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.

Respiratory symptoms and peak expiratory flow in survivors of the Nyos disaster.

In August 1986, gases from the Nyos volcanic lake killed 1,746 persons in northwestern Cameroun, but 1,500 others living in the affected area survived. Gas emanations contained carbon dioxide, sulfur dioxide, and hydrogen sulfide. The objective of this study was to evaluate the delayed respiratory consequences of the inhalation of such volcanic gases. Two groups of subjects living in the same area, exposed (Nyos group; n = 381) or not exposed (control group; n = 128) to Nyos gases, were evaluated with a short questionnaire and by measurement of peak expiratory flow (PEF, percent predicted) in March 1991. Eleven percent of the subjects smoked, more often men than women (23% vs 4%; p < 0.001). In the whole population (exposed and unexposed), smoking was associated with a 3.6-fold increase in the frequency of cough (p < 0.001) and with a 6-fold increase in the frequency of sputum production (p < 0.005), but not with a decrease in PEF. There was no difference in the frequency of dyspnea, cough, sputum production, and PEF between Nyos and control groups. We conclude that 55 months after the emanation of gases from Nyos volcanic lake, there was no difference in respiratory symptoms, and PEF between survivors who inhaled volcanic gases and control subjects, whereas smoking was associated with cough and sputum production.

[Effects of preliminary muscular exercise on body temperature, water loss and physical performance]. / Effets d'un exercice musculaire préliminaire sur la température centrale, les pertes hydriques et la performance physique.

We investigated the effects of preliminary exercise (muscular warm-up) on body temperature, water loss and physical performance during consecutive sustained exercise. Thirty-one untrained men aged 21 to 30 years old (mean 25.12 +/- 2.92) were subjected to two physical trial tests at 75% Pma. One trial. (T - PE) was performed without preliminary exercise (PE) and the other (T + PE) was preceded by 15 minutes of preliminary exercise performed at 50% Pma. The trials involved pedaling an ergocycle until exhaustion, followed by a 30 minutes period of inactive recovery. The rate of increase of body temperature during the work consecutive to preliminary exercise (T + PE) was lower than that of the work without preliminary exercise (T - PE). The energy output and water loss during T + PE were significantly (P < 0.01) greater than during T - PE. However, the body temperatures at the end of the two tests were identical. The rate of decrease of body temperature, measured after 30 minutes of recovery, was higher for T + PE than T - PE. The duration of work was increased by PE for 25 (80.65%) subjects and decreased for 6 (19.35%). We conclude that preliminary exercise allows better adjustment of thermohydric regulation by moderating the rise in body temperature and increasing water loss during physical work. For most subjects, these adjustments allow improved endurance.

Dissociation of systemic GH-IGF-I axis from a genetic basis for short stature in African Pygmies.

OBJECTIVES: To test the hypothesis that the primary cause of short stature in African Pygmies resides in low levels of insulin-like growth factor I (IGF-I), and to evaluate whether any observed alterations in their systemic IGF-I status can be dissociated from the effects of malnutrition and/or altered immune status. SETTING: Expedition to camps of partially sedentarized African Pygmies and neighbouring Bantu farmers living in the equatorial rain forest of Eastern Cameroon. DESIGN: Serum assays for hormonal and immune status were conducted for individuals (children, adolescents, young and old adults) showing no overt clinical nor biochemical signs of malnutrition, as judged from anthropometry, clinical examinations and serum assays of albumin, pre-albumin, retinol-binding protein, transferrin, iron, zinc, magnesium and calcium. RESULTS: African Pygmies did not differ from Europeans or Bantus in mean serum IGF-I concentrations, nor in the relationship between serum IGF-I and its major binding protein (IGFBP-3). However, although in both African groups the immunoglobulins IgG, IgM and IgE as well as the C-reactive protein and ceruloplasmin were above the normal range of European references, the Pygmies differed from their Bantu neighbours in their much higher IgG and IgM serum levels. A plot of serum IGF-I against these immunoglobulins in Pygmies revealed a reverse sigmoidal relationship, with the low IGF-I values associated with serum levels of IgG and IgM which clearly exceeded those found in the Bantus. CONCLUSIONS: This study indicates that in growing and adult African Pygmies showing no clinical nor biochemical signs of nutritional deficiency, serum IGF-I and IGFBP-3 (hence IGF-I bioavailability to its receptors) are essentially normal, and that low circulating levels of IGF-I in Pygmies reside in differential exposure and/or responsiveness to environmental challenge (e.g. infections) rather than in an inherited defect in the systemic growth-hormone (GH)-IGF-I axis.

