Physiologically speaking, however.....
“Physiological adaptations in response to physical training are highly specific to the nature of the training activity. Furthermore, the more specific the training program is to a given sport or activity, the greater the improvement in performance in that sport or activity.” - J.H. Wilmore, D.L. Costill, W.L. Kenney
Hmm....ok then, so if the body adapts very specifically to the type of training performed wouldn't it then follow that “cross training” is mostly a waste of time? Shouldn't runners just run, cyclists just bike, swimmers just swim, triathletes just swim, bike, run and so on? The short answer: Yes. The long answer: mostly, if they are getting closer to a peak event or if time is limited but not really, if they are in their off-season or early base training period or when recovering from an injury that prevents or limits training in their primary sport.
So, where does cross training fit in your training plan? Or should it? Well, like the answer to many (most) training questions, how it can and should fit is very individual and depends on a lot of factors.
If we look at a typical training progression, early season or “base training” should be fairly general, late season or “pre-competition training” should be more specific. In this context, particularly during the winter months, when training in your primary sport might be limited or require indoor vs. outdoor training, cross training can be a huge asset and great alternative. Any activity that has an aerobic component is fair game when it comes to building your training base, i.e., more volume, more volume, more volume... In the spring and summer when the important races are looming in your headlights, cross training should be considered a bit more carefully and judiciously.
Training in a variety of activities that develop the aerobic system or build strength can allow for a much needed break from the “same old, same old” while still moving you toward your goal. There are so many options when it comes to 'cross training'. Swimming, deep water running, in-line skating, cycling, mountain biking, rock climbing are among the many possibilities. Play with your kids! Soccer, tennis, kick ball, “catch”, etc. etc. Cross country skiing, snowshoeing and even shoveling snow are great ways to be outside – either as a supplement to or in place of running or cycling indoors.
All are good options. As they say, variety is the spice of life. A recent Facebook discussion brought up the question of whether shoveling snow could actually be considered a “workout”. I can say, without question, I have made shoveling snow a strength/core workout and at other times an endurance workout – either way, always worthy of entry in my training log!
Ok, ok, fair enough but, seriously, I'm a serious competitor, what about when it's crunch time and I need to get ready to race and peak for my event(s)? It is absolutely true that the best workouts are the ones that are most specific to the demands of the event for which you are training. If I am training to compete in a 5k run, workouts with efforts at 5k goal pace are the highest priority as I get closer to the race. However, that doesn't mean I won't continue to include a longer run and other runs at slower paces in my routine. It's all about a shift of focus and emphasis. Likewise, while cross training may not be a top priority, it can still have a place in your repertoire. Let's say you are a runner and just happen to have in excess of 10 hours per week to devote to training. Not unreasonable for most of us. Unless you have been building up to it and/or have superior genetics and biomechanics, it is highly unlikely that running that many hours per week, week in, week out is going to be kind to your body. However, the cumulative of effect of maintaining that volume of aerobic training stimulus will only help, especially if it promotes faster recovery from the more specific training that you do. If time is limited and it's already hard enough to get in enough training in your primary sport, then, no, cross training is probably not the best idea.
There are a few things you need to keep in mind when approaching cross training – whether it's during the general phase or specific phase of your training season. Because your fitness level really is very sport-specific, approach ANY new activities with caution. Don't think that just because you are a super fit cyclist that you are ready to go out and run for any prolonged length of time. I've seen more than a few very competitive cyclists wreck themselves for several weeks by going out for “just a 5 mile run”. Limit any “first” workout in any new activity to about 15-25 minutes or less and keep it really easy. While, ultimately, cross training can be a great way to add volume to your training week, initially it is better to substitute rather than add a workout or two with new cross training efforts until some adaptation to the new stimulus has taken place. As you do get closer to your competitive season, it is not necessary to eliminate your cross training efforts but it is important to avoid any cross training sessions that compromise any of your key sport specific workouts.
What about days “off”? Is it better to rest or train easily or cross train when your muscles are too sore for specific training? In most cases, easy activity that promotes blood flow and avoids causing further trauma or breakdown to muscle tissue is better than complete rest and will enhance recovery. That's not to say there isn't a time and place for a complete rest day. If you are sick with a fever or you have an injury or what feels like the beginning of an injury, taking a day or two completely off is likely to help more than it will hurt. Never be afraid to take a day off. When I was training and competing full time, I found I needed a regularly scheduled rest day – at times it was weekly – at others it was every few weeks – it was as much a need for a mental break as it was a physical break. Now, because training time is much more limited, I find almost never take a complete rest day. Easy exercise feels much better than no exercise. Again, it's all about a shift of focus and emphasis.
Jeff Devlin is a coach, father and world class athlete: "I have 24 years of triathlon and endurance sport experience. I competed in my first triathlon in 1986 and my first Hawaii Ironman in 1988. From 1989 through 1997 I competed at a world class level, including 5 top ten finishes and twice placing 3rd in Hawaii. In 1993, while still competing, I started coaching a few athletes and by 1996 realized that was my real passion."