We conducted a 12-wk resistance training program in elderly women [mean age 69 
+/- 1.0 (SE) yr] to determine whether increases in muscle strength are 
associated with changes in cross-sectional fiber area of the vastus lateralis 
muscle. Twenty-seven healthy women were randomly assigned to either a control or 
exercise group. The program was satisfactorily completed and adequate biopsy 
material obtained from 6 controls and 13 exercisers. After initial testing of 
baseline maximal strength, exercisers began a training regimen consisting of 
seven exercises that stressed primary muscle groups of the lower extremities. No 
active intervention was prescribed for the controls. Increases in muscle 
strength of the exercising subjects were significant compared with baseline 
values (28-115%) in all muscle groups. No significant strength changes were 
observed in the controls. Cross-sectional area of type II muscle fibers 
significantly increased in the exercisers (20.1 +/- 6.8%, P = 0.02) compared 
with baseline. In contrast, no significant change in type II fiber area was 
observed in the controls. No significant changes in type I fiber area were found 
in either group. We conclude that a program of resistance exercise can be safely 
carried out by elderly women, such a program significantly increases muscle 
strength, and such gains are due, at least in part, to muscle hypertrophy.