What can be seen from the force measurements?
Below graphs shows underwater part of stroke. Time begins when hand submerger and ends when hans raises from the water.
- Green: propulsive force
- Red: vertical force
- Yellow. Lateral force
Y-axis shows numerical value (Newtons) of each direction of the force at specific time.
The ability to produce high maximum force is important especially in sprint distances.
It is equally important that the duration of the force is long, in order to get a large impulse to the hand stroke.
Force x Time = Impulse
In the example below, swimmer A produces a higher maximum force. However, swimmer B generates a higher impulse and is swimming faster, because the duration of the force is longer.
Swimmer A: Force 42N, Impulse 18.6Ns, Time 1:32 / 100m
Swimmer B. Force 35N, Impulse 24.5Ns, Time 1:11 / 100m
Any break in the generation of the force reduces its effectiveness substantially and prevents the swimmer to reach the top speed.
In the example below, the drops in the force mean that the impulse of the stroke decreases by 25-30%. At the same time, the stroke is relatively tiring as the maximum force applied is high.
The drops in the force may be related to non-optimal orientation of the hand. If the palm is not facing the movement of the hand, it does not generate force efficiently.
The force is also reduced, if there is a break in the muscle chain used for the stroke.
Force dropping during stroke:
In addition to the magnitude of the force, SmartPaddle displays also its direction. Ideally, the magnitude and length of the force in forward direction should be maximized, while keeping force in other directions minimal.
In the example below forward, lateral and vertical directions are presented in green, yellow and red colours respectively. The swimmer applies relatively high force in vertical direction (red) especially in the beginning of the stroke. Such stroke typically leads to a non-optimal body posture.
Stroke references found in the Analysis Centre show, how top level swimmers apply the force in different directions. The references may help in improving the efficiency of the hand strokes.
In all swimmers the hand creates some drag, especially when it enters the water. If the velocity of the hand is slow or its direction changes, it can start to resist the swimmers movement even during the stroke.
In the picture below the resistance of the hand is visualized as negative values of the force. In this example the resistance is even greater than the impulse of the stroke. The drag force is especially high, when the hand enters the water. The force graph shows also significant negative values at the end of the stroke, when the swimmer is pulling the hand upwards.
Minimizing the drag force may in some cases be even more important than increasing the impulse of the hand stroke.
If the strength of the strokes is not evenly balanced between the right and the left hand, it can easily lead to fluctuation in the body speed. Any such deviation from a constant speed increases power consumption. With the SmartPaddle the balance of the hands can easily be checked.
In the example below the force profile of the left hand is presented with dotted lines on top of the right hand profile. It can be seen that both the maximum force and the impulse of the right hand is substantially larger. In addition, the right hand starts to produce force earlier in the stroke than the left hand.
Typically, the impulse of the hand strokes decreases with increasing speed. It becomes progressively harder to maintain the force of the hand stroke when the body is moving faster to the opposing direction. The decreasing impulse is often the factor limiting the maximum speed of the swimmer.
Also the balance between the hands may change as the swimming speed increases. The example below shows the impulse measured from the right (green) and the left (orange) hand in different swimming speeds. It is evident that in this case the difference in the impulses increases when the swimmer is speeding up.
In addition to the balance between the right and the left hand, SmartPaddle application offers a view to the development of the swimmer over time as well as an easy comparison between different swimmers.
The strength of the hand strokes may vary greatly from one stroke to another, especially if the swimmer has difficulties in maintaining the body posture. For example the breathing rhythm can often be seen from the variation in the stroke impulses.
An example of a significant stroke to stroke variation can be seen in the figure below. The difference between individual strokes causes fluctuation in the swimming speed as well. The mean velocity of the swimmer decreases since part of the power is consumed by acceleration.
Swimmers can rarely maintain optimal technique when the swimming distance increases. Typically the strength of the strokes decreases as the muscles get tired, even if the swimmer is able to maintain a constant frequency. This change is usually evident also from the decreasing stroke length and swimming speed.
The figure below shows the development of the stoke impulse during an 800 m swim. It can be seen that the strength of the hand strokes decreases significantly during the first 100 m. Thereafter the swimmer is able to maintain the impulse in a stable level. It is also evident that the stroke to stroke variation increases when the swimmer gets tired.
The analysis of the swimmers technique is usually based on tests carried out over relatively short distances. This example shows that it does not necessarily help in optimizing the technique for long distance swimmers.