Loss of muscle oxidative capacity after an extreme endurance run: the Paris-Dakar foot-race.

We measured changes in maximal oxygen uptake capacity (VO2max), ventilation, heart rate, plasma lactate and speed at the end of an incremental exercise test as a consequence of a relay foot race from Paris to Dakar in 6 subjects. Additionally, anthropometric measurements were taken and muscle biopsies from M. vastus lateralis were obtained before and after the race. The latter were analyzed with morphometric methods for fiber size, capillarity and muscle ultrastructural composition. Weight specific VO2max was significantly reduced from 62.4 to 60.5 ml/min.kg after the race while absolute VO2max and the other endurance related functional variables remained unchanged. Body fat, thigh cross-sectional area and thigh volume showed tendential reduction immediately after the race but regained pre-race values within a few days. Fiber size and capillarity were not affected by the race. Volume density of total mitochondria was significantly reduced from 6.98 to 4.89% of fiber volume. Both subsarcolemmal and interfibrillar mitochondria were significantly reduced by 59 and 21%, respectively. The volume density of satellite cell was increased about three-fold whereas the content of lipofuscin remained constant. It is concluded that extreme endurance events such as a multi-stage relay race may induce a considerable loss of oxidative capacity of skeletal muscle tissue.

Pygmy locomotion.

The hypothesis that Pygmies may differ from Caucasians in some aspects of the mechanics of locomotion was tested. A total of 13 Pygmies and 7 Caucasians were asked to walk and run on a treadmill at 4-12 km.h-1. Simultaneous metabolic measurements and three-dimensional motion analysis were performed allowing the energy expenditure and the mechanical external and internal work to be calculated. In Pygmies the metabolic energy cost was higher during walking at all speeds (P < 0.05), but tended to be lower during running (NS). The stride frequency and the internal mechanical work were higher for Pygmies at all walking (P < 0.05) and running (NS) speeds although the external mechanical work was similar. The total mechanical work for Pygmies was higher during walking (P < 0.05), but not during running and the efficiency of locomotion was similar in all subjects and speeds. The higher cost of walking in Pygmies is consistent with the allometric prediction for smaller subjects. The major determinants of the higher cost of walking was the difference in stride frequency (+9.45, SD 0.44% for Pygmies), which affected the mechanical internal work. This explains the observed higher total mechanical work of walking in Pygmies, even when the external component was the same. Most of the differences between Pygmies and Caucasians, observed during walking, tended to disappear when the speed was normalized as the Froude number. However, this was not the case for running. Thus, whereas the tested hypothesis must be rejected for walking, the data from running, do indeed suggest that Pygmies may differ in some aspects of the mechanics of locomotion.

Infections among pygmies in the Eastern Province of Cameroon.

The health requirements of pygmies is poorly understood because of their continued isolation from the other tribes in Central Africa. This study was undertaken among the Baka pygmies of the Eastern Province of Cameroon to generate basic health data among them. A total of 141 adults (18-45 years) were tested for the hepatitis B surface antigen (HBsAg), antibody to the surface antigen (anti-HBs), antibody to the core antigen (anti-HBc) and antibody to the hepatitis C virus (anti-HCV). All HBsAg-positive sera were tested for the hepatitis B e antigen (HBeAg) and antibody (anti-HBe). The presence of antibodies to the hepatitis D virus was determined in most of the anti-Hbs-positive sera, and some of the HBsAg-positive sera. In addition to these, previous infection with syphilis, measles, HIV 1/2 and HTLV were determined by looking for the specific antibodies. We found HBsAg in 14.2% (20/141), anti-HBs in 93.6% (132/141), anti-HBs in 52.2% (73/140), anti-HCV in 7.9% (11/139, measles antibody in 99.3% (139/140), antibody to Treponema pallidum in 13.4% (18/134), antibody to HTLV-1 in 10.9% (15/138) and antibody to HIV-1 in 0.7% (1/140) of the sera tested.

