Biomechanical Race Analysis by Bruce R. Mason, Ph.D. (1999)


Published


How Biomechanics can enhance elite performance.

A bio mechanist can most influence performance in elite swimming by being a support provider to the coach. The Bio mechanist is not a technique coach but rather provides advice to the coach on technique matters. This is achieved in three ways:

  1. SERVICING

Accurate and objective Biomechanical analysis that is presented in an easily interpreted form.

Advice to the coach on the basis of Biomechanical knowledge and Physics principles

Advice on equipment used in the sport Competition Analysis information

  1. RESEARCH

Research in swimming to answer questions of a biomechanical nature.

  1. EDUCATION

The coach needs to be aware of what Biomechanics can provide and be familiar with using the output from Biomechanical systems.

 

The Competition Model

In modem times races are not won by the swimmer in elite swim competitions, getting out and giving it all they have. Races are won by careful preparation which involves developing a good game plan or competition model for the swimmer concerned. The competition model for a particular swimmer in a specific event is developed by assessing a swimmer’s goals, by measuring the swimmer’s competition characteristics, by analyzing what the swimmer’s competition model should be, by utilizing appropriate training programs to prepare the swimmer for the competition model and by the swimmer being able to implement the competition model during competition.

 

The development of the competition model by the coach incorporates the time that the coach believes that the swimmer needs to complete the event to achieve their goal. This involves an understanding of the expected winning time for the event and a knowledge of the swimmer’s abilities in the various sections of the race e.g. start, free swimming, turns and finish.

 

The swimmer cannot be expected to implement the complete game plan during training but should be trained to be capable of completing various aspects of it in parts. However, small sections of the race should not be dealt with in isolation. E.g. turns by themselves.

The competition model involves swimming at set swimming speeds during the various parts of the race and this requires the discipline to maintain stroke lengths and stroke frequencies. The swimmer must be capable of keeping track of what they are doing in competition splits for various laps, stroke counts etc. so that they are able to keep to the competition model during the race.

 

Competition Analysis

The most effective time to assess a competitive swimmer’s overall competitive performance is during major competition meets when the swimmer is competing to their absolute limit. Competition analysis provides feedback to the coach as to how well the swimmer is capable of staying with the competition model. It provides information about the start, turns, finish and free swimming aspects of the race. If possible, sport science staff or helpers should be used to provide the competition analysis . This will allow coaches to watch their swimmer’s performances, rather than to spend their time writing down splits from the timing board or monitoring stroke frequencies from the watch.

 

Comparisons can be made between the swimmer concerned and the swimmer’s competitors. This will disclose why the swimmer is slower or faster than other swimmers. Small adjustments may be made in tactics between the heats & semis and between semifinals & finals. Changes to the competition model may occur between one competition and future competitions and the swimmer needs to be trained to incorporate these changes into the new Competition Model. Inefficiencies in technique can be identified by competition analysis. It is more productive to work on improving a swimmer’s inefficiencies than working on their strengths. Research from the output of competition analysis in elite competition may bring about a better understanding of how performance may be improved.

Parameters Measured

START time for the head to reach the 15m mark after start signal. If working with the ARES Omega timing system it also provides the time for the swimmer to leave the blocks after the starting signal. Start velocity is calculated by dividing 15 by the starting time.

TURNS Time from the head at the 7.5 meter mark on the way in until the head again passes the 7.5 meter mark on the way out. Our competition analysis system also provides the turn time in and the turn time out as well as the ratios of these times is provided. Turn velocity is calculated by dividing 15 by turn time. FINISH Time from the 5 meter mark out from the wall. Finish velocity is calculated by dividing 4.5 by the finish time.

The velocity for each of these aspects of the race are provided so that comparisons can be made between velocity in these aspects and the adjacent free swimming velocities.

 

Swimming Speed

Competition analysis provides information about the free swimming phases throughout the race. It provides as well as swim velocities the components that make up those velocities.

 

Stroke length is the distance the swimmer moves through the water from right hand entry to the next right hand entry. This is the distance traveled by the head in a complete swimming cycle. Measured in meters Stroke frequency is the number of such cycles that would occur in a minute if the present stroke rating were continued. Measured in strokes per minute.

Stroke frequency should not be confused with stroke count which is the number of arm cycles completed ‘m a lap. Stroke count gives a practical indication of stroke length for the swimmer to keep track of stroke length.

Another measure is that of efficiency index. The efficiency index is the product of stroke length and swim velocity. It implies that it is better to have a long stroke length at a high swimming speed than to reduce the stroke length and increase the stroke frequency to attain a high swim velocity.

