Scientists reveal more evidence of how pedalling a low gear at a high cadence could waste a cyclist's energy
Scientists have discovered a new reason why it’s bad to imitate Chris Froome‘s fast pedalling. The ratio between oxygen delivered to muscles in your thighs and the oxygen that they take up simply is too low when you keep a high cadence – if you are in a relatively low gear.
“We’ve discovered an additional mechanism why fast spinning can be so inefficient in a gear that’s too low. Blood flow to the thighs falls so not enough oxygen can get to the biggest muscles in the body, the ones that should be driving you forward,” says Dr Federico Formenti, senior lecturer in human physiology at King’s College, London. “It happens when exercise intensity is moderate, near the so called ‘ventilatory threshold’.”
For riders with experience this is not a problem because they tend to change up through the gears until comfortable with the higher intensity of exercise at their preferred cadence.
But novices and recreational cyclists sometimes stay in a low gear and spin quickly, even though the overall intensity of their exercise is relatively moderate.
New experiments from the UK-Japan research collaboration have revealed one of the factors which makes that kind of pedalling wasteful.
“When the cyclists pedalled close to the ‘ventilatory threshold’ at 90rpm we were able to see the oxygen level in the thigh muscles had fallen, compared with lower cadences at the same exercise intensity,” says Formenti. “Participants’ heart rates increased by 15 per cent, yet their exercise efficiency actually decreased.”
The nine lab rats who pedalled on stationary bicycle ergometers had small near-infrared spectroscopy monitors strapped to their thighs to shine light on the muscles. Sensors detected how much light was absorbed and reflected by haemoglobin so the scientists could calculate how much oxygen was actually being delivered by the blood to the muscles, and how much of that oxygen was being taken up by the muscles.
So why do newbies try spinning in a low gear when it is isn’t worth it? Formenti has a theory. “They might presume that the smoother blood flow at a higher cadence keeps the exercising muscle well oxygenated. They may be right but we now know that it comes at the cost of reduced efficiency,” he says.
This latest finding adds to scientists’ understanding of how cyclists’ bodies behave. Four years ago the same team showed that a high cadence/low intensity combination is not a good cycling technique. “When a rider pedals at a high cadence in a low gear, 60% of their power is used moving their legs up and down, while only 40% goes into turning the cranks,” he says, “It is massively inefficient but we didn’t know all the reasons why.”
Physiologists know that muscle efficiency all comes down to the speed at which your muscles can contract. If you choose a gear and cadence that allows your muscles to contract at one third of their maximum velocity, you’ll maximise your power output.
The pedalling efficiency evidence from Formenti’s team was actually part of more significant research that could improve how sports scientists estimate energy consumption on stationary cycle ergometers. Pro cyclists predict their performance with such tests so if they are made more accurate, they could help them ride faster.
But these tests have to rely on a limited set of measurements from a rider and they’re put into an equation to estimate their oxygen uptake (VO2) because it’s an indication of how well their body is performing.
“It’s not feasible to measure directly how much fuel your body uses in exercise so oxygen uptake (VO2) is a good indicator,” says Formenti. “The conventional equation for doing this is from the American College of Sports Medicine and it includes body mass and external work rate. Perhaps surprisingly for a test done on a bicycle ergometer, the equation ignores pedalling rate.”
Formenti’s team ran its experiments and has shown that, by adding pedalling rate, they can now improve its accuracy of the equation at predicting how well a rider performs when they are working just a little below his or her VO2 maximum.
“We conclude that pedalling rate is an important determinant of human VO2 during cycling exercise and it should be considered when predicting oxygen consumption,” says Dr Formenti.
In some ways it’s yet another case of science explaining what cyclists have learned from experience. “Cyclists and coaches are well aware of the importance of pedalling rate in cycling,” says Professor Louis Passfield of the University of Kent who was British Cycling’s lead scientist in preparation for the Barcelona, Atlanta and Beijing Olympics.
“Both riders and coaches and cyclists spend some time manipulating their cadence in order to maximise their training effects,” says Professor Passfield.
“As scientists we are struggling to explain the underlying mechanisms for how it makes a difference. It’s all the more challenging as pedalling a bike seems a relatively straightforward task when taken at face value,” says Professor Passfield.
A significant mystery still remains to be solved by science, he says. “Cyclists do not, in practice, choose to pedal at the cadences that scientists find to be the most economical in terms of oxygen cost. Instead they choose to pedal notably faster than this,” says Professor Passfield.
So more studies are needed to find out why cyclists prefer slightly higher cadence than current scientific knowledge says is the most energy efficient.
One thing is for sure, though – no pro is going to waste any energy by pedalling quickly in a low gear.