Adaptations of bone and bone vasculature to muscular stretch training

Julia Eazer; Mina Barsoum; Cole Smith; Kazuki Hotta; Brad Behnke; Christina Holmes; Jacob Caldwell; Payal Ghosh; Emily Reid-Foley; Hyerim Park; Michael Delp; Judy Muller-Delp

doi:10.1093/jbmrpl/ziad019

Adaptations of bone and bone vasculature to muscular stretch training

JBMR Plus. 2024 Jan 4;8(3):ziad019. doi: 10.1093/jbmrpl/ziad019. eCollection 2024 Mar.

Authors

Julia Eazer¹, Mina Barsoum², Cole Smith¹, Kazuki Hotta^{1

3}, Brad Behnke⁴, Christina Holmes⁵, Jacob Caldwell¹, Payal Ghosh⁶, Emily Reid-Foley¹, Hyerim Park⁶, Michael Delp⁶, Judy Muller-Delp¹

Affiliations

¹ Department of Biomedical Sciences, Florida State University, Tallahassee, Fl, 32304, United States.
² Department of Chemical Engineering, Florida State University, Tallahassee, Fl, 32304, United States.
³ Department of Physical Therapy, Niigata University of Health and Welfare, Niigata, Japan.
⁴ Department of Kinesiology & Johnson Cancer Research Center, Kansas State University, Manhattan, KS, 66506, United States.
⁵ Department of Biomedical Engineering, Florida State University, Tallahassee, FL, 32310 United States.
⁶ Department of Nutrition and Integrative Physiology, Florida State University, Tallahassee, Fl, 32304, United States.

Abstract

The magnitude of bone formation and remodeling is linked to both the magnitude of strain placed on the bone and the perfusion of bone. It was previously reported that an increase in bone perfusion and bone density occurs in the femur of old rats with moderate aerobic exercise training. This study determined the acute and chronic effects of static muscle stretching on bone blood flow and remodeling. Old male Fischer 344 rats were randomized to either a naive or stretch-trained group. Static stretching of ankle flexor muscles was achieved by placement of a dorsiflexion splint on the left ankle for 30 min/d, 5d/wk for 4wk. The opposite hindlimb served as a contralateral control (nonstretched) limb. Bone blood flow was assessed during and after acute stretching in naive rats, and at rest and during exercise in stretch-trained rats. Vascular reactivity of the nutrient artery of the proximal tibia was also assessed in stretch-trained rats. MicroCT analysis was used to assess bone volume and micro-architecture of the trabecular bone of both tibias near that growth plate. In naive rats, static stretching increased blood flow to the proximal tibial metaphasis. Blood flow to the proximal tibial metaphysis during treadmill exercise was higher in the stretched limb after 4 wk of daily stretching. Daily stretching also increased tibial bone weight and increased total volume in both the proximal and distal tibial metaphyses. In the trabecular bone immediately below the proximal tibial growth plate, total volume and bone volume increased, but bone volume/total volume was unchanged and trabecular connectivity decreased. In contrast, intravascular volume increased in this region of the bone. These data suggest that blood flow to the tibia increases during bouts of static stretching of the hindlimb muscles, and that 4 wk of daily muscle stretching leads to bone remodeling and an increase in intravascular volume of the tibial bone.

Keywords: blood flow; endothelium; microCT; radioactive microspheres; tibia; tibial nutrient artery.