I've some experiences in the gym for at least 8 years and I've done personal research in fitness and sport for quite some time. There's often the question what muscle one should train to get better in badminton, e.g. should I train the bicept to get a stronger smash ? The standard answer is , that it is more about technique than about muscle size, but why ? I will try to give an short overview about muscles and what would be a good idea to train in relation to badminton. Skeletal muscle structure Skeletal muscle consists of different fibers which have different tasks. There are fibers which can twitch really fast, really strong, or which can contract for a really long time. Each muscle is a mix of these fibers. E.g. muscles which need to stabilize your spine will consists of more enduring fibers, muscles which need to move fast but are not "active" all the time, will have more fast twitching fibers. Movement, power and muscle size There are more than 400 muscles which are responsible to move your skeleton. Each muscle consists of multiple fibers of different fiber type. These muscles are controlled by the central nervous system (CNS). When you execute a movement, that is one or more bones are moved connected by a joint, then the CNS need to coordinate and control the movement of many muscles and many more fibers. Even a bicept curl, which should isolate the bicept, will involve a lot of other muscles. So, do you need bigger muscles to get more powerful ? Not really, at least not at the beginning. Compare the muscles and CNS to an orchestra. You put a whole orchestra, lot of professional musicians, in a room and tell them to play a piece of music. It will not work, even thought that all these musicians are experts. Then you add a conductor and it will suddenly start to sound like it could be music, but still chaotic. And eventually you give them time to practise this special piece of music, and suddenly it starts to sound harmonically. What happened ? Do we try to exchange the musicians by better one ? No, they are already experts ! The "same" happens when you regard movement. The movement is like a piece of music, the CNS is the conductor and the muscles are the already profesional musicians. To improve your movement and therefor the efficiency and power, you need to get the coordination of your muscles right. And this is done by practising the movement, so that your CNS learns to coordinate your muscles in harmony. But like an orchestra cannot play every piece of music without practise, each movement needs to get its own portion of exercises. This alone will grant you a really great gain in power and strength, this is the reason that some thin yoga girl is able to do a handstand and some pumped up fitness freak is unable to do so. Eventually there will be limits and larger muscles are needed to give you more strength, but I think that this is really not necessary to be a very good badminton player. Still want to hit the gym ? Okay, you still want to hit the gym. This isn't bad, I think that fitness should not be covered by a single sport and that doing more different active things will help you to keep a healthy body. I think that training the lower body (legs, calves, gluets) will grant you the most benefits in gaining some additional power in badminton. I don't think, that shoulder and arm train will help you much in regard of gaining some more power, but training these areas will help you to protect your from injuries. At last the core, which is involved in almost every kind of active sport where you need to utilize upper and lower body, will help you in your performance and protect you from injuries. So, I would focus on component exercises, exercises which involves multiple joints and therefor a whole bunch of muscles: - deadlifts (whole body, lower body focus) - squats (whole body, lower body focus) - chin/pullup (back + arms support) - rows (back,arms) - dips (breast ,shoulders, arms) - core training (not just the abs! there are a lot more muscles involved) - shoulder rotators (really important for the health of your shoulder joints) Limit isolation exercises, exercises which involved only one joint, like the bicept curl. You can add these when you hit the gym >3 times in a week, but for a supportive training it is more or less waste of time and energy. I think, that this will get you quite far. There will be more specialized exercises you could do to improve beyond a certain stage, but once you have reached this stage in badminton, it is likely that you are with a coach who will tell you what you need to do.