Front and lateral raises are both exercises that work different parts of your shoulder. Front raises focus on the front or anterior part, while lateral raises hit the side or medial head. You can perform these as part of a shoulder session, an upper body workout or a total body workout. The amount of weight you should choose depends on your level of strength and ability to keep good form while doing the movements.
Front Raises
To perform front raises, stand with a dumbbell in each hand in front of your thighs with palms facing toward you and then lift them straight up in front until they're the same height as your shoulders. Because these are an isolation movement and only work one joint and muscle group, you will find them extremely challenging. The fact that the finishing position is a fair distance from your center of gravity means you won't be able to go heavy on these. If you're completely new to training, start with 3 pounds, or if you're a little more experienced, use 5 to 6 pounds and master the technique before you attempt to go heavier.
Lateral Raises
Much like front raises, lateral raises are an isolation movement for which you should use light weights. Instead of lifting the dumbbells out in front though, you lift them out to your sides. You won't find much difference in your strength levels between these and front raises, so again start with dumbbells that are 3, 5, or 6 pounds.
Progression
Just because you start with lighter dumbbells doesn't mean you have to stick with them for the long term. While the traditional notion that high reps with light weights are better for fat loss and toning is entirely false, front and lateral raises are more effective if you do slightly higher reps. Going too heavy on them, however, will encourage poor form and could create stress on your shoulder, elbow and wrist joints. Once you can complete three sets of 12 reps fairly comfortably with one pair of dumbbells, increase the weight by 1 or 2 pounds.
Considerations
Both front and lateral raises can be highly effective for sculpting your shoulders, but they should only play a small role in your training routine. Isolations have a place in your program, but compound exercises, which work multiple muscles and joints simultaneously, are far more effective for getting stronger and losing fat, writes strength coach Nia Shanks in her article "Muscle Sculpting Workout Tips." Therefore, you should perform other upper body exercises such as dumbbell presses, pushups, rows and pull-downs before getting carried away with raises and other isolations.
