Coral reef benthic productivity based on optical absorptance and light-use efficiency

In the interest of determining productivity across a range of spatial scales (meters to many kilometers) and in different reef environments, this paper proposes a technique for measuring productivity based on remote sensing of optical absorptance and light-use efficiency. The concept is straightforward: gross primary production equals plant-incident irradiance multiplied by plant absorptance multiplied by the plant’s light-use efficiency (GPP = E _d Aε). Both E _d and A are derivable from various remote sensing data sources, thus the approach is feasible. This paper presents a demonstration of the application for Kaneohe Bay, Oahu, HI based on Quickbird satellite imagery and SHOALS LIDAR data. E _d is modeled at every point in the image, and the image itself is inverted to provide A. Organismal-scale ε reported in the literature is taken as a surrogate for community-scale ε. The resulting GPP image compares well with the range of GPP values for reef-flats in general, as well as the distribution and range of GPP for Kaneohe Bay in particular. Though results likely can be improved by using spectral imagery and more accurate values for ε, this concept study demonstrates the tractability of this approach for measuring coral reef GPP.     

Breathing pattern in highly competitive cyclists during incremental exercise

The purpose of our investigation was to analyse the breathing patterns of professional cyclists during incremental exercise from submaximal to maximal intensities. A group of 11 elite amateur male road cyclists [E, mean age 23 (SD 2) years, peak oxygen uptake (VO2peak) 73.8 (SD 5.0) ml kg(-1) min(-1)] and 14 professional male road cyclists [P, mean age 26 (SD 2) years, (VO2peak) 73.2 (SD 6.6) ml kg(-1) min(-1)] participated in this study. Each of the subjects performed an exercise test on a cycle ergometer following a ramp protocol (exercise intensity increases of 25 W x min(-1)) until the subject was exhausted. For each subject, the following parameters were recorded during the tests: oxygen consumption (VO2), carbon dioxide output (VCO2), pulmonary ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen (VE x VO2(-1)) and carbon dioxide (VE x VCO2(-1)), end-tidal partial pressure of oxygen and partial pressure of carbon dioxide, inspiratory (tI) and expiratory (tE) times, inspiratory duty cycle (tI/tTOT, where tTOT is the time for one respiratory cycle), and mean inspiratory flow rate (VT/tI). Mean values of VE were significantly higher in E at 300, 350 and 400 W (P < 0.05, P < 0.05 and P < 0.01, respectively); fb was also higher in E in most moderate-to-maximal intensities. On the other hand, VT showed a different pattern in both groups at near-to maximal intensities, since no plateau was observed in P. The response of tI and tE was also different. Finally, VT/tI and tI/tTOT showed a similar response in both P and E. It was concluded that the breathing pattern of the two groups differed mainly in two aspects: in the professional cyclists, VE increased at any exercise intensity as a result of increases in both VT and fb, with no evidence of tachypnoeic shift, and tE was prolonged in this group at high exercise intensities. In contrast, neither the central drive nor the timing component of respiration seem to have been significantly altered by the training demands of professional cycling.     

Ventilatory efficiency and exercise tolerance in 101 healthy volunteers

The ventilatory equivalent for CO₂ defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16–75 years, measuring ventilation and gas exchange at rest (n = 64) and on exercise (modified Naughton protocol, n = 101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output (V˙ _E:V˙CO₂), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output (V˙ _E vs V˙CO₂ slope), oxygen uptake at the anaerobic threshold and at maximum (V˙O_2AT,V˙O_2max, respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [V˙ _E:V˙CO₂ 50.5 (SD 8.8) vs 57.6 (SD 12.6) P<0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: (V˙ _E vs V˙CO₂ slope = 0.13 × age + 19.9; women: V˙ _E vs V˙CO₂ slope = 0.12 × age + 24.4). The V˙O_2AT and V˙O_2max were 23 (SD 5) and 39 (SD 7) ml O₂ · kg · min⁻¹ in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The V˙O_2AT was reached at 58 (SD 9)% V˙O_2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults. Accepted: 11 June 1997     

Estimating crop yield using a satellite-based light use efficiency model

Satellite-based techniques that provide temporally and spatially continuous information over vegetated surfaces have become increasingly important in monitoring the global agriculture yield. In this study, we examine the performance of a light use efficiency model (EC-LUE) for simulating the gross primary production (GPP) and yield of crops. The EC-LUE model can explain on average approximately 90% of the variability in GPP for 36 FLUXNET sites globally. The results indicate that a universal set of parameters, independent of crop species (except for C4 crops), can be adopted in the EC-LUE model for simulating crops’ GPP. At both irrigated and rainfed sites, the EC-LUE model exhibits a similar level of performance. However, large errors are found when simulating yield based on crop harvest index. This analysis highlights the need to improve the representation of the harvest index and carbon allocation for improving crop yield estimations from satellite-based methods.     

