You can’t target one part of a muscle
All over the web you’ll find bodybuilding articles about shaping your muscles. In these articles, authors claim that you can modify the shape of your muscles by training them in various, unconventional ways. A case in point is the all-too-common apocryphal advice about “peaking your biceps”. The writers of articles such as those will have you performing all sorts of bicep peak exercises that are purported to change the shape of the muscle.
The truth is: you can’t change a muscle’s shape, only its overall size. The muscle origin and insertion is fixed, you won’t alter it with training other than to strengthen your tendons (or damage them with ultra-intense isolation movements).
Muscle groups are not muscles
Understand that what we commonly refer to as muscles are actually muscle groups. For example, your chest is not a single muscle; it consists of two muscles, the pectoralis majora and the pectoralis minora – the lower pecs and the upper pecs. You can preferentially work parts of a muscle group – it is possible to build your lower pecs and neglect the upper pecs, and vice versa.
Bodybuilders who want to “shape” their muscle groups know many techniques that allow them to focus on one part of a muscle group to the exclusion of the others. The rest of us – who presumably are interested in bulking up and developing an overall level of fitness – don’t need to worry about techniques such as those.
Train movements, not muscles
Yes, it’s true that you can add a bit of size to your arms by doing curls and triceps extensions. However, it won’t make you look any bigger. You’ll still have a skinny body and you won’t be any stronger when it comes to real-life tests of strength. Arm isolation exercises don’t build real strength; they just pump up your arms.
If you are a skinny guy who wants to bulk up, you should stick to compound movements that work multiple muscle groups. That is the path to real strength and size.
Don’t obsess over body parts like your biceps peak
Don’t obsess over body parts like your biceps peak or the sweep of your outer thigh. Instead, work to become stronger throughout your entire body. Treat the body as a whole rather than as a collection of unrelated parts. It’s a more difficult path to follow than doing bicep curls, but it will make you stronger and more capable, and if you bulk up at the same time, you’ll lose that skinny-guy look.
Stick to compound exercises
Training can’t alter muscle origin and insertion, it can only make the overall muscle larger or smaller. There is very little point in engaging in dubious practices that supposedly help you change the muscle’s shape.
So don’t worry about building your biceps peak. Experienced lifters know that the best biceps workout is a good set of pull ups or barbell rows. Compound exercises like these will build your biceps, strengthen your tendons and ligaments, and prevent you from developing any weak spots that might betray you in real-life situations where strength is called for.