Phase III V̇O 2 increase does not lead to V̇O 2 values higher than V̇O 2max during prolonged intense exercises in humans

Abstract This study tested the hypothesis that maximum O₂ uptake (V̇O_2max) sets the uppermost limit to O₂ flow. If this is so, the V̇O₂ increase with time during high intensity prolonged exercises (slow component) cannot reach V̇O₂ levels higher than V̇O_2max. To this aim, on 15 amateur cyclists (age, 24±4 years; mean ± S.E.M.) V̇O_2max was measured during graded cycloergometric exercise. On different days, the subjects performed exercises at 80% and 90% of the previously determined V̇O_2max up to exhaustion (Ẇ₈₀ and Ẇ₉₀, respectively). Measured variables included time to exhaustion (T_lim), power output, V̇O₂, CO₂ production (V̇CO₂), ventilation (V̇E) and blood lactate concentration ([La]). V̇O_2max was 4.05±0.08 L•min^-1. At the end of Ẇ₈₀ (T_lim 1649±145 s) and Ẇ₉₀ (T_lim 733±65 s), V̇O₂ was 3.77±0.13 and 4.08±0.12 L•min^-1 respectively. V̇O₂ at the end of Ẇ₉₀ was similar to V̇O_2max, while at the end of Ẇ₈₀ it was significantly lower. [La] was increased at the end of prolonged exercises not only with respect to rest, but also compared to values at exercise minute 5, indicating anaerobic lactic metabolism contribution to energy production. Compensation of lactic acidosis led to significant increases in V̇E and V̇CO₂ at the end of Ẇ₈₀ and Ẇ₉₀. In conclusion, the present results support the hypothesis that V̇O_2max really reflects the individual maximum aerobic power, without being limited by factors intrinsic to the experimental procedures.     

Quantification of baboon cortical S2 serotonin receptors in vivo with 3-N-(2′-Fl8)fluoroethylspiperone and positron emission tomography

We used the ligand 3-N-(2-F 18)fluoroethylspiperone (FESP) and positron emission tomography (PET) to quantify in vivo serotonin S₂ neuroreceptor density and affinity in the baboon frontal cortex. In the cortex, FESP binds specifically and exclusively to S₂ receptors, and an equilibrium is reached when the rate of ligand-receptor association and dissociation become equal. Using multiple studies in the same baboon, an equilibrium (saturation) analysis approach provided a linear Hill plot with a slope of 1.02 (r ² =0.988,P <0.0001), indicative of ligand binding to a single receptor class. Using serial PET scans, a dynamic approach was also used to quantify S₂ receptors in the frontal cortex of the baboon, which provided an estimate of receptor densityB _max =35.6 ± 10.9 pmol/g. The rate constants corresponding to transport into and out of tissue wereK _* ¹ = 0.2720 ± 0.0299 mol/min g andk _* ² = 0.0786 ± 0.0315 min^–1, respectively. The ligand-receptor dissociation constant wask _* ⁴ = 0.0154 ± 0.0109 min^–1.     

Submaximal field testing validity for aerobic fitness assessment in recreational football

Submaximal field tests are especially recommended when repeated testing is warranted. This study aimed at assessing the validity of the submaximal versions of the Yo-Yo intermittent tests in male recreational football players in untrained and trained status. The participants’ (n = 66; age 39.3 ± 5.8 years, VO_2max 41.2 ± 6.2 mL·kg⁻¹·min⁻¹, body mass 81.9 ± 10.8 kg, height 173.2 ± 6.4 cm) heart rate after 2 minutes (HR_2min) during the level 1 (YYIE1_HR2min) and 2 (YYIE2_HR2min) versions of the Yo-Yo intermittent endurance test and the level 1 version of the Yo-Yo intermittent recovery test (YYIR1_HR2min) was plotted against individual VO_2max values. Thirty-two participants performed all the tests after a 12-week recreational football intervention for test responsiveness. Associations between VO_2max and YYIE1_HR2min were large to small (P = .0001). Large to trivial associations were found between YYIE2_HR2min, YYIR1_HR2min, and VO_2max (P < .01). Maximal Yo-Yo performances were large, significant, and inversely related to HR_2min (−0.68 to −0.49, P < .0001). Pre- to post-intervention ICC values were good for YYIE1_HR2min and YYIE2_HR2min, and excellent for YYIR1_HR2min. Post-intervention associations between HR_2min and Yo-Yo maximal performances were large to very large (−0.55 to −0.72; P < .002, n = 32). Training-induced changes in VO_2max moderately correlated with YYIR1_HR2min (−0.48; P = .007; n = 32). HR_2min lower than 89%, 98%, and 91% HR_max for YYIE1_HR2min, YYIE2_HR2min, and YYIR1_HR2min, respectively, may be considered as signs of good to excellent VO_2max levels. Since in the YYIE1_HR2min, the participants attained 84% HR_max and test specificity increased for HR_2min values <89%, this test may be the preferred choice when repeated assessment of aerobic fitness, using submaximal intermittent Yo-Yo tests, is considered in recreational football.     