Continuous monitoring of lactate during exercise in humans using subcutaneous and transcutaneous microdialysis

We have evaluated the possibility of monitoring the plasma lactate concentration in human volunteers during cycle ergometer exercise using subcutaneous and transcutaneous microdialysis. In transcutaneous microdialysis, the relative increase in dialysate lactate concentration exceeded that of plasma lactate concentration by a factor of 6 during exercise due to exercise-induced lactate secretion in sweat. During exercise the subcutaneous microdialysis dialysate lactate concentration underestimated the plasma lactate concentration possibly due to diffusion limitation or adipose tissue lactate production. While it was demonstrated that microdialysis can be used for on-line lactate monitoring, neither subcutaneous nor transcutaneous dialysate lactate concentration were linearly related to the plasma lactate concentration during exercise, and it was found therefore that it was not possible to monitor directly plasma lactate concentration during exercise.     

Maximal mechanical power output and capacity of cyclists and young adults

The maximal average power output (Wmax) has been examined in 10 male students, 22 pursuit and 12 sprint cyclists. In 24 of these subjects (8 students, 10 pursuit and 6 sprint cyclists), estimates of the maximal capacity (Wcap) of the short-term anaerobic energy yielding processes were made. The results show that the sprinters had a higher absolute Wmax (1241 +/- 266 W) and Wcap (16.7 +/- 4.9 kJ) than either the students (1019 +/- 183 W, 14.7 +/- 2.8 kJ) or the pursuit cyclists (962 +/- 206 W, 14.0 +/- 2.9 kJ). However, the differences were removed when the values were standardised for muscle size. In the sprinters the Wmax was attained at an optimal pedal frequency Vopt of 132 +/- 3 min-1 and the estimated maximal velocity of pedalling (V0) was 262 +/- 8 min-1. The comparable figures in the students and pursuit cyclists were 118 +/- 8 min-1, 235 +/- 17 min-1 and 122 +/- 6 min-1, 242 +/- 12 min-1 respectively. The coefficient of variation of duplicate measurements of Wcap was found to be +/- 9%. Using data of Wilkie (1968) for muscle phosphagen and glycolytic stores (27 mmol.kg-1), it was estimated that the probable efficiency of the anaerobic processes during maximal cycling was 0.22. It was concluded that Wmax and Wcap are largely determined by body size and muscularity. The efficiency of anaerobiosis appears to be of the same order of magnitude as found for oxidative work.     

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

The purpose of the study was to define a relationship between plasma ammonia [NH3]pl and blood lactate concentrations [la-]b after exercise in children and to find out whether the [NH3]pl, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH3]pl and [la-]b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH3]pl during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mumol.l-1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH3]pl correlated positively with [la-]b (r = 0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r = 0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH3]pl obtained during the treadmill test and the times of 30- and 60-m runs (r = -0.676 and -0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH3]pl during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [la-]b.(ABSTRACT TRUNCATED AT 250 WORDS)     

The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit

The regression of oxygen uptake (O₂) on power output and the O₂ demand predicted for suprapeak oxygen uptake (O_2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean O_2peak = 67.9 (SD 4.2) ml · kg^–1 · min^–1] and nine active, yet untrained men [UT, mean O_2peak = 54.1 (SD 6.5) ml · kg^–1 · min^–1]. The O₂-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%–85% O_2peak. Minute ventilation (_E), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([1a^–]_b) and rectal temperature (T _re) were measured at rest and during CON4. The slope of the O₂-power regression was greater (P 0.05) in C [12.4 (SD 0.7) ml · min^–1. W^–1] compared to UT [11.7 (SD 0.4) ml · min^–1 W^–1]; as a result, the O₂ demand (at 432 W) was also higher (P 0.05) in C [5.97 (SD 0.23) l · min^–1] than UT [5.70 (SD 0.15) 1 · min^–1]. ExerciseR and [la^–]_b were lower (P 0.05) in C .in comparison to UT at all power outputs, whereas _E and HR were relatively lower (P 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in O₂-power slopes between the groups and up to 46% of the difference in O₂ at a given intensity. Although the O₂-power regressions were linear for C [r = 0.997 (SD 0.001)] and UT [r = 0.997 (SD 0.001)], the O₂-power slope was higher at power outputs at or above the lactate threshold (13.2 ml · min^–1 · W^–1 than at lower intensities (11.6 ml · min^–1 · W^–1) in C, an effect which was less profound in UT. As a result, the exclusion of O₂ at the highest power outputs completely abolished the difference in O₂-power slopes between C and UT. Thus, the relatively higher O₂ during incremental exercise in C can be almost entirely attributed to the higher O₂ cost of cycling at higher power outputs. In addition, the presence of non-linear responses in O₂ at higher intensities also confirms the invalidity of describing the O₂ response across a wide range of power outputs using a linear function, and challenges the validity of predicting the O₂ demand of more intense exercise by a linear extrapolation of this same function.     

