What are the pros and cons of sub muscular and dual plane breast implants?

Hello and thank you for your question.  Dual plane has the advantage of providing a slight lift of the nipple in relation to the breast tissue.   There are several advantages
and disadvantages to over vs under the muscle.  Under the muscle and dual plane both have the
advantage of lower capsular contracture rates, less risk of rippling, and
better visualization with future mammograms.  The size, shape,
and profile of the implant is based on your desired breast
size/shape, your chest wall measurements, and soft tissue quality. 
This decision should be based on a detailed discussion with
equal input from both you and your surgeon.   Make sure you specifically look at before
and after pictures of real patients who have had this surgery performed by your
surgeon and evaluate their results.   The
most important aspect is to find a surgeon you are comfortable with. I
recommend that you seek consultation with a qualified board-certified plastic
surgeon who can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.  FACS
Harvard-trained plastic surgeon

Most of the time under muscle placement uses the dual plane technique, which cuts part of the muscle from its attachment resulting in weakening of the muscle and greater likelihood of animation deformities. The split muscle technique (also called muscle splitting biplane) preserves upper pole coverage without muscle detachment. I do a lot of corrections for animation caused by the dual plane by converting to the split muscle. You could also go over the muscle but in athletic women there is often low body fat so coverage of the implant is not as good. 

Hello Scallywag.For someone who lifts lifts of weight, creating a dual plane could have som advantages and lead to less animation when the muscle moves. Complete under muscle will likely lead to increased movement of the breast implant, but not a higher risk reduction in CC. See at least 3 plastic surgeons before committing to an operation. Good luck. Dr. Aldo

When undergoing breast augmentation there are a number of choices which need to be made: saline or silicone? Volume: Larger or smaller? Incision? However, one of the most commonly debated choices is that of implants placement: subglandular/ submammary vs. subpectoral/ submuscular? While many surgeons recommend submuscular placement there are distinct differences to each approach.
 Subglandular Augmentation (“overs”): 
Subglandular augmentation means place of the implant underneath the breast tissue but above the pectoralis muscle. Subglandular placement spares the pectoralis muscle which leads to reduced post operative pain/discomfort and no impact on muscle function post augmentation. Recovery is also fasterSubglandular augmentation can impact mammographic evaluation of the breast. However, as dedicated breast radiography has become more prevalent this has become less of an issue. Fellowship trained radiologists have become familiar with evaluating breasts post augmentation. It is also important to note that implant position does not interfere with visualization of breast tissue via contrast enhanced MRI (the most sensitive and specific study available for breast cancer detection).Studies suggest there is an increased risk of capsular contracture when implants are placed in a subglandular space.Aesthetically, implants placed superficial to the pectoralis major create a rounded, convex appearing breast profile. This effect is camouflaged, at least initially in larger breasted patients. However, as a woman ages fat atrophies and breast tissue descends. The result is a more noticeable implant specifically in the upper pole. Similarly, patients who have thin coverage superiorly are more likely to be able to perceive the implants and at higher risk of visible rippling when compared to subpectoral augmentation.Subglandular implants can also create the illusion of improved cleavage by preferential over-dissection of the central/medial pocket allowing the implants to be forced more to the midline. There is no limiting muscle as there is in a submuscular augmentation. 
Subpectoral Augmentation/Sub-muscular (“unders”): 
Subpectoral augmentation is technically a bit of a misnomer. Traditionally, subpectoral augmentation involves the release of the pecotralis major muscle from its lower attachments. This allows the muscle to “window-shade.” The upper hemisphere of the implant sits underneath the muscle (dual plane). This release contributes much of the discomfort encountered postoperatively by patients.Subpectoral implants have a lower rate of capsular contracture.Aesthetically, in contrast to submammary implants (which are prominent in the upper pole- especially in thinner patients), the pectoralis muscle both conceals the underlying implant and flattens the upper pole. This flattening effect creates a natural sloping as one proceeds from the upper portion of the implant to the lower portion.The most commonly cited drawback to sub-muscular augmentation is the animation deformity associated with contraction of the overlying muscle.One of the more commonly noted differences is one of "shape." As described above the pressure of the muscle overlying the upper pole of the device in a submuscular augmentation contributes to a more gradual incline as opposed to the rounding noted in subglandular augmentation. This is not necessarily an issue of size but rather projection. Some will argue submuscular is more natural (and for the vast majority of patients this may be true) but ultimately this is a question of anatomy and expectations. Some patients are seeking an augmented look with upper pole fullness and rounding while others are seeking subtlety.
With regards to your specific question, there is a slight sacrifice of strength associated with a submuscular/dual plane approach. The release of the muscle can impact exercise. However, the impact is minimal for most patients.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

Most of the time, this is one and the same. The lower lateral portion of the implant is not covered by muscle. Behind the muscle provides more "cover" for the implant to better hide the negative aspects of an implanted look and also provides an environment for a lower rate of capsular contracture. While this will NOT cause any long term loss of strength in your chest muscles, you may have a bit more issue with animation deformity with strong pecs and lower body fat. There are trade offs either way and the decision is personal - submuscular vs subglandular.

Thank you for the question. Semantics can be confusing.  When surgeons talk about placing breast implants "behind the muscle", they are usually referring to  "partial" or "dual plane"  positioning. In other words, all of these terms refer to the same sub muscular (as opposed to sub glandular positioning) positioning of breast implants.
Dual plane breast augmentation refers to the technique where breast implants are placed under the muscle superiorly and in the sub glandular  position inferiorly.  I think this is the best way to go for most patients. On the one hand, patients benefit from the sub muscular position with increased tissue coverage of the breast implant, less chance of encapsulation, less potential for rippling/palpability of the implants and less interference with mammography.
On the other hand, because the implants are not completely sub muscular there is the potential for less “distortion” of the breast implants with pectoralis movement. Generally, in my opinion, the breasts also look better with breast implants in this position.
I hope this helps.