In bodybuilding, no matter what level you are, there always has been these muscles that lagged behind the rest of the body, even for professional bodybuilders, it exists.

While it may be a result of not optimally training this body part, the best way it should, it also depends very much on your genetics, genetics defines us, and different body parts respond differently to training. This doesn't mean you can blame genetics entirely on your weak body parts, no matter what weak muscles you got, with the right hard of work and commitment, you can improve them.

Now let's take a look of what can be done in order to improve your weak parts, whether it's your chest, shoulders, arms, legs or any other muscles.

1- Principle of priority training
With principle of priority, you focus on the weak part at the beginning of the workout, as the muscles are fresh and capable of handling more than at the end of the workout.
Lets say you got weak upper chest, then start your workout with incline barbells or dumbbells press, it wont be wise to start with flat bench, by the time you finish it, your muscles will be too tired to perform optimally on the incline.
another examples for the legs, most bodybuilders have weak hamstrings, at the same time most bodybuilder trains hamstrings at the end of the legs workout, with one or two exercises, try to start with training your hamstrings first, and do 3-4 exercises for them, you can even split the legs day to two days split, putting hamstrings on a day of its own, to better focus on training them right.

2- Training based on muscles fibers type
As a simple way to say, there are two muscles fibers for us to know, fast twitch and slow twitch fibers, fast twitch requires heavy weight/resistance with low repetition to stimulate growth, while slow twitch requires moderate weights/ resistance.
Different body part have different mix of these fibers, if you were doing always the same range of reps for your weak muscles, you may want to change by increasing or decreasing, both the weight and repetition. Then you may start seeing good results coming just from this change.

To know more about muscles fibers, check (Muscles fibers and exercise).

3- Frequency and volume
modification on the frequency and volume of training is a good way in overcoming lagging parts, but unfortunately many will end up over doing it, which may results in over training, for these type of people, they benefit from decreasing both frequency and volume, if you have a weak biceps for example, training it daily is not a very smart idea, neither is training it for 2 hours.
Muscles take time to heal, usually 48 hours for small muscles and 72 hours for larger ones, that's after intense workouts. It also depends on many factors, such as sleep, nutrition, type of rest, individual response.
You can probably train small muscles group like calves or biceps as much as every other day, if you do reasonable training volume.
Training volume is to increase the number of sets and reps for each body part, variation through it, and watching the body response is the best thing you can do.
If you do it too much it won't grow, and if you do it too less it also won't grow, figure out your range, by trial and error.

4- Extra care on the training day
At the day scheduled for the weak body part training, make sure you use put your body in the best way to perform and grow.
Nutrition is very important in all days, but for the day you are training in the weak body part, you should make the best of this day, by eating very high protein intake and good carbohydrate meal for energy and glycogen replenishing.
You should make sure you took good rest the day before it, and take good rest after working out, good night sleep, mid of the night protein shake and don't miss any supplement you are using.

5- Using hardcore training methods
Utilizing many of the hard core training methods for the weak body part may kick it off its plateau, use pre exhaustion, beyond failure, drop sets, supersets, partial, and other ways to increase you intensity.

6- Variation
Variation in all aspect of training is a great key to continous results, if you do what you always do, expect what you always got.
Muscles growth depends on muscle adaptation, new stress on the muscles, stimulate the muscle growth in size and strength, any added new stress to the body will result on it trying to adopt.
surprise your body, one day just do super heavy sets for the weak part, the next workout it, high reps as high as 30 with low weight, change exercises, change angles, change supplement, change routine, change is the flavor of life, and with the right experience, you will know your body like no one does, it is yours after all, keep on watching and feeling different results from different techniques, and switch and modify your training program.

7- Site injection
I kept this point as the last one, cause usually bodybuilder use it as the first, site injection can help improving lagging body part if used wisely, but it can also result in deformed body parts and even result in death if used unwisely, read(site injection) for more information.

You should never give up if you have a weak muscles, instead you should work harder on it to make it keep up with the rest of the body. hard work is never a waste.

Shady Eid is a certified personal trainer, writer and competitive bodybuilders based in UAE, for questions and comments you can contact him at: Shady@arabianmuscles.com