Arm strength among starting pitchers isn’t fully developed until they have worked 60 to 70 regular season innings. It has been a staple of the craft forever. So, it wasn’t surprising to hear Masahiro Tanaka say he continues to build arm strength after two subpar starts, in which he has worked a total of nine innings. He starts Saturday night against the Rays at Tropicana Field. “I was building arm strength right at the same time [last year] as well,’’ said Tanaka, who is 0-2 with a hefty 7.00 ERA. Last year, he was 6-0 with a 2.70 ERA in his first eight starts before suffering a loss. But last year, Tanaka wasn’t coming off a small tear of the ulnar collateral ligament in the right elbow like he was this year. The Yankees worked him slowly in spring training (four games; 14 ²/₃ innings) to make sure the elbow was built for a full season after he appeared in just 20 games last season and only two — in September — after July 8. “I don’t look in the past saying I should have thrown more in spring training,’’ Tanaka said. Manager Joe Girardi said Tanaka’s velocity is down less than a mile per hour than where it was at this time a year ago. “Is there more to come, I think there is,’’ Girardi said. “Is there a lot more to come? That remains to be seen. I wouldn’t think so. We have seen him as high as 94 in spring training. What’s the hardest we saw him last year, 95, 96?’’ Brett Gardner took batting practice, but wasn’t in Friday night’s starting lineup for the third straight game because of a bone bruise in his right wrist suffered on Monday night in Baltimore when he was hit by a pitch. Inserted as a pinch-runner in the eighth inning after Carlos Beltran singled, Gardner stole second and scored on Alex Rodriguez’s single to center that accounted for the winning run in a 5-4 Yankees victory.