Swimming Speed = Stroke length * Stroke frequency

 

Stroke Length

It is my opinion that the coach should concentrate upon optimizing a swimmer’ stroke length rather than adjust the stroke frequency. The complete stroke of the swimmer needs to be examined periodically to ensure inefficiencies don’t creep into a swimmer’s stroke technique which will reduce the stroke length.

 

A swimmer is more efficient if he is able to get propulsion through the entire stroke than to increase the stroke frequency as a way of compensating for a stroke length inefficiency, The way to optimize stroke length is through the use of underwater video filming. Filming should be performed from directly in front and directly from the side using a moving camera. This is done so as not to identify things that don’t really exist. Such illusions can occur using an oblique angled   camera.

E.g. dropping elbow in the back sweep . Filming should not be done as a one off activity but should occur reasonably frequently in the program. Once the stroke length has been optimized then variations in stroke frequency are used to alter swim velocity.

Ingredients associated with good stroke length include: Technique

Flexibility Strength Power Endurance

 

Optimizing Stroke Length

Some people believe that the key to fast swimming is to maximize stroke length. I certainly do not believe this to be true. We need to optimize stroke length for each swimmer, not to maximize it. An analysis of swim performances at the World Swimming Championships for the top 16 swimmers in each event identified that the race results were very highly correlated with the swimming speeds of the swimmers concerned. This was the case in almost all events for both genders at the 0.01 level of significance. Correlational statistics were performed between the swim times obtained by the top 16 swimmers and a number of other variables that represented the swim performances of these swimmers. Three of these variables included: average swim speed, average stroke length and average stroke frequency. As can be expected the swimming speed did relate to the race result at the highly significant level. However, stroke length and stroke frequency very rarely correlated with the race result. This indicating that there was no significant relationship between stroke length, stroke frequency and the ability to perform well in the competition.   This gives credence to my supposition that stroke length and stroke frequency are a very individual thing. A swimmer needs to optimize their stroke length not maximize it Maximizing the stroke length will not improve a swimmer’s prospects of winning but may actually decrease the chances of winning. However, I believe there is certainly an advantage to optimizing stroke length by getting the full distance out of each stroke by applying good technique through the entire stroke. The optimum stroke length will vary considerably for each swimmer.

 

Stroke Length and the More Elite Swimmer

A more elite swimmer will tend to have a more consistent stroke length and will maintain it to a greater extent throughout the race than a less experienced swimmer. I believe this to be the case because the more elite swimmer has stabilized his or her stroke length by utilizing good technique that he or she is able to sustain throughout the race. If the stroke length remains reasonably constant, swimming speed is increased by increasing stroke frequency. However as the stroke frequency increases there tends to be a marginal drop off in stroke length. Inexperienced swimmers increase their swim speed by increasing their stroke frequency too much. Initially the increase in stroke frequency will increase swimming speed but due to fatigue there is a consequential drop off in stroke length over time which will not keep pace with the increase in stroke frequency. This will result in a drastic drop off in swimming speed.

 

Increasing Swimming Speed

The speed that a swimmer is able to reach is determined by two forces which when they reach equilibrium determine swimming speed. The two forces are the propulsive force that the swimmer is able to generate against the water and the other is the resistance force of the water acting against the swimmer’s forward motion. The two ways to increase swimming speed are to generate more forward propulsive force or to reduce the resistance force, A coach should first focus more on reducing the resistance forces than to increasing propulsive force as this requires less energy expenditure on the part of the swimmer. When this has been achieved greater propulsive forces are needed if the swimmer is to swim faster. The active drag is a measure of the resistive force on the swimmer at the particular swimming speed. What we need is to be able to effectively measure active drag at the swimmer’s maximum swimming speed. The monitoring of active drag for elite swimmers at their maximum speed of swimming will provide a valuable indication of the quality of their technique.

 

Drag Resistance

There are three major sources of drag on the swimmer. Form Drag occurs as a consequence of the form or shape of the body exposed to the oncoming flow of water. It is produced by presenting the frontal surface of the body to the oncoming flow of water. This is the major cause of resistance for a swimmer. It can be reduced by utilizing better technique during propulsive actions and better streamlining during recovery.

Wave Drag When an object moves along the surface of water it produces waves. The production of these waves causes energy to be dissipated from the action of forward motion. Probably the best example of this occurred in the 1956 Olympic games when the Japanese breaststrokers swam the length of the of the pool under the water and as a consequence were a body length in front of other competitors. Their actions resulted in a rule change for Breaststroke.

