Get access to everything we publish when you sign up for Outside+.
Does cross training (like biking) help training?
—Josh F., Charlestown, New Hampshire
Cross training (like biking or swimming or playing aggressive tug of war with your dog) is surprisingly controversial in the coaching world, a place where controversies are delightfully low stakes. But the general principle from the research is that cross training as a supplement to running is beneficial, and as a substitute for running may be beneficial in some circumstances and detrimental in others.
Many studies show that adding cross training is helpful if running volume stays the same. So if you like to bike in the afternoons after a morning run, that should be great.
Where it gets murkier is when cross training replaces some or all running volume, with conflicting results across studies. Cross training should be good for aerobic adaptations, primarily by increasing blood volume and mitochondria and capillary density. Activities like biking can increase muscle strength. And low-impact cross training decreases injury risk, which is especially beneficial for injury-prone or older athletes.
However, some of those positive adaptations could be offset by running-specific benefits to higher-volume training, primarily those related to running economy, or how much energy it takes to go a given pace, which has large neuromuscular and biomechanical components.
Thinking about pro cyclists may be helpful. In Boulder, some of the fastest running times on local hill climbs are held by cyclists. That makes sense when you think about it—they are aerobic monsters with strong legs. Since climbing workouts place fewer demands on the neuromuscular system (running fast/coordination) and biomechanical system (absorbing impact forces), they translate well to your fitness. However, if the same pro cyclist tried to run a 10K on the track, they’d get lapped many times over.
Lacking definitive answers, it’s important to find what works for your body and mind. For my athletes, the general rules are: they can always add cross training except during the specific phase of training in the final month before a key race; athletes that are susceptible to injury can cross train to replace some miles; and athletes over 40 can cross train more aggressively.
Finally, remember the golden rule of training: the body knows stress, not miles, so don’t overdo it.
This article originally appeared in the June 2018 issue of Trail Runner.