When mileage is low and pace is slow: evaluating XT effort.

As we saw in this issue's exploration Of lipid metabolism, when the goal is achieving energy balance, heart rate and overall intensity of exercise are not important; rather the sheer sum of energy expenditure appears to be the key. By contrast, runners who crosstrain--with the hope of substituting a low-impact activity once or more a week but reaping similar fitness gains as running--are wise to focus on sustaining an elevated heart rate to match that caused by running. This assures that the gains from running in cardiovascular fitness and maximal oxygen consumption are not lost.

Running burns more calories than most other forms of physical activity. Some notable exceptions include boxing, competitive racquetball, judo, rock climbing, fast rope jumping, and vigorous rowing. To burn the equivalent of running at 10:00/mile pace (6 mph, a fairly leisurely pace for most runners), you'd have to cycle between 14 and 16 mph, at a vigorous effort. Walking very briskly (15:00/mile or 4 mph) burns half the calories of a 10:00/mile running pace. To burn the equivalent walking, you'd have to walk while carrying a 50- to 74-lb load upstairs.

When crosstraining, then, make an effort to keep your heart rate up in order to get the equivalent workout of a run. This becomes important in particular when you are using crosstraining to maintain fitness while recovering from an injury. Losses in aerobic conditioning can occur rapidly.

One thing you should not do is try to convert the crosstraining activity to equivalent running miles using a time, or even a perceived exertion, formula. This is because the activity is almost always less familiar to you than running, and can feel much more difficult than it really is. Many a runner has looked frustratingly down at the elliptical trainer's calorie expenditure readings (approximate though they are anyway), facing the realization that no matter how difficult or monotonous the movements seem, they do not match running's caloric burn. Indeed, plan to spend more time crosstraining than you do running.

Similarly, ignore pace and mileage reports on these machines--it will only frustrate you further. Suffice it to say, the basic motion of elliptical training is not an efficient way to get around in the real world. Often we feel like we've been working very hard, only to see that we've "traveled" a piddling two miles. It's best to get in an elevated cardio zone (70 to 80 percent MHR) and stay there for a set length of time (an hour or more).

Why, when crosstraining, does there so often seem to be a disconnect between how hard we think we're working, and how many calories we actually are burning, or how far or how fast we are going? The answer is that the mismatch between your highly developed cardiovascular fitness and your lack of experience with an alternative aerobic activity can confound attempts to monitor your true effort by way of your perceived effort. On a stationary bike, have you ever experienced the rapid tiring-out of your quadriceps, even though your breathing remains completely under control? This is a good example of this mechanism at work.

Elliptical trainers, too, are notorious for generating huge amounts of sweat. This is partly due to working out in a warm gym in one place without wind. Elliptical trainers have less of an effort discrepancy with running than cycling does, which helps somewhat. Figure one and a half times your normal running time when using these machines. The problem is that this amount of time in one place staring at the wall can be difficult psychologically, which certainly adds to the perception of effort.

We runners are used to the great outdoors, and all the accompanying sights and sounds that distract and delight us as we rack up the road miles. Still, ignoring distance and pace, you can play games on the elliptical--such as trying to keep your heart rate in an optimal zone--that will keep things interesting or at least keep you sufficiently distracted. Also, adding hills to the workout can give you short-term goals as you train that will help stave off the tedium. Adding inclines can also help you keep your heart rate up to running levels.

And finally, you can also add interval workouts more frequently than once per week while crosstraining on the elliptical or stationary bike, given the decreased loading associated with these activities. See "In Winter, Don't Detrain--Get Indoors" for sample time-based workouts that will translate well into crosstraining. In the end, there is no substitute for running; but low-impact, alternate activities are beneficial in the long term and can in and of themselves provide a relief from training monotony. Just avoid comparing them too closely and exactingly with your first, and may he only, true love.

ACSM, Compendium of Physical Activities, http://personal.unce.edu/jtlightf/classmats/assessment/ainsworth MSSE 32 2000.pdf

Run Strong, 2005, Human Kinetics, Champaign, IL, "Retaining Fitness While Recovering from Injury," by Scott Douglas, pp. 225-237