LONG DISTANCE: A YEAR OF LIVING STRENUOUSLY

After ''a boyhood spent as a wimp,'' author and environmental activist McKibben (The End of Nature) devotes a year to developing his potential as a cross-country skier. He goes all out, acquiring a coach and embarking on a grueling training program. His goal? Not only to see ''what life lived through the body felt like'' but to silence those intimations of weeniness. Although he gains strength and endurance, he often questions himself, remarks on his own selfishness, and compares himself unfavorably to his father. Despite seeking change, he substitutes effort for introspection, which keeps the reader at a distance, as does his reportorial (though earnest) tone. Things change when his father is diagnosed with a fatal brain tumor. As he reflects on his father's life, McKibben begins to understand what he wants, which isn't freedom through sweat but freedom from self-absorption. B+