The ventilation, lactate and electromyographic thresholds during incremental exercise tests in normoxia, hypoxia and hyperoxia

These experiments examined the effect of hypoxia and hyperoxia on ventilation, lactate concentration and electromyographic activity during an incremental exercise test in order to determine if coincident chances in ventilation and electromyographic activity occur during an incremental exercise test, despite an enhancement or reduction of peripheral chemoreceptor activity. In addition, these experiments were completed to determine if electromyographic activity and ventilation are enhanced or reduced in response to the inspiration of oxygen-depleted and oxygen-enriched air, respectively. Seven subjects performed three incremental exercise tests, until volitional exhaustion was achieved, while inspiring air with a fractional concentration of oxygen of either 66%, 21% or 17%. In addition, another single subject completed two tests while inspiring air with a fractional concentration of either 17% or 21%. During the tests, ventilation, mixed expired oxygen and carbon dioxide, arterialized venous blood and the electromyographic activity from the vastus lateralis were sampled. From these values ventilation, electromyographic and lactate thresholds were detected during normoxia, hypoxia and hyperoxia. The results showed that although ventilation and lactate concentration were significantly less during hyperoxia as compared to normoxia or hypoxia, the carbon dioxide production values were not significantly different between the normoxic, hypoxic and hyperoxic conditions. For a particular condition, the time, carbon dioxide production and oxygen consumption values that corresponded to the ventilation and electromyographic thresholds were not significantly different, but the values corresponding to the lactate threshold were significantly less than those for the electromyographic and ventilation thresholds. Comparisons between the three conditions showed that the time, carbon dioxide production and oxyen consumption values corresponding to each of these thresholds were not significantly different. These findings have led us to conclude that the changes in lactate concentration observed during exercise may not be directly related to the fractional concentration of inspired oxygen, and that the peripheral chemoreceptors may not be the sole mediators of the first ventilatory threshold. It is suggested that this threshold may be mediated by an increase in neural activity originating from higher motor centers or the exercising limbs, induced in response to the need to progressively recruit fast twitch muscle fibers as exercise power output is increased and as individual muscle fibers begin to fatigue.     

Ventilatory threshold and work efficiency during exercise on cycle and paddling ergometers in young female kayakists

The aim of this study was to assess the effects of increasing specific (paddling erogmeter) and non-specific (cycle ergometer) exercise on parameters relating to the ventilatory threshold (Th_vent) and work efficiency in 11 young female flat-water kayakists. When these trained subjects were tested using non-specific workloads, their oxygen uptake (VO₂) values at Th_vent, as a percentage ofVO_2max (%VO_2max), were close to those of untrained subjects [74.2 (5.6) %VO_2max, mean (SD)]. However, when we tested the same subjects using specific exercise, we recorded values typical of highly trained athletes [84.8 (4.7) %VO_2max). For the non-specific exercise on the cycle erogmeter, we recorded work efficiency values close to those of untrained subjects [22.3 (2.5) %]; however, for the specific exercise on the paddling ergometer, we recorded much lower values [13.4 (3.0) %] both at the level of Th_vent. The work efficiency at two warm-up submaximal exercise loads on the paddling ergometer was non-significantly lower than values at Th_vent [12.3 (2.8) % and 12.9 (2.9) % respectively]. Significant correlations were found between maximal-performanceVO₂ (ml · kg^–1 · min^–1) and performance at Th_vent during paddling and race performance (0.623, 0.630 and 0.648 respectively, allP<0.05). Because the results of both specific and non-specific submaximal exercise tests are different, we suggest caution in the interpretation of physiological variables that may be sensitive to training status. The evaluation of Th_vent and work efficiency as supplementary parameters during laboratory studies enables the determination of the effectiveness of the training process and the specific adaptation of the subjects.     

