These two machines go hand in hand, and if you want balanced lower body musculature, you need to work both, not just one or the other. These are isolation movements, which means they only focus on one joint and muscle group. Leg curl works on knee flexion, hitting primarily your hamstrings, while the leg extension works on the extension, hitting mainly your quads. Both exercises isolate the muscles, making them perfect for people who are interested in toning specific muscle groups. However, it is best that you do them combined with compound movements such as squats or leg presses, to get the most benefits. After all, muscles are designed to work in synergy with one another, and you should treat them that way.
These machines target the calves, one of the hardest and most stubborn muscle groups to grow. Calves are 90% genetics, but that doesn't mean you shouldn't work hard with what you got. There are so many buff dudes out there with chicken legs. And sometimes, having big glutes and quads will make your skinny calves look even worse, so make sure you hit those calf raises.
These machines are sometimes combined into one that lets you move your leg in different directions. But usually, they are separate pieces of gym equipment for sale.
They are designed to hit smaller muscle groups, primarily around your hips, and alongside your inner and outer thighs. These muscles, although small, are very important, and they assist you in major lifts such as deadlifts and squats and promote hip health and stability.
All the machines mentioned above are fantastic, but nothing beats free weights. Also, your gym might not have all that equipment, but all have gym sets of dumbbells and barbells. For that reason, you have no excuse, and you should incorporate squats, deadlifts, lunges, good mornings and hip thrusts into your routine. While doing these weight lifting exercises, your muscles need to work overtime, as they have to keep things balanced and under control, boosting your gains.