Sprint Interval Training Induces A Sexual Dimorphism but does not Improve Peak Bone Mass in Young and Healthy Mice

Abstract

Elevated peak bone mass in early adulthood reduces the risk for osteoporotic fractures at old age. As sports participation has been correlated with elevated peak bone masses, we aimed to establish a training program that would efficiently stimulate bone accrual in healthy young mice. We combined voluntary treadmill running with sprint interval training modalities that were tailored to the individual performance limits and were of either high or intermediate intensity. Adolescent male and female STR/ort mice underwent 8 weeks of training before the hind legs were analyzed for cortical and trabecular bone parameters and biomechanical strength. Sprint interval training led to increased running speeds, confirming an efficient training. However, males and females responded differently. The males improved their running speeds in response to intermediate intensities only and accrued cortical bone at the expense of mechanical strength. High training intensities induced a significant loss of trabecular bone. The female bones showed neither adverse nor beneficial effects in response to either training intensities. Speculations about the failure to improve geometric alongside mechanical bone properties include the possibility that our training lacked sufficient axial loading, that high cardio-vascular strains adversely affect bone growth and that there are physiological limits to bone accrual.

Young and healthy C57BL/6 J mice performing sprint interval training reveal gender- and site-specific changes to the cortical bone

“…It therefore seems suggestive that male and female C57BL/6 J mice indeed benefit from different training regimen. Moreover, by confirming that our SIT not only leads to loss of cortical bone in the high bone mass STR/ort but also in the low bone mass C57BL/6 J mice 14 , we were able to show that it is not the underlying bone phenotype that impacts on the bone’s capacity to respond to physical strain but rather the sex 8 . Indeed, previous publications on the role of the bone phenotype on the response to physical activity are conflicting 15 , 16 .…”

“…We thus designed a high intensity sprint interval training (SIT) with the sprints providing a high frequency of strains and the intervals reducing the fatigue adoption of bone as a reaction to an otherwise monotonous stimulus. Surprisingly, in our previous experiments, both sexes failed to improve geometric alongside mechanical bone properties 8 . In order to find out whether these findings were strain specific, we here turned to the C57BL/6 mouse and hypothesized that the low bone mass phenotype of C57BL/6 mice might be more permissive for bone accrual following physical strain.…”

“…The present study is a direct continuation of former experiments 8 and differs from previously described bone stimulating training programs by the use of sprint intervals as opposed to endurance running. The aim behind our sprint interval training was to increase the frequency of the strain and to add a systemic impact that resulted from exceeding the anaerobic threshold.…”

“…We thus picked up on the hypothesis that an increased bone accrual can be achieved by increasing the frequency of the impact, the intensity of the strain or a combination of both 6 , 7 . However, our previous study on the high bone mass mouse STR/ort already showed that female and male mice responded differently to the training 8 . While the female STR/ort bones remained unaffected by the SIT, the males showed a diaphyseal decrease of tibia’s cortical bone and a reduced femoral strength.…”

“…In order to design a physiological training program that in the future can be applied to prevent osteopenia in patients at risk, we previously turned to the STR/ort mouse as a model and the treadmill as training device 8 . As an improvement of geometric and mechanical bone properties following moderate treadmill training in young and middle-aged mice had already been described 9 , 10 , the aim of our previous study was to combine existing training programs with the insight gained from in vivo mechanical loading experiments.…”