The Answer

Sub questions:

Intro

Swimming performance is measured ultimately by the sum of time taken starting, stroking and turning. Each phase needs to be executed with precision technique in order to complete each element in optimal time therefore completing the race in the best possible time. The dive is therefore one of the most important aspects to a competitive swimming race, this is especially true for the shorter distances where the start has been estimated to contribute up to 30% of the total race in the 50m sprint.( Lyttle, & Benjanuvatra, 2013)

The velocity achieved by a swimmer is greatest during the starting phase, therefore it is important for a swimmer to maintain the velocity achieved off the start block for as long as possible before slowing to race pace (Welcher, Hinrichs, & George, 2008)

I have chosen to give a brief overview of the three different dive starts used in competitive swimming today. Followed by a more in depth biomechanical explanation of the Grab start. I chose the grab start not because it has been categorically proven to be the most effective rather it is the most commonly used in competitive swimming today. In very recent years they have introduced blocks that feature handles, I haven’t added this as one of my block starts as most swimming pools would not have this as an option. However this will be the design of nay Olympic swimming pool made from now.

Grab Start

The grab start is the best known out of all the starts, and one could speculate it remains the most used of all starts for ventral events. (Honda, Sinclair, Mason, & Pease, 2013)

How to perform this dive:

·      Swimmer positions both feet at about 0.15 - 0.30 m apart with toes curled over front edge of block

·      The knees were flexed slightly and the hips well flexed

·      Hands grasp the front edge of block on the command “take your mark”

·      In this position, the swimmer’s center of gravity is placed as far forward as possible. (This results in only a small forward displacement of the CG being required for the body to effectively generate forward propulsion.)

·      The arms provide stability and support for maintaining balance

·      On the starting signal, the hands pull downward and let go of the block.

·      Both arms are swung straight out towards far end of the pool, both legs drive powerfully and simultaneously off the block

·      Work by Kruger et al. (2003) has shown that the back muscles are pre-activated allowing a more powerful extension of the body to occur after the starting signal. The main contributors to the take-off force were found to be the knee and hip extensors.

(Lyttle, & Benjanuvatra, 2013)  (Vilas-Boas, Cruz, Sousa, Conceica, Fernandes, & Carvalho, 1975)

Track Start

The track start was proposed almost 30 years ago, and has increased in popularity and started to become more and more used in competitions (Vilas-Boas, et all 1975).

The track start simulates the sprint running bunch start, which requires an initial rear leg drive, followed by a front leg drive. The track start employs a wider base of support than the grab start resulting in greater stability for the swimmer (Guimaraes, & Hay, 1985)

How to perform this dive:

·      Upon mounting the starting block, the swimmer places one foot near the back of the block, while the other is positioned so that the toes are curled around the front edge

·      The front leg provides greater contribution of the total propulsive force and, hence, should be the dominant leg of the swimmer (The dominant leg is defined as the one you would kick a ball with)

·      On the “take your mark” command, swimmer grasps the front edge of the block with center of gravity well balanced towards the front edge of the block.

·      On the starting signal the swimmer initially pulls on the block with the arms as well as driving forward with the rear foot. Once the CG passes over the front edge of the block, the front leg dominates force production.

(Lyttle, & Benjanuvatra, 2013)

Slingshot or Rear-Weighted Track Start or handle start

This technique is an adapted version of the track start

How to perform this dive:

·      Rather than placing the body weight towards the front edge of the block, this technique requires the swimmer to lean back as much as possible, placing tension on the shoulders and the front leg.

·      Swimmers curl toes over starting block

·      The swimmer’s center of gravity is positioned towards the rear of the blocks in the slingshot track start.

·      Longer block time means that swimmers are able to generate greater impulse (a product of force x time) and therefore greater take-off velocity.

·      Leaning back means that swimmers can ‘preload’ the muscles of the arms and shoulders. This has been shown to enhance force production capability (Welshe et al., 1998).

·      The arms are used almost exclusively to generate horizontal propulsion in the early part of the dive.

·      When the swimmer is moving forward on the blocks, the legs are used to further accelerate the swimmer forward.

·      As with the front-weighted track start, the dominant force producing leg should be positioned forward and is responsible for the greatest amount of force production.

(Lyttle, & Benjanuvatra, 2013)

Mechanical principles of the grab dive

Basic principles: 

The objective in performing a swimming start is to get the fastest starting time possible. The principle considered to produce a dive is:

(a) The time from the starting signal until takeoff from the block—the block time

(b) The time the swimmer spent in the air—the flight time,

(c) The time from the first contact with the water until first contact with a bulkhead placed 9 m from the start—the water time.

Each of these partial times is determined by a number of variables.

The block time is determined by the horizontal and vertical displacements of the center of mass, and by the average horizontal and vertical velocities with which these displacements occur.

The flight time is determined by the three characteristics (a) the vertical velocity at takeoff, (b) the height of the Mass at takeoff relative to its height at landing or entry, and (c) the air resistance encountered in flight.

The water time is determined by the water distance—that is, the horizontal distance between the Centre Mass of the swimmer at entry and the bulkhead and by the average velocity of the swimmer over this distance (Guimaraes, & Hay, 1985)

Equipment:

The angle of the block and the angle at which the diver travels towards the water are key factors in achieving the forward motion of the dive. A swimming block is slightly inclined so that you can have more force and power going out. This application of force causes the swimmer to have a higher velocity entering the water. This force of course has an equal and opposite reaction, this is called Newton’s third law. This then causes what’s known as the projectile motion (Simpson, Rutah, Luber, 2011)

Swimmer body shape:

The way a swimmer contortions their body also has an impact on the effectiveness of the dive. To optimize trajectory competitive swimmers are taught to make a parabolic shape with their bodies as they move towards the water. The swimmers body has a constant horizontal velocity, whilst the gravity is pulling him down, this causing the desired shape. (Simpson et al 2011)