QUESTION

As a casual skater I normally cover 9.5 to 10 miles in approximately 45 to 50 min. My question, how many calories am I burning and is it enough to reach my goal of losing 10 lb and 4" off my waist?

- Andrew Whittaker

ANSWER

Andrew -

Based on the limited amount of information you've provided I can't really answer specifically, but I can offer general information about calories burned while skating and make suggestions that might help. In order to determine the number of calories burned while skating, we need to have a few pieces of information (not necessarily in order of importance):

• Body weight
• Speed
• Skate Type
• Surface
• Duration of Skating Session

Body Weight

Without knowing body weight, there is no reliable way to estimate the calories burned while skating. A heavier skater is moving more weight while skating, and will burn more calories every mile than a lighter one. However, calory burned isn't linear; (a 200 lb. skater doesn't burn twice the calories that a 100 lb. skater burns per mile), but there is a difference.

Let's use an arbitrary number - 160 lbs. If we use that as our basis, we can make some reasonable estimates.

Skating Speed

Obviously, skating faster burns more calories than skating slower. As you reach higher speeds (16+ mph), the increase in calories used rises quite rapidly. This is due to additional work required to overcome wind resistance at higher speeds.
The fact that you skate between 9.5-10 miles in 45-50 minutes equals traveling approximately 11.5-13.5 miles per hour, putting you into the "non-aerodynamically-challenged" category.

Equipment (Skate Type)

Recreational skates (shorter frames, 3 or 4 wheels) require more effort at a given speed than fitness or racing skates (longer frames, 4 or 5 wheels). Most rec skates have plastic boots and frames, while most fitness/racing skates have leather and/ or composite boots and metal/composite frames.

Based on pilot research studies my colleagues and I did in '94 and '95, frame length has a significant effect on calorie cost of skating, longer frames requiring less energy for a given speed. Therefore, if you're skating on rec skates, you're actually burning more calories per mile than by using fitness/racing skates (at the same speed), making you less efficient. This could work in your favor, especially if you're trying to lose weight. For racing, you'd want to be more efficient, so you'd select longer frames.

The difference in calories burned with rec vs. fitness/racing skates appears to be dramatic with rec skates burning as much as 20 - 40% more in terms of calories for a given speed.

Skating Surface

The major components of skating surface are:

• slope; and
• surface type

Slope

The slope is the average gradient on which you skate. Is it a level surface or hilly? Hill climbing takes quite a bit more energy than skating level ground. The increase in calories burned is related to the slope of the hill as well as the time spend skating a hill.

Surface Type

Surface type refers to 'smooth pavement,' 'rough asphalt,' and 'indoor wood floor.' Pavement comes in varying degrees of 'smoothness,' but once you skate a surface, it is obvious whether or not it slows you down quickly when you're gliding. If it slows you down quickly, you will be burning more calories as you skate on it (relative to a smoother surface).

Duration

This one is simple: the longer you skate at a given speed, the more calories you'll burn.

Putting it all together

Now let's take a look at your situation, plugging in some sample numbers and factors, and see if we can come up with some answers for you.

We'll use the following information:

• Body Weight: 160 lbs.
• Speed: 11.5 - 13.5 m.p.h.
• Type of skates: Recreational
• Surface: Mostly flat, smooth pavement
• Duration: 45-50 minutes

Based on this and results from three research studies done on inline skating, your caloric expenditure is between 12.5 and 14 calories per minute. Multiplied by the duration per session, your total caloric expenditure per session is probably around 630 calories.

This alone should get you started on your way to achieving your stated goals. Let's look at those goals with respect to your current activity pattern.

You would like to lose 10 lbs. and 4" off of your waist. Losing 10 lbs. will be easier to target than losing 4", since there is no such thing as 'spot reduction' (other than surgery).

To lose 10 lbs. of fat, you need to reach a deficit of 36,000 calories. You can: intake less calories (eat less), expend more calories (exercise more), or both.

At 630 calories per session, you need to skate 57 sessions (at 5 per week, that's 12 weeks) to expend 36,000 calories. Increasing sessions to 90 minutes, you can expend that number of calories in only 6 weeks. If you do, make sure you're ready for it before you start. You don't want to end up with muscle strains or cramps, or feel exhausted all of the time.

