you are getting poor value for your training right now.
definitely spend some SP to take STR to next cap (61) now ... that way, you will be getting good value by continuing to train it ...
Im assuming that you are finished adding SP to your 3 majors of THR / VIS / CON .. so now its a question of pumping STR. you want it up to 83 ASAP.
In order to maximise training values, you might want to siphon off a few SP from pumping STR, to take either AGL or STA to their next cap along the way
(basically, you get much better training bang for your buck just after you reach a cap, and sucky training value as you approach the next cap - eg training STR at 59 is horrible value, but training it at 61 is sweet)