Oxygen uptake kinetics during heavy submaximal exercise: Effect of sickle cell trait with or without alpha-thalassemia.

Sickle cell trait (SCT) is a genetic disease affecting the synthesis of normal hemoglobin (Hb) marked by the heterozygous presence of HbA and HbS. It is thought that exercise tolerance and aerobic capacity could be limited in SCT carriers, but that the co-existence of alpha-thalassemia with SCT (SCTAT) could improve exercise response. To examine these issues, we compared the characteristics of VO2 kinetics during a constant heavy exercise among athletes carrying either the SCT (n = 6), the SCTAT (n = 9), or the normal Hb (control group; n = 10). After determination of maximal power output (Ppeak), all subjects underwent a constant heavy cycling exercise lasting 9 min at approximately 70 % Ppeak. Pulmonary VO2 and cardio-respiratory parameters were measured breath-by-breath and the VO2 response was modelled using non-linear regression techniques. The time constant of the VO2 primary component and oxygen deficit were not significantly different among the three groups. The VO2 slow component was 28 % and 33 % higher (p < 0.05) in SCT and SCTAT than in the control groups, respectively. Altogether, athletes with the SCT and the SCTAT had higher heart rate at the beginning (+ 5.2 %) and the end (+ 7.4 %) of the slow component compared to the control group (p < 0.05). These results suggest that SCT and SCTAT subjects are not limited during the first exercise minutes, but are prone to exercise intolerance and to lower aerobic capacity thereafter, due to a higher VO2 slow component, and that alpha-thalassemia does not improve exercise response. The finding of a higher slow component in SCT and SCTAT athletes was possibly due to the loss of O2 availability to muscles, additional fiber recruitment and/or higher cardiac load with time.

Metabolic and cardioventilatory responses during a graded exercise test before and 24 h after a triathlon.

Previous studies have reported respiratory, cardiac and muscle changes at rest in triathletes 24 h after completion of the event. To examine the effects of these changes on metabolic and cardioventilatory variables during exercise, eight male triathletes of mean age 21.1 (SD 2.5) years (range 17-26 years) performed an incremental cycle exercise test (IET) before (pre) and the day after (post) an official classic triathlon (1.5-km swimming, 40-km cycling and 10-km running). The IET was performed using an electromagnetic cycle ergometer. Ventilatory data were collected every minute using a breath-by-breath automated system and included minute ventilation (V(E)), oxygen uptake (VO2), carbon dioxide production (VCO2), respiratory exchange ratio, ventilatory equivalent for oxygen (V(E)/VO2) and for carbon dioxide (V(E)/VCO2), breathing frequency and tidal volume. Heart rate (HR) was monitored using an electrocardiogram. The oxygen pulse was calculated as VO2/HR. Arterialized blood was collected every 2 min throughout IET and the recovery period, and lactate concentration was measured using an enzymatic method. Maximal oxygen uptake (VO2max) was determined using conventional criteria. Ventilatory threshold (VT) was determined using the V-slope method formulated earlier. Cardioventilatory variables were studied during the test, at the point when the subject felt exhausted and during recovery. Results indicated no significant differences (P > 0.05) in VO2max [62.6 (SD 5.9) vs 64.6 (SD 4.8) ml x kg(-1) x min(-1)], VT [2368 (SD 258) vs 2477 (SD 352) ml x min(-1)] and time courses of VO2 between the pre- versus post-triathlon sessions. In contrast, the time courses of HR and blood lactate concentration reached significantly higher values (P < 0.05) in the pre-triathlon session. We concluded that these triathletes when tested 24 h after a classic triathlon displayed their pre-event aerobic exercise capacity, bud did not recover pretriathlon time courses in HR or blood lactate concentration.

Metabolic and hormonal responses during repeated bouts of brief and intense exercise: effects of pre-exercise glucose ingestion.

We investigated metabolic and hormonal responses during repeated bouts of brief and intense exercise (a force-velocity test; Fv test) and examined the effect of glucose ingestion on these responses and on exercise performance. The test was performed twice by seven subjects [27 (2) years] according to a double-blind randomized crossover protocol. During the experimental trial (GLU), the subjects ingested 500 ml of glucose polymer solution containing 25 g glucose 15 min before starting the exercise. During the control trial (CON), the subjects received an equal volume of sweet placebo (aspartame). Exercise performance was assessed by calculating peak anaerobic power (W(an,peak)). Venous plasma lactate concentration increased significantly during the Fv test (P < 0.001), but no difference was found between CON and GLU. Blood glucose first decreased significantly from the beginning of exercise up to the 6-kg load (P < 0.001) and then increased significantly at W(an,peak) and for up to 10 min during the recovery period (P < 0.001) in both CON and GLU. Insulin concentrations decreased significantly in both groups, but were higher at W(an,peak) in GLU compared with CON (P < 0.05). Glucagon and epinephrine did not change significantly in either group, but epinephrine was significantly lower in GLU after glucose ingestion (P < 0.05) and at W(an,peak) (P < 0.05). W(an,peak) was not significantly different between CON and GLU. In conclusion, blood glucose and insulin concentrations decreased during repeated bouts of brief and intense exercise, while blood lactate concentration increased markedly without any significant change in glucagon and epinephrine concentrations. Glucose ingestion altered metabolic and hormonal responses during the Fv test, but the performance as measured by W(an,peak) was not changed.

