Effect of prolonged exercise on arterial oxygen saturation in athletes susceptible to exercise-induced hypoxemia

This study examined the effect of prolonged endurance exercise on the development of exercise-induced hypoxemia (EIH) in athletes who had previously displayed EIH during an incremental maximal exercise test. Five male and three female endurance-trained athletes participated. Susceptibility to EIH was confirmed through a maximal incremental exercise test and defined as a reduction in the saturation of arterial oxygen (SpO(2)) of >/=4% from rest. Sixty minutes of running was conducted, on a separate day, at an oxygen consumption corresponding to 95% of ventilatory threshold. Immediately following the 60 min exercise bout, athletes commenced a time trial to exhaustion at 95% maximal oxygen consumption (VO(2max)). The reduction in SpO(2) was significantly greater during the maximal incremental test, than during the 60 min, or time trial to exhaustion (-8.8+/-1.4%, -3.3+/-1.1%, and -4.1+/-2.3%, P<0.05, respectively). The degree of desaturation during the 60 min was significantly related to the relative intensity of exercise at 95% ventilatory threshold (adjusted r(2)=0.54, P=0.02). In conclusion, athletes who did not exercise at greater than 73% VO(2max) during 60 min of endurance exercise did not display EIH, despite being previously susceptible during an incremental maximal test.     

Non-linear relationships between central cardiovascular variables and VO2 during incremental cycling exercise in endurance-trained individuals

AIM: The purpose of this study was to examine the relationships between the central cardiovascular variables (cardiac output, stroke volume and heart rate) and oxygen uptake (VO2) during continuous, incremental cycle exercise to maximal aerobic capacity (VO2max). METHODS: Twenty-one moderately to highly trained males (n=19) and females (n=2) participated in the study. A baseline maximal exercise test was performed to measure VO2max. Following the initial VO2max test, cardiac output was measured (CO2 rebreathing technique) at rest and 3 times during each of 4 exercise trials (2 submaximal tests to 90% VO2max and 2 maximal tests). Stroke volume and arteriovenous O2 difference were calculated using standard equations. RESULTS: Significant non-linear relationships were found between all central cardiovascular variables and VO2 (P<0.01). A plateau in cardiac output at VO2max was identified in 3 subjects. Stroke volume plateaued at an average of 37+/-12.5% of VO2max in 18 subjects and increased continuously to VO2max in 3 subjects. The arteriovenous O2 difference progressively increased to VO2max in 17 subjects and revealed a plateau response in 4 subjects. CONCLUSIONS: Our data suggest that there is a significant non-linear relationship between the central cardiovascular variables and VO2 during incremental exercise to VO2max. Furthermore, depending on the person, VO2max may be limited by cardiac output (evidence of cardiac output[Q] plateau) or peripheral factors (continued increase in Q).     

Oxygen uptake response to an 800-m running race

We tested the hypothesis that time course of O (2) uptake (VO (2)) measured during a supramaximal exercise performed in the field is driven to maximal oxygen uptake (VO (2max)). On an outdoor track, five middle-distance male runners first performed a test to determine VO (2max) and a supramaximal 800-m running test at least two days apart. VO (2) response was measured from the start to the end of exercise with the use of a miniaturised telemetric gas exchange system (Cosmed K4). VO (2max) was reached by all subjects 45 +/- 11 s (mean +/- SD) after the onset of the 800-m race (i.e., 316 +/- 75 m), and was maintained during the next 33 +/- 6 s (i.e., 219 +/- 41 m). The mean relative exercise intensity of the 800 m was 120 % VO (2max). An unexpected significant decrease in VO (2) (24.1 +/- 7.0 %; p < 0.05) was observed in all subjects during the final 38 +/- 17 s (i.e., the last 265 +/- 104 m). We concluded that, at onset of a simulated 800 m running event, VO (2) is quickly projected towards the VO (2max), and then becomes limited by the achievable VO (2max). This race profile shown by all athletes is in some contrast to what can be expected from earlier findings in a laboratory setting.     

Physiological response to water aerobics.

