Phosphate homeotasis in healthy subjects during prolonged periodic and continuous hypokinesia

Objective: This study aimed to show that during hypokinesia (HK), phosphate (Pi) imbalance increases more with higher than lower physical activity and that Pi absorption reduces more with higher than lower Pi imbalance in subjects with higher than lower muscular activity. Methods: Studies were conducted on 30 healthy male subjects during 364 days of HK. They were equally divided in three groups: unrestricted active control subjects (UACS), continuously hypokinetic subjects (CHKS) and periodically hypokinetic subjects (PHKS). CHKS were kept under average walking distances of 0.5 ± 0.2 km day− 1 PHKS were kept under average walking distances of 0.5 ± 0.1 and running average distances of 8.7 ± 1.2 km day− l for 5 days and 2 days per week, respectively. UACS were placed under average running distances of 8.7 ± 1.2 km day− l. Results: Pi imbalance, serum, urine and fecal Pi levels, and urine and serum calcium (Ca2+) levels increased significantly (p < 0.05) and Pi absorption, and serum intact parathyroid hormone (iPTH) and 1,25-dehydroxyvitamin D (1,25 (OH)2 D3) levels decreased significantly (p < 0.05) in CHKS and PHKS compared with their pre-HK values and their respective active control (UACS). However, the Pi imbalance, serum, urine and fecal Pi levels, and serum and urine Ca2+ levels increased more significantly (p < 0.05), and Pi absorption and serum iPTH and 1,25 (OH)2 D3 levels decreased more significantly in PHKS than in CHKS. Conclusions: Higher Pi imbalance with higher than lower physical activity shows that the risk of higher Pi imbalance is inversely related to the intensity of physical activity. Lower Pi absorption with higher than lower Pi imbalance shows that the risk of lower Pi absorption is inversely related to magnitude of Pi imbalance. In conclusion Pi imbalance increases more with higher than lower physical activity and that Pi absorption decreases more with higher than lower Pi imbalance indicating that during HK the use of Pi decreases more with higher than lower physical activity.