Surface Drag This is a resistance to forward motion as a consequence of the surface texture of the swimmer resisting forward motion. This is the least important form of resistance for swimmers. Surface drag can be reduced by shaving down prior to major swim events or of wearing more frictionless swimwear.

 

Statistical Analysis from the 1998 World Swimming Championships

In order to investigate the factors that were related to performance, correlational statistics were used. Competition analysis information from the top 16 swimmers in each event were examined. Start time, average turn time, average free swim velocity, average stroke length, average stroke frequency, the average efficiency index and finish time was correlated with the resulting swim time as a measure of swimming performance.

A significant relationship between one of these variables and swim time would indicate to the coach that the relationship should be examined with a view to utilizing the information in the training of elite swimmers. However, a significant Statistical significance does not imply a cause and effect relationship. Significance also relates to common trends  for all the swimmers involved. A low correlation coefficient does not preclude a relationship for a particular swimmer but which does not hold true for the group as a whole.

It should also be remembered that the 16 finalists are a very small and exclusive group which has low variability at the high end of the scale, making it more difficult to have a significant relationship.

 

Applicable Correlation relationships for Freestyle Events

Strong relationship in all Freestyle events between swim Velocity and swim performance

  • Sprint Events slight relationship between start & turn performance and the swim performance

50 meter events finish time related to swim performance

100 meter men’s stroke length related to swim performance

  • Middle Distance Events strong relationship between turn performance and swim performance
  • Distance Events Swim performance had a significant relationship in the Men’s 1500 meters with Efficiency Index but no significant relationship with turn

 

Correlation Relationships within the Distance Freestyle

 

Events

Correlational statistics were carried out between the average velocity in the first half the race and that in the second half the race in relation to swim performance at the 1998 World Championships. The swimming speed in both the first half and the second half of the distance freestyle races correlated with the result at a highly significant level. This was to be expected. However in both cases the swim velocity in the second half of the race correlated more highly with the result indicating that race performance was reflected more in the swimmer’s velocity toward the later stages of the race than toward the start of the race.

 

Applicable Correlation Relationships for Form Stroke and Individual Medley Events

With all the form strokes there was a high relationship between swim velocity and the swim performance. For the individual strokes as well as this:

Butterfly Turn times related to swim performance Backstroke Start and Turn times related to swim performance

Breaststroke Start, Turn and Finish times related to swim performance

Individual Medley Turn and Finish times related to swim performance

 

Correlation Relationships within Individual Medley Events

Correlational statistics were carried out between the average swim speed during the various strokes in relation to swim performance at the 1998 World Championships. The relationship between the swimming speed in each of the strokes and performance in the race indicated that in all but the men’s 200 in individual medley the correlation was highest for the Backstroke, followed by the Butterfly, followed by the Breaststroke and finally the Freestyle. In the men’s 200m Individual Medley the freestyle swim velocity was the only stroke that correlated significantly with performance.

 

Tables 1 to 5 provide correlation coefficients for the relationships between the criteria variable (swim result time) and each of the independent variables in all events at the 1998 World Swimming Championships in Perth.

 

Competition Analysis Systems

There are a number of groups around the world who perform Competition Swimming Analysis

The system that we use is very labor intensive and uses 7 cameras and 8 work stations to analyze the information gathered from the competition. We are also interfaced to the pools timing system to ensure we get accurate split times. Four groups of 10 people work around the clock to process the data and produce the report.

 

SWAN Competition analysis System

SWAN is an acronym for Swimming Analysis. The SWAN System is capable of being operated by a single person.   It

is designed to provide immediate feedback as well as provide video footage of the performance being analyzed. It is a versatile system that can operate without a camera at all with simply press buttons and no external information apart from a skilled operator watching the event. It is also capable of holding up using telemetry to the pools timing system to increase its accuracy. A number of other people can also be used to further increase its accuracy by pressing buttons at significant events.

The SWAN puts all its feedback onto the video tape upon which the swimmers image is recorded so that the data supplied by SWAN is available when viewing the tape. There is also a printed report available immediately. The video can be reviewed at a later stage and corrections made to increase the accuracy of the Output.

 

Key Aspects Involved in Starts

There are a number of things to watch with regard to Starts. Time off the block from the starting signal swimmer should be relaxed and ready to respond . Good take off angle and good distance to entry Swimmer should go out rather than up. Entry into water stiff body, streamlined, enter through the one hole. The swimmer is going faster here than at any other part of the race and must maintain as much speed  into the water as possible. Good Streamlining in Under water don’t commence kicking until speed has reduced to swim speed. Good Underwater propulsion use appropriate kicking fast dolphin kicks from the legs rather than hips and turned partially to the side. Good ascent angle ascend at an even rate to the break out. Good transition at break out into swimming stroke.