Heart rate (HR) and oxygen uptake (VO2) measured during water aerobics (WA) were compared to maximal values obtained during an incremental treadmill test to assess the energy demand and potential cardiorespiratory (CR) training effects of WA. Sixteen college-age females served as subjects (mean +/- SD = 20.4 +/- 1.6 years). WA elicited a mean HR of 162 b.min-1 and a mean VO2 of 18.4 ml.kg-1.min-1 which represented 74% of HR reserve, 82% of maximal HR, and 48% of VO2 max. Average caloric expenditure was 5.7 kcal.min-1. HR values for WA were consistent with guidelines established by the American College of Sports Medicine for developing and maintaining CR fitness in healthy adults. However, the VO2 fell just below the recommended minimum threshold level. It was concluded that WA may provide an attractive alternative to traditional modes of exercise for improving CR fitness, however, HR measures may overestimate the metabolic intensity of the exercise.     

Effect of exercise intensity on relationship between VO2max and cardiac output

PURPOSE: The purpose of this study was to determine whether the maximal oxygen uptake (VO2max) is attained with the same central and peripheral factors according to the exercise intensity. METHODS: Nine well-trained males performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with VO2max (pVO2max) and maximal cardiac output (Qmax). Two days later, they performed two continuous cycling exercises at 100% (tlim100 = 5 min 12 s +/- 2 min 25 s) and at an intermediate work rate between the lactate threshold and pVO2max (tlimDelta50 +/- 12 min 6 s +/- 3 min 5 s). Heart rate and stroke volume (SV) were measured (by impedance) continuously during all tests. Cardiac output (Q) and arterial-venous O2 difference (a-vO2 diff) were calculated using standard equations. RESULTS: Repeated measures ANOVA indicated that: 1) maximal heart rate, VE, blood lactate, and VO2 (VO2max) were not different between the three exercises but Q was lower in tlimDelta50 than in the incremental test (24.4 +/- 3.6 L x min(-1) vs 28.4 +/- 4.1 L x min(-1); P < 0.05) due to a lower SV (143 +/- 27 mL x beat(-1) vs 179 +/- 34 mL x beat(-1); P < 0.05), and 2) maximal values of a-vO2 diff were not significantly different between all the exercise protocols but reduced later in tlimDelta50 compared with tlim100 (6 min 58 s +/- 4 min 29 s vs 3 min 6 s +/- 1 min 3 s, P = 0.05). This reduction in a-vO2 diff was correlated with the arterial oxygen desaturation (SaO2 = -15.3 +/- 3.9%) in tlimDelta50 (r = -0.74, P = 0.05). CONCLUSION: VO2max was not attained with the same central and peripheral factors in exhaustive exercises, and tlimDelta50 did not elicit the maximal Q. This might be taken into account if the training aim is to enhance the central factors of VO2max using exercise intensities eliciting VO2max but not necessarily Qmax.     

Comparison of muscle oxygen consumption measured by near infrared continuous wave spectroscopy during supramaximal and intermittent pedalling exercise

The two purposes of the present study were 1) to determine the oxygen consumption in working skeletal muscle from the oxygenation measured by near-infrared continuous-wave spectroscopy (NIRcws) with the arterial occlusion method during the resting condition, INT(VT), and INT(MAX) and 2) to examine whether the decline rate of oxygenation is related to maximal oxygen uptake. Eight healthy males (aged 19.8 +/- 0.4 yr, height 166.9 +/- 17.4 cm, weight 62.1 +/- 2.5 kg, and maximal oxygen uptake [VO2max] 55.9 +/- 1.9 ml/kg x min(-1)) took part in this study. The oxygenation was measured by NIRcws during the Wingate anaerobic test (WAnT) and two intermittent pedalling exercises of VT (INT(VT)) and maximal (INT(MAX)) work intensity. The decline rates of oxygenation obtained during the resting condition, INT(VT), and INT(MAX) with arterial occlusion were 0.43 +/- 0.05%/sec, 4.94 +/- 0.31%/sec, and 8.16 +/- 0.38%/sec, respectively, and that during the WAnT without arterial occlusion was 8.73 +/- 0.49%/sec. The decline rate of oxygenation during the WAnTwas significantly (p < 0.0001) related to maximal oxygen uptake (VO2max). These findings indicate that O2 is utilized from the early phase, even during a supramaximal pedalling exercise, and that the oxidative metabolic capacity may be a factor contributing to supramaximal exercises. Therefore the arterial occlusion method with NIRcws is suitable for the evaluation of the muscle O2 consumption during exercise noninvasively.     

The effect of exercise training on salivary immunoglobulin A and cortisol responses to maximal exercise.