Aerobic exercise capacity at sea level and at altitude in Kenyan boys, junior and senior runners compared with Scandinavian runners

The aim of this study was to characterize Kenyan runners in regard to their oxygen uptake and blood and ammonia responses when running. Untrained Kenyan boys (14.2±0.2 years) and Scandinavian runners were included for comparison. The studies were performed at altitude (～2.000 m.a.s.l.) and, for several Kenyan and Scandinavian runners, at sea level as well. At altitude sedentary adolescent Kenyan boys had a mean maximal oxygen uptake (Vo_2max) of 47 (44–51) ml · kg^?1· min^?1, whereas similarly aged boys regularly walking or running but not training for competition reached above 62 (58–71) ml · kg^?1· min^?1 in Vo^2max. Kenyan runners in active training had 68±1.4 ml · kg^?1· min^?1 at altitude and 79.9±1.4 ml · kg^?1· min^?1 at sea level, with individuals reaching 85 ml · kg^?1· min^?1. The best Scandinavian runners were not significantly different from the Kenyan runners in Vo_2max both at altitude and at sea level, but none of the Scandinavians reached as high individual values as observed for some Kenyan runners. The running efficiency, determined as the oxygen cost at a given running speed, was less in the Kenyan runners, and the difference became more pronounced when body weight was expressed in ml · kg^?0.75 min^?1. Blood lactate concentration was in general lower in the Kenyan than in the Scandinavian runners, and the Kenyans also had extremely low ammonia accumulation in the blood even at very high exercise intensities. It is concluded that it is the physical activity during childhood, combined with intense training as teenagers that brings about the high Vo_2max observed in some Kenyan runners. Their high aerobic capacity, as well as their good running economy, makes them such superior runners. In addition, their low blood lactate and ammonia accumulation in blood when running may also be contributing factors.     

Test‐retest variability of VO2max using total‐capture indirect calorimetry reveals linear relationship of VO2 and Power

This study aimed to analyze the intra‐individual variation in VO_2max of human subjects using total‐capture and free‐flow indirect calorimetry. Twenty‐seven men (27 ± 5 year; VO_2max 49‐79 mL?kg^?1?min^?1) performed two maximal exertion tests (CPETs) on a cycle ergometer, separated by a 7 ± 2 day interval. VO₂ and VCO₂ were assessed using an indirect calorimeter (Omnical) with total capture of exhalation in a free‐flow airstream. Thirteen subjects performed a third maximal exertion test using a breath‐by‐breath calorimeter (Oxycon Pro). On‐site validation was deemed a requirement. For the Omnical, the mean within‐subject CV for VO_2max was 1.2 ± 0.9% (0.0%‐4.4%) and for ergometer workload P _max 1.3 ± 1.3% (0%‐4.6%). VO_2max values with the Oxycon Pro were significantly lower in comparison with Omnical (P < 0.001; t test) with mean 3570 vs 4061 and difference SD 361 mL?min^?1. Validation results for the Omnical with methanol combustion were ?0.05 ± 0.70% (mean ± SD; n = 31) at the 225 mL?min^?1 VO₂ level and ?0.23 ± 0.80% (n = 31) at the 150 mL?min^?1 VCO₂ level. Results using gas infusion were 0.04 ± 0.75% (n = 34) and ?0.99 ± 1.05% (n = 24) over the respective 500‐6000 mL?min^?1 VO₂ and VCO₂ ranges. Validation results for the Oxycon Pro in breath‐by‐breath mode were ‐ 2.2 ± 1.6% (n = 12) for VO₂ and 5.7 ± 3.3% (n = 12) for VCO₂ over the 1000‐4000 mL?min^?1 range. On a Visual analog scale, participants reported improved breathing using the free‐flow indirect calorimetry (score 7.6 ± 1.2 vs 5.1 ± 2.7, P = 0.008). We conclude that total capturing free‐flow indirect calorimetry is suitable for measuring VO₂ even with the highest range. VO_2max was linear with the incline in P _max over the full range.     

