There are three planes of motion in which the human body moves. If you think about it, we usually use a mixture of movements in different planes. Most of your movements aren’t side to side nor are they straight up and down especially when it comes to sports. So you should never just train in one.
The Sagittal plane bisects the body dividing it into right and left halves. Movements in this plane are flexion (decreasing the relative angle of two segments) and extension (increasing the relative angle of two segments). Some examples of exercises in this plane of motion are biceps curls, squats and running.
The frontal plane bisects the body into front and back. Movements in this plane are lateral movements, called abduction (movements made away from the midline of the body) and adduction (movements toward the midline). Some examples of frontal plane exercises are side lateral raises and side lunges.
This plane bisects the body into top and bottom. Movements in this plane occur around the longitudinal axis. Movements in this plane of motion include internal rotation (rotation of a joint towards the midline of the body) and external rotation (rotation of a joint away from midline of the body). Some examples of movements and exercises in this plane of motion are golfing, swinging a bat and turning lunges.
So when you create your training programs, be sure to add some frontal, sagittal and transverse plane exercises.