Having done some digging, I can see that the difficulty here is that the word "planos", in Spanish, is used in at least 3 different ways, as far as I can see. It is used to describe anatomical/geometrical planes (plano anatómico), to describe muscle "layers" (as some of you have indicated), but also less commonly to describe the abdominal regions and quadrants (planos abdominales). There is some limited evidence that "planes" is used in English to refer to the regions and quadrants of the abdomen, e.g.
https://emedicine.medscape.com/article/1923166-overview However, as far as I can see, it is not used in English as a synonym for muscle "layers".
The meaning of the source text seems to me to refer to "layers", although a less likely possibility is that it refers to the anatomical planes which, as Muriel pointed out, are used in kinesiology. I am, therefore, inclined to think that the Spanish text is referring to the muscle "layers".
peer agreement (net): +1