Reproducibility and validity of physiological parameters measured in cyclists riding on racing bikes placed on a stationary magnetic brake

The purpose of this study was: 1) To evaluate the reproducibility of physiological parameters measured during cycle exercise, and 2) To validate the predictive capacity of physiological parameters related to endurance performance. Therefore, physiological variables were measured twice during cycling exercise in a group of seven cyclists. Each cycle exercise session was separated by one week and included progressive submaximal cycling followed by a 5-km time trial. Two and three weeks later, endurance performance was evaluated by calculating average work output during a 50-km time trial (W_50km). To simulate cycle performance, the cyclists’ private racing bikes were placed on a stationary magnetic brake. No differences were observed between paired physiological observations in the test-retest (P>0.05). The coefficient of variation (CV) was calculated from the differences between test-retest parameters. CV for the maximal oxygen uptake (VO_2max), average work output during the 5-km trial (W_5km), the calculated work intensity which increased the blood lactate concentration to 2 and 4 mmol/1 (W_2mM and W_4mM) and W_50km were 1.9, 2.7, 6.1, 5.9 and 6.3%, respectively, while the 95% confidence interval (CI) showing the expected range for variation in a retest was calculated to be 80 ml.min^?1, 9, 16, 18 and 18 W, respectively. Simple linear regression showed significant correlations between VO_2max, W_5km, W_2mM, W_4mM and W_50km (r-values: range 0.83–0.98, P<0.01). In conclusion: 1) Physiological parameters can be reproduced during an exercise test procedure in cyclists riding on racing bikes placed on a stationary magnetic brake, and 2) The validity of VO_2max,W_5km, W_2mM, and W_4mM as predictive parameters of endurance was demonstrated.     

The upper limit of the cardiorespiratory training zone (40–84%HRR) is overestimated for postmenopausal women

Objective: The purpose of this study was to examine the heart rate reserve (HRR) at first and second ventilatory thresholds (VT's) in postmenopausal women and compare it with optimal intensity range recommended by the ACSM (40–84%HRR). An additional aim was to evaluate whether a higher aerobic power level corresponded to a higher HRR at VT's.Methods: Fifty-eight postmenopausal women participated in this study (aged 48–69). A graded 25 W min^?2 cycle ergometer (Monark E839) exercise protocol was performed in order to assess aerobic power. The heart rate and gas-exchange variables were measured continuously using a portable gas analyzer system (Cosmed K4b). The first (VT₁) and the second (VT₂) VT's were determined by the time course curves of ventilation and O₂ and CO₂ ventilatory equivalents. A K-means clustering analysis was used in order to identify VO_2max groups (cut-off of 30.5 ml kg^?1 min^?1) and differences were evaluated by an independent sample t-test. Bland–Altman plots were performed to illustrate the agreement between methods.Results: The women's HRR values at VT₁ were similar to 40%HRR in both VO_2max groups. At VT₂ both VO_2max groups exhibited negative differences (P < 0.01) for the predicted 84%HRR intensity (?14.46% in the lower VO_2max group and ?16.32% in the higher VO_2max group).Conclusions: An upper limit of 84% overestimates the %HRR value for the second ventilatory threshold, suggesting that the cardiorespiratory target zone for this population should be lower and narrower (40–70%HRR).     

The repeatability and criterion related validity of the 20 m multistage fitness test as a predictor of maximal oxygen uptake in active young men

Objective: To investigate the repeatability and criterion related validity of the 20 m multistage fitness test (MFT) for predicting maximal oxygen uptake (Vo_2max) in active young men. Methods: Data were gathered from two phases using 30 subjects (±s; age = 21.8±3.6 years, mass = 76.9±10.7 kg, stature = 1.76±0.05 m). MFT repeatability was investigated in phase 1 where 21 subjects performed the test twice. The MFT criterion validity to predict Vo_2max was investigated in phase 2 where 30 subjects performed a continuous incremental laboratory test to volitional exhaustion to determine Vo_2max and the MFT. Results: Phase 1 showed non-significant bias between the two applications of the MFT (_diff±s_diff = –0.4±1.4 ml kg^–1 min^–1; t = –1.37, p = 0.190) with 95% limits of agreement (LoA) ±2.7 ml kg^–1 min^–1 and heteroscedasticity 0.223 (p = 0.330). Log transformation of these data reduced heteroscedasticity to 0.056 (p = 0.808) with bias –0.007±0.025 (t = –1.35, p = 0.190) and LoA±0.049. Antilogs gave a mean bias on the ratio scale of 0.993 and random error (ratio limits) x/÷1.050. Phase 2 showed that the MFT significantly underpredicted Vo_2max (_diff±s_diff = 1.8±3.2 ml kg^–1 min^–1; t = 3.10, p = 0.004). LoA were ±6.3 ml kg^–1 min^–1 and heteroscedasticity 0.084 (p = 0.658). Log transformation reduced heteroscedasticity to –0.045 (p = 0.814) with LoA±0.110. The significant systematic bias was not eliminated (_diff±s_diff = 0.033±0.056; t = 3.20, p = 0.003). Antilogs gave a mean bias of 1.034 with random errorx/÷1.116. Conclusions: These findings lend support to previous investigations of the MFT by identifying that in the population assessed it provides results that are repeatable but it routinely underestimates Vo_2max when compared to laboratory determinations. Unlike previous findings, however, these results show that when applying an arguably more appropriate analysis method, the MFT does not provide valid predictions of Vo_2max.     