The salivary immunoglobulin A (s-IgA) and cortisol responses to maximal exercise were examined in 24 adult males (X +/- SD; 22.1 +/- 3.0 yrs) before and after 10 weeks of run training. The subjects performed an incremental treadmill test to exhaustion and were randomly assigned to one of three groups: control (CON; n = 5), low intensity training (LO; n = 8), or high intensity training (HI; n = 11). Following the ten weeks of training, the subjects performed a second maximal treadmill test. Saliva samples were collected before, as well as immediately and 1 hr following each of the maximal treadmill tests and were analyzed for s-IgA and salivary cortisol. Maximal oxygen consumption (VO2max) increased significantly (p < 0.05) in the LO and HI groups but remained unchanged in the CON group. The s-IgA levels decreased significantly (p < 0.05) immediately post-exercise but returned to pre-exercise levels by one hour recovery. In addition, s-IgA and cortisol levels were not significantly (p > 0.05) correlated at any of the sampling times. These findings indicated that the s-IgA response to maximal exercise was unaffected by moderate (70% of VO2 max) to heavy (86% of VO2max) training (designed to develop cardiorespiratory fitness in healthy non-athletic adults) and independent of salivary cortisol.     

Cardiorespiratory and metabolic responses during straight and bent knee cycling

BACKGROUND: This study examined the influence of knee angle on the cardiorespiratory system loading during submaximal and maximal stationary cycle ergometry. METHODS: Experimental design and participants: eighteen untrained women (age: 21+/-1.88 years, weight: 57+/-5.75 kg, height: 165+/-5.03 cm, values are mean+/-SD) volunteered as subjects and underwent two-cycle ergometer incremental (Jaeger ER900) tests: 1) straight knee (180 degrees), 2) bent knee (140 degrees). Measures: oxygen uptake (VO2), ventilation (VE) and respiratory exchange ratio (RER) were measured continuously during each test using an open circuit spirometry and blood lactate concentration was determined by means of an enzymatic method. RESULTS: Comparing cycling with "straight knee" to cycling with "bent knee" at 50 W, heart rate (HR), V(E) and VO2 were significantly higher (10.6%, 12.5%, 17.8%). At 100 W, blood lactate was significantly lower (10.8%) while VO2 and RER was higher (5.5%, 7.1%). During maximal exercise, the total exercise time was significantly longer (11.2%) and VE, VO2 and HR were significantly higher during cycling with "straight knee" compared to cycling with "bent knee". No significant difference in peak lactate was evident between the two sitting positions. CONCLUSIONS: The results of this study indicate that cycling with bent knee requires lower oxygen uptake while pedaling with straight knee is the only way to reach VO2max during cycle testing, since the cardiorespiratory system is fully taxed.     

Effect of a prior intermittent run at vVO2max on oxygen kinetics during an all-out severe run in humans

BACKGROUND: The purpose of this study was to examine the influence of prior intermittent running at VO2max on oxygen kinetics during a continuous severe intensity run and the time spent at VO2max. METHODS: Eight long-distance runners performed three maximal tests on a synthetic track (400 m) whilst breathing through the COSMED K4 portable telemetric metabolic analyser: i) an incremental test which determined velocity at the lactate threshold (vLT), VO2max and velocity associated with VO2max (vVO2max), ii) a continuous severe intensity run at vLT+50% (vdelta50) of the difference between vLT and vVO2max (91.3+/-1.6% VO2max)preceded by a light continuous 20 minute run at 50% of vVO2max (light warm-up), iii) the same continuous severe intensity run at vdelta50 with a prior interval training exercise (hard warm-up) of repeated hard running bouts performed at 100% of vVO2max and light running at 50% of vVO2max (of 30 seconds each) performed until exhaustion (on average 19+/-5 min with 19+/-5 interval repetitions). This hard warm-up speeded the VO2 kinetics: the time constant was reduced by 45% (28+/-7 sec vs 51+/-37 sec) and the slow component of VO2 (deltaVO2 6-3 min) was deleted (-143+/-271 ml x min(-1) vs 291+/-153 ml x min(-1)). In conclusion, despite a significantly lower total run time at vdelta50 (6 min 19+/-0) min 17 vs 8 min 20+/-1 min 45, p=0.02) after the intermittent warm-up at VO2max, the time spent specifically at VO2max in the severe continuous run at vdelta50 was not significantly different.     

