Brief Answer:
as explained in details.

Detailed Answer:
Hi.
Thanks for your query and clear pictures.
To recapitulate: Male 16 - lifting weights daily - for football - very lean - noticed a marble sized bump - several days ago - on inner aspect of biceps - not really noticeable when the elbow is straight - can see clearly when the biceps is flexed - thinks it is a little larger now ...

As per the description and the pictures, this may be;
- lipoma
- sebaceous cyst
- small muscular hernia
- not likely to be a lymph node as there are no known lymph nodes in this situation.

The characters as per the possibilities are:
- Lipoma: freely XXXXXXX non-tender, stand out on flexion of biceps as the muscle mass increases on flexion hence the bump stands out. It still will keep the characters of mobility and non-tenderness, very smooth the palpate.
- Sebaceous cyst: may have similar characters unless frankly infected but is usually attached to the skin making it less XXXXXXX non-tender if not infected, mobility will be a bit restricted on flexion of biceps. Skin usually will have a black/blue spot, the punctum with which it will be attached to. Being noticeable within the last several days and little larger indicate mild infection.
- Muscle herniation: rare but most known at biceps. Since your son is lifting weight, a small tear in the capsule of the muscle can allow projection of the muscles through a small rent. This will allow to get prominent on flexion of biceps, but will be strictly non-mobile on flexion of biceps. Usually non-tender.
- There can be rare things that are seen only by investigations or by removal and subjecting the bump for histopathological examination.

I would like to request you to conducts the tests and match with the description to get a probable cause.
Another way is to get a clinical examination by a Doctor, preferably a General Surgeon and get high resolution ultrasonography and if required FNAC done to get the proper diagnosis.
The best diagnosis is done by excision of the bump for 2 reasons:
1. The patient gets rid of the mass which is not a normal part of the body.
2. One gets a correct diagnosis by histopathology examination.

I hope this answer helsp you, please feel free to ask for further relevant queries if you feel that there s a gap of communication and give the feedback.

---

Brief Answer:
Please give feedback on Monday

Detailed Answer:
Thanks for your appreciation.
Please give me the feedback on Monday after the check-up.
No, it does not matter if it is painful.
Difficult to comment upon the bumps which you have had, but now you may please refer to out above discussion to compare your bumps too.

Have a great day.

---