uspta--钟摆式发球是力量储备的基础
The key to a powerful serve is a smooth motion. A hitch in your swing impedes the progression of your arm and makes it more difficult to generate service power. To ensure a fluid motion, envision the pendulum on an antique clock. Notice how the pendulum swings effortlessly back and forth. .......
要发好球，特别是有力量的发球，就要有力量的储备量。从人体生物力学的原理来看，发球的前奏，就要有储备阶段。这储备阶段，就象钟的摆动那样，有节奏的摆动，才会产生力量的储备。这样才使身体有一个很好的协调链，形成良好的线动力，使发球有一个流畅的动作。