Exercise mode affects the time to achieve VO2max without influencing maximal exercise time at the intensity associated with VO2max in triathletes

The objective of this study was to analyze, in triathletes, the possible influence of the exercise mode (running x cycling) on time to exhaustion (TTE) and oxygen uptake (VO2) response during exercise performed at the intensity associated with the achievement of maximal oxygen uptake (IVO2max). Eleven male triathletes (21.8 +/- 3.8 yr) performed the following tests on different days on a motorized treadmill and on a cycle ergometer: 1) incremental tests in order to determine VO2max and IVO2max and, 2) constant work rate tests to exhaustion at IVO2max to determine TTE and to describe VO2 response (time to achieve VO2max - TAVO2max, and time maintained at VO2max-TMVO2max). No differences were found in VO2max, TTE and TMVO2max obtained on the treadmill tests (63.7 +/- 4.7 ml . kg (-1) . min (-1); 324.6 +/- 109.1 s; 178.9 +/- 93.6 s) and cycle ergometer tests (61.4 +/- 4.5 ml . kg (- 1) . min (-1); 390.4 +/- 114.4 s; 213.5 +/- 102.4 s). However, TAVO2max was influenced by exercise mode (145.7 +/- 25.3 vs. 176.8 +/- 20.1 s; in treadmill and cycle ergometer, respectively; p = 0.006). It is concluded that exercise modality affects the TAVO2max, without influencing TTE and TMVO2max during exercise at IVO2max in triathletes.     

The lactate minimum test protocol provides valid measures of cycle ergometer VO(2)peak

AIM: The aim of the present study was to investigate the validity of the Lactate Minimum Test (LMT) for the determination of peak VO(2) on a cycle ergometer and to determine the submaximal oxygen uptake (VO(2)) and pulmonary ventilation (VE) responses in an incremental exercise test when it is preceded by high intensity exercise (i.e., during a LMT). METHODS: Ten trained male athletes (triathletes and cyclists) performed 2 exercise tests in random order on an electromagnetic cycle ergometer: 1). Control Test (CT): an incremental test with an initial work rate of 100 W, and with 25 W increments at 3-min intervals, until voluntary exhaustion; 2). LMT: an incremental test identical to the CT, except that it was preceded by 2 supramaximal bouts of 30-sec (approximately 120% VO(2)peak) with a 30-sec rest to induce lactic acidosis. This test started 8 min after the induction of acidosis. RESULTS: There was no significant difference in peak VO(2) (65.6+/-7.4 ml x kg(-1) x min(-1); 63.8 +/- 7.5 ml x kg(-1) x min(-1) to CT and LMT, respectively). However, the maximal power output (POmax) reached was significantly higher in CT (300.6+/-15.7 W) than in the LMT (283.2+/-16.0 W). VO(2) and VE were significantly increased at initial power outputs in LMT. CONCLUSION: Although the LMT alters the submaximal physiological responses during the incremental phase (greater initial metabolic cost), this protocol is valid to evaluate peak VO(2), although the POmax reached is also reduced.     

Effect of high-intensity submaximal work, with or without rest, on subsequent VO2max

PURPOSE: In practice, tests of maximal oxygen uptake (.VO2max) are often preceded by a lactate profile, a highly intense but submaximal exercise bout. The .VO2max response to preceding high-intensity submaximal exercise, with or without a rest period, has not been determined. If .VO2max is limited after a lactate profile, exercise-induced hypoxemia (EIH) may explain the deficit. The purposes of this study were to: 1) examine the effects of high-intensity submaximal exercise, with or without rest, on subsequent .VO2max; and 2) evaluate the role of EIH in causing any observed changes. METHODS: Ten healthy, well-trained, male cross-country skiers (age = 20.5 +/- 4.7 yr, height = 181.6 +/- 6.0 cm, mass = 72.1 +/- 5.7 kg) completed three exercise trials: an incremental run to fatigue (MAX), MAX preceded by a high-intensity submaximal run (lactate profile) and a 20-min rest period (discontinuous protocol [DC]), and MAX preceded by a high-intensity submaximal exercise run with no rest (continuous protocol [C]). .VO2max, minute ventilation, and arterial oxygen saturation were measured throughout, and diffusion capacity was evaluated 2 min postexercise.RESULTS No significant between trial differences were observed, although the difference between .VO2max determined during the MAX trial (62.7 +/- 6.7 mL.kg-1.min-1) and during the DC trial (58.3 +/- 4.4 mL.kg-1.min-1) approached significance (P = 0.059). DC .VO2max responses could be separated into two groups: five responders whose .VO2max suffered during the DC trial (decreased >7.5% from MAX) and five nonresponders, whose .VO2max was unaffected by preceding submaximal exercise and a rest period. Responders showed greater aerobic capacity during the MAX trial. CONCLUSION: .VO2max is significantly reduced in approximately 50% of cross-country skiers when a maximal exercise test is preceded by high-intensity submaximal exercise and a 20 min rest period; the role of EIH in causing these reductions is unclear.     

