If you do a cardio workout and resistance training during the same session, it doesn’t matter which you do first in terms of long-term benefits, suggests a small Finnish study recently published in Medicine & Science in Sports & Exercise.
The study involved physically active men, ages 18 to 40, who performed either a cardio workout followed immediately by strength training or vice versa, for 90 to 120 minutes, two or three times a week, for 24 weeks. Though muscle gains were initially less in the cardio-first group (presumably because the muscles were more tired by the time weights were lifted), by the end of the study the two groups had similar improvements in aerobic capacity, muscle mass, time to exhaustion, blood cholesterol and other biological adaptations to exercise.
Results may vary, however, depending on what kind of workouts you do and your personal preferences. See what works best for you.