GS-C improved to 0.54 m/s at 30 weeks without use of an FDS ( effect size = 0.75 ) and 0.54 , 0.55 , 0.58 , 0.60 , and 0.61 m/s at 6 , 12 , 30 , 36 , and 42 weeks with use of an FDS , respectively ( effect size 0.84 at 42 weeks ) .