What is the fine-grained topic of the following text: This causes the muscles of the neck, shoulders, upper back, and chest to alter their length and efficiency as they struggle to counter-balance the weight of the heavy head against the pull of gravity — with the muscles in the neck and front body becoming tight and short and those in the mid back and the back of the shoulders becoming weak and overstretched. Only return the topic.
Effects of heavy head on upper body muscles