The best cycling posture is very important for cycling performance, comfort and avoidance of sports injuries. Even though good physical fitness, expensive bikes or long-term training, bad cycling postures can’t make them work. The factors that affects the cycling posture comes from the five contact points between the person and the bike: both hands, hips, and both legs, and the cycling posture affects the Cylcing Performance, Aerodynamics and Comfort/Sustainability These elements, balancing these elements is the key of Bike Fitting.
Riding posture and bicycle settings completely depend on your goals: power output, comfort, and aerodynamics.
These three goals are weighed against each other. For example, the posture of indoor track bike rider is very aggressive,
because the competition time is less than 5 minutes, so they pay more attention to power output and aerodynamics,
while comfort is relatively unimportant. For a commuter, the setting may focus more on comfort.
When setting a bicycle, it is usually not considered to set the most perfect posture, because the flexibility of the joints of the rider is different every day, and will deteriorate by time and injury, so adjust the bicycle setting within a range ( this range is called Bike Fit Windows), and each person's Bike Fit Windows will vary according to the individual's flexibility.
The following measurement are the specifications used by British Cycling Association and British professional cycling team Team Sky (the specifications may not apply to everyone)：
Riding a bike will not hurt your knees as long as the size of the frame and the setting is correct, the knees aren’t too outward or inward, and overused. Instead, cycling can protect your knees. Cycling can stimulate the growth of the quadriceps muscles. With a strong quadriceps muscles, it can effectively protect the knee joints.
Phil Burt(2014):Bike Fit: Optimise Your Bike Position for High Performance and Injury Avoidance. Bloomsbury Publishing