Oxygen consumption and heart rate responses during and after constant load and alternating intensity exercise at 105% of lactate threshold.

AIM: The purpose of this study was a secondary-analysis of previously published data, in order to compare the acute VO2 responses, the time spent at high percentage of VO2max and total VO2 consumed (TVO2) between constant and alternating intensity exercise of the same intensity and duration. This study also aimed to examine VO2 and heart rate (HR) responses one hour after both exercises. METHODS: Ten recreationally trained men (24.7±4.7 years) completed the following two exercise tests lasting an hour each and having the same mean intensity at 105% of lactate threshold (70% VO2max): 1) constant load cycling (CON), and 2) alternating intensity exercise (ALT), during which 40 seconds of light exercise (47% VO2max) were alternated with 20 seconds of supramaximal intensity at 120% of VO2max. RESULTS: TVO2 (69.89±7.02 vs. 58.22±9.13 mL/kg/min, P=0.03) and HR (142±16, 128±12, P=0.04) was higher in CON exercise compared to ALT. All participants reached 70% and 80% of VO2max irrespective of the exercise protocol. In ALT exercise the time spent at 90% was higher compared to CON exercise (70.81±21.37 vs. 36.88±11.88 seconds). Also, TVO2 recovery values after ALT exercise was higher compared to CON (11.1 ±2.93 vs. 9.94±3.54 mL/kg/min). CONCLUSION: ALT exercise allowed participants to spend longer time at 90% of VO2max, even if TVO2 in CON exercise was higher, suggesting that in ALT exercise greater aerobic stress (as based on exercise intensity) is imposed on the athletes. While VO2 recovery values were higher in ALT compared to CON, indicating different substrate utilization during and after exercise.

Immune responses during and after exercise of constant and alternating intensity above the lactate threshold.

AIM: Intense and prolonged exercise greatly affects circulating cytokine levels. The purpose of this study was to investigate the possible changes in tumour necrosis factor -a (TNF-a), interleukin 6 (IL-6) and cortisol concentrations during and after prolonged exercise of constant and alternating intensity of the same duration and total work performed. METHODS: Ten male subjects underwent two main cycling exercise trials lasting one hour each. On one occasion, exercise intensity was alternated between 46.5±1.9% of maximal oxygen uptake (VO2max ) for 40 s and 120% of VO2max for 20 s, so that the mean intensity corresponded to 105% of the lactate threshold. On the other occasion, exercise intensity was constant at 105% of the lactate threshold. Levels of TNF-a, IL-6 after lipo polysaccharide (LPS) stimulation as well as cortisol were measured at rest, 30 and 60 minutes of exercise and 1 hour after. RESULTS: No significant differences were observed in TNF-a concentrations between the two exercise protocols (P= 0.75), but there was a significant time effect (P<0.01). TNF-a was increased in both groups from a resting value of 436.1±102.5 to 649.5±187.7 pg/mL (P<0.05) at the end of exercise and was subsequently decreased 1 hour post exercise to 305.9±78.8 pg/mL (P<0.01). No significant difference in IL-6 and cortisol concentrations was observed between the two exercise protocols (P=0.13, P=0.10 accordingly). CONCLUSION: In conclusion, prolonged constant and alternating intensity exercise of the same mean intensity and duration seemed to provoke similar changes in aspects of immune response in healthy subjects.

Exercise induced arterial hypoxemia in swimmers.

AIM: Exercise induced arterial hypoxemia (EIAH) is a reduction in arterial oxygenation, which may result from a drop in arterial oxygen pressure and therefore in oxygen saturation. We examined EIAH in swimmers, while till now it was known to occur in cyclists and runners. METHODS: We studied 8 male highly trained swimmers (age: 23+/-1.7; (.-)VO(2peak), 5.3+/-0.1 l/min and 8 male ex-swimmers (age: 21.5+/-0.6; (.-)VO(2peak), 3.4+/-0.3 l/min). All subjects performed 200-meter freestyle at maximum effort. Hemoglobin saturation (SaO(2)%) was measured using a finger pulse oximeter before exercise in the water in an upright position and immediately after exercise, within 5 seconds. RESULTS: Highly trained swimmers developed a statistically significant decrease in SaO(2)% (from 98.3+/-0.3 to 94+/-0.9, p= or <0.01) after exercise, while ex-swimmers did not (from 98.4+/-0.3 to 96.8+/-0.3 ns). The 4% decrease in SaO(2)% observed in highly trained swimmers can be characterized as mild EIAH. CONCLUSIONS: Our study suggests that highly trained swimmers but not ex-swimmers may develop mild EIAH after 200 meters freestyle swimming at maximum effort.