This paper has interesting insights on how mechanical loading and gravity can enhance longitudinal bone growth.
“Our goal was to study the role of mechanical loading (one of the components of ambulation) on endochondral ossification and longitudinal bone growth. Thus, we applied cyclical, biologically relevant strains for a prolonged time period (4 weeks) to one tibia of juvenile mice, while using the contralateral one as an internal control. By the end of the 4-week loading period, the mean tibial growth of the loaded tibiae was significantly greater than that of the unloaded tibiae. The mean height and the mean area of the loaded tibial growth plates were greater than those of the unloaded tibiae. In addition, in female mice we found a greater expression of PTHrP in the loaded tibial growth plates than in the unloaded ones.”
This suggests that possibly boosting PTHrP directly could induce additional longitudinal bone growth.
“Mechanical forces related to gravitational changes, ambulation, and exercise may contribute to modulate bone growth.”<-this suggests that exercises that invert and every may modulate longitudinal bone growth.
“daily physical activities transmit complex mechanical loads including tension, compression, torsion, and shear to the skeleton”<-there are many ways to load bones that are under explored.
“Seventy-five 4-week old TOPGAL mice were exposed to mechanical loading using a Bose ElectroForce 3220 dynamic loading system. Before each loading session, mice were anesthetized with 3.5% isoflurane. Each loading session included 100 compressive loading cycles of 5 Newton (N) force to the right tibia at the frequency of 2 Hz per cycle”<-the reason that cyclic loading is more effective than static loading is likely related to fluid flow.
“mean tibial growth of the loaded tibiae was significantly greater than that of the unloaded tibiae, in the whole sample of mice “
“Gravity and physical activity generate mechanical forces on the long bones and on the growth plates that may be involved in the regulation of bone growth.”<-one of the reasons why lateral loads are so effective is that it applies loads in a different mannerism against gravity.
“Of note, the stimulatory effect of mechanical loading on tibial growth persisted in the 4 weeks following the cessation of loading.
In addition, at the end of the 4-week loading period the whole growth plate and the epiphyseal zone heights, as well as the overall area of the loaded tibial growth plates were significantly greater than those of the unloaded growth plates. Such finding suggests a loading-mediated enhanced growth plate chondrocyte formation”
The study mentions that too high load can suppress growth. So maybe lighter weights are better and applying it the right way is more important but that may be for growth plates and not bones. Higher loads may be needed to stimulate growth in adult bones as bones are tougher tissue than catilage.
“similar studies in rodents indicate that elevated loading forces tend to inhibit longitudinal growth, while strains of lower intensity (like ours) tend to stimulate it. “
“After 4 weeks of loading, we found a greater Pthrp gene expression in the growth plate chondrocytes of the female mouse loaded tibiae, while no difference was found in male mice” however male mice also had greater length. So this suggests that mechanical loading also influences length by mechanisms not related to PTHrP.