Sunday, 13 September 2015
Tuesday, 8 November 2011
Cyclists need to understand aerodynamic drag in order to beat it. Cycling coach Joe Beer gives the low-down on cycling aerodynamics and presents some of his own recently collected data…
Although cyclists have to overcome the forces of gravity and the rolling resistance of tyres on roads/moving components on the bike, once your speed exceeds around 15mph, it's aerodynamic drag that becomes your main enemy. Drag is a frictional force caused by the turbulence of displacing air that is pushed out of the way as you pass through it. Pedalling along at 20mph requires the displacement of no less than 1000lbs of air per minute1!
Aerodynamic drag increases as the square of velocity; if you double your speed, you will expend 4 times the energy to overcome drag. Expressed another way, for every increment of extra power you apply at the pedals, your increase in speed becomes progressively smaller. Eg, it requires 7.2 watts of power per mph to sustain 19mph on the flat; to sustain 30mph requires no less than 13.1 watts per mph!
Because energy-sapping aerodynamic drag is always present when cycling, learning how to minimise drag is vital for riding fast. Studies show that around one third of drag is caused by the bike, and two thirds by the rider, so reducing rider drag is the number one priority2. And the best way to achieve this is to hone the riding position so that maximum power can be achieved with minimum drag.
Aerodynamics and riding position
The optimum riding position will depend on the type of bike being ridden, but below are listed some of the best ways to reduce drag:
• Try and keep the torso as flat as possible, ensuring the knees don't hit the stomach or rib cage at the top of the pedal movement;
• Use aerobars to keep the forearms around 15-20cms apart and kept roughly horizontal;
• Ensure the knees stay close to the bike frame and don't splay outwards;
• Tuck down on drop handlebars and adopt a 3 & 6 o'clock position with the feet on the pedals during long descents.
However, while the most aerodynamic position is rarely going to be the most comfortable, you should ensure that you're still comfy enough to produce near maximum power, because it's power that you need to overcome drag!
It's not just riding position that affects drag, but the tactics you use when you ride. Studies have demonstrated that if you can tuck in behind another rider and stay around 30cms from the back wheel, drag is reduced by around a fifth at 20mph3. The faster your riding speed, the greater the potential energy savings to be made. This explains why stage race riders only appear at the front of the pack at the end of stage; they shield themselves using other riders until their sprinting or climbing legs are needed.
Once you've addressed your riding position and tactics, you can think about equipment:
• Bars - aerobars allow a narrower arm position and promote a horizontal torso, thereby reducing drag. Studies have shown that although aerobars slightly reduce pedalling efficiency (by around 9 watts), in elite cyclists, they can reduce wasted energy due to drag by up to 100 watts4. Even swapping standard handlebars for basic 'cow-horn' shaped bars (popular in the 90s) can reduce the amount of energy required to maintain a speed of 25mph by 7%;
• Helmets – can also make significant contributions to drag reduction. We recently conducted tests with industry experts and discovered that an aerodynamic helmet produced significant reductions in drag compared to a normal vented helmet. Our data revealed that at a power of 300 watts, a rider using an aero-helmet could travel over a mile further during an hour's pedalling or, expressed another way, could chop around 2 minutes off a 25-mile time trial!
• Bike frames and wheels – over a 40km time trial, an aerodynamically designed frame can knock off upwards of a minute, and over 2 minutes for an elite cyclist5! Wheels can also contribute time savings; a box-rim with 20-30 spokes will cost an extra half minute or so over 40km compared to an aero 'deep-dish' or composite wheel5. As a rule of thumb, the lower the spoke count, the better; solid disk wheels with no spokes give the largest time savings;
• Clothing – can make a big difference to the amount of drag experienced. The lowest drag clothing is both tight fitting and has a low 'surface drag' as the air flows over it. For time trialling, a tight fitting one-piece suit without pockets (or other features that could flap around in the wind) is hard to beat. Road riders should at least ensure they wear a snug fitting top. Exotic purpose-designed suits (eg Nike's Swift Spin suits) may offer the best performance of all, but they are expensive and rarely find their way onto the general market.
Minimising drag requires a combination of correct rider position, riding tactics and equipment. The first two strategies are cheap – a simple drop in stem height or addition of aerobars can knock minutes off a 25-mile time trial. Going 'aero' with your bike and its components on the other hand could cost hundreds or even thousands of dollars! However, never loose sight of the fact that while reducing drag is a worthwhile goal, it shouldn't be at the expense of building a strong cycling engine. Remember, it's power you need to overcome drag!