Or reduce caloric intake by 300 calories a day (roughly 2 cans of regular soda) and increase workout time to 60 minutes per day 5 days per week. Together this totals 1,050 calories per day and will take only 48 exercising days to reach your goal (10 weeks). If you cut out the 300 calories 7 days of a week, you'll cut your time to to 43 exercising days (less than 9 weeks).

For the '4" off the waist'... unfortunately, there are no secrets to losing weight off of certain body parts -- where you gain fat last is typically where you lose it first. I suggest that unless there is a medical reason to not do abdominal exercises, incorporate them into your daily routine. Even if you don't lose 4" from your waist, your waistline will look better if your abdominal muscles are firm.

Follow-up:

After sending the above information, Andrew send us another e-mail with the following details:

• Body weight: approx 200 lb.
• Speed: 10 to 15 m.p.h.
• Type of skates: Fitness - 4 wheels
• Surface: Rolling terrain incorporating several hills and usually strong head winds at 15-25 mph.
• Duration: 45 to 55 min.

Here are the updated results:

There's good news and bad news. The good news is that Andrew is increasing his efficiency by using fitness skates. The bad news is that this efficiency advantage versus the assumed use of rec skates in our initial example is lost in terms of calories burned per minute, due to his body weight and skating surface (plus skating against a headwind) increase the energy cost of skating. Based on the new info, Andrew's energy expenditure is closer to 14-19 calories/minute. Not bad news for Andrew, since he is trying to lose weight.

Since he skates for 45-55 minutes per session, a few recalculations provide us with the following numbers for Andrew:

If he skates 5 days per week without changing his calorie intake, it should take 7 to 11 weeks to lose 10 lbs., depending on his speed, wind conditions, etc. Skating at a faster speed into a headwind will burn more calories and take less time. Skating at a slower speed with less wind will result in the loss taking 11 weeks.

If Andrew decreases his calorie intake by 300 calories per day as in the first example, it will reduce the time to reach his goal to a very manageable 5 to 7 weeks.

Looking at the numbers in the example above versus the initial hypothetical example, you can see that the time taken to lose 10 lbs. is similar. This may seem unfair - he's skating faster, into headwinds, and won't lose weight any quicker than someone who skates slower? Actually, the comparison demonstrates the significant affect that body weight and equipment can have on energy expenditure. A 160 lb. person will burn fewer calories per minute than a 200 lb. person but only if they're skating at a given speed, using the same equipment on the same course. However, we had a number of inequalities from example to example. Andrew's weight, speed, equipment and surface (and presence of a new variable, a headwind) were different from our initial example didn't clearly show how significant the effects of some of these factors could be on the results.

The table to the right highlights the factors listed above and their effect on energy expenditure. An 'up arrow' indicates that a given option for a factor requires more energy per minute versus the other option (with all other factors being equal). For example, a higher body weight will burn more calories per minute than a lower body weight, using the same skate type, at the same speed, on the same surface, with the same wind conditions. Similarly, using fitness skates burns fewer calories per minute than using rec skates, all other factors being equal.

Looking at the table, if Andrew used rec skates instead of fitness skates, he could burn more calories. The increase would be 2-3 calories per minute more. This increase in energy cost alone would decrease the time it would take to reach his goal from 7-11 weeks (with no calorie intake reduction) to 6-10 weeks. If he included calorie reduction, it would take only 4-1/2 to 6 weeks.

There are other factors that can affect energy expenditure while skating, such as body position, drafting, stroke rate, stride length, wheel diameter and wheel durometer, but this table provides at least a basis for understanding the more common, easy-to-measure components and their effect on energy cost.

QUESTION

Where can I buy an inline skate speedometer/computer (the type that does not require a special wheel)?

- Cindy Darrow

ANSWER

There are a few skate speedometers available, but one that doesn't require a special wheel narrows your options. Your best bet maybe a Sigma Sport Inline Skate 800. This computer is small, uses a magnet that mounts in your skate wheel, and is mounted on top of your skate (using the laces). It provides current, average and maximum speed, along with distance, time, etc. It's also reasonably priced. While some skate computers cost $90, this one retails at around $35 and you can probably pick it up for less online. One shop that carries it is Branford Bike (www.branfordbike.com), and you can order it online.

Table and Text © 2001, Frank J. Fedel, C.E.S.