Why cross-training helps runners
Swimming and cycling can keep your heart and lungs working while giving your joints a break from running’s repeated impact. That matters if you’re building aerobic fitness, recovering between runs, or managing an injury. The catch is that cardio fitness doesn’t automatically prepare your legs and tendons for running.
Running puts substantial loads on joints, muscles, tendons, and bones, says Jennie Hansen, a USAT Level 1-certified triathlon coach. Cross-training usually carries a lower orthopedic cost. And while some muscle and tendon adaptations are specific to running, the heart, lungs, and blood vessels adapt to many forms of exercise that raise your heart rate, Hansen says. That can improve [VO2 max](https://www.runnersworld.com/training/a70019851/the-runners-world-guide-to-vo2-max/) and general fitness. Cross-training may also build [strength](https://www.runnersworld.com/training/a73506025/strength-tests-for-runners/) in areas running leaves underworked.
Swimming and cycling both offer low-impact cardio, but they train the body differently. Here’s how to choose between them.
🏃🏻♀️ For ideas on pairing running with strength work and injury prevention, see the [Runner’s World Guide to Cross-Training](https://www.runnersworld.com/training/a74068946/runners-world-guide-to-cross-training/).
What swimming offers
Swimming works the whole body while taking pressure off the legs, making it a useful option for recovery days or periods when injury limits impact, says Laura Bruck Renzelman, a NASM-CPT and USAT Level 2-certified triathlon coach. Kristen Hislop, a USAT Level 1-certified triathlon coach, adds that swimmers can challenge their cardiovascular system while giving their legs a break.
The pool can also teach runners to breathe more deliberately. Hislop says new runners often take shallow breaths as fatigue sets in. Swimming requires a full exhale underwater, a habit that can carry over to running. It may also improve how efficiently you use oxygen. [Research](https://pmc.ncbi.nlm.nih.gov/articles/PMC4933622/) suggests respiratory training can strengthen the diaphragm and rib-cage muscles, reducing the effort spent breathing.
There’s a strength benefit, too. Swimming works the shoulders, chest, and upper back—areas that runners may neglect, Hansen says.
Where swimming falls short
Swimming has a learning curve. Poor technique can leave runners battling the water and tiring before they get a strong cardiovascular workout, Hansen says. That can make the pool frustrating for beginners.
Its low impact can also create a mismatch during injury recovery. Fitness may return faster than the muscles, tendons, and bones’ ability to tolerate running loads. Swimming also doesn’t reproduce running’s movement pattern. For a closer low-impact substitute, Hislop recommends [aqua jogging](https://www.runnersworld.com/training/a43518252/benefits-of-aqua-jogging/): moving your legs through water adds resistance in both directions and permits a wider range of motion than running on land.
What cycling offers
Cycling works many of the same muscles as running, including the quadriceps, glutes, and hamstrings, Bruck Renzelman says. Riders can adjust effort using heart rate, [cadence](https://www.runnersworld.com/training/a64422354/why-cadence-matters-for-running/), and power, giving workouts a clear target and plenty of room for variation, Hansen says.
The type of ride matters. Road cycling makes it easier to hold a steady effort, so it suits long Zone 2 sessions and [active recovery](https://www.runnersworld.com/health-injuries/a70772923/active-recovery-for-runners-50-plus/). Gravel brings changing surfaces, climbs, and effort levels; Bruck Renzelman says those demands build aerobic and strength endurance, while the need for core stability can help runners [maintain efficiency](https://www.health.harvard.edu/blog/understanding-and-improving-core-strength-2018090414662).
Mountain biking is less predictable still. Short climbs can develop power and muscular strength, repeated accelerations challenge aerobic and anaerobic fitness, and rough trails test balance and coordination, Bruck Renzelman says. That variety is useful, though it also makes mountain biking a less controlled way to target a specific effort.
Where cycling falls short
Getting the same cardio stimulus on a bike can take longer than getting it on a run. Hansen and Bruck Renzelman both say raising your heart rate may be harder while cycling. Hansen estimates that an equivalent training load often takes about three miles of cycling for every mile of running, or twice as much cycling time as running time.
There’s a more important gap for runners: cycling doesn’t prepare the lower body for the eccentric contractions and tendon energy storage and release involved in running, Hansen says. It can help maintain cardiovascular fitness, but runners returning from injury still need to rebuild their legs’ capacity for impact. The same applies if you’re trying to improve [running performance](https://www.runnersworld.com/training/a69018617/5-components-physical-fitness/).
Choosing the right activity
Your training history, goals, and [injury history](https://www.runnersworld.com/training/a73485023/guide-to-common-running-injuries-program/) should shape the choice, Bruck Renzelman says. A shoulder injury may make swimming uncomfortable; knee, hip, or lower-back problems may call for changes to bike position, resistance, or ride length. Cross-training should support your running, she says, rather than add pain or excessive fatigue. For a significant injury or medical condition, she advises working with a healthcare professional to choose appropriate activities.
After that, the practical question is which workout you’ll keep doing. Hansen says runners who are often sore or [muscularly fatigued](https://www.runnersworld.com/training/a71887463/muscular-fatigue-resistance-workouts-runners/) may benefit more from swimming or other pool workouts that unload the legs. Those looking to add fitness while building [leg strength](https://www.runnersworld.com/training/a64796593/strength-training-for-runners-lower-body-workout/) may prefer cycling. The right choice depends on what your running needs—and what your body can comfortably handle.
