Loosen Up, Then Compose Accordingly
Look at a few of the faces and necks and shoulders in these pictures: gritting, grimacing, flexing. Think about all of the tension each person is holding and how that tension affects the rest of their body and performance.
When such stress and tension are allowed to build, your brain is thinking your body is working harder than it is and may actually need to be. To respond and deal with that perception, the brain further increases its own activity, which tells your body to put out even more, which tells your brain that the body is working even harder, which even further stresses the brain and drains the body. All of this amounts to an excessively damaging feedback loop and a worser-feeling and lesser-performing you.
You may be saying well this is only the start of the race; everything should be smooth at the start and why would it not be? And to that I say, exactly; you should be smooth, especially at the start. If you are excessively wound up at the beginning, when all tanks are full and systems are go, think about how much less efficient you are, how much more quickly your form will fall apart, and how much worse off you will be throughout the race and nearing the finish line.
Yes certain levels of tension and attention are required; laziness or inattentiveness can be just as damaging as their opposites. But if you cannot compose and control yourself, especially when you are at your freshest, your fuel efficiency and handling and horsepower, your performance, will all decline even more dramatically.
Loosen up, then compose accordingly.