Effect of muscle mass on lactate formation during exercise in humans

To elucidate the mechanisms of lactate formation during submaximal exercise, eight men were studied during one- (1-LE) and two-leg (2-LE) exercise (approximately 11-min cycling) using the catheterization technique and muscle biopsies (quadriceps femoris muscle). The absolute exercise intensity and thus the energy demand for the exercising limb was the same [mean 114 (SEM 7) W] during both 1-LE and 2-LE. At the end of exercise partial pressure of O₂ and O₂ saturation in femoral venous blood were lower and arterial adrenaline and noradrenaline were higher during 2-LE than during 1-LE. Mean arterial blood lactate concentration increased to 10.8 (SEM 0.8) (2-LE) and 5.2 (SEM 0.4) mmol · 1^–1 (1-LE) after 10 min of exercise. The intramuscular metabolic response to exercise was attenuated during 1-LE [mean, lactate = 49 (SEM 9); glucose 6-P = 3.3 (SEM 0.3); nicotinamide adenine dinucleotide, reduced = 0.17 (SEM 0.02); adenosine 5-diphosphate 2.7 (SEM 0.1) mmol · kg dry mass^–1] compared to 2-LE [76 (SEM 6); 6.1 (SEM 0.7); 0.21 (SEM 0.02); 3.0 (SEM 0.1) mmol · kg dry mass^–1, respectively]. To elucidate whether the lower plasma adrenaline concentration could contribute to the attenuated metabolic response, additional experiments were performed on four of the eight subjects with infusion of adrenaline during 1-LE (1-LEE). Average plasma adrenaline concentration was increased during 1-LEE and reached 2–4 times higher levels than during 2-LE. Post-exercise muscle lactate and glucose 6-P contents were higher during 1-LEE than during 1-LE and were similar to those during 2-LE. Also, leg lactate release was elevated during 1-LEE versus 1-LE. It was concluded that during submaximal dynamic exercise the intramuscular metabolic response not only depended on the muscle power output, but also on the total muscle mass engaged. Plasma adrenaline concentrations and muscle oxygenation were found to be dependent upon the working muscle mass and both may have affected the metabolic response during exercise.     

Effects on the crank torque profile when changing pedalling cadence in level ground and uphill road cycling

Despite the importance of uphill cycling performance during cycling competitions, there is very little research investigating uphill cycling, particularly concerning field studies. The lack of research is partly due to the difficulties in obtaining data in the field. The aim of this study was to analyse the crank torque in road cycling on level and uphill using different pedalling cadences in the seated position. Seven male cyclists performed four tests in the seated position (1) on level ground at 80 and 100 rpm, and (2) on uphill road cycling (9.25% grade) at 60 and 80 rpm.The cyclists exercised for 1 min at their maximal aerobic power. The bicycle was equipped with the SRM Training System (Schoberer, Germany) for the measurement of power output (W), torque (Nm), pedalling cadence (rpm), and cycling velocity (km h(-1)). The most important finding of this study indicated that at maximal aerobic power the crank torque profile (relationship between torque and crank angle) varied substantially according to the pedalling cadence and with a minor effect according to the terrain. At the same power output and pedalling cadence (80 rpm) the torque at a 45 degrees crank angle tended (p < 0.06) to be higher (+26%) during uphill cycling compared to level cycling. During uphill cycling at 60 rpm the peak torque was increased by 42% compared with level ground cycling at 100 rpm.When the pedalling cadence was modified, most of the variations in the crank torque profile were localised in the power output sector (45 degrees to 135 degrees).     

Oxygen uptake efficiency slope as a useful measure of cardiorespiratory functional reserve in adult cardiac patients

In this study we aimed to elucidate the validity and usefulness of the oxygen uptake efficiency slope (OUES) in the evaluation of adult cardiac patients. Cardiopulmonary exercise tests were performed on a treadmill by 50 adult patients with chronic heart failure. The OUES was calculated from data for the first 75%, 90%, and 100% of exercise duration. The OUES is derived from the following equation: VO(2)=ax logV(E)+b, where VO(2) is oxygen uptake (ml/kg/min), V(E) is minute ventilation (l/kg/min), and the constant "a" represents OUES. We also determined the ventilatory anaerobic threshold (VAT). The correlation coefficient of the logarithmic curve-fitting model was [mean (SD)] 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Association functional classes (P < 0.001). OUES and maximum VO(2) were significantly correlated (r=0.78, P < 0.01). Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intraclass correlation coefficient = 0.99). Our results suggest that OUES is applicable to adult cardiac patients as an objective, effort-independent estimation of cardiorespiratory functional reserve.     

