W/kg and climbing

There is a general and tenacious belief that lightweight people have an advantage while climbing steep hills. José Rujano from Venezuela was nicknamed El Condor and at 1.62 m and only 47 kg was one of the fastest climbers of his time. He managed to win 3 climbing stages in the Giro a Italia. It is easy to think his light weight was an advantage. How wrong can you be when thinking this way. In fact when two riders, one light and one heavier, are climbing side by side the lightweight one actually has to produce more power per bodyweight than the heavier one. It simply means that the lighter one is penalized. How can that be ?

Gravity pulls us down with a force that is proportional to our own mass plus the mass of all other stuff like water bottles, helmet, shoes and last but not least our bicycle. When talking about climbing power or Watts per kg we have to distinguish between intrinsic W/kg and actual W/kg

Riding uphill is like running or walking uphill with a backpack full of pebbles. Unfortunately the weight of the pebbles is the same whether you are small and light or big and heavy.

Suppose Alberto weighs 62 kg and has an intrinsic climbing power of 341 W or 5.5 W/kg
With a bag of pebbles of 7 kg his actual climbing power is reduced to 341 / 69 = 4.94 W/kg

José weighs 47 kg and has an intrinsic climbing power of 259 W or also 5.5 W/kg , exactly identical to Alberto. Intrinsically Alberto and and José are on a par.
With the bag of pebbles of 7 kg Josés actual climbing power is reduced to 259 /54 = 4.80 W/kg

Conclusion; Albero will climb approximately 2.9 % faster than José. If José wants to win he must produce much more intrinsic relative power than Alberto..

Dr. Ferrari introduced the VAM number, or Velocita Asensionale Media that says how much altimeters we can gain in a 1 hour ride. Obviously the person with the highest actual Watt/kg has the highest VAM and will ride fastest.

Here is the real VAM with corrections for bicycle weight, aerodynamic drag and for rolling resistance for 3 riders of different weight. At 5.5 W/kg intrinsic climbing power, the heaviest rider has 5.04 W/kg effective climbing power, the middle one has 4.94 W/kg effectieve climbing power while the lightweight has only 4.80 effective climbing power. As a result their VAM values are 1713 m/h, 1683 m/h and 1638 m/h.

If the rider of 62 kg wants to have the same VAM of 1713 m/h he must produce an intrinsic W/kg of 5.62 W/kg, and the rider of 47 kg must produce an intrinsic W/kg of 5.76 W/kg in order to keep pace with the others.

Conclusion; when the lightweight climbs faster, it is not because he is so light but because he is capable of producing more aerobic W/kg during longer time. Strictly speaking he is not stronger but has a higher aerobic fitness.
Still it is hard to believe that the lightweight climber is in disadvantage because everyday experience seems to indicate the contrary. How many top climbers are 70 kg or more ?

Let us suppose we could construct the ideal bionic climber out of standard concepts and elements. How would we do this ?

1. Consider that on a long climbs almost all necessary energy is delivered by our aerobic metabolisme. On a 40 min climb or longer the anaerobic metabolism will contribute less than 3 % to the total effort. Our bionic man would receive a very well developped aerobic metabolism and a high amount of Type1 muscle fibers

2. Because type 2 anaerobic muscle fibers contribute so little, we might as well reduce them as much as possible to the advantage of Type 1 aerobic fibres. For the real climber Type 2 fibers are nothing less than ballast, just as an extra water bottle or as excess food in your pocket.

3. Because our bionic climber has less then average Type 2 muscle fibers, and a normal amount of fat, his BMI would be less than average.

Unfortunately we did not find any scientific study about the relation between climlbing ability and BMI. Therefore we look at a number of results on the Angliru and the Zoncolan. Data were registered for all top-10 arrivals in a total of 6 events.

These are the top-10 arrivals at 6 climbs on the Angliru and Zoncolan. This graph supports the hypothesis that there is a trend for increasing BMI with increasing weight. We may even distighuish 2 groups. The group with wight between 59 and 62 kg has an average BMI of 20.6 and a second somewhat heavier group with weight between 68 and 71 kg has an average BMI of 21.5