"Overhead" sports gesture: functional and technical-sporting incidence factors

By Dr. Alessio Capobianco

Many sports are characterized by specific athletic gestures that involve repeated movements of the upper limb above the head: they are defined overall by the Anglo-Saxon overhead term.

The biomechanical model that assimilates these sports among them is that of the launch, carried out by baseball players, football players and javelin throwers, but it also concerns tennis players, swimmers, volleyball players and in some exercises even gymnasts and golfers.

In overhead athletes there is a particularly high incidence of lesions affecting the shoulder, whose pathological susceptibility is linked to the intrinsic lack of static stability and to the complexity of dynamic stability, which depend on its unusual anatomy and the extremely wide range of motion allowed . Overhead technical-sporting gestures require a delicate balance between muscular activity and capsuloligamentous containment when they are performed at the extreme limits of glenohumeral mobility, with very high angular velocities and torsional forces; the structures of the shoulder, subjected to the repetition of these stresses, can therefore easily be damaged by wear on a micro - polytraumatic basis.

Functional factors

These include the prevalent muscle contraction modality and the importance of the demand for muscular strength, the type of kinetic chain, the importance of the agonist muscular action.

Overhead sports specialties can present technical gestures characterized by a concentric, eccentric or pliometric muscle contraction regime; the concentric contraction, in reality, is an alternation of concentric and eccentric contractions as occurs in basketball, swimming and climbing. The demand for muscular strength (organic-muscular aspect) depends largely on the weight of the "bullet" (intended as the object to be thrown), which influences the amount of acceleration that the sportsman gives to it. It is possible to identify a prevalent use of fast force, of pure strength, of explosive force, respectively in the disciplines of basketball, weight-throw and volleyball (figure). Sports specialties with a prevalent demand for explosive power seem to involve a greater risk, compared to the disciplines with the prevalent use of other regimes of contraction.

In some technical gestures the antagonist musculature assumes importance, as a need for a braking effect in the phase immediately following the launch, called by the American authors, follow-through ("follow to the end"); this action takes place mostly through eccentric muscular contraction and depends, in some way, on the characteristics of the launched object which, in turn, influence the speed that the athlete can give to it.

Plyometric contraction involves a "prestiramento-shortening" cycle; in the technical gestures of throwing or ballistic sports, plyometric muscle contraction is used to obtain the desired efficacy and eccentric contraction is used to regulate the gesture.

The correct condition of balance and coordination between fixator muscles (or stabilizers) and agonist effectors (or motor muscles) also affects the rehabilitative or preventive training program.

The muscular action is in turn influenced by the characteristics of the object to be launched.

The kinetic chain can be open or closed; the open chain provides that the upper limb is free from gripping or support constraints.

Otherwise, as in the example of four-way locomotion, or of the suspension of a handle, it is a closed kinetic chain; in fact the criteria are strictly only when the limb is in support. Among the most common sports with an open kinetic chain are swimming, among those with a closed kinetic chain include the disciplines of artistic gymnastics and sport climbing.

The gestures in closed kinetic chain would seem to favor the stability of the glenohumeral joint and therefore present a lower pathogenetic incidence compared to the gestures performed in the open kinetic chain.

However, if the limb is used for locomotion-support, the high weight load on the glenohumeral joint should be considered, as well as the caudo-cranial direction with which the load is applied and which can cause subacromial conflict; an example of this condition is found in artistic gymnastics.

All launch overhead activities use the open kinetic chain, which constitutes an increase in risk to stability, compared to the closed kinetic chain.