"If your mobility is compromised enough to make you compensate, the sensory input that you have to your reflexive behavior is askew—you have an overload of information or an underload of information. Either way, you’re not receiving the information you need. If sensory information is not converted to perception and perception is not converted to action, you’re not going to get better without embracing the idea of changing mobility."
- Gray Cook, from his presentation entitled Continuums
Without appropriate mobility in the right places in the body, an athlete will be at much higher risk of injury AND won't perform to their true potential.
Restricted mobility in the hips and ankles means that athlete can't attentuate gravity or ground reaction forces. As a result, their calves or legs or low-back must step in and compensate, often resulting in pain, injury, and frustration. There's also the issue of poor economy or efficiency resulting from that restricted freedom of movement. To put it another way, that athlete simply has to work harder (higher heart rate, more effort, and thus more fatigue and less endurance) at any effort level to produce the same relative speed or power.
IF YOU are short on mobility in the right places, you're very likely much closer to injury than you realize, AND you're slower and less efficient than you could be also.
Here's a short 2-minute video that I hope helps you get a bit more freedom of movement from your hips and ankles. Enjoy!