Clearance of thallium-201 from the peripheral blood: Comparison of immediate and standard thallium-201 reinjection

As several reinjection procedures have shown encouraging results in terms of imaging, we investigated whether the kinetics of thallium-201 would differ between the standard stress-redistribution-reinjection approach and the stress-immediate reinjection approach. In 53 consecutive patients with undiagnosed chest pain, 75 MBq (2 mCi)²⁰¹Tl was injected at maximal exercise. In 26 of these patients (group I), 37 MBq (1 mCi)²⁰¹Tl was reinjected immediately after completing the exercise images (the immediate reinjection procedure) and in 27 patients (group II), 37 MBq (1 mCi)²⁰¹Tl was reinjected after completing 3-h redistribution images (the standard reinjection procedure). Mean peak²⁰¹Tl blood activity after exercise was 17.7±12.5 kBq/ml (4.8±3.4 mCi/ml) for group I versus 16.4±9.2 kBq/ml (4.4±2.5 mCi/ml) for group II (NS). The relative increase in²⁰¹Tl blood activity after reinjection of half the initial dose [37 MBq (1 mCi)] exceeded 50% of the initial peak in both groups. The relative amount of²⁰¹Tl delivered to the myocardium was assessed by the area under the curve after both exercise and reinjection, and was 117%±72% for group I and 112%±73% for group II (NS). Blood clearance of²⁰¹Tl was at least biexponential. Mean early decay constants (₁) after exercise and reinjection were 0.30±0.18 min^–1 and 0.22±0.046 min^–1 respectively for group I (T _1/2 2.3 min and 3.2 min respectively, NS), and 0.30±0.12 min^–1 and 0.24±0.07 min^–1 respectively for group II (T _1/2 2.3 min and 2.9 min respectively, NS). For both procedures no significant differences were found between ₁ after exercise and ₁ after injection. The mean late clearance (₂) from the blood was 0.032±0.056 min^–1 and 0.012±0.012 min^–1 respectively for group I (T _1/2 21.6 min and 57.7 min respectively, NS), and 0.036±0.030 min^–1 and 0.014±0.014 min^–1 respectively for group II (T _1/2 19.3 min and 49.5 min respectively, NS). Also, no significant differences were found between ₂ after exercise for both groups and between ₂ after reinjection for both groups. We conclude that reinjection of 37 MBq (1 mCi)²⁰¹Tl (half the initial dose) results in a relative increase in the initial peak and a relative increase in the amount of²⁰¹Tl delivered to the myocardium of more than 50% for both the standard and the immediate reinjection procedure. The clearance of²⁰¹Tl from the blood was not influenced by exercise or by the time of reinjection. Based on²⁰¹Tl kinetics as measured in the peripheral blood, there is no reason to postpone reinjection until 3–4 h following exercise.     

Correlation of apparent diffusion coefficients measured by 3T diffusion-weighted MRI and SUV from FDG PET/CT in primary cervical cancer

