"Clemens' longevity was due to his ability to adjust his style of pitching as he got older, incorporating his very effective split-finger fastball to offset the decrease in the speed of his regular fastball caused by aging," said the report, created by Randy Hendricks and two associates at his firm.

Clemens' former trainer, Brian McNamee, claimed in last month's Mitchell Report on drugs in baseball that he injected the pitcher with steroids and human growth hormone at least 16 times in 1998, 2000 and 2001. Clemens vehemently denies the allegations, and Clemens and McNamee are among five witnesses scheduled to testify before a House committee on Feb. 13. Clemens also has sued McNamee for defamation.

Hendricks' report, which includes 38 charts, in some ways resembles a salary arbitration case. One of the charts shows Clemens' ERA was lower than the league average in all but two of his 23 major league seasons. The report also compares variations in Clemens' career with those of Randy Johnson, Curt Schilling and Nolan Ryan, and maintains slumps often can be correlated with injuries.

"Of the six years that feature Clemens' best ERA margins, two occurred in Boston, after he had been in the major leagues for several years; two occurred in his two years in Toronto; and two occurred after he switched leagues and pitched for the Houston Astros," the report said.

Clemens went 40-39 in his last four seasons with the Red Sox, and when the pitcher left Boston's general manager at the time, Dan Duquette, said Clemens was in the "twilight" of his career. Clemens was 192-111 with the Red Sox and won three Cy Young Awards and an MVP, then went 162-73 with Toronto, the New York Yankees and Houston, winning four Cy Youngs.