Sister chromatid exchange frequency,cellular replication and relative cloning efficiency in human teratocarcinoma-derived cells

To determine the relationships between the induction of specific biological responses and exposure to DNA-damaging agents, human teratocarcinoma-derived cells were exposed to either ethyl methanesulfonate or to methyl methanesulfonate, and sister chromatid exchange, cellular proliferation and relative cloning ability measured. SCE increased while cellular proliferation and relative cloning ability each decreased in a concentration-dependent manner. Methyl methanesulfonate was consistently more efficient in inducing biological responses than was ethyl methanesulfonate. When the individual responses were compared, the decrease in cellular proliferation paralleled the reduction in cloning efficiency. A strong correlation was also observed between the reduction in relative cloning ability and sister chromatid exchange frequency. Because these relationships are similar to those previously described in other mammalian cell lines, the observations in our study suggest that the P3 cell line is an appropriate choice for modeling effects of toxicant exposure in human cells.Abbreviations AGT average generation time - BUdR 5-bromodeoxyuridine - CHO Chinese hamster ovary - EMS ethyl methanesulfonate - ENU N-ethyl-N-nitrosourea - MMS methyl methanesulfonate - MNU N-methyl-Nnitrosourea - SCE sister chromatid exchange     

Urinary Levels of 8-Hydroxydeoxyguanosine as a Marker of Oxidative Damage in Road Cycling

We have determined the urinary 8-hydroxydeoxyguanosine (8-OHdG) levels of eight professional cyclists during a 4-day and a 3-week stage races. Monitoring of heart rates was used to establish zones corresponding to different intensities of exercise. The urinary 8-OHdG excretion, expressed by body weight, increased significantly in the first day or the first week of each race, respectively, and did not show further increases thereafter. Maximum 8-OHdG levels were reached in parallel to longer times spent at high intensities of exercise. Urinary excretion of creatinine increased with exercise, and changes in 8-OHdG levels were not detected when corrected by creatinine excretion. Serum glutathione concentrations did not change significantly at any point during exercise. We conclude that road cycling courses with an oxidative damage to DNA, which is sustained as long as the exercise is repeated. Both adaptation of antioxidant defenses and a decreased capacity to maintain a high intensity of effort may contribute to explain the absence of progressive increases in 8-OHdG excretion. The results of this study also confirm that the correction procedure using the amount of creatinine excreted should not be used when studying effects of exercise on urinary 8-OHdG.     

Oxygen uptake does not increase linearly at high power outputs during incremental exercise test in humans

A group of 12 healthy non-smoking men [mean age 22.3 (SD 1.1) years], performed an incremental exercise test. The test started at 30 W, followed by increases in power output (P) of 30 W every 3 min, until exhaustion. Blood samples were taken from an antecubital vein for determination of plasma concentration lactate [La⁻]_pl and acid-base balance variables. Below the lactate threshold (LT) defined in this study as the highest P above which a sustained increase in [La⁻]_pl was observed (at least 0.5 mmol · l⁻¹ within 3 min), the pulmonary oxygen uptake (V˙O₂) measured breath-by-breath, showed a linear relationship with P. However, at P above LT [in this study 135 (SD 30) W] there was an additional accumulating increase in V˙O₂ above that expected from the increase in P alone. The magnitude of this effect was illustrated by the difference in the final P observed at maximal oxygen uptake (V˙O_2max) during the incremental exercise test (P _max,obs at V˙O_2max) and the expected power output at V˙O_2max(P _max,exp at V˙O_2max) predicted from the linear V˙O₂-P relationship derived from the data collected below LT. The P _max,obs at V˙O_2max amounting to 270 (SD 19) W was 65.1 (SD 35) W (19%) lower (P<0.01) than the P _max,exp at V˙O_{2max .} The mean value of V˙O_2max reached at P _max,obs amounted to 3555 (SD 226) ml · min⁻¹ which was 572 (SD 269) ml · min⁻¹ higher (P<0.01) than the V˙O₂ expected at this P, calculated from the linear relationship between V˙O₂ and P derived from the data collected below LT. This fall in locomotory efficiency expressed by the additional increase in V˙O₂, amounting to 572 (SD 269) ml O₂ · min⁻¹, was accompanied by a significant increase in [La⁻]_pl amounting to 7.04 (SD 2.2) mmol · l⁻¹, a significant increase in blood hydrogen ion concentration ([H⁺]_b) to 7.4 (SD 3) nmol · l⁻¹ and a significant fall in blood bicarbonate concentration to 5.78 (SD 1.7) mmol · l⁻¹, in relation to the values measured at the P of the LT. We also correlated the individual values of the additional V˙O₂ with the increases (Δ) in variables [La⁻]_pl and Δ[H⁺]_b. The Δ values for [La⁻]_pl and Δ[H⁺]_b were expressed as the differences between values reached at the P _max,obs at V˙O_2max and the values at LT. No significant correlations between the additional V˙O₂ and Δ[La⁻]_pl on [H⁺]_b were found. In conclusion, when performing an incremental exercise test, exceeding P corresponding to LT was accompanied by a significant additional increase in V˙O₂ above that expected from the linear relationship between V˙O₂ and P occurring at lower P. However, the magnitude of the additional increase in V˙O₂ did not correlate with the magnitude of the increases in [La⁻]_pl and [H⁺]_b reached in the final stages of the incremental test. Accepted: 30 October 1997     

