求翻译：由直体仰卧开始，向上抬起双腿，使其与上身成90度直角，稍微弯曲双腿膝盖，然后先是左腿压右腿，再是右腿压左腿，如此交叉进行运动，快速地进行15次左右即可。注意在进行的过程中，放松肌肉以及掌握练习的速度。是什么意思？

Starting from the straight supine body, lift your legs up to 90 degree angle with the upper body, legs, knees slightly bent, left leg first, then press the right leg, right leg and then press the left leg, cross-exercise so quickly can be about 15 times. Note that during the process, relax muscles a

Sidestepping the straight upward, beginning with its legs and upper body, 90 degrees, with a slightly bent at right angles, then double-knee is putting pressure on his left leg, and then his right leg, left leg and right leg was crushed so cross-cutting exercise, conducted 15 around quickly. Note Th

Lies supine the start by the straight body, lifts the both legs upwardly, causes it to have 90 degrees right angles with the upper body, the curving both legs knee, then first is slightly the left leg presses the right leg, then is the right leg presses the left leg, so does alternately the movement

Starting straight back, lift the legs to upper body 90 degrees right angle, slightly bent knees legs, right leg then first left leg pressure, then right thigh left leg, so Cross movement, quickly around 15 times. Note in the process, relax muscles and mastered the practice speeds.

Starting from straight back, lift the legs, so that it is the torso into a 90-degree right angle, knee slightly bent double leg, right leg and then first left leg pressure, then right leg is the left leg, so cross-campaign quickly about 15 times. Note in the process, relax muscles and mastered the p