PIP: Pygmies remain isolated from other tribes and urban communities in central Africa. This study was undertaken among the Baka pygmies of the Eastern Province of Cameroon in an effort to redress the lack of published information on the health needs of that population. 141 adults aged 18-45 years were tested for the hepatitis B surface antigen (HBsAg), antibody to the surface antigen (anti-HBs), antibody to the core antigen (anti-HBc), and antibody to the hepatitis C virus (anti-HCV). HBsAg-positive sera were tested for the hepatitis B e antigen and antibody, while the presence of antibodies to the hepatitis D virus was determined in most of the anti-HBs-positive sera and some of the HBsAg-positive sera. Furthermore, previous infection with syphilis, measles, HIV-1 and HIV-2, and HTLV were determined by looking for the specific antibodies. Test results identified HBsAg in 14.2%, anti-HBc in 93.6%, anti-HBs in 52.2%, anti-HCV in 7.9%, hepatitis D in 46%, measles antibody in 99.3%, antibody to Treponema pallidum in 13.4%, antibody to HTLV-1 in 10.9%, and antibody to HIV-1 in 0.7% of sera tested. This prevalence of HIV-1 infection is lower than the estimated 1-1.5% projected for the sexually active general population.

Energetics of locomotion in African pygmies.

The energy cost of walking (Cw) and running (Cr), and the maximal O2 consumption (VO2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. The Cw varied from 112 ml.kg-1.km-1, SD 25 [velocity (v), 4 km.h-1] to 143 ml.kg-1.km-1, SD 16 (v, 7 km.h-1). Optimal walking v was 5 km.h-1. The Cr was 156 ml.kg-1.km-1, SD 14 (v, 10 km.h-1) and was constant in the 8-11 km.h-1 speed range. The VO2max was 33.7 ml.kg-1.min-1, i.e. lower than in other African populations of the same age. The Cr and Cw were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pygmies may be different from that observed in Caucasians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The low Cr values observed enable Pygmies to reach higher running speeds than would be expected on the basis of their VO2max.

The energy cost of running increases with the distance covered.

The net energy cost of running per unit of body mass and distance (Cr, ml O2.kg-1.km-1) was determined on ten amateur runners before and immediately after running 15, 32 or 42 km on an indoor track at a constant speed. The Cr was determined on a treadmill at the same speed and each run was performed twice. The average value of Cr, as determined before the runs, amounted to 174.9 ml O2.kg-1.km-1, SD 13.7. After 15 km, Cr was not significantly different, whereas it had increased significantly after 32 or 42 km, the increase ranging from 0.20 to 0.31 ml O2.kg-1.km-1 per km of distance (D). However, Cr before the runs decreased, albeit at a progressively smaller rate, with the number of trials (N), indicating an habituation effect (H) to treadmill running. The effects of D alone were determined assuming that Cr increased linearly with D, whereas H decreased exponentially with increasing N, i.e. Cr = Cr0 + a D + He-bN. The Cr0, the "true" energy cost of running in nonfatigued subjects accustomed to treadmill running, was assumed to be equal to the average value of Cr before the run for N equal to or greater than 7 (171.1 ml O2.kg-1.km-1, SD 12.7; n = 30).(ABSTRACT TRUNCATED AT 250 WORDS)

Slow upward drift of VO2 during constant-load cycling in untrained subjects.