Glucose administration before exercise modulates catecholaminergic responses in glycogen-depleted subjects.

In glycogen-depleted subjects (GD) a nonlinear increase in epinephrine (Epi) and norepinephrine (NE) parallels blood lactate (La) during graded exercise. The effect of glucose (Glc) supplementation and route of administration on these relationships was studied in 26 GD athletes who were randomly assigned to receive 1.3 g/kg Glc by slow intravenous infusion (IV; n = 9), oral administration (PO; n = 9), or artificially sweetened placebo in 1 liter of water (Asp; n = 8) in the 2 h preceding a graded maximal exercise. Performance and La were similar among the three groups in normal glycogen (NG) or GD conditions. However, slightly improved performances were observed in GD compared with NG and were associated with a shift to the right in La curves. Blood Glc concentrations were higher in IV and PO before exercise, but they rapidly decreased to lowest levels in IV, gradually decreased over time in PO, and remained stable in Asp or NG. Insulin concentrations were highest in IV and lowest in Asp and NG at onset of exercise, rapidly decreasing in IV and PO although remaining at higher levels than in Asp or NG. In contrast, higher serum levels of free fatty acids were measured during exercise in Asp with no significant differences in glucagon or glycerol among the three groups. Free and sulfated NE increases were smaller in IV than in PO and Asp on exhaustion. In contrast, free and conjugated Epi were most increased in IV, with smallest increases in Asp. Dopamine levels were most increased in IV at exhaustion. We conclude that the changes of Epi and NE concentrations, associated with the activation of glucoregulatory mechanisms, including hyperinsulinemia, display different magnitude and time courses during exercise in GD subjects who receive oral vs. intravenous load of Glc before exercise. We speculate that the magnitude of insulin surge after acutely increased Glc before exercise in GD subjects may exert dissociative effects on adrenal-dependent glycogenolysis and on sympathetic responses.

Hyperoxia during recovery from consecutive anaerobic exercises in the sickle cell trait.

The sickle cell trait (HbAS) does not affect anaerobic exercise performance. However, lower blood lactate concentrations ([La-]) are consistently found during repeated anaerobic exercise in HbAS, and could be related to type of recovery. To study this, on three different occasions 17 HbAS and 17 matched control athletes (HbAA) underwent a series of three maximal cycle exercise tests of approximately 2-min duration, separated by 10-min recovery periods of rest, breathing either room air (P) or 100% oxygen (H), or of light pedaling (A). In all tests, work performed, heart rate, blood hematocrit, and [La-] were measured. Despite similar evolution of performance in each series of three anaerobic exercises, significantly lower [La-] were consistently found in HbAS in P and A, compared to HbAA (P < 0.0001). However, in H, similar [La-] was found in HbAS and HbAA. Higher mean heart rates were consistently measured in HbAS at exhaustion, and during the first 4 min of recovery, these differences being unrelated to type of recovery. We conclude that type of recovery does not influence subsequent performance in HbAS or HbAA. We speculate that improved regional oxygen availability in exercising muscle is associated with marked modification of lactate kinetics in highly trained HbAS, but not in similarly fit HbAA athletes.

Sickle cell trait performance in a prolonged race at high altitude.

The limitation of aerobic exercise capacity of athletes with the sickle cell trait (SCT), under conditions of limited oxygen availability, is still controversial. To study this, we took advantage of an unique setting, the International Mount Cameroon Ascent Race, a 34.1-km race over difficult terrain, slopes ranging from 7 to 40%, and altitudes varying from 615 to 4095 m, combined with high prevalence rates of SCT among the African runners. Of 266 Cameroonian runners, SCT was detected in 33 athletes (12.4%), a prevalence similar to that of the ethnically corrected general population. However, in runners of the Bakoueri tribe whose performance is contingent with social stature, SCT was present in only 1 of 41 runners (2.4%), as compared with 15.6% in the general population of the Bakoueri tribe (P < 0.03). In general, performance times of SCT runners were not different from non-SCT runners, except during the portion of the race at altitudes ranging from 3800 to 4095 m, where significantly longer times were clocked by SCT subjects (P < 0.02). We conclude that prolonged aerobic efforts in hypobaric hypoxic conditions may be associated with a detrimental effect on performance in SCT carriers. If this is true, it might account for the reduced prevalence of SCT among those runners representing the Bakoueri tribe, provided an objective measure of performance at altitude was employed to select these representatives.

