Reflex Activity During Bone-Loading Exercises

Background and Objectives: Wolff was the first to propose that the microarchitectural structure and mechanical resistance of bone are remodeled in response to mechanical loads it experiences. Frost further expanded on this concept with the mechanostat theory, suggesting that bone formation and resorption remain in balance during routine daily activities. Decreased activity leads to increased bone resorption, while increased activity stimulates bone formation. Consequently, the microarchitectural structure and strength of bone weaken or strengthen accordingly. Recently, the bone reflex has been defined, suggesting that the central nervous system controls the local regulatory mechanisms described by Wolff and Frost. The bone reflex describes how osteocytes are stimulated by mechanical loading, leading to the neural regulation of bone formation and resorption according to mechanical needs (bone osteoregulation reflex). Additionally, it describes a mechanism by which the nervous system reflexively regulates the activity of surrounding muscles to optimally position the bone to resist applied mechanical load (bone myoregulation reflex).

Load-bearing exercises are well-established as beneficial for bone health, with their role in promoting healthy bone development and managing osteoporosis being widely recognized. However, the neural mechanisms underlying the positive biomechanical effects of jumping-based load-bearing exercises, such as running, volleyball, basketball, tennis, and rope skipping, remain unclear. The aim of this study is to investigate whether jumping-based load-bearing exercises activate bone myoregulation reflex activity.

Methods: The study will be conducted with a total of 40 healthy volunteers aged 20-50, comprising both women and men. Participants will be recruited from individuals who either regularly engage in jumping-based sports activities (e.g., volleyball, marathon running, and tennis) or those who perform typical daily living activities without regular sports engagement. Participants will be divided into two groups based on their activity levels: Group 1 (Normally Active Individuals) and Group 2 (Athletic Individuals).

Procedures:

Bone myoregulation reflex activity of the soleus and tibialis anterior muscles will be assessed in both groups during whole-body vibration and jumping using surface electromyography.

• Jumping Test: Participants will be instructed to jump in place 20 times, similar to rope skipping, with a 5-second rest interval between each jump.
• Whole-Body Vibration: Participants will stand on the plate and undergo low-amplitude (1.2 mm) whole-body vibration at eight different frequencies (25, 27, 29, 31, 33, 35, 37, and 39 Hz) using a Powerplate Pro5 (Netherlands) device. Each vibration session will last for 10 seconds, with a 5-second rest interval between frequencies.

Inclusion criteria

• Age: Between 20-50 years old
• Gender: Male or female
• Health status: Good general health
• Physical activity: Normally Active Individuals or Regularly engaging in jumping sports activities such as volleyball, marathon, or tennis, or not engaging in such activities

Exclusion criteria

• Individuals who cannot tolerate whole-body vibration
• Individuals with a history of neuromuscular disease
• Individuals with a history of skeletal disease