Evidence for an inadequate hyperventilation inducing arterial hypoxemia at submaximal exercise in all highly trained endurance athletes

PURPOSE: The majority of highly trained endurance athletes with a maximal oxygen uptake greater than 60 mL x min(-1) x kg(-1) develop exercise-induced hypoxemia (EIH). Yet some of them apparently do not. The pathophysiology of EIH seems to be multifactorial, and one explanatory hypothesis is a relative hypoventilation. Nevertheless, conflicting results have been reported concerning its contribution to EIH. The aim of this study was to compare the cardiorespiratory responses to maximal exercise of highly trained endurance athletes demonstrating the same aerobic capacity without EIH (N athletes) and with EIH (H athletes). METHODS: Ten N athletes and twelve H athletes performed an incremental exercise test. Measurements of arterial blood gases and cardiorespiratory parameters were performed at rest and during exercise. RESULTS: All athletes presented a significant decrease in PaO2 (P < 0.05) from rest up to 80% VO2max associated with an increase in PaCO2, both findings consistent with a relative hypoventilation. Then the H athletes, who had a greater training volume per week and a higher second ventilatory threshold than the N athletes (respectively, 17 +/- 1.1 vs 13.1 +/- 0.7 h x wk(-1); 91.8 +/- 1.7 vs 86.1 +/- 1.8% VO2max), presented a continuous PaO2 decrease up to VO2max. This was associated with a widening (Ai-a)DO2. CONCLUSION: This study showed that a relative hypoventilation, probably induced by a high level of endurance training, induced hypoxemia in all athletes. However, a nonventilatory mechanism, perhaps related to the volume of training, seemed to affect gas exchanges beyond the second ventilatory threshold in the H athletes, thereby enhancing EIH.     

Maximal physiological responses between aquatic and land exercise in overweight women

PURPOSE: To investigate the maximal physiological responses between aquatic and land-based graded exercise tests in overweight women. METHODS: Twenty healthy, overweight (body mass index (BMI) > or = 25 kg.m(-2)), Caucasian women (mean +/- SD; age 48 +/- 7 yr, BMI 30 +/- 4 kg.m(-2)) completed a deep water running (DWR) and treadmill walking (TMW) graded exercise test. Maximal responses during the DWR and TMW graded exercise tests were compared using paired t-tests. Comparisons were made in the incidence of achievement of maximal oxygen consumption (VO2max) criteria between DWR and TMW protocols. Criteria were a plateau in VO2 (change < 2.1 mL.kg.min(-1)), heart rate (HR) equal to or above the age-adjusted maximum, and respiratory exchange ratio (RER) > or = 1.15. RESULTS: Maximal responses for VO2max (22.5 +/- 4.86 vs 27.7 +/- 4.73 mL.kg.min(-1)), HRmax (159 +/- 16 vs 170 +/- 12 bpm), and RER (1.03 +/- 0.06 vs 1.10 +/- 0.06) were significantly lower (P < 0.01) for the DWR test compared with the TMW test, respectively. Achievement of various VO2max criteria was demonstrated more consistently during the TMW test than the DWR test. CONCLUSION: Maximal physiological responses of overweight women to DWR and TMW are significantly different but are comparable with other populations. As the maximal responses for DWR compared with TMW differ, the use of land-based criteria for VO2max is not recommended for a graded DWR exercise test.     

