Which physical change is typically observed in boys during puberty?

During puberty, boys typically experience significant physical changes due to hormonal shifts, particularly the increase in testosterone. One of the most notable changes is the widening of the shoulders. This change is related to the growth of muscle mass and bone density, contributing to a more masculine physique. The shoulders become broader as a result of the development and growth of the skeletal structure, which is one of the characteristics that distinguishes male physical development during this stage.

The other choices present variations in physical condition that do not typically correspond with the changes seen specifically during puberty in boys. For instance, an increase in blood pressure can occur for various reasons but is not a hallmark physical change of puberty itself. Similarly, a decrease in testicular size would not be an expected change; rather, testicular size typically increases as they mature. Lastly, hair thickness usually increases during puberty, so the notion of thinner body hair contrasts with the expected development during this growth phase.