Factors to evaluate with respect to body position are:

• Head in a natural position
• Hips at or near the surface
• Natural body roll
• Body does not fishtail side to side

Here are two views of Ian Thorpe, illustrating a relatively high head position but you can see in the side view that his hips remain near the surface and both videos illustrate a strong body roll.

In contrast, look at the head position of the swimmers in the following video. The Total Immersion instructor in particular actually totally submerges his head at some points.

However, note that in this picture of Cullen Jones during an actual race he has a somewhat higher head position.

Michael Phelps on the other hand when swimming at speed actually submerges for a good part of his stroke cycle:

In the end, head position must be evaluated in terms of whether it causes the hips to drop. Any position between the forhead and the back of the head at water position may be acceptable. The head should not be tilted down beyond the neutral position so that it digs under the water, nor so high that the swimmer cannot maintain a "swimming downhill" body position without relying excessively on kicking to lift the legs.

Rotation

Ian Thorpe:

High head position

If lifting the head causes the hips to drop the head position should be adjusted downward.

Dropped hips and/or legs

Whether due to a raised head or otherwise, a swimming uphill position in the water will significantly increase drag and the level of effort required to swim a particular pace.

Lack of roll

Swimming flat has a few disadvantages: the large muscles on the torso can most effectively be utilized when the elbow is out to the side of the torso, but stroking out to the side will push the body laterally in the water causing fishtailing and increased drag, swimming flat also makes it difficult to recover the arms, and it makes it difficult to breath.

Hips and legs fishtail side to side

If the arms are too wide in the pull phase or during the recovery, usually due to lack of body rotation, large lateral forces are generated that will cause the body to move side to side instead of in a straight line forward, and the result is more resistance from the water and wasted energy.

The most effective video angle for evaluating body position is an underwater tracking shot from the side. This will clearly show dropped hips or legs (swimming uphill). Above water video from the side will generally show dropped hips or leg, although not as clearly due to perspective and turbulance on the water surface.

Under water video from the front and side is useful for evaluating body roll.The front view will clearly show degree of rotation of the shoulders, the side view can illustrate the extent of whole-body rotation versus merely rotating the shoulders. The hips should not necessarily rotate to the same degree as the shoulders, but the roll should extend beyond merely lifting the shoulders out of the water for the arm recovery.

Swimming style and body position will vary with the speed and distance. Distance swimmers will generally keep the head in line with the spine while sprinters may use a higher head position. Head position may also vary with individual stroke style. Sprinters may swim with their bodies higher in the water.