An Investigation Into The Effects Of Brief Diverse Exercise On Bone

Abstract

Rationale Physical inactivity (PA) is a modifiable risk factor for reduced bone mineral density (BMD) associated with sedentary behaviour, and bone impairment in states of low energy availability has been demonstrated in lean athletes, such as ballet dancers. Team sport is shown to provide an anabolic stimulus to bone; however, it is not known whether there is an osteogenic effect at reduced exercise duration. To address this, we investigated the effects of brief bouts of team sports activity in two populations associated with potential impairment to bone health: sedentary females and ballet dancers, to evaluate the potential for an osteogenic effect of low-volume, diverse exercise. Methods Brief bouts of small-sided football (SSG) were investigated in sedentary females (SF) and a novel diverse HIIT protocol (DM-HIIT) in SF and female (DF) and male ballet dancers (MBD). Chronic effects of exercise were measured with DXA (SSG) and calcaneal QUS (DM-HIIT) and bone turnover markers (BTM) were used to characterise acute responses to exercise (SSG) and background bone metabolism (SSG, DM-HIIT). Gonadal hormones were measured at rest (DF, MBD). Locomotor profile was characterised by distance using GPS activity domains (SSG) and by duration for tri-orthogonal acceleration data (DM-HIIT) in bands from low (1 – 1.5 g) to high (> 3 g) threshold. Results Whereas diverse exercise as SSG increased total hip BMD in SF and acutely elevated bone formation, there was no effect of 12 weeks DM-HIIT on calcaneal bone (SF, DF, MBD) or background BTMs (SF, MBD), however in DF bone resorption decreased and accelerations > 3 g significantly increased after 12 weeks training. Gonadal hormone profile (DF) indicated menstrual dysfunction in female dance cohorts. Participants achieved HIIT intensity thresholds during DM-HIIT and there was a direction-specific effect on vertical accelerations, which increased after 12 weeks training in all bands (SF, DF, MBD), and significantly above 3 g (highest threshold) in female dancers. Conclusion We demonstrated an osteogenic effect on hip BMD and elevation in bone formation for low-duration SSG, and background bone resorption was reduced after 12 weeks diverse HIIT in female ballet dancers. However, bone formation did not increase, which was speculatively attributed to impairment in gonadotropic hormone profile in the dancers. High-intensity accelerations are proposed to represent the potential osteogenic signal elicited by diverse HIIT. Longer (> 4 months) studies using pQCT/ DXA and BTMs to characterise acute, as well as background, bone metabolic responses are recommended to investigate the potential of brief, diverse HIIT in populations who may benefit from exercise to improve bone health.