Figure 2.

There are both positive and negative factors secreted by muscle and bone. Contraction of muscle and loading of bone appear to induce the release of positive factors. The muscle factor myostatin not only has negative effects on muscle mass but also on bone. The factors RANKL and TGFβ, released during bone resorption, have negative effects on muscle. At this time, the effects of exercise, age, stress, and circadian rhythm on this crosstalk is unknown providing a fertile area for future investigations.