Asymmetric chainrings are not a recent innovation: already in the 90's, cyclists in the professional team Castorama were proposed an alternative to the traditional circular chainrings.
Brochard, Moreau, Thierry Marie and others tested the "Plateau Harmonic" both in laboratory and on-the-road simulated time trials, experiencing unlikely benefits (5"/km).
The chainring was used by some riders of the French team during the racing season, but it was abandoned rather quickly.
In more recent years, asymmetric chainrings as proposed by Rotor and Osymetric have been used by a number of professional cyclists (Julich, Sastre, and others) and Ironman triathletes.
The recent success of Wiggins, Froome and team Sky have been attributed by some, at least in part, to the use of Osymetric chainrings, both in time trials and standard races.
The manufacturers advertise significant benefits, which have not been confirmed by scientific studies published in international journals (Int J Sports Physiol Perform 2010; 5:459-468, Eur J Appl Physiol 2004, 91:100-104.
Intrigued, I tested it on myself for over six months, installing the Osymetric chainrings (France).
I have been cycling for over 30 years, I cover about 14,000 km/year both on the flats and uphill, I have an anaerobic threshold at 4 mM of lactate of about 320w, with 72 kg of weight. I use 170mm cranks.
For the first four months I ALTERNATED sessions using the standard circular chainrings with others using the Osymetric. I made this choice in order to avoid an addiction to the use of a chainrings set rather than the other, which would have obviously affected the test.
The pedalling gesture is definitely perceived as different: in particular, the bottom dead spot "passes away" more quickly, while the pushing phase between 45° and 135° requires a higher peak force. Even the back of the thigh and buttocks muscles work harder than normal, causing a slight soreness in the 24-48h after training, especially in the first few weeks of use.
Over the following two months I made 10 tests (5 with each of the two chainrings sets), measuring my Anaerobic Threshold on a climb, alternating the use of both.
The tests were carried out on a weekly basis, while maintaining the same training pattern for 3 days before each test (Rest - 2h30min with climbs at Medio - 2h flat course Lento).
I used the same climb with an average gradient of 7.5%, repeating 4min efforts between 200w and 350w, with 2min recovery (riding back down).
Lactate was measured by the finger (Lactate Scout, SensLab GmbH), the average heart rate with a heart rate monitor (Polar Electro, Finland), the average Watts of each uphill effort using the same Power Tap wheel hub (CycleOps, USA).
These are the results:
200w = 1.4 mM/l; 130 bpm
225w = 1.8 mM/l; 141 bpm
250w = 2.3 mM/l; 145 bpm
275w = 2.7 mM/l; 151 bpm
300w = 3.6 mM/l; 156 bpm
325w = 4.7 mM/l; 160 bpm
350w = 7.1 mM/l; 165 bpm
200w = 1.3 mM/l; 132 bpm
225w = 1.6 mM/l; 140 bpm
250w = 1.9 mM/l; 147 bpm
275w = 2.3 mM/l; 153 bpm
300w = 3.3 mM/l; 157 bpm
325w = 4.4 mM/l; 161 bpm
350w = 6.9 mM/l; 166 bpm
N.B.: the values of lactate and Heart Rate reported above are the average of 5 measurements, obtained in 5 different tests, performed at intervals of one week.
As you can see, there is NO significant difference in values of lactate and heart rate in the 10 tests performed on myself in the arc of two months.
While Richie Porte has returned to the circular chainrings, as we could see in his recent dominating victory at Paris-Nice, Froome and Wiggins continue to use Osymetric: it is possible that tall athletes may have a slight advantage, supported by using longer cranks.