Parathyroid hormone concentrations during and after two periods of high intensity exercise with and without an intervening recovery period

The purpose of this study was to examine the effect of a recovery period between two periods of exercise on bone metabolism and related hormones. Concentrations of serum parathyroid hormone ([PTH]), plasma ionized calcium ([Ca2+]) and total calcium were measured. A group of 12 healthy men aged 20-27 years participated in this study. They took part in two exercise protocols (P-1 and P-2) on two separate weeks. The exercise in P-1 comprised two successive periods of 21 min each at 70% and 85% of maximal oxygen uptake; P-2 comprised two periods of exercise at the same intensities but separated by 40 min of recovery. Venous blood samples were collected I day before the sessions (control), before each protocol, during (7th and 21st min), at the end (42nd min in P-1 and 82nd min in P-2) and after 24 h of recovery. The [PTH] was significantly elevated during the two protocols (P < 0.0 1), remained raised in P-1 after 24 h of recovery (P < 0.05) and was significantly lower (P < 0.01) at the end of P-2 when compared to P-1. The [Ca2+] decreased significantly during and at the end of the two protocols (P < 0.01) and had returned to control values after 24h of recovery. Plasma lactate concentration increased during the two protocols (P < 0.01) and returned to control values after recovery. These results indicate firstly that [Ca2+] decreases during continuous exercise as [PTH] increases and remains raised after 24 h of recovery, secondly that a recovery period between two periods of exercise attenuates the variations in [Ca2+] and [PTH], and thirdly that recovery may have anabolic effects on bone. However, the small physiological changes observed prevent us from forming any firm conclusion about this.