At 6 and 12 months , respectively , mean ( SD ) values for strength ( presented as proportion of maximum strength score evaluated using manual muscle testing ) was 92 % ( 8 % ) and 93 % ( 9 % ) , 6-minute-walk distance ( as percent-predicted ) was 64 % ( 22 % ) and 67 % ( 26 % ) , and SF-36 Physical Function score ( as percent-predicted ) was 61 % ( 36 % ) and 67 % ( 37 % ) .