Purpose  Diffusion-weighted magnetic resonance imaging (DWI) and fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) are oncological feasible techniques. Currently, apparent diffusion coefficient (ADC) measured by DWI and standard uptake value (SUV) from FDG PET/CT have similar applications in clinical oncology. The aim of this study was to assess the correlation between ADC and SUV in primary cervical cancer. Materials and methods  Patients with documented primary cervical cancer were recruited. All participants underwent abdominopelvic DWI at 3T and FDG PET/CT within 2 weeks. For the primary tumor, ADC was measured as minimum ADC (ADC_min) and mean ADC (ADC_mean) within the whole tumor by DWI. Maximum SUV (SUV_max) and mean SUV (SUV_mean) were measured by FDG PET/CT. Results  A total of 33 patients were included. There was no significant correlation either between ADC_min and SUV_max or between ADC_mean and SUV_mean. The relative ADC_min (rADC_min) defined as ADC_min/ADC_mean ratio was significantly inversely correlated with the relative SUV_max (rSUV_max) defined as SUV_max/SUV_mean ratio (r = –0.526, P = 0.0017) in all study patients. A significantly inverse correlation between rADC_min and rSUV_max was observed in patients with adenocarcinoma/adenosquamous carcinoma (r = –0.685, P = 0.0012) and those with well-to-moderate differentiated tumor (r = –0.631, P = 0.0050). No significant correlation was demonstrated in patients with squamous cell carcinoma or poorly differentiated tumor. Conclusions  The significantly inverse correlation between rADC_min and rSUV_max in primary cervical tumor suggests that DWI and FDG PET/CT might play a complementary role for the clinical assessment of this cancer type.     

Changes in physical activity, maximal isometric strength and maximal oxygen uptake from late teenage to adulthood: an eight-year follow-up study of adolescents in Denmark

A randomly selected group of 88 men and 115 women, aged 23–27 years in 1991, were tested as teenagers in 1983, and then followed-up in 1991. A mean increase of 15% in maximal voluntary isometric strength was found in men, and no change was found in women over the 8 years. Body weight increased 14% in men and 6% in women. Strength in relation to body weight (N · kg^?1) did not change in men, but a small decrease of 3% was found in women. Strength in abdominal muscles decreased in blue-collar workers but increased in students. Maximal oxygen uptake (V?_o2max (ml · min^?1kg^?1) decreased 9% in men and 3% in women. The values in 1991 were 47.9 and 39.5 ml · min^?1kg^?1 for men and women, respectively. Participation in leisure sport activities decreased 1.7 h · week^?1 in men and 1.2 h · week^?1 in women. Seventy percent of the men and 74% of the women participated in regular leisure sport activity, which was a marked increase from 8 years before, when only 54% of the men and 57% of the women were similarly active. The overall decrease in V?_O2max in men was due primarily to a decrease among blue-collar workers and unemployed men: 19%vs 4% in other occupational groups. Only 20% of the blue-collar workers participated in sport activities for more than 4 h · week^?1, and 47% did not participate at all. In women, changes in strength and V?_O2max were related to motherhood. Abdominal muscle strength decreased, but arm flexor strength increased in women who had become mothers. V?_O2max decreased 14% in mothers vs 2% in other women. Changes over 8 years in V?_O2max and strength did not relate to changes in physical activity, but a significant relationship between decrease in physical activity and gain in body fat was found in men. Changes in body weight and body fat were the only variables that correlated with changes in strength. None of the observed changes related to changes in V?_O2max (ml · min^?1kg^?1). For the 23- to 27-year-olds, the level of physical activity assessed in h · week^?1 was almost as high in women as in men.     

<Emphasis Type="Italic">V</Emphasis>O<Subscript>2Max</Subscript> and <Emphasis Type="Italic">V</Emphasis>O<Subscript>2AT</Subscript>: athletic performance and field role of elite soccer players

Purpose

Maximal oxygen consumption (VO_2max) and oxygen consumption at anaerobic threshold (VO_2AT) are commonly measured parameters to test elite soccer players; however, studies relating metabolic parameters of professional soccer players with performance and best fitting to the field role are scarce. Our aim was to study the relations of VO_2max and VO_2AT with the field role of elite soccer players to generate a robust dataset with a solid statistical analysis.

Method

Over a 12-year period we performed 953 field evaluation tests of VO_{2 max} and VO_2AT on 450 elite soccer players of 13 professional teams by incremental, continuous and exhausting test modified from Conconi’s test. Statistical analysis was performed by one-way ANOVA followed—when appropriate—by Tukey post hoc test. Effect size was evaluated by the Cohen D test and η partial squared test. Statistical significance was set for p < 0.05.

Results

VO_2max mean values increased at the beginning of season by 1.073 ± 0.06 respect to pre-season then decreased again up to pre-season levels and remained stable, while VO_2AT did not change during time. VO_2max differences were also related to players’ field role. VO_2max mean value for Goalkeeper was 50.85 ± 4.2, for central Defender was 57.58 ± 4.3, for Winger-sides back was 60.53 ± 5.02, for Midfielder was 59.53 ± 5.08, for Forward was 56.52 ± 4.14. On the contrary, as expected, VO_2AT percentage variations among the roles were not significant.

