Adaptation of Bone to Mechanical Strain—Reply

Abstract

To the Editor In a mixed longitudinal study of healthy children, adolescents, and young adults (n = 2014; 50.7% female and 23.8% African American), McCormack et al 1 showed that peak height velocity was followed by peak acquisition of whole-body bone mineral content (BMC) and the age of peak acquisition of skeletal site-specific as well as whole-body BMC was younger in females compared with males. 1 These findings are in agreement with a natural homeostatic system in the skeleton.Mechanical loading engendered by habitual physical activities results in elastic deformation (strain) of bone, and its structure is normally within control of the mechanical strainrelated stimulus. 2 Because a decrease in bone material stiffness increases the resulting strain level, the low degree of mineralization caused by high bone remodeling during growth can support rapid increases in whole-body and skeletal sitespecific BMC through the enhancement of mechanical strainrelated stimuli. 3 The compensatory adaptation of bone to mechanical strain is consistent with peak height velocity followed by peak acquisition of whole-body BMC 1 ; bone gain results from height gain but not vice versa. The degree of skeletal mineralization could be estimated using circulating systemic markers of bone turnover 4 and the younger age of peak acquisition of BMC in females compared with males 1 is also compatible with a sex difference in the age with peak concentrations of serum bone formation and resorption markers. 5 Compensatory skeletal adaptation to mechanical strain resulting from physical activity mentioned previously is an excellent mechanism during growth, which agrees with the finding that both BMC and lean soft tissue were higher in African American children and adolescents compared with non-African American children and adolescents. 1 However, at the same time, this system has also the Achilles' heel: high physical activity increases the risk of trauma, and the low degree of mineralization causes fragile bone tissue. These weaknesses seem to be linked to an increased incidence of fractures during childhood, in addition to the lag between height and bone gains. 1 Finally, I agree with the authors that late adolescence is an important opportunity to maximize peak bone mass. 1 Although an increase in whole-body BMC after the cessation of linear growth 1 might be partly associated with an increase in the degree of mineralization from a decrease in bone remodeling, 5 it is likely that the capacity of skeletal response to mechanical loading is still high during this period, and therefore, high-impact dynamic exercise would be expected to stimulate bone modeling.

Taohong Siwu Decoction Promotes Osteo-Angiogenesis in Fractures by Regulating the HIF-1α Signaling Pathway

“…Approximately 10% of fractures fail to heal normally, which results in pain, disability, and repetitive operative interventions [ 2 ]. The process of fracture treatment is affected by multiple biological factors, including inflammation [ 3 ], oxygen content [ 4 ], hormone [ 5 ], and mechanical stimulation [ 6 ]. It is necessary to explore effective agents or methods to repair the condition of the injury in fracture healing.…”