Fastest Instantaneous Downhill Running Speed???
Author | Date | Message |
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John Heraty | Aug 24 2009, 10:28pm | With Bolt having recently broken the 100m Im curious exactly how fast runners can go downhill (I think around 27mph is the instantaneous record for sprint events).Ive done a bit of Googling on this without much success.Id guess AVERAGES wouldnt be that mind blowing -some only suggest 5 or 6 minute downhill miles, no doubt due to having to slam on the anchors on sharp dangerous sections .But I reckon that from my very limited experience of downhill running that some crazy speeds must be reached on 'safe' downhill straights with 'good' surfaces...you guys got any idea what sort of MPH figures we'd be talking about at regular amateur/national/world class standard ?Its got to be in the 30s (of mph) surely ....I remember some of the downhill running races I did when compared with cycling downhill didnt see THAT much slower -ok so we're not gonna see a runner pass a cyclist on a straight 50mph plus descent but on an average to slow downhill the cyclist mightnt be THAT much faster over a short distance...I guess theres got to be some kind of 'physiological/anatomical limit '...I wonder what it is ? |
Rene Borg | Aug 24 2009, 11:42pm | Its an interesting question and not I believe there is much research on yet. On my Garmin I've certainly measured speeds well in excess of 30kph on good downhills (and my leg speed would be very slow compared to race winners we have). 30kph of course don't compare very favourably with the approx 37.5kph that Usain Bolt ran. Only the alactic (creatine phosphate-based) energy systems can generate such speeds and this energy systems shuts off after approx. 10 seconds of exercise (slightly longer if your genetics are right). Arranging a downhill sprint would certainly be interesting. I can see several factors constraining your max speed but the most obvious is leg turn-over. The brain can only recruit so many motor-neurons at a time and if your cadence moves into a zone that requires greater recruitment than your brain is currently conditioned to do (or greater than your genetic potential), you will either slow down or you will fall. Any exercise that increases leg-turnover thus increases max attainable downhill speed. Running downhill reduces the energy required for propulsion by approx. 4% per 1% descent grade. So running down a 5% slope requires 20% less energy. If you ignore all other possible constraints you could speculate that Bolt could thus run 20% faster downhill (45kph). To continue the discussion I would suggest the following factors would constrain the max attainable downhill speed (ignoring terrain): - Maximal leg-turnover (motor-unit recruitment capability of the brain and full available motor units) - Damage from eccentric muscle contractions on the downhill - Running technique (the worse technique the more braking movement, higher ground contact time and greater impact force on the lower legs) - Wind resistance (the higher your speed the greater this impact becomes) - Unknown physiological and physical barriers to max attainable human speed (heat generation, breaking point for ligaments and bones etc.) |