Study: Effects of Creatine Loading

Study 1: The study investigated the effect of dietary creatine supplementation on skeletal muscle creatine levels and urinary creatinine excretion. Muscle creatine concentration increased by 20% after 6 days of supplementation with 20 g/day, and this increase was maintained with a daily supplementation of 2 g for 30 days. Muscle creatine concentration declined when supplementation was stopped. A similar increase in muscle creatine was observed with a daily supplementation of 3 g over 28 days. In conclusion, ingesting 20 g of creatine for 6 days followed by a maintenance dose of 2 g/day can rapidly increase and maintain muscle creatine levels, while 3 g/day can also be effective in the long term.

Study 2: The study investigated the time course of ventilatory failure, pump failure, and diaphragm peripheral fatigue during the application of inspiratory resistive loads in anesthetized rabbits. Ventilatory failure, indicated by increased spontaneous diaphragm activity, hypercapnic acidosis, and hypoxemia, occurred before any signs of contractile fatigue or pump failure. The diaphragm’s ability to generate force remained stable until respiratory arrest (apnea), when it decreased. The study suggests that ventilatory failure is due to central fatigue, while pump failure is caused by multiple factors.

Study 3: The study examined the effect of inspired oxygen concentration on blood lactate accumulation during exercise. Eleven men performed cycling exercise at different intensities while breathing varying levels of oxygen. Leg lactate release in the muscles accounted for 90% of the variability in blood lactate concentration. The study concluded that the rate of net lactate release in locomotory muscles primarily determines blood lactate accumulation during exercise, regardless of the inspired oxygen concentration.

Study 4: The study investigated whether autologous erythrocyte infusion could improve maximal oxygen uptake (VO2max) in lowlanders at high altitude. Sixteen men had their VO2max measured at sea level and on the 1st and 9th days of high-altitude residence. One group received an erythrocyte infusion, while the control group received saline. Despite higher arterial hematocrit and oxygen content in the erythrocyte-infused group, there was no difference in VO2max between the groups at high altitude. The study concluded that erythrocyte infusion did not mitigate the decrement in VO2max at high altitude.

Study 5: The study examined the role of the sensory nerve inhibitory system in modulating contraction in rat intrapulmonary bronchi. Desensitization of sensory nerves, antagonizing neurokinin NK1 receptors, and inhibiting cyclooxygenase enhanced contractions induced by electrical field stimulation (EFS) but had no effect on acetylcholine-induced contractions. Substance P, an inhibitory neuropeptide, significantly reduced EFS-induced contractions but had a modest effect on acetylcholine-induced contractions. The study concluded that the sensory nerve inhibitory system modulates cholinergic contractions and plays a role in regulating airway smooth muscle tone.