Conclusions

VO_2max is the choice parameter to consider for the metabolic compliance of athletes to the field role requirements, consequently influencing training programs, recovery and injury prevention strategies.

     

In vivo determination of the kinetic parameters of glucose transport in the human brain using 11C-methyl-d-glucose (CMG) and dynamic positron emission tomography (dPET)

A method was developed to measure simultaneously (1) the rate constants for glucose influex and glucose efflux, and (2) the Michaelis-Menten constant (K _M ) and maximal velocity (V _max) for glucose transport across the blood-brain barrier (BBB) in any selected brain area. Moreover, on the basis of a mathematical model, the local perfusion rate (LPR) and local unidirectional glucose transport rate (LUGTR) are calculated in terms of parameters of the time-activity curves registered over different brain regions; ¹¹C-methyl-d-glucose (CMG) is used as an indicator. The transaxial distribution of activity in the organism is registered using dynamic positron-emission tomography (dPET). The method was used in 4 normal subjects and 50 patients with ischemic brain disease. In normals, the rate constant for CMG efflux was found to be 0.25±0.04 min^-1 in the cortex and 0.12±0.02 min^-1 in white matter. In the cortex, the K _M was found to be 6.42 mol/g and the V _max was 2.46 mol/g per minute. The LUGTR ranged from 0.43 to 0.6 mol/g per minute in the cortex, and from 0.09 to 0.12 mol/g per minute in white matter. The LPR was calculated to be 0.80–0.98 ml/g per minute for the cortex and 0.2–0.4 ml/g per minute for white matter. In patients with stroke, the ischemic defects appeared to be larger in CMG scans than in computed x-ray tomography (CT) scans. Prolonged reversible ischemic neurological deficit was associated with a significant fall in the LUGTR but no change in the LPR in the corresponding cerebral cortex. Normal LUGTR and significantly decreased LPR were registered in a patient with progressive occlusion of the middle cerebral artery. In a patient with transient ischemic attacks, a slightly reduced LPR and a disproportionally reduced LUGTR were observed before operation. After extra- and intrac-ranial bypass surgery, the LPR became normal, whereas the LUGTR increased but did not achieve normal values.     

Combining areal DXA bone mineral density and vertebrae postero-anterior width improves the prediction of vertebral strength

Objective

Areal bone mineral density (aBMD) measured by dual-energy X-ray absorptiometry (DXA) is an important determinant of bone strength (BS), despite the fact that the correlation between aBMD and BS is relatively weak. Parameters that describe BS more accurately are desired. The aim of this study was to determine whether the geometrical corrections applied to aBMD would improve its ability for BS prediction. We considered new parameters, estimated from a single DXA measurement, as well as BMAD (bone mineral apparent density) reported in the literature.

Materials and methods

In vitro studies were performed with the L3 vertebrae from 20 cadavers, which were studied with DXA and quantitative computed tomography (QCT). A mechanical strength assessment was carried out. Two new parameters were introduced: $ vBM{D}_{min}=\frac{ aBMD}{W_{PA}^{min}} $ and $ vBM{D}_{av}=\frac{ aBMD}{W_{PA}^{av}} $ (W _PA ^min —minimal vertebral body width in postero-anterior (PA) view, W _PA ^av — average PA vertebral body width). Volumetric BMD measured by QCT (vBMD), aBMD, BMAD, vBMD_min, and vBMD_av were correlated to ultimate load and ultimate stress (P_max) to find the best predictor of vertebrae BS.

Results

The coefficients of correlation between P_max and vBMD_min, vBMD_av, as well as BMAD, were r?=?0.626 (p?=?0.005), r?=?0.610 (p?=?0.006) and r?=?0.567 (p?=?0.012), respectively. Coefficients for vBMD and aBMD are r?=?0.648 (p?=?0.003) and r?=?0.511 (p?=?0.03), respectively.

Conclusions

Our results showed that aBMD normalized by vertebrae dimensions describes vertebrae BS better than aBMD alone. The considered indices vBMD_av, vBMD_min, and BMAD can be measured in routine PA DXA and considerably improve BS variability prediction. vBMD_min is superior compared to vBMD_av and BMAD.     

Acute downhill running does not induce fat oxidation

Objectives

Eccentric exercise has been suggested for its potential to increase several health outcomes, including exercise-induced fat oxidation. Comparison of exercise intensity rather than exercise workload is required.

