Final answer:
Extreme negative energy balance most directly affects reproductive function, leading to hormonal imbalances that interfere with reproductive health. It can also result in muscle loss and decreased bone density, increasing the risk for osteoporosis.
Step-by-step explanation:
Extreme negative energy balance can affect reproductive function, muscle growth, and bone density. When the body is in a state of negative energy balance, it is consuming fewer calories than it expends. This can lead to muscle loss due to the body breaking down muscle tissue for energy. Reproductive function may be impaired because the body prioritizes survival over reproduction when energy is scarce. Bone density can also decline, increasing the risk of developing osteoporosis, as the body may lack the necessary nutrients to maintain strong bones.
Regarding the choices presented in the question, option c) reproductive function is directly affected by extreme negative energy balance. Such a condition could lead to hormonal imbalances that interfere with the reproductive system, making it difficult to maintain a pregnancy or reducing fertility. Bone disorders like osteoporosis are also related to inadequate nutrition and can result from long-term negative energy balance. Lastly, options a) weight gain and b) muscle growth are typically associated with positive energy balance rather than negative.