Morton's model is a good descriptor of the mechanics of ramp tests. Further developments of Morton's model demonstrated that, whereas [Formula: see text] is a protocol-dependent variable, the difference between [Formula: see text] and CP is a constant, so that their values do not depend on the protocol applied.

The lack of steady phase during exercise apnoeas suggests that the conditions determining R3 were already attained at the end of E1. This being so, E2 would correspond to R3.

Exercise and nutrition are often used in combination to lose body fat and reduce weight. In this respect, exercise programs are as important as correct nutrition. Several issues are still controversial in this field, and among them there are contrasting reports on whether training in a fasting condition can enhance weight loss by stimulating lipolytic activity. The authors' purpose was to verify differences in fat metabolism during training in fasting or feeding conditions. They compared the effect on oxygen consumption (VO2) and substrate utilization, estimated by the respiratory-exchange ratio (RER), in 8 healthy young men who performed the same moderate-intensity training session (36 min of cardiovascular training on treadmill at 65% maximum heart rate) in the morning in 2 tests in random sequence: FST test (fasting condition) without any food intake or FED test (feeding condition) after breakfast. In both cases, the same total amount and quality of food was assumed in the 24 hr after the training session. The breakfast, per se, increased both VO2 and RER significantly (4.21 vs. 3.74 and 0.96 vs. 0.84, respectively). Twelve hours after the training session, VO2 was still higher in the FED test, whereas RER was significantly lower in the FED test, indicating greater lipid utilization. The difference was still significant 24 hr after exercise. The authors conclude that when moderate endurance exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization; rather, physical activity after a light meal is advisable.

a b s t r a c tPurpose: We hypothesized that the third dynamic phase ( 3) of the cardiovascular response to apnoea requires attainment of the physiological breaking point, so that the duration of the second steady phase ( 2) of the classical cardiovascular response to apnoea, though appearing in both air and oxygen, is longer in oxygen. Methods: Nineteen divers performed maximal apnoeas in air and oxygen. We measured beat-by-beat arterial pressure, heart rate (f H ), stroke volume (SV), cardiac output (Q ). Results: The f H , SV andQ changes during apnoea followed the same patterns in oxygen as in air. Duration of steady 2 was 105 ± 37 and 185 ± 36 s, in air and oxygen (p < 0.05), respectively. At end of apnoea, arterial oxygen saturation was 1.00 ± 0.00 in oxygen and 0.75 ± 0.10 in air. Conclusions:The results support the tested hypothesis. Lack of hypoxaemia during oxygen apnoeas suggests that, if chemoreflexes determine 3, the increase in CO 2 stores might play a central role in eliciting their activation.