Wednesday, 12 October 2011
Sprinting – why short to long could be better than long to short!
Most sprint athletes tend to use a 'long to short' training approach, where they perform slower aerobic and anaerobic work at the beginning of the training year and then progress to faster and faster anaerobic work as the season approaches and during the season itself. However, it doesn't have to be this way; some coaches believe that that this methodology is not only outdated but also that by turning convention on its head and using a 'short to long approach', better results can be achieved.
The short to long approach emphasises speed through the year with athletes performing sprint training right from the beginning of the season. Proponents of this approach (such as Charlie Francis, the coach of ex-100m world record holder Ben Johnson) claim it can enhance speed development, allow for more 'speed peaks' through the season and reduce injuries that often occur when sprinters try to pick up the pace from their early season slow pace training.
Because aerobic conditioning serves as a 'base conditioning' for health and fitness, it has formed the core of training programs for a number of different sports, including those where sprinting is the main type of activity. However, take a look at the actual volume of aerobic work performed by sprint athletes and sportsmen and you'll see it's very low indeed. Not only may time be spent training an energy system that will hardly be used, the slower pace of training can also serve to blunt the speed and power output in the fast twitch muscles that are required for sprinting.
Short to long proponents like Charlie Francis recommend that experienced runners from 100-400m need only spend a short 6-week period at the start of the season performing training with an aerobic element, and even then, it shouldn't be long, slow runs but instead based on sets of short distance tempo runs of 100-300m performed at around 75% maximum speed.
Intensity is the key for maximum sprint performance
The short to long approach emphasises intensity throughout the year; a steady increase in training volume is not required or recommended – indeed volume may even decrease. This allows an athlete to remain close to his or her peak sprinting condition through the season, which in turn means that multiple peaks are possible through the season. The role of the coach is to try and successfully combine all the elements of perfect sprint performance (acceleration, absolute speed and speed endurance) seamlessly into these peaks, while simultaneously monitoring athletes to ensure adequate recovery is occurring and injury risk is minimised.
The maintenance of power throughout the season is also important. Charlie Francis for example advocates that workouts to develop power such as maximum strength workouts in the gym should accompany all phases of the training. The exception to this however is during the maximum sprint-speed training phase, where the addition of maximum weight workouts could overload the athlete and produce burnout. He prefers instead to combine plyometrics and fast sprinting to produce maximal power.
Blending sprinting speeds
The short to long approach advocates using a blend of sprint speeds to achieve and maintain maximum sprint condition throughout the year. The sprint speeds recommended are between 75% and 105% of maximum sprint speed (NB – 105% sprint speed refers to assisted 'overspeed' training techniques such as downhill running or bungee chords). Examples of these are shown in the table below:
100-300m distances on the track run at 75-85% of maximum speed
6 x 200m at 75% effort concentrating on form with 5 minutes recovery between each run
Intense sprints over 60-120m designed to improve the ability to maintain flat out speed.
2 x 120m 100% sprints - full recovery
95% effort speed
Run at just below flat out speed designed to develop flawless technique without over-stressing the athlete
3 x 120m each with 7mins recovery in between
Out and out speed
Very intense runs performed at 100% effort
Sets of 4 x 40m sprints using blocks with a full recovery between runs
Performed at 105% of top speed using overspeed methods
4 x 30 m downhill runs, each with full recovery in between
Training for speed-endurance
Reaching top speed is one thing. Being able to maintain top speed is another. Developing speed endurance enables an athlete to carry his or her speed for longer without fading and is therefore crucial – eg for a 200m athlete to maintain top speed down the home straight. The amount of speed-endurance training required will depend on the nature of the sport and the role in that sport. For example, a football midfielder needs more speed endurance than a goalkeeper who may have to occasionally sprint, but only for very short distances.
A typical speed endurance workout for example might involve something like 5 sets of [sprint 20m, jog 20m, sprint 20m, walk 20m]. In the context of the short to long approach to sprinting however, the important thing to note is that speed-endurance training can and does blend seamlessly with the type of training an athlete will be performing anyway. For a full discussion and for detailed examples of speed-endurance workouts, readers are directed to George Dintiman's 'Sports Speed' (Dintimen G - Sports Speed, 3rd edition, Human Kinetics 2002), which provides an excellent treatment of this topic.
The key to the short to long approach is that it continually emphasises the need to move at maximum speed and to this end it strips out any training approaches that could be detrimental to achieving this goal. It is also very carefully constructed to allow the athlete to optimally adapt and recover.