 

SWAN Analysis of Starts

The SWAN Analysis system that we use at National event camps and at National team camps is able to break the start down into phases to identify if any sub phase of the start that is causing a problem or could be improved.

 

The Phases of the start are:

-Start signal INITIATION

  • Feet Leave Blocks FLIGHT PHASE
  • Head Entry UNDERWATER PHASE

-Head Resurface

ABOVE WATER PHASE

-Head at 15 meters

 

Under water and above water video views of the start are provided with the analysis overlaid on the video image. A printed sheet is provided with times, distances and velocities included. Qualitative comments about each phase are also provided to give the coach an indication of the quality of each phase. The system averages 3 starts and also provides comments for the composite start.

 

Hardcopy output from SWAN system START ANALYSIS (See appendix G)

 

Key Aspects involved in Turns

Many swimmers don’t prepare for the turn by watching the cross on the bottom of the pool but rather they look for the wall and therefore need to adjust at the last moment. In the Freestyle and Backstroke the swimmers lift their heads and bob them into the water to initiate rotation rather than using an elliptical movement path of their head under the water. Swimmers tend to reverse direction rather than continue their momentum with a change in direction. Swimmers are Inconsistent as to the way they approach the wall every turn is different and needs major adjustment at the last moment. Turns should be nearly a closed loop skill.

Leg speed is slow onto the wall and swimmers often rotate the legs over in the turn with only a small amount of tuck. Leg speed in the rotation remains constant with the distance of the event but should vary with the distance of the event.

Good position in push off and good streamlining off wall is required before the kick is initiated. Change in body alignment with keyhole pull in Breaststroke with good streamlining during recovery Need quick kicking in underwater dolphin kick with drive in the legs not the hips. Good even ascent angle required with clean break out. Use the underwater phase to advantage and use the full distance that is permitted. Need good transition at breakout into the stroke. Don’t breath on the first stroke.

 

SWAN Analysis of Turns

The SWAN Analysis system that we use at National event camps and at National team camps is able to break the turn down into phases to identify any sub phase of the turn that is causing a problem or could be improved.

 

The Phases of the turn are:

FREE/BACK                        BREAST/FLY/

I.M. Interchange

  • Head 7.5 m out Head 5 m

out

IN TURN

  • Head Bob Hand touch

pad ROTATION

  • Feet touch pad Feet touch pad

A printed sheet is provided with times, distances and velocities included. Qualitative comments about each phase of the turn are also provided to give the coach   an indication of the quality of each phase. The system averages 3 turns and also provides comments to quantify the composite turn.

 

Key Aspects involved in Finishes

The speed into the wall should be as least as fast as the last free swimming phase. Swimmers must finish the race and not stop before the wall. Don’t look to the clock before the wall has been touched. The timing system measures the official time not the swimmer’s eyes. Make sure that the hand moves directly at the wall rather than lifting it up and over the water. Many a race has been lost on the wall by a very small margin. Hit the pad hard to ensure that the touch has registered. Omega pads are not infallible.

 

Hardcopy output from SWAN system TURN ANALYSIS (See appendix H)

 

Improving Starts, Turns and Finishes

Once a problem in starts or turns is detected by Race analysis it is beneficial to analyze the particular aspect of the race using a biomechanical analysis system such as SWAN. However, even without the access to such a system the following principles should be observed. It is imperative that the coach has regular weekly training sessions where the starts and turns are monitored and corrected.

 

When starts, turns and finishes are practiced they should not be dealt with in isolation of the free swimming. A swimmer turns in competition when they are working at an intense level. The swimmers need to practice their turns in the same state. If corrections in turns, starts or finishes are required they should be handled when the swimmer is fresh and in isolation of other aspects of the training. In general training, the swimmers should not be allowed to use turns as rest periods nor to float into the wall at the end of a swim. If the swimmers do this in training they will inevitably do the same thing in competition when the pressure is on. The coach needs to constantly monitor all aspects of competitive swimming.

 

PUSH-OFF UNDERWATER OUT-TURN

7.5 out

 

  • Feet leave pad Feet leave pad

 

  • Head resurface Head resurface

 

  • Head 7.5 m out Head

 

 

In addition, the velocity of the free swimming in and out of the turn are measured for comparison with the velocity throughout the turn. Under water and above water video views of the turn are provided with the analysis overlaid on the video image.

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