Cycling Versus Running

Stu07 said:

Is there a rule of thumb anyone would use to work out the equivalence of cycling to running

cycling = fun
running = not fun

therefore

cycling != running

Q.E.D.

Stu07 said:

Is there a rule of thumb anyone would use to work out the equivalence of cycling to running (i suppose in terms of energy usage)?

McArdle, Katch, and Katch use the rule of thumb that running on firm, level ground has a net energy expenditure of about 1 kcal/kg/km, regardless of speed. For example, a 75kg guy running on firm level ground would expend 750 kcal above basal expenditure to cover 10 km.

For cycling, there are several cycling power calculators on the net. Most of those calculators will include a kcal calculation.

RChung said:

McArdle, Katch, and Katch use the rule of thumb that running on firm, level ground has a net energy expenditure of about 1 kcal/kg/km, regardless of speed. For example, a 75kg guy running on firm level ground would expend 750 kcal above basal expenditure to cover 10 km.

For cycling, there are several cycling power calculators on the net. Most of those calculators will include a kcal calculation.

Someone correct me if I get this wrong:

750kcal = 3,142,500 joules (4.19 j per cal)
At an efficiency of 23%, that would mean only 722,775 j made it to the rear wheel (rest is body heat mostly)
At 250 watts that would take
772,775 j /250 watts = 2891 seconds = little over 48 minutes

So at
150W = 1:26 hrs:min
200W = 1:04
250W = 0:48
300W = 0:43

It sounds simple, but I really do think about 3:1 bike:run mileage is fairly reasonable. This depends on the person and their weight, running form, etc., though. A 275 lb guy will be able to bike 30 miles without a lot of difficulty but will require tons of energy to run 10, since it's so weight bearing.

Stu07 said:

Is there a rule of thumb anyone would use to work out the equivalence of cycling to running (i suppose in terms of energy usage)?

How long a ride would be the equivalent of completing a marathon? (I realise that there would be lots of variable here, like how hilly, how fast etc, but any basic rule of thumb that anyone uses that comes up with a reasonable guesstimate?)

i asked this same question back in 1984 when i started triathlons. by correlating the world record times for running and biking at various distances and venues (track, road) the ratio was dam close to 3:1.

sure the pole hole diggers (PhD) will say this is wrong it's actually 2.76972........but WTF i like things simple.

Alex Simmons said:

Someone correct me if I get this wrong:

It's sightly simpler if you use a gross efficiency of .238 rather than .23-- in that case a kcal converts to a kJ. In that case, one way to think of this is that a 65kg guy running 20k would use 1300 kcal. If he could run that 20k in world record time of 56 minutes he'd be putting out 1300 kJ / 3360 seconds = 387 watts. A 65 kg guy putting out 387 watts averages 6 watts/kg. So bottom line, the 1 kcal/kg/km seems to be ballpark valid: it makes a world-class running effort look pretty much like a world-class cycling effort.

Interesting comparison here; had never seen power figures for runners, but it makes sense that they would be similar to cycling. Just to go one step further, a bike calculator program shows that 387 watts is good for about 26.5 mph. If true, the cyclist would cover 20K in 28 minutes, or half the time of the world-record runner.

dhk2 said:

Interesting comparison here; had never seen power figures for runners, but it makes sense that they would be similar to cycling. Just to go one step further, a bike calculator program shows that 387 watts is good for about 26.5 mph. If true, the cyclist would cover 20K in 28 minutes, or half the time of the world-record runner.

I suppose this is true, the best cyclists are pretty close to twice as fast as the best runners (a bit faster than twice), from world record 5ks (about 13.5 minutes, ~13.8 mph) to marathons (smidge over two hours, ~12.5 mph).

I suppose this is why triathlons generally favor, if one had to pick a discipline, a strong cyclist.

dhk2 said:

Interesting comparison here; had never seen power figures for runners, but it makes sense that they would be similar to cycling.

Based on data grabbed from some random duathlon, with two runs sandwiched around a bike leg:

dhk2 said:

Interesting comparison here; had never seen power figures for runners, but it makes sense that they would be similar to cycling. Just to go one step further, a bike calculator program shows that 387 watts is good for about 26.5 mph. If true, the cyclist would cover 20K in 28 minutes, or half the time of the world-record runner.

confused, if your comparing apples to apples wouldn't a world class biker do 20k in 21-23 minutes and a world class runner do 20k in 59-61 mins??

blkhotrod said:

confused, if your comparing apples to apples wouldn't a world class biker do 20k in 21-23 minutes and a world class runner do 20k in 59-61 mins??

Yes, suppose you're correct on the "world class" or record 20K TT's times being over 30 mph average. I was just taking the 26.5 mph avg speed from a bike calculator program @387 watts: that speed equates to a 28 min 20K. This estimate was based on figures for a standard bike, "racer's tuck" position that I plugged in.

Would expect an elite TT rider on a TT bike with skinsuit and aero helmet would go a 2-3 mph faster on the same wattage. Plus, the top record holders may be able to sustain more than that 387 watts output for 20K.

Suppose saying cyclists go twice as fast as runners is a pretty rough comparison.

RChung, if I'm interpreting the graphs correctly, the "two-to-one" factor seems to hold up for the 55K bike to 3K run. But comparing the bike portion to the 15K run speed, the factor is about 2.5.

dhk2 said:

RChung, if I'm interpreting the graphs correctly, the "two-to-one" factor seems to hold up for the 55K bike to 3K run. But comparing the bike portion to the 15K run speed, the factor is about 2.5.

Yeah, you're interpreting the graph correctly, but I think the graph emphasizes something slightly different. However, before we get into what that is, note that these were the same athletes doing two activities, not two world-class athletes each doing their own activity. That's important because the OP was interested in how to compare his own running and cycling energy expenditures -- I gave the original McArdle, Katch, and Katch rule of thumb and example to show that 1 kcal/kg/km met a face validity test.

The real lesson of the graph is that a simple rule of thumb is just a rule of thumb, and that while fast runners tend to be fast cyclists, there is a great deal of individual variability around the fitted lines. We know that at the speeds cyclists go, power increases with the cube of speed, so the bottom line is that if you're interested in making cross-sport comparisons of energy expenditure, you're probably better off using the 1 kcal/kg/km rule of thumb for running and actually calculating the cycling expenditure from an on-line calculator.