Relationships between postcompetition blood lactate concentration and average running velocity over 100-m and 200-m races.

The relationships between anaerobic glycolysis and average velocity (v) sustained during sprint running were studied in 12 national level male sprinters. A blood sample was obtained within 3 min of the completion of semi-finals and finals in the 100-m and 200-m Cameroon national championships and blood lactate concentration ([la-]b) was measured. The 35-m times were video-recorded. The 100-m and 200-m [la-]b were 8.5 (SD 0.8) and 10.3 (SD 0.8) mmol.l-1, respectively. These were not correlated with the performances. Over 200 m [la-]b was correlated with the v sustained over the last 165 m (r = 0.65, P < 0.05). In the 9 athletes who participated in both the 100-m and 200-m races, the difference between the [la-]b measured at the end of the two races was negatively correlated to the difference in v sustained over the two races (r = 0.76, P > 0.02). Energy expenditure during sprint running was estimated from the [la-]b values. This estimate was mainly based on the assumption that a 1 mmol.l-1 increase in [la-]b corresponds to the energy produced by the utilization of 3.30 ml O2.kg-1. The energy cost of running was estimated at 0.275 (SD 0.02) ml O2.kg-1.m-1 over 200-m and 0.433 (SD 0.03) ml O2.kg-1.m-1 over 100-m races. These results would suggest that at the velocities studied anaerobic glycolysis contributes to at least 55% of the energy expenditure related to spring running. However, the influence of both mechanical factors and the contribution of other energy processes obscure the relationship between [la-]b and performance.

The effect of various recovery modalities on subsequent performance, in consecutive supramaximal exercise.

Different recovery strategies from maximal exercise seem to induce different lactate utilization patterns without significantly affecting performance on one subsequent maximal exercise. It remains unclear however, how varying recovery modalities affects repeated maximal exercise. To study this, we examined in 16 subjects, the influence of passive (P), active leg (L) and active arm (A) twenty minutes recovery periods separating a series of four exhaustive exercises, up to two minutes duration. Significant decreases in performance between the first and fourth exercise were observed in all recovery series but a significant decrease in performance in the second exercise was observed during passive recovery alone (p < 0.01). When the different types of recovery are compared, a more pronounced decrement in performance was found during passive recovery when first and last exercises are compared (p < 0.04). Pedaling duration in each successive exercise was unaffected in A or L but was significantly shorter in P (p < 0.03). Highly significant differences in mean blood lactate kinetics were found for the three recovery patterns used, with more elevated peak and nadir levels in passive recovery, intermediate values in active arm and lowest concentrations in active leg recovery. However, no correlation was found between performance and lactate concentration at the onset of exercise (r = -0.15; p = NS). Mean heart rates were similar throughout the experimental protocol except for a lower cardiac frequency during the last 5 minutes of passive recovery (p < 0.01). Blood hematocrits showed higher hemoconcentrations in repeated exercise during passive recovery (p < 0.01) despite significantly lower total fluid losses in this group. A significant correlation between peak hematocrit and blood lactate was also found (r = 0.67; p < 0.001). We conclude that the type of recovery has a significant effect on blood lactate elimination kinetics, and active recovery is beneficial in the preservation of performance during repeated maximal exercise. Furthermore, plasma shifts across the extra and intravascular spaces are induced by maximal exercise, and appear to closely follow blood lactate kinetics.

Effect of different modalities of exercise and recovery on exercise performance in subjects with sickle cell trait.

The sickle cell trait (HbAS) does not seem to affect exercise performance. It remains unclear, however, whether the capability to sustain repeated brief maximal effort and recovery by HbAS subjects, is also preserved. To study this, nine HbAS and nine matched controls underwent on two different occasions, a series of four, approximately 2-min duration, maximal cycle exercise tests separated by 20-min recovery periods of either absolute rest (P) or light pedaling (A) as well as an incremental test to exhaustion. In all tests, work performed, heart rate, blood hematocrit, lactate, and serum creatine kinase (CK), lactate dehydrogenase (LDH), and aspartate aminotransferase (GOT) were measured. Performances were similar in HbAS and HbAA subjects in both the predominantly anaerobic and aerobic exercise series. There were no observable differences in work, power, or heart rate in the two groups both during peak exercise or recovery periods. A significant hemoconcentration was observed during P, with hematocrit increasing in HbAS from 46.4 +/- 0.7% to 48.3 +/- 0.4% at the end of the last recovery period. Similar changes were seen in HbAA. Significantly greater fluid losses were found during A (1.3 +/- 0.2 l in A and 0.6 +/- 0.1 l in P for HbAS; P < 0.001), but fluid losses were similar in each type of recovery in the two groups. Despite similar performance, significantly lower blood lactate concentrations were consistently found in HbAS in each of the three exercise series (P < 0.001). Lower lactate levels in HbAS were observed only at exercise loads above the lactate threshold during the incremental test (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)