense of this, think of your fitness as two systems.
The engine: your heart, lungs, blood volume, and the mitochondria in your muscles. It doesn’t care whether you pedal or run. To your heart, an easy run and a Zone 2 spin are much the same workout, which is why aerobic gains carry over so well between sports.
The frame: your muscles, tendons, bones, and the way they fire. Here the two sports could hardly be more different. Cycling is a smooth, seated push with your body weight supported by the saddle. Running is a series of landings, with your Achilles tendon and calves loading like springs and firing back at every step.
Each sport slightly favouring its own test fits this picture neatly. It’s the old specificity principle: the best training for cycling is still cycling. Tellingly, two of the trials also lost participants to musculoskeletal injuries – a hint of the frame problem we’ll come back to.
The real reasons to run
So, running won’t boost your FTP. But that was never its best selling point.
Bone health: Cycling puts almost no impact through your skeleton, and bone needs impact to stay strong. In a University of Missouri study of 43 male recreational athletes, 63% of the cyclists had osteopenia (low bone density) of the spine or hip, compared with 19% of the runners. The study was small and observational, so it doesn’t prove cause and effect, but the pattern is hard to ignore in a sport where most of us eventually hit the tarmac.
Time efficiency: There’s no coasting on a run. A 25-minute run is 25 minutes of continuous work, while a ride of the same length rarely is. On busy weeks, a short run stops your engine from leaking away.
Winter safety: When the temperature drops, running can also be the safer choice. Hitting a patch of black ice at 30 km/h on narrow tyres can end your season in a split second. Slipping on foot still hurts, but at running speed, you’re far less likely to come away with a serious injury.
Robustness: Done gradually, running builds stiffer tendons, more stable hips, and better movement quality, things that pedalling alone tends to neglect. Pair it with strength training for a more durable body under the Lycra.
What’s the takeaway?
Running won’t make you a faster cyclist, and if pure bike performance is your goal, spend those hours in the saddle. But for stronger bones, time-crunched weeks, and a tougher body, a couple of easy runs a week earn their place. Just let your tendons, not your lungs, set the pace.