Effects of training at simulated altitude on performance and muscle metabolic capacity in competitive road cyclists

Differences between the effects of training at sea level and at simulated altitude on performance and muscle structural and biochemical properties were investigated in 8 competitive cyclists who trained for 3-4 weeks, 4-5 sessions/week, each session consisting of cycling for 60-90 min continuously and 45-60 min intermittently. Four subjects, the altitude group (AG), trained in a hypobaric chamber (574 torr = 2300 m above sea level), and the other four at sea level (SLG). Before and after training work capacity was tested both at simulated altitude (574 torr) and at sea level, by an incremental cycle ergometer test until exhaustion. Work capacity was expressed as total amount of work performed. Venous blood samples were taken during the tests. Leg muscle biopsies were taken at rest before and after the training period. AG exhibited an increase of 33% in both sea level and altitude performance, while SLG increased 22% at sea level and 14% at altitude. Blood lactate concentration at a given submaximal load at altitude was significantly more reduced by training in AG than SLG. Muscle phosphofructokinase (PFK) activity decreased with training in AG but increased in SLG. All AG subjects showed increases in capillary density. In conclusion, work capacity at altitude was increased more by training at altitude than at sea level. Work capacity at sea level was at least as much improved by altitude as by sea level training. The improved work capacity by training at altitude was paralleled by decreased exercise blood lactate concentration, increased capillarization and decreased glycolytic capacity in leg muscle.     

Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet

These studies investigated the effects of 2 weeks of either a high-fat (HIGH-FAT: 70% fat, 7% CHO) or a high-carbohydrate (HIGH-CHO: 74% CHO, 12% fat) diet on exercise performance in trained cyclists (n = 5) during consecutive periods of cycle exercise including a Wingate test of muscle power, cycle exercise to exhaustion at 85% of peak power output [90% maximal oxygen uptake ( O_2max), high-intensity exercise (HIE)] and 50% of peak power output [60% O_2max, moderate intensity exercise (MIE)]. Exercise time to exhaustion during HIE was not significantly different between trials: nor were the rates of muscle glycogen utilization during HIE different between trials, although starting muscle glycogen content was lower [68.1 (SEM 3.9) vs 120.6 (SEM 3.8) mmol · kg ^–1 wet mass, P < 0.01] after the HIGH-FAT diet. Despite a lower muscle glycogen content at the onset of MIE [32 (SEM 7) vs 73 (SEM 6) mmol · kg ^–1 wet mass, HIGH-FAT vs HIGH-CHO, P < 0.01], exercise time to exhaustion during subsequent MIE was significantly longer after the HIGH-FAT diet [79.7 (SEM 7.6) vs 42.5 (SEM 6.8) min, HIGH-FAT vs HIGH-CHO, P<0.01]. Enhanced endurance during MIE after the HIGH-FAT diet was associated with a lower respiratory exchange ratio [0.87 (SEM 0.03) vs 0.92 (SEM 0.02), P<0.05], and a decreased rate of carbohydrate oxidation [1.41 (SEM 0.70) vs 2.23 (SEM 0.40) g CHO · min^–1, P<0.05]. These results would suggest that 2 weeks of adaptation to a high-fat diet would result in an enhanced resistance to fatigue and a significant sparing of endogenous carbohydrate during low to moderate intensity exercise in a relatively glycogen-depleted state and unimpaired performance during high intensity exercise.