I have a young hopeful training under my supervision, but he has a problem that you may be able to advise me on.
The inside front of the collar bone at both sides of the neck need development (High Pectoral).
What can you suggest to build this area?
The area you describe is the pectoral attachment to the clavicle bones, and the key exercise is the incline Dumbell Press.
This exercise is performed on a 45° incline bench. Supine position with two dumbbells using 1/3rd of the maximum weight your student can handle for 6 reps.
The second set, use 50% of the maximum weight 6 reps, and the third set, 75% of maximum weight. 4th set, work up to 100%; again to 75%; and 6th set, 50% maximum. 7th set, 1/3rd maximum weight.
This should be enough work for a boxer to develop the clavicular area.
The exercise is best performed with the dumbbells held with the knuckles facing the body. Do not hold the dumbbells as you would a barbell, because this position is 75% deltoid, and you are trying to develop pectoral.