How do you run hills – go hard to reduce the time you are slowed down by the hill, keep your pace the same all the time, or keep it relaxed going up and then surge after? That’s the question that researchers had with this study: What is the best way to tackle the hills?
Before we get into the details, we have to cover some geeky stuff. “Ventilatory Threshold” (VT) is when you start breathing heavily (when exercising! ;)) due to lactic acid accumulation. Lactate Threshold is the point at which lactic acid produced in the muscle is not cleared as fast as it is being produced. This lactic acid is then broken into lactate and acid (hydrogen ions). The lactate is recycled and used as an energy source, while the hydrogen ions are neutralized in the blood, with a by-product being CO2. The CO2 then needs to be expelled through ventilation. This is called Ventilatory Threshold (VT) and is characterized by a sudden heavy ventilation and an increase in CO2 being expelled in the breath.
The researchers took experienced runners (all with a PR of under 40 mins for a 10K) and had them do a 3 loop, undulating 10K course, all the while hooked up to a portable gas analyzer, heart monitor , accelerometer to measure stride length and frequency, and a Global Positioning System (GPS) receiver to provide continuous velocity and location data.
Here’s what they found:
· Runners ran 13.8% faster on the downhill’s and 23% slower on the uphill’s compared to the flat sections
· Stride frequency was remarkably similar across all sections
· Stride length was 20.5% shorter going uphill and 16.2% longer going downhill compared to the flat sections
· Going uphill, runners averaged just over 100% of their VT. In other words, they were limited by their cardiovascular system
· Going downhill, runners averaged just under 80% of their VT, however there was a large range here (between 64.5- 93.7 % of VT). In other words, some were not even close to being limited by their cardiovascular system
· This is a big key point: There was a “lag effect” when transitioning between gradients. For example, following an uphill, speed increased relative to the uphill speed, but there is a lag time before the runners got back to normal speed. In this case, an average of just under 80 seconds before they got up to normal level ground speed. Presumably this is due to runners being forced to recover from the high anaerobic cost of the uphill.
· There was also a lag effect on speed following downhill sections: Speed remained elevated following a downhill on subsequent level sections where this “lag effect” on speed persisted for almost 80 seconds. In other words, following a downhill section, speeds remained increased for a period on the flat section. In part, this may be due to momentum, but also to a gradual return to increased oxygen consumption.
Why all this minutia is important:
· Since it took an average of almost 80 seconds to recover from an uphill run, the researchers calculated that it would be better to take the uphill’s slower to avoid the needed recovery from the hill. In other words, if the time you lose going up the hill slowly is made up by a quicker recovery, your overall time will be faster.
· This was confirmed because the runners in the study who had large variations in pace with respect to the uphill or downhill had the fastest overall times. This is because they slowed going uphill, but took advantage of the flats and the downhill’s.
· Taking advantage of the downhill’s also takes advantage of the lag time when you hit the flat section at the bottom. If your speed is increased for nearly 80 seconds without approaching your VT, that would be an advantage.
· The idea is to not vary your oxygen consumption much. For example – going hard uphill can use up to and over 100% of your VT, while taking it easy downhill can take as little as 64% of your VT. If you keep it consistent, it would mean going slower uphill – say 90% of your VT and then going harder downhill – say 85% of your VT. The researchers stated ” One possible suggestion for minimizing time then on hilly courses may be to balance the time cost of running slightly slower uphill’s, with the potential time saving if runners can return to a faster speed on the level in a shorter time frame. Similarly, runners should take full advantage of running faster on level sections following a downhill but limit increases to keep VO2 just below their ventilatory threshold. This was supported by our findings on the effect of hills on subsequent level sections where a lag effect on speed persisted for almost 80 seconds. This research has suggested that these level sections following hills represent the most likely source of potential improvements for runners wishing to minimize their overall time in distance races on hilly courses.”
OK, here’s the caveat…
Running downhill fast is hard on the knees! When running down a -9% grade at 3 m/s, it has been shown to increase normal and shear forces on the knees by 54% and 73% respectively, when compared to running on flat ground (full study found here). Therefore, it’s possible that some people may need to slow down on the downhill, simply as injury prevention to reduce the shock on the knees. This puts the limiting factor on downhill speed as a biomechanical limitation, rather than a physiological one.
One way to attenuate the risk of injury of downhill running is to….(are you ready for this?….this is great because it dovetails with the last newsletter)…strength training!!