Incremental test protocol, recovery mode and the individual anaerobic threshold

The individual anaerobic threshold (IAT) is defined as the highest metabolic rate at which blood lactate (LA) concentrations are maintained at a steady-state during prolonged exercise. The purpose of this study was to compare the effects of active and passive recovery on the determination of IAT following both a submaximal or maximal incremental exercise test. Seven males (VO2max = 57.6 +/- 5.8 ml.kg-1.min -1) did two submaximal, incremental cycle exercise tests (30 W and 4 min per step) and two maximal incremental tests. Blood was sampled repeatedly during exercise and for 12 min during the subsequent recovery period, which was passive for one submaximal and one maximal test and active (approximately 35% VO2max) during the other tests. An IAT metabolic rate and power output were calculated for the submax-passive (IATsp, LA = 1.85 +/- 0.42 mmol.l-1), max-passive (IATmp, LA = 3.41 +/- 1.14 mmol.l-1), submax-active (IATsa, LA = 2.13 +/- 0.45 mmol.l-1) and max-active (IATma, LA = 3.44 +/- 0.73 mmol.l-1) protocols. At weekly intervals, the subjects exercised for 30 min at one of the four IAT metabolic rates. Active recovery did not affect the calculation of IAT, but following the maximal incremental tests, IAT occurred at a higher (p less than 0.05) power output, absolute VO2 and %VO2max (71% VO2max) compared with the IAT determined with the submaximal incremental tests (61% VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)     

Frequency of the VO2max plateau phenomenon in world-class cyclists

We aimed to determine the frequency of the VO2max plateau phenomenon in top-level male professional road cyclists (n = 38; VO2max [mean +/- SD]: 73.5 +/- 5.5 ml.kg(-1).min(-1)) and in healthy, sedentary male controls (n = 37; VO2max: 42.7 +/- 5.6 ml.kg(-1).min(-1)). All subjects performed a continuous incremental cycle-ergometer test of 1-min workloads until exhaustion. Power output was increased from a starting value of 25 W (cyclists) or 20 W (controls) at the rate of 25 W.min(-1) (cyclists) or 20 W.min(-1) (controls) until volitional exhaustion. We measured gas-exchange and heart rate (HR) throughout the test. Blood concentrations of lactate (BLa) were measured at end-exercise in both groups. We defined maximal exercise exertion as the attainment of a respiratory exchange rate (RER) >or= 1.1; HR > 95 % age-predicted maximum; and BLa > 8 mmo.l(-1). The VO2max plateau phenomenon was defined as an increase in two or more consecutive 1-min mean VO2 values of less than 1.5 ml.kg(-1).min(-1). Most cyclists met our criteria for maximal exercise effort (RER > 1.1, 100 %; 95 % predicted maximal HR [HRmax], 82 %; BLa > 8 mmol.l(-1), 84 %). However, the proportion of cyclists attaining a V.O (2max) plateau was considerably lower, i.e., 47 %. The majority of controls met the criteria for maximal exercise effort (RER > 1.1, 100 %; predicted HRmax, 68 %; BLa > 8 mmol. l(-1), 73 %), but the proportion of these subjects with a VO2max plateau was only 24 % (significantly lower proportion than in cyclists [p < 0.05]). Scientists should consider 1) if typical criteria of attainment of maximal effort are sufficiently stringent, especially in elite endurance athletes; and 2) whether those humans exhibiting the VO2max plateau phenomenon are those who perform an absolute maximum effort or there are additional distinctive features associated with this phenomenon.     

Effects of breathing a normoxic He-O2 gas mixture on exercise tolerance and VO2 max

The purpose of these experiments was to compare the effects of breathing air (79% N2-21% O2) and a normoxic helium oxygen gas mixture (He-O2) (79% He-21% O2) on maximal oxygen uptake (VO2 max) and work tolerance during both incremental and high-intensity constant load exercise. First, eight subjects underwent two separate short incremental cycle ergometer exercise tests until the subject could not maintain the desired power output. Second, four subjects exercised to exhaustion on two separate occasions at a constant exercise intensity (100% VO2 max). Each exercise protocol required the subject to breathe air on one test and a normoxic He-O2 mixture on an additional occasion. Data analysis revealed higher (P less than 0.05) minute ventilations, an increased time to exhaustion, and a greater VO2 max during He-O2 breathing in both exercise conditions. Small but significant (P less than 0.05) differences existed in the percent hemoglobin saturated with O2 (% SO2) at exercise demands greater than 120 W during the incremental experiment and during each minute of the constant load test with He-O2 giving the higher value. These data support the hypothesis that breathing a normoxic He-O2 gas mixture during exercise elevates VO2 max and increases exercise tolerance. Further, although it appears that breathing a He-O2 mixture results in higher %SO2 during intense exercise, the increase in arterial O2 content is small and probably does not fully account for the higher VO2 max observed under these conditions.     

