Swimmers lack a fixed point in the water from which to push. In moving the body forward, the swimmer also moves water backwards. The water acquires a
kinetic energy change. Thus, propulsion in swimming involves two forms of power output: 1) to move the body forward by overcoming drag, and 2) that
imparted to the "compression" of the water that is moved backwards. If gravitational and hydrostatic forces are ignored (the velocities occurring in the vertical
direction are rather small), two forces remain: the propulsive force acting on the hands and feet and the drag force acting on the body.

This study used the MAD system developed in Holland to measure forces associated with horizontal movement. Special facial valves were developed to
minimize increased drag so that gas analyses could be measured.

The gross efficiencies ranged from 5.1% to 9.5%, measures that are slightly below those obtained for arm cranking and wheelchair riding. The reduction is
probably due to the extra energy required to overcome the hydrostatic pressure on the thoracic cavity and to compensate for heat loss of the body to the
water. The amount of power consumed to push the water ranged from 30-50%.

Implication. Efficiency increases as the speed of swimming increases. Therefore, when considering efficiency it must be relevant to a particular speed. There is
no difference between males and females in movement efficiency at the same speed of swimming.

When looking at other studies concerning efficiency, it is necessary to determine if those studies have or have not accounted for the movement of water
backward in their assessments.

The relationships between swimmers' biomechanical arm pulling pattern and technical ability were assessed in four "skilled" and five "less-skilled" athletes (the
grouping being determined by a statistical method using all measures). The freestyle stroke was divided into five phases: entry (plus flight), downsweep,
insweep, outsweep, and upsweep (round-out). VO2max, height, arm span, hydrostatic lift (maximum weight to maintain a balanced position under water),
speed on a standardized 400 yd swim, and competition 500 yd time were measured.

VO2max explained 64% of a 400 yd swim performed at 94% of 500 yd pace. Hydrostatic lift was the next most important structural variable. There was no
significant difference between the two performance groups on any anthropometric, performance, or physiological variable.

Biomechanical variables did differentiate the groups although there was great variation between individuals (e.g., as much as four times for entry duration and
more than twice the time taken on the other stroke sections):

stroke rate was higher in the skilled group;
stroke rate was negatively related to stroke length;
stroke length was shorter in the skilled group;
both entry and stroke pattern were related to hydrostatic lift;
downsweep phase was inversely related to upsweep; and
longer outsweep and superposition of arm actions favored better swimming efficiency.

Swimming mechanics were the primary factors differentiating the two groups. Even though the size of the groups was small, these variables were strong enough
to overcome that deficiency.

Implications

1.Having a good aerobic capacity is the basic requirement for fast long-distance swimming performances.
2.The stroke pattern should emphasize the last part of the underwater stroke rather than the entry.
3.Gliding and excessive stretching under water after the entry should be minimized so that deceleration between individual arm cycles does not occur.
4.Swimming improvements are likely to be greater and more easily achieved through technique developments rather than through physiological and
anthropometric factors.


Frontal areas, cross-sectional areas, and lengths of body segments were measured on 12 members of the University of Iowa men's swimming team during the
Big Ten Championships over two years. Data were gathered through photographic procedures. Stroke length, stroke frequency, and swimming speed were
determined from five films of competitive events for each subject. Anthropometric variables were correlated with the three performance variables.

Six variables, five of them determined genetically, were significantly related to one or more performance variables.

1.Stroke length was correlated positively with axilla cross-sectional area (.74), arm length (.68), hand cross-sectional area (.57), leg frontal area (.61), and
foot cross-sectional area (.68).
2.Stroke frequency was correlated negatively with axilla cross-sectional area XSA (-.73), arm length (-.59), leg length (-.64).
3.Swimming speed was not correlated with any of the variables.

Anthropometric variables accounted for 89% of stroke length, 41% of stroke frequency, and 17% of speed variances. The axilla cross-sectional area was
shown to have the