Methods

Thirteen moderately active young men (mean age, 24.6 ± 5.6 years; body mass index, 23.76 ± 3.24 kg/m²; maximal oxygen consumption (VO_2max), 49.00 ± 3.19 ml/kg/min) performed two counterbalanced running sessions for 40 min at 60% VO_2max, either running flat (Con-Exe) or running downhill at a gradient of ? 12% (Ecc-Exe). The volumes of oxygen and carbon dioxide (VO₂ and VCO₂) were collected during exercise sessions, and fat oxidation was calculated.

Results

There was no significant interaction between exercise condition and exercise duration (p > 0.05), and individual variations in fat oxidation during Con-Exe and Ecc-Exe were large and inconsistent.

Conclusion

Downhill running at 60% VO_2max and inclination of ? 12% does not induce fat oxidation.

     

Tetrahydrobiopterin restores impaired coronary microvascular dysfunction in hypercholesterolaemia

Purpose Tetrahydrobiopterin (BH₄) is an essential co-factor for the synthesis of nitric oxide (NO), and BH₄ deficiency may cause impaired NO synthase (NOS) activity. We studied whether BH₄ deficiency contributes to the coronary microcirculatory dysfunction observed in patients with hypercholesterolaemia.Methods Myocardial blood flow (MBF; ml min^–1 g^–1) was measured at rest, during adenosine-induced (140 g kg^–1 min^–1 over 7 min) hyperaemia (mainly non-endothelium dependent) and immediately after supine bicycle exercise (endothelium-dependent) stress in ten healthy volunteers and in nine hypercholesterolaemic subjects using ¹⁵O-labelled water and positron emission tomography. Measurements were repeated 60 min later, after intravenous infusion of BH₄ (10 mg kg^–1 body weight over 30 min). Adenosine-induced hyperaemic MBF is considered to represent (near) maximal flow. Flow reserve utilisation was calculated as the ratio of exercise-induced to adenosine-induced hyperaemic MBF and expressed as percent to indicate how much of the maximal (adenosine-induced) hyperaemia can be achieved by bicycle stress.Results BH₄ increased exercise-induced hyperaemia in controls (2.96±0.58 vs 3.41±0.73 ml min^–1 g^–1, p<0.05) and hypercholesterolaemic subjects (2.47±0.78 vs 2.70±0.72 ml min^–1 g^–1, p<0.01) but had no influence on MBF at rest or during adenosine-induced hyperaemia in controls (4.52±1.10 vs 4.85±0.45 ml min^–1 g^–1, p=NS) or hypercholesterolaemic subjects (4.86±1.18 vs 4.53±0.93 ml min^–1 g^–1, p=NS). Flow reserve utilisation remained unchanged in controls (70±17% vs 71±19%, p=NS) but increased significantly in hypercholesterolaemic subjects (53±15% vs 66±14%, p<0.05).Conclusion BH₄ restores flow reserve utilisation of the coronary microcirculation in hypercholesterolaemic subjects, suggesting that BH₄ deficiency may contribute to coronary microcirculatory dysfunction in hypercholesterolaemia.The first two authors have contributed equally to the present project.An erratum to this article can be found at     

Aerobic work capacity in young sedentary men and active athletes in India

Maximal oxygen uptake (O₂ max) was determined in 40 sedentary men aged 17-25 years and in 96 active athletes of the same age participating in 5 different kinds of sport. The O₂ max in the sedentary group was found to be 36.8 ± 4.0 (SD) ml.kg.^-1 min^-1. The results in the sedentary group were found to be lower than those recorded on inactive populations in other countries by 12-35%, possibly due to the low participation rate in sport among Indians. The mean O₂ max in 96 active athletes was 48.4 ± 5.1 ml.kg.^-1 min^-1 which is slightly low as compared to O₂ max values recorded in active populations in other countries. The difference in the mean O₂ max of sedentary group and that of the active one was found to be statistically significant. The highest mean O₂ max was recorded in the group of long distance runners (56.4 ml.kg.^-1 min^-1) while lowest mean O₂ max values were recorded in the group of football players 44.2 + 2.1 ml.kg.^-1 min^-1).     

Enhancing the efficacy of the 20 m multistage shuttle run test

Objective: Maximal oxygen uptake (Vo_2max) of 44 ml kg^–1 min^–1 is an accepted criterion (Vo_2CR) below which health and fitness for young male adults may be compromised. New algorithms validated for Vo_2CR screening using the 20 m multistage shuttle run test (20mMST) were developed.

Methods: Vo_2max was assessed in 110 males using a stationary gas analyser in a treadmill test (TT) and in 40 of these subjects using a portable gas analyser in the 20mMST. Vo_2max predicted from the 20mMST in 70 subjects was used for cross validation. Two equations predicting Vo_2max during 20mMST (EQ_MST) and TT (EQ_TT) were developed.

