Runners have long used low- and non-impact forms of cardiovascular exercise to keep in shape when unable to run due to injury.
But today many elite runners perform endurance cross-training workouts throughout the training cycle to promote recovery and to provide an additional training stimulus without increasing the risk of injury.
The current standard among the elite runners who take this approach is one active recovery workout in the pool or on the bike each week.
But a few cutting-edge runners do a lot more endurance cross-training -- sometimes as much as they do running -- because they experience a significant crossover fitness benefit alongside substantially reduced injury risk.
It makes sense. The pounding that running inflicts on the body causes it to break down through injury well before its fitness potential is tapped out.
Adding an activity like pool running, bicycling, or walking to one's running allows a runner to realize more of this fitness potential without additional pounding.
Here are basic guidelines for the three uses of endurance cross-training:
Active recovery
As a baseline, do one workout per week in your cross-training modality of choice. Maintain a steady, moderate intensity for 30 to 60 minutes.
Replace scheduled runs with additional endurance cross-training workouts when you are feeling especially sore or are experiencing warning signs of a potential running-related injury (pain felt in a specific area during and/or following runs).
Injury rehabilitation
When you have an injury that limits your running or makes running impossible but allows you to safely perform at least one type of non-impact alternative to running, simply maintain the structure of your running program but replace runs with pool runs, bike rides, or whatever.
In other words, perform endurance cross-training workouts that imitate as closely as possible the duration, intensity, and structure of the land running workouts you would be performing if you were healthy.
For example, if you were scheduled to perform a dozen 400-meter repeats on the track at 90 seconds per quarter, then perform a dozen hard 90-second intervals in the pool or on the bike separated by rest intervals that also match what you normally do on the track. Be sure to warm up and cool down as normal, too.
Performance enhancement
If you wish to use endurance cross-training to enhance your running performance, you'll need to experiment a little.
The core of your training program will remain your key run workouts (mainly your long runs and high-intensity runs). There is no substitute for these.
How much more additional running you do depends on how much more you feel you need, but should remain well within the range of what you know you can handle.
At first, add just one easy endurance cross-training workout to your schedule of run workouts. When you've adjusted to this, add another, and so on.
If you're highly competitive and seem to derive a lot of benefit from endurance cross-training, you can do as many as six such workouts per week at appropriate times in the training cycle.
Most or all of these workouts should be active recovery or foundation-type workouts, but you can experiment with some high-intensity work if you wish, as long as it does not interfere with your key run workouts.
Four modalities
The best endurance cross-training modalities for runners are those that are most similar to running in terms of the manner in which they engage and affect various systems of the body, because these activities will offer the greatest crossover fitness benefit.
Swimming and rowing are rather dissimilar to running as compared to some other choices, so they are not the best options. The four modalities I recommend are:
1. Pool running
Pool running, or deep-water running, when done correctly, is the cross-training modality that is most similar to land running in terms of the demands it places on the body.
Studies have shown that runners are able to maintain a high level of running-specific fitness through as much as six weeks of exclusively pool-based training. It's no surprise that pool running is the endurance cross-training modality of choice among today's elite runners.
When running in water it is important to emulate a natural land-running stride as closely as possible. This is next to impossible if you're not wearing a pool running vest such as an AquaJogger vest. These cost $40 to $60 and are available at many running specialty shops.
Because it is totally non-weight-bearing, pool running is the best land-running substitute to use when rehabilitating bone strains and stress fractures.
However, because it is totally non-weight-bearing, pool running exclusively for a few weeks or more will result in steady diminishment of the shock-absorbing capacity of your lower extremities, putting them at greater risk of re-injury when you return to running.
So it's best to mix pool running with a weight-bearing activity such as walking during long periods of rehabilitation.
2. Elliptical training
The elliptical trainer was specifically designed to simulate running without impact. This makes it an excellent endurance cross-training modality for active recovery, injury rehabilitation, and performance enhancement.
The only significant drawback of elliptical training is that it is rather boring in the opinion of many runners (including this one).
3. Bicycling
Bicycling is not quite as similar to running as pool running or elliptical training, but it has been used effectively by many top runners, including 5000-meter American record holder Bob Kennedy. One advantage of bicycling is that it builds muscle strength in the legs.
4. Inline skating
Inline skating is unique among running alternatives in that it tends to strengthen several of the important stabilizing muscles that are commonly underdeveloped in runners, and whose weakness leads to many overuse injuries.
Specifically, inline skating strengthens the hip abductors and hip external rotators, the vastus medialis (a quadriceps muscle), the lower back, and the ankle dorsiflexors on the front of the lower leg.
At the same time, inline skating provides an excellent non-impact cardiovascular workout. Its chief disadvantage is that it requires a very smooth, relatively flat skating surface and good weather.
Part 1: Intro to cross-training Part 2: Strength training Part 3: Stretching Part 5: Form training Part 6: Shoe and foot science