Methods of Movement Analysis
A number of methods are used in analysing movement. The method selected depends on the knowledge and experience of the observer and the context in which the analysis is being performed. The three main methods of analysing the biomechanics of sport movements are movement phases, free body diagrams and deterministic models. Movement phases and free body diagrams are more frequently used by coaches and sports scientists, whereas deterministic models are used in more complex movement analysis and therefore more often in sports research.
A sport movement, especially for ballistic actions such as hitting, throwing and kicking, generally contain three main phases:
The preparation phase contains all of the movements that prepare an athlete for the performance of the skill, such as the backswing during cricket batting and the run-up in long jumping. The execution phase is the performance of the actual movement that often includes a point of contact with an object (e.g., contact of the baseball bat and ball), the release of an object (e.g., discus) or a flight phase (e.g., long jump). Finally, the follow-through refers to all of the movements that occur after the execution phase (e.g., leg lift after kicking a football) that slow the body’s momentum to prevent injury, to get ready for another movement or both. These three main phases are often further broken into subphases or key elements.
Overarm throwing such as baseball pitching has three subphases for the preparation phase: the wind-up, the stride and arm cocking (see figure 11.4). Similarly, a standing shot in netball has three preparation subphases: stabilisation and preparation, aiming and loading. Other more complicated sport actions such as gymnastics vaulting can also be broken into movement phases, subphases and points of interest.
Gymnastics vaulting contains seven general phases: (1) the run-up; (2) the transition, which typically includes a hurdle step but may be also preceded by a round-off; (3) the board contact phase; (4) the preflight phase; (5) the table (horse) contact phase; (6) the postflight phase; and (7) the landing. The board contact phase can be broken into two subphases, the downward compression (loading and storage of energy in the springs) of the board and the upward reaction (recoil of the springs imparting energy back to the gymnast). A point of interest, for example, is the gymnast’s take-off angle from the board and the table contact angle at the end of the preflight phase.
Free Body Diagrams
A free body diagram is a visual diagram of the expected or predicted movement pattern; it is usually drawn as a simple stick figure. Coaches and researchers often use the technique to describe a subphase or point of interest in a movement pattern. Coaches may use free body diagrams to communicate to athletes or to illustrate to other coaches what they believe is good technique.
In research, a free body diagram defines the extent of the analysis and identifies the significant forces involved in the action using arrows, along with the directional coordinates relevant to that movement pattern (e.g., a two-dimensional or three-dimensional coordinate system). The free body diagram typically shows only the forces acting on the system and not those within the system (e.g., muscle forces).
A deterministic model is a concept map that describes the biomechanical factors determining a movement or action, starting with the primary performance factor(s) (e.g., jump displacement for long jump, race time in sprinting), followed by a breakdown into secondary factors (or derivatives) and so on. Hence, a deterministic model can have many levels. Figure 11.5 provides an example of a deterministic model. More examples of deterministic models can be found in The Biomechanics of Sports Techniques (Hay, 1993).
Regardless of the technique employed, movement analysis requires careful planning. These techniques may also suit qualitative or quantitative analyses of movement. Qualitative analysis assesses the technical quality of the movement (e.g., rhythm, posture), whereas quantitative techniques assess the movement using numbers (e.g., angles, distance, speed, force).