Effect of exercise-induced arterial O2 desaturation on VO2max in women

PURPOSE: We have recently reported that many healthy habitually active women experience exercise induced arterial hypoxemia (EIAH). We questioned whether EIAH affected VO2max in this population and whether the effect was similar to that reported in men. METHODS: Twenty-five healthy young women with widely varying fitness levels (VO2max, 56.7 +/- 1.5 mL x kg(-1) x min(-1); range: 41-70 mL x kg(-1) x min(-1)) and normal resting lung function performed two randomized incremental treadmill tests to VO2max (FIO2: 0.21 or 0.26) during the follicular phase of their menstrual cycle. Arterial blood samples were taken at rest and near the end of each workload during the normoxic test. RESULTS: During room air breathing at VO2max, SaO2 decreased to 91.8 +/- 0.4% (range 87-95%). With 0.26 FIO2, SaO2, at VO2max remained near resting levels and averaged 96.8 +/- 0.1% (range 96-98%). When arterial O2 desaturation was prevented via increased FIO2, VO2max increased in 22 of the 25 subjects and in proportion to the degree of arterial O2 desaturation experienced in normoxia (r = 0.88). The improvement in VO2max when systemic normoxia was maintained averaged 6.3 +/- 0.3% (range 0 to +15%) and the slope of the relationship was approximately 2% increase in VO2max for every 1% decrement in the arterial oxygen saturation below resting values. About 75% of the increase in VO2max resulted from an increase in VO2 at a fixed maximal work rate and exercise duration, and the remainder resulted from an increase in maximal work rate. CONCLUSIONS: These data demonstrate that even small amounts of EIAH (i.e., >3% delta SaO2 below rest) have a significant detrimental effect on VO2max in habitually active women with a wide range of VO2max. In combination with our previous findings documenting EIAH in females, we propose that inadequate pulmonary structure/function in many habitually active women serves as a primary limiting factor in maximal O2 transport and utilization during maximal exercise.     

Effects of short-term endurance training on muscle deoxygenation trends using NIRS

PURPOSE: This study examined changes in cardiorespiratory responses and muscle deoxygenation trends to test the hypothesis that both central and peripheral adaptations would contribute to the improvements in VO(2max) and simulated cycling performance after short-term high-intensity training. METHODS: Eight male cyclists performed an incremental cycle ergometer test to voluntary exhaustion, and a simulated 20-km time trial (20TT) on wind-loaded rollers before and after training (60 min x 5 d x wk(-1) x 3 wk at 85-90% VO(2max). Near-infrared spectroscopy (NIRS) was used to evaluate the trend in vastus medialis hemoglobin/myoglobin deoxygenation (Hb/Mb-O(2) during both tests pre- and post-training. RESULTS: Training induced significant increases (P 0.05) in the VO(2) (4.02 +/- 0.52 to 4.04 +/- 0.51), heart rate (176 +/- 9 to 173 +/- 8 beats x min ) or O pulse (22.4 +/- 3.2 to 23.5 +/- 2.8 mL O(2) x beat(-1)). However, mean muscle deoxygenation during the 20TT was significantly lower after training (-550 +/- 292 to -707 +/- 227 mV, P 相似文献   

The relationship between power and the time to achieve .VO(2max)

PURPOSE: The severe exercise intensity domain may be defined as that range of work rates over which .VO(2max) can be elicited during constant-load exercise. The purpose of this study was to help characterize the .VO(2) response within this domain. METHODS: Eleven participants performed cycle ergometer exercise tests to fatigue at several discrete work rates between 95% and 135% of the maximum power (P(max)) achieved during an incremental exercise test. RESULTS: As previously demonstrated, the relationship between power and time to fatigue was hyperbolic. The asymptote of power (critical power, P(critical)) was 198 +/- 44 W. The rapidity of the .VO(2) response increased systematically at higher work rates such that the relationship between power and time to .VO(2max) was also well fit by a hyperbola. The power asymptote of this relationship (196 +/- 42 W) was not different from P(critical)(P > 0.05). The two hyperbolic relationships converged at 342 +/- 70 W (136% P(max)). CONCLUSION: These data suggest that, for this population of male and female university students, the upper boundary of the severe exercise intensity domain is approximately 136% P(max). This upper boundary is the highest work rate for which exercise duration is prolonged sufficiently (in this study, 136 +/- 17 s) to allow .VO(2) to rise to its maximal value. The lower boundary for severe exercise is just above P(critical), which is the highest work rate that is sustainable for a prolonged duration and that will not elicit .VO(2max).