Pilates will significantly increase your abdominal strength and endurance and can also be used to strengthen upper and lower limbs as well as working on postural awareness and stability. However, if you are looking at improving your overall muscle strength, weight training in the gym is best for this. This is because to increase muscle size you have to expose it to more load then Pilates can offer, particularly mat Pilates. Some group Pilates classes will include weights and combine it with common gym exercises but a typical Pilates class will not. Try combining a variety of exercises to get the best results.