Results: Significant energy cost variance (EC_V) was detected between TT and 20mMST (p<0.001), correlated significantly with subject height, and was a significant predictor of Vo_2max differences between TT and 20mMST. The r² of EQ_MST was 0.92 (p<0.001). Predicted Vo_2max values from EQ_MST correlated with directly measured 20mMST Vo_2max at r = 0.96 (p<0.001). ANOVA detected no mean difference (p>0.05) between predicted and measured values. Prevalence of low fitness based on Vo_2CR was 0.37. McNemar χ² indicated significant differences in sensitivity (p<0.001) and specificity (p<0.05) between the original 20mMST equation (EQ_LÉG) and EQ_TT, regarding Vo_2CR screening. Cohen's κ demonstrated higher agreement with TT Vo_2max for EQ_TT (p<0.001) than EQ_LÉG (p<0.05). TT Vo_2max correlated with the end result of both EQ_LÉG and EQ_TT at r = 0.75 (p<0.001). Unlike EQ_TT (p>0.05), mean predicted Vo_2max from EQ_LÉG was significantly higher compared to TT Vo_2max (p<0.001).

Conclusion: These algorithms increase the efficacy of 20mMST to accurately evaluate aspects of health and fitness.

     

The relationship between vLTP and vVO2max during an incremental test to exhaustion in professional endurance runners

The minimal running velocity at which maximal oxygen uptake (VO_2max) is elicited during an incremental test to exhaustion has been used to prescribe training for competitive middle- and long-distance runners. The purpose of this study was to determine the relationship between velocity at lactate turnpoint (vLTP) and vVO_2max in long-distance runners. For this purpose 11 highly trained endurance runners were selected randomly from the national team. The average age, height and mass of the subjects were 24.36±1.1 years, 1.73±0.02 m and 63.25±21 kg respectively. The first test was used to determine vVO_2max and VO_2max (a continuous run to exhaustion with the start velocity at 10 km/h and the velocity increased 1 km/h per minute). The second test was used to determine vLTP (start velocity was 10 km/h and velocity increased 1 km/h for 4 min to reach lactate concentration over 5 mmol/l). The average VO_2max and vVO_2max of subjects were 58.54±2.8 ml/kg/min and 19±0.29 km/h respectively. Pearson’s correlation coefficient and SPSS 12 software were used for analysing data. There was a positive moderate correlation between vLTP and vVO_2max (p=0.037, r=0.63). This study may indicate that, the more the athlete is capable of delaying the accumulation of his/her lactate, and the higher the velocity at which the accumulation takes place, the higher vVO_2max he/she can have. On the other hand, coaches can design training programmes at vVO_2max intensity to promote a higher vLTP.     

In‐season changes in heart rate recovery are inversely related to time to exhaustion but not aerobic capacity in rowers

To determine if in‐season changes in heart rate recovery (HRR ) are related to aerobic fitness and performance in collegiate rowers. Twenty‐two female collegiate rowers completed testing before and after their competitive season. Body fat percentage (BF %) was determined by dual‐energy X‐ray absorptiometry. Maximal aerobic capacity (VO _2max) and time to exhaustion (T _max) were determined during maximal rowing ergometer testing followed by 1 minute of recovery. HRR was expressed absolutely and as a percentage of maximal HR (HRR %_1 min). Variables were compared using paired Wilcoxon tests. Multivariable regression models were used to predict in‐season changes in HRR using changes in VO _2max and T _max, while accounting for changes in BF %. From preseason to post‐season, VO _2max and BF % decreased (3.98±0.42 vs 3.78±0.35 L/min, P =.002 and 23.8±3.4 vs 21.3±3.9%, P <.001, respectively), while T _max increased (11.7±1.3 vs 12.6±1.3 min, P =.002), and HRR %_1 min increased (11.1±2.7 vs 13.8±3.8, P =.001). In‐season changes in VO _2max were not associated with HRR %_1 min (P >.05). In‐season changes in T _max were related to changes in HRR %_1 min (β=−1.67, P =.006). In‐season changes in BF % were not related to changes in HRR (P >.05 for all). HRR _1 min and HRR %_1 min were faster preseason to post‐season, although the changes were unrelated to VO _2max. Faster HRR %_1 min post‐season was inversely related to changes in T _max. This suggests that HRR should not be used as a measure of aerobic capacity in collegiate rowers, but is a promising measure of training status in this population.