This is an excerpt from Biomechanics of Sport and Exercise-3rd Edition by Peter M. McGinnis.
Qualitative Anatomical Analysis Method
The purpose of a qualitative anatomical analysis is to determine the predominant muscular activity during specific phases of a performance and to identify instants when large stresses may occur due to large muscle forces or extremes in joint ranges of motion. The teacher or coach may complete such an analysis on a student or on an elite performer who demonstrates effective technique. The analysis of the elite performance identifies which muscles are involved in performance of the most effective technique, whereas the analysis of the student identifies the muscles used in performing the specific technique. In either case, the methods used to identify the muscles involved are the same.
Let’s think for a minute. Do you already know of any methods for identifying what muscles are active during a sport or movement? One way is to touch and feel the performer’s superficial muscles during the movement. If the muscle is firm and rigid, it is actively developing force. If the muscle is soft and flabby, it is inactive. This method works only if the activity involves static positions or slow movements (and if the performer is comfortable with being touched). Certain weightlifting exercises and gymnastics routines are examples of movements that may be appropriate for this type of analysis. Obviously, this method is impractical for analyzing dynamic activities such as throwing or running. The method is also intrusive and affects how the subject performs.
Another qualitative method for determining which muscles are active during an activity is to perform the activity vigorously and then wait a day or two to see which muscles become sore. This works only when the person hasn’t been practicing the activity regularly. It may also identify only those muscles that experience large eccentric activity during the performance, because it is eccentric muscular action that is associated with muscle soreness.
Quantitatively, a researcher can wire the performer’s muscles with electrodes and use electromyography to monitor the electrical activity of the muscles. The EMG recordings of a muscle indicate whether or not the muscle was active. Further analysis of the EMG signal will provide a general idea of the magnitude of the muscular action. This type of quantitative analysis is expensive, time-consuming, and unavailable to most teachers and coaches. In addition, the electrodes and associated wiring are likely to cause the athlete’s performance to differ from a typical performance.
Another quantitative method involves recording the movement on film or videotape and then digitizing the film or video to get a complete kinematic description of the movement. Force platforms or transducers can also be used to measure any external contact forces acting on the subject. Anthropometric measurements are then taken from the subject to estimate body segment masses and moments of inertia. Free-body diagrams of each segment are then used to identify the resultant joint forces and torques that cause acceleration of the segments. Equations of motion based on Newton’s second law are solved to determine these forces and torques. The computed resultant joint torques are related to the muscles crossing those joints and indicate which muscles are active. This type of mechanical analysis, called an inverse dynamic analysis, is also one that few coaches or teachers have the equipment, time, or expertise necessary to complete.
None of these methods are practical or reasonable for coaches or teachers to use. Muscle activity cannot be directly observed; however, we can get a general idea of which muscles are active based on the principles used in an inverse dynamic analysis. This type of qualitative anatomical analysis may be practical for coaches and teachers, and it provides reasonable results for most activities. The following are step-by-step procedures for completing a qualitative anatomical analysis:
- Divide the activity into temporal phases.
- Identify the joints involved and the movements occurring at those joints.
- Determine the type of muscular contraction (concentric, eccentric, or isometric) and identify the predominant active muscle group at each joint.
- Identify instances when rapid joint angular accelerations (rapid speeding up or slowing down of joint motions) occur and where impacts occur.
- Identify any extremes in joint ranges of motion.
The results of a qualitative anatomical analysis can then be used to determine appropriate strength or flexibility exercises for the muscle groups identified. The five steps of a qualitative anatomical analysis are described and illustrated next.