What do Paula Radcliffe and Chris Froome have in common, in addition to being British? 
Both adopt a special breathing technique, very similar to each other. 

Looking Froome in action on the Mont Ventoux during the TdF 2013, one can't help but notice that the English cyclist rhythmically lowers his head, with a frequency that tends to increase along with the pace of the riding: every 5-7 seconds when the effort is moderate, every 2-4 seconds when he attacks, as he did 5-6 km from the finish line on the French mountain. 

Some observers have attributed these movements of the head to the obsessive need of "robo-athlete" to check watts and heart rate from the SRM mounted on the handlebar. 
I disagree: any lowering of the head by Froome corresponds to a forced expiration, implemented with a special technique. 
Bowing the head facilitates the elevation of the diaphragm, further encouraging the complete emptying of the lungs: the anterior myofascial tension (from the jaw to the symphysis pubis), proper of the position in hyperextension of the head of the rider looking forward, is in fact reduced, thus facilitating the full expiration. 

A complete elevation of the diaphragm reduces the intra-abdominal pressure, effectively promoting the venous and lymphatic return from the lower limbs, whose action, relieved from toxic elements, becomes "lighter". 

The next deep breath, made ​​through the nose and mouth and with the head in hyperextension (looking forward for the cyclist, up slightly for the runner), in addition to oxygenate the air in the lungs, reduces the endothoracic pressure by increasing diastolic filling and cardiac output and therefore the amount of oxygen that gets to the muscles. 

When the effort is moderate forced expiration-inspiration occurs every 3-4 breaths (as suggested by Obree), when the effort is high every 1-2 breaths (as done by Froome during his attack on the Ventoux). 

I tried this technique on myself in the past few weeks: I noticed that lowering the head the full diaphragmatic expiration is easier, and if you ride at high RPM (like Froome... ), each exhalation is accompanied by a 15-20% increase in instantaneous watts (better venous return? Less myofascial tension?). 

I believe that this breathing technique, adequately trained and associated with a strengthening of the respiratory muscles, may bring advantages over an "uncontrolled" breathing , so frequent even among top athletes.