In performing a DWR workout, proper body positioning is important. The depth of the water should be sufficient to cover the entire body: Only the tops of the shoulders, the neck, and the head should be above the surface of the water. The feet should not touch the bottom of the pool. Runners tend to have more lean body mass than swimmers, making them less buoyant; therefore, a flotation device will be necessary. If a flotation device is not worn, body position can become compromised and an undue emphasis is placed on the muscles of the upper body and arms to keep the body afloat.
Once buoyed in the water, assume a body position similar to dryland Running. Specifically, the head is centered, there is a slight lean forward at the waist, and the chest is “proud,” or expanded, with the shoulders pulled back, not rotated forward. Elbows are bent at 90 degrees, and movement of the arms is driven by the shoulders. The wrists are held in a neutral position, and the hands, although not clenched, are more closed than on dry land in order to push through the resistance of the water. The strength gained from performing wrist curls and reverse wrist curls are beneficial for this.
Leg action is more akin to faster-paced Running than general aerobic Running because of the propulsive force needed for overcoming the resistance caused by the density of the water. The knee should be driven upward to an approximate 75-degree angle at the hip. The leg is then driven down to almost full extension (avoiding hyperextension) before being pulled upward directly under the buttocks before the process is repeated with the other leg.
During the gait cycle, the feet change position from no flexion (imagine standing on a flat surface) when the knee is driving upward to approximately 65 degrees of plantarflexion (toes down) at full extension. This foot movement against resistance both facilitates the mechanics of Running form and promotes joint stability and muscle strength as a result of overcoming the resistance caused by drag.
Due to the unnatural training environment (water) and the resistance created when driving the arms and legs, improper form is common when beginning a DWR training program. Specifically, it is common to make a punting-like motion with the forward leg instead of snapping it down. This error is due to fatigue of the hamstrings from the water resistance, resulting in poor mechanics. To correct this error, rest at the onset of the fatigue, and don’t perform another repetition until the time goal is met. Do not try to push through it. You won’t gain fitness, and you will gain poor form.
DWR is effective because it elevates the heart rate, similar to dryland Running. And because of the physics of drag, it requires more muscular involvement, thus strengthening more muscles than dryland Running does without the corresponding overuse injuries associated with such training. Specifically, it eliminates the thousands of impact-producing foot strikes incurred during non-DWR Running.
This is an excerpt from Running Anatomy.