“Cross-training” is a term that refers to the aerobic or cardio-respiratory exercise that long-distance runners perform in addition to running. Popular modes of cross-training include biking, Stairmaster or stepping machine, elliptical training, swimming or pool-running. Cross-training is a great way to improve aerobic fitness without adding the additional “pounding” of running more and more miles. Additionally, runners who have an injury that precludes running may still be able to safely and productively cross-train. An important consideration for cross-training that most runners and coaches are unaware of: Cross-training does not have to “look” like running or mimic running in any way. Most runners assume that in order to improve their running performance, they should choose a mode of cross-training that most closely mimics running. For this reason, the cross-training option of choice for many runners is the elliptical machine and/or pool-running. However, motor learning research shows us that if the mode of exercise or activity is even slightly different than the mode of activity we aim to improve, there is no “transfer” of training. Stated otherwise, the “skill” of running is completely different than the “skill” of elliptical or pool-running; even if they seem remarkably similar. Cross-training is still incredibly valuable for the distance runner (injured or healthy); but they shouldn’t aim to mimic running whatsoever. Instead, the sole focus of cross-training is to increase the function of the cardio-respiratory system (referred to as improved aerobic capacity or VO2 max). An improved cardio-respiratory capacity will contribute to faster running times. The important message is that cardio-respiratory fitness can be improved using a wide array of cross-training modes, and they do not need to mimic running. Simply pick the exercise/activity that allows you to elevate your heart rate most effectively. Many trained distance runners choose to cross-train on an elliptical machine but at the same time complain that they feel that they can’t elevate their heart rate high enough while on the machine; however, they continue to stick with the elliptical machine because they assume it “transfers” to running. This runner would be wise to select a mode of cross-training that allows a sufficient stress to the cardio-respiratory system (perhaps the Stairmaster Stepmill or a Spin class). Stepping or spinning “look” nothing like running but they are effective ways to improve cardio-respiratory function and thus are great modes of cross-training for runners. Take-home message: When cross-training, you are concerned only with elevating your heart-rate, not the actual movements or motions of your body.
A side note:
If you are interested in improving running performance; running trumps cross-training (because cardio-respiratory fitness is improved and the “skill” of running is improved). This follows the principle of specificity: If you want to get better at something, you have to perform that EXACT something.