Professor Mike Holmes, Head of Graduate Research School, and Alison Naylor, went to meet with Dr Howard Hurst to talk about his research and work in downhill mountain biking.
I’m researching the physiological and biomechanical characteristics of downhill mountain biking. I started looking into this several years ago for my Masters Degree. People often questioned me on how hard downhilling could be? – you start at the top of a hill and roll down to the bottom, gravity does the work for you! However, as an athlete myself, I knew just how physically hard it was, but trying to quantify that was quite difficult. Originally I started looking at heart-rate monitoring, but soon realised that it didn’t reflect the very high intensity, intermittent nature of the sport, which led to me investigating the effectiveness of different power meter systems for monitoring performance in downhill as an alternative.
As a result of that research I did some work with British Cycling to help them to develop their Level 3 Coaching Manuals for mountain biking. More recently I was approached by the Swedish Cycling Federation, who wanted to collaborate on some work with their National Downhill Team.
When I originally looked at heart rates in downhilling they were very high, upwards of 90% of maximum values but very consistent and one of the proposed reasons for this was because of isometric contraction of upper body muscles. Therefore the aim of this research was to quantity upper body contribution during downhill though analysis of muscle EMG activity. Then the Swedish Olympic Committee heard about our research through the National Cycling Organisation and they agreed that if we opened it up to the cross-country / Olympic team then they would give us further funding for the work. So what started out as a relatively small scale study on two or three riders turned into something significantly bigger with sixteen riders and the Olympic Cross-Country Team. Subsequently, the aims changed slightly to look at differences between Cross-Country and Downhill riders during downhill riding to help determine how much time should be spent on conditioning the upper body muscles.
It would seem to me that there is a lot of control issues here: not so much the physical effort of pedalling, but actually controlling the bike and getting it in the right place.
Yes, physiologically there is little difference between riders at the top level, but skill plays a significant role in performance. That’s why we’re trying to identify what makes the difference and what influences those skills, such as upper body activity. We looked at EMG in the biceps, triceps and the back muscles and found no difference between the cross-country and downhill riders, which was quite surprising given the much more severe nature of the downhill courses. We got them to do runs on two courses, a ‘technical’ course and a ‘non-technical’ course, and we tried to design the courses in a way that they would reflect the condition each group would encounter at a world-cup event. However, there were no differences irrespective of technicality. We expected there to be a much greater percentage of maximum voluntary muscle contraction in the downhillers than in the cross-country riders due to the much larger drops and jumps encountered on their courses, but that wasn’t the case. So what we now need to do is try and evaluate why there were no differences and I suspect it is possibly due to the setup of the bikes and the differences in speed. Cross-country bikes have 80-100 millimetres of suspension travel at the front and rear, whereas downhill bikes have 200-220 millimetres. In addition there was almost 10 km.h difference in mean velocity between groups. The combination of the two may have influenced the forces exerted on the riders. Currently we are in the process of analysing GPS and accelerometer data that may help further explain the EMG findings.
They are very different in nature. A typical downhill race would last about three to five minutes at world-cup level, whereas cross-country races typically last up to three hours. Twenty years ago, when the sport was in its infancy, you would get a lot of riders who would race cross-country on the Saturday and downhill on the Sunday. I do not know of any professional rider who races both disciplines now though, as the training requirements are so different.
Downhill riders tend to be taller in stature and have greater muscle mass: around 180-190cm tall and 75-85 kg. The longer limbs help to provide a mechanical advantage to lever the bike over rocks and obstacles, whilst the greater muscle mass also helps with manoeuvring the heavy downhill bikes, which typically weigh around 35-40lbs. However, as approximately 60% of a cross-country race is climbing, there is a greater emphasis on power-to-weight ratio. Therefore cross-country riders tend to be much smaller: on average they are 165-170cm tall and 60-65 kg, so they are much slighter in build whilst cross-country bikes are also considerably lighter at around 20lbs.
As the pedal/shoe interface is one of the primary contact points with the bike, while over in Sweden we also looked at foot forces using some inserts that were originally designed for skiing to measure the foot pressure in ski boots. However, we have one rider over there, who is the current Swedish National Downhill Champion, and he is already looking ahead to the World Championships next year, which is being held in South Africa. The course has a long very flat section in the middle which requires a lot of pedalling, unlike most other world-cup courses, where the emphasis is more on skill than fitness. He realises that if wants to do well he may to have to switch to clipless road-riding type pedals from his preferred BMX type pedals to allow him to be able to actively pull up with greater force and efficiency on the pedals. What we want to do is work with him to find out whether there is a performance advantage using a particular pedal/shoe setup during these type of sections and also whether there is a trade-off to performance in other more technical sections to allow him to make his final decision. Additionally, we plan to do a follow up study looking at hand grip and braking forces by instrumenting the handlebars and brake levers with strain gauges. This will hopefully help us to devise more effective training programmes.
Generally changes are made to bike setup for each rider depending on course and riding style, though our data on foot pressure in particular could be of interest to manufacturers of mountain bike cycling shoes. Ideally I would like to get data from all world-cup courses so that the data could be used to help riders in there setup and for training for different courses. Following publication of the current data I plan to approach the world governing body for Cycling, the Union Cycliste Internationale, and try and get further funding from them for a bigger research project. We have links with the riders and the coaches, we just need to funding to take things forward.
Yes. Certainly at an elite level and particularly in downhill, they accept that as they leave the start gate they are putting themselves at risk of serious injury. However when races are won and lost by hundredths of a second, they need to take risks. These guys are travelling at over 40 miles an hour, down very steep and often loose terrain, and there have been a number of high profile cases of paralysis over the last couple of years. So it is very much a psychological game as much as a physiological game and from just chatting some of the riders at races, how they deal with that is quite diverse. Some of them are really chilled out and they don’t really think about it, while others get nervous to the point of almost being sick. I know from my own experience I used to get very nervous in the start hut but within two seconds of starting all that would go and I would focus on what I needed to do.
I think you can. Road-riding has been researched extensively over the last 30 years and currently there is a huge emphasis on power output analysis, elite rider train and race by numbers, to the point the fun element disappears. Though power analysis does help with efficiency, how you get from point A to point B doesn’t really matter as long as you finish in from of the other riders. The difference with downhill and cross-country is that, even though it has been around for about 25 years, they are still new sports in terms of research and we are still trying to find what the main performance determinates are.
As much as I have enjoyed working with them [Swedish Team] and I hope to do more work in the future, I wish them luck but I have got to back the Brits!