Contemporary psychoanalysis focuses on the creation and maintenance of the self through interaction with others. Kohut and Lacan, for example, discuss the self as a creation of the "mirror;" how the self comes to know itself through its experience of the gaze of the other.  

Lacan suggests that such a self becomes alienated in that the self that the child imagines he sees in the eyes of the other possesses a unity and integrity which he does not experience within himself; within his own body.  Thereafter, he struggles to "recapture" the self he imagined he once was, to recreate the unity he believed he once possessed.

In adult life, we observe the consequence of this "relational" source of the self in the dependence of individuals upon others as a source of identity. People seek "status" or "prestige," to establish a  reputation, "face," etc. We seek to be positively perceived by others, to experience ourself in the eyes and minds of others. 

When we speak about a reputation, we suggest that individuals internalize the opinions of imagines others. An interpersonal perspective, in short, focuses upon ways in which the self is a self-concept whose source is the internalization of the ideas and the gaze of others.

Interaction with others, obviously, is essential in the development of a healthy self.  However, this is not the same as saying that the sole source of selfhood is interaction with others; that the self only exists by virtual of the gaze of others. What this conceptualization lacks is a view of the subjective, experiencing self; the self as an autonomous center of will and action.z
 
Naturally, human beings seek confirmation and self-validation through interactions with others.  But there is another part of the self that seeks not to interact with others, which seeks autonomy and separateness, seeking to be absolutely sufficient unto its self with no need of support or validation from others.

Athletic activities such as body-building and long-distance running are undertaken, I believe, in the name of experiencing this separate (separated) self; of intensifying knowledge of that part of the self that does not require the gaze or support of the other in order to know it exists.

The athlete seeks to so concentrate his will and so intensify stimulation within his body that he cannot escape the realization that he is a singular self; a unified being separate from all other beings.  The purpose of athletic activity is to intensify the body's experience of its own reality and simultaneously to "drop off" the social self; the self-dependent upon others.

Whether in the "thrill of victory" or the "agony of defeat," the athletic self cannot escape the reality of existence; cannot run to symbols or abstractions for support.  In the passion of the moment, in the throes of concentrated effort, the will and the body unify in the struggle to achieve the task at hand.  In these moments, the "other" is not needed, can provide no comfort, no assistance, no validation.  As the fantasy that others are connected to the self fades, the body itself comes into prominence as the location of the self. 

Body-building exercises, then, intensify the cathexis of one's musculature as one withdraws libidinal energy from objects outside the self.  Libido is confined to the narrow space of one's own body.

The self seeks to abandon its attachment to people, places, and things; to withdraw energy from concepts and symbols, to return to the source of life, the place at which life and death actually occurs. 

Narcissistic withdrawal, then, has the purpose of intensifying cathexis of the self in its actual, present, concrete existence.  But there is another meaning of body-building, and that is to liberate the body by confronting internalized objects which are experienced as if embedded within the self.