The oxygen uptake kinetics during constant-load exercise when sitting on a bicycle ergometer were determined in 7 untrained subjects by measuring breath-by-breath VO2 during continuous exercise to volitional exhaustion (mean endurance time = 1160 +/- 172 s) at a pedal frequency of 70 revolutions.min-1. The power output, averaging 189.5 W, was set at 82.5% of that eliciting the individual VO2max during a 5 min incremental exercise test. Throughout the exercise period, the VO2 kinetics could be appropriately described by a two-component exponential equation of the form: VO2(t) = Ya[1 - exp(-kat)] + Yb[1 - exp(-kbt)] where VO2 is net oxygen consumption and t the time from work onset. VO2 measured at the end of exercise was close to VO2max (98% VO2max) and the mean values of Ya, ka, Yb and kb amounted to 1195 ml O2.min-1, 0.034 s-1, 1562 ml O2.min-1, and 0.005 s-1 respectively. The initial rate of increase in VO2 predicted from the above equation is slower than that calculated, for the same work intensity, on the basis of the data obtained by Morton (1985) in trained subjects. For t greater than 480 s, however, the two models yield substantially equal results.

Hemodynamic effects of resistive breathing.

To examine the acute hemodynamic effects induced by large swings in intrathoracic pressure such as may be generated by obstructive lung disease, airway obstruction was simulated by means of two different fixed external alinear resistances and the results were compared with those for unobstructed breathing (C). Eight normal subjects breathed through external resistances during inspiration (I), expiration (E), or both (IE) at rest (Re) and exercise (Ex). The resistances were chosen to induce similar mouth pressure (Pm) swings at Re and Ex. Pleural pressures (Ppl) were found to correlate closely with Pm. During IE resistive breathing mean swings in Pm were -31 and +19 cmH2O at Re and -38 and +22 cmH2O at Ex, with a corresponding decrease in minute ventilation (-30 and -18%) and an increase in end-tidal PCO2 (+5.6 and +4.2 Torr); these were associated with an increase in heart rate (delta HR = 4 and 6 beats/min) and systolic systemic arterial pressure (delta Psas = 10 and 14 Torr at Re and Ex, respectively). O2 consumption and cardiac output did not change. The myocardial O2 consumption, estimated from the product HR X (Psas--Ppl), increased by 17 and 20% at Re and Ex, respectively. Changes in mechanics, gas exchange, and hemodynamics were less pronounced during I or E resistive loading. It is concluded that breathing through a tight external resistance during IE at Re and Ex increases the metabolic load on the myocardium.

The energetics of endurance running.

Maximal O2 consumption (VO2max) and energy cost of running per unit distance (C) were determined on the treadmill in 36 male amateur runners (17 to 52 years) who had taken part in a marathon (42.195 km) or semi-marathon (21 km), their performance times varying from 1.49 to 226 and from 84 to 131 min, respectively. VO2max was significantly (2p less than 0.001) greater in the marathon runners (60.6 vs 52.1 ml . kg-1 . min-1) while C was the same in both groups (0.179 +/- 0.017, S.D., mlO2 . kg-1 . m-1 above resting), and independent of treadmill speed. It can be shown that the maximal theoretical speed in endurance running (vEND) is set by VO2max, its maximal sustainable fraction (F), and C, as described by: vEND = F . VO2max . C-1. Since F was estimated from the individual time of performance, vEND could be calculated. The average speed of performance (vMIG) and vEND (m . s-1) were found to be linearly correlated: vMIG = 1.12 + 0.64 vEND (r2 = 0.72; n = 36). The variability of vMIG explained by vEND, as measured by r2, is greater than that calculated from any one regression between vMIG and VO2max (r2 = 0.51), F . VO2max (r2 = 0.58), or VO2max . C-1 (r2 = 0.63). The mean ratio of observed (vMIG) to theoretical (vEND) speeds amounted to 0.947 +/- 0.076 and increased to 0.978 +/- 0.079 (+/- S.D.; n = 36) when the effects of air resistance were taken into account. It is concluded that vEND = F . VO2max . C-1 is a satisfactory quantitative description of the energetics of endurance running.