Molecular correlates for maximal oxygen uptake and type 1 fibers

Maximal oxygen uptake (Vo(2max)) and the amount of type 1 fibers are interrelated, but the underlying unifying molecular mechanisms are poorly understood. To explore these mechanisms, we related gene expression profiles in skeletal muscle biopsies of 43 age-matched men from published datasets with Vo(2max) and the amount of type 1 fibers and replicated some of the findings in muscle biopsies from 154 young and elderly individuals using real-time PCR. We identified 66 probe sets (genes or expressed sequence tags) positively and 83 probe sets inversely correlated with Vo(2max) and 171 probe sets positively and 217 probe sets inversely correlated with percentage of type 1 fibers in human skeletal muscle. Genes involved in oxidative phosphorylation (OXPHOS) showed high expression in individuals with high Vo(2max), whereas the opposite was not the case in individuals with low Vo(2max). Instead, genes such as AHNAK and BCL6 were associated with low Vo(2max). Also, expression of the OXPHOS genes NDUFB5 and ATP5C1 increased with exercise training and decreased with aging. In contrast, expression of AHNAK in skeletal muscle decreased with exercise training and increased with aging. Eleven genes (NDUFB4, COX5A, UQCRB, ATP5C1, ATP5G3, ETHE1, FABP3, ISCA1, MYST4, C9orf3, and PKIA) were positively correlated with both Vo(2max) and the percentage of type 1 fibers. Vo(2max) closely reflects expression of OXPHOS genes, particularly that of NDUFB5 and ATP5C1, in skeletal muscle, suggesting good muscle fitness. In contrast, a high expression of AHNAK was associated with a low Vo(2max) and poor muscle fitness.     

Effect of changes in arterial oxygen content on circulation and physical performance.

To evaluate the effect of different levels of arterial oxygen content on hemodynamic parameters during exercise nine subjects performed submaximal bicycle or treadmill exercise and maximal treadmill exercise under three different experimental conditions: 1) breathing room air (control); 2) breathing 50% oxygen (hyperoxia); 3) after rebreathing a carbon monoxide gas mixture (hypoxia). Maximal oxygen consumption (Vo2 max) was significantly higher in hyperoxia (4.99 1/min) and significantly lower in hypoxia (3.80 1/min) than in the control experiment (4.43 1/min). Physical performance changes in parallel with Vo2 max. Maximal cardiac output (Qmax) was similar in hyperoxia as in control but was significantly lower in hypoxia mainly due to a decreased stroke volume. A correlation was found between Vo2 max and transported oxygen, i.e., Cao2 times Amax, thus suggesting that central circulation is an important limiting factor for human maximal aerobic power. During submaximal work HR was decreased in hyperoxia and increased in hypoxia. Corresponding Q values were unchanged except for a reduction during high submaximal exercise in hyperoxia.     

Effects of exercise training on acclimatization to hypoxia: systemic O2 transport during maximal exercise.

Acclimatization to hypoxia has minimal effect on maximal O2 uptake (Vo2 max). Prolonged hypoxia shows reductions in cardiac output (Q), maximal heart rate (HR-max), myocardial beta-adrenoceptor (beta-AR) density, and chronotropic response to isoproterenol. This study tested the hypothesis that exercise training (ET), which attenuates beta-AR downregulation, would increase HRmax and Q of acclimatization and result in higher Vo2 max. After 3 wk of ET, rats lived at an inspired Po2 of 70 Torr for 10 days (acclimatized trained rats) or remained in normoxia, while both groups continued to train in normoxia. Controls were sedentary acclimatized and nonacclimatized rats. All rats exercised maximally in normoxia and hypoxia (inspired Po2 of 70 Torr). Myocardial beta-AR density and the chronotropic response to isoproterenol were reduced, and myocardial cholinergic receptor density was increased after acclimatization; all of these receptor changes were reversed by ET. Normoxic Vo2 max (in ml.min-1.kg-1) was 95.8 +/- 1.0 in acclimatized trained (n = 6), 87.7 +/- 1.7 in nonacclimatized trained (P < 0.05, n = 6), 74.2 +/- 1.4 in acclimatized sedentary (n = 6, P < 0.05), and 72.5 +/- 1.2 in nonacclimatized sedentary (n = 8; P > 0.05 acclimatized sedentary vs. nonacclimatized sedentary). A similar distribution of Vo2 max values occurred in hypoxic exercise. Q was highest in trained acclimatized and nonacclimatized, intermediate in nonacclimatized sedentary, and lowest in acclimatized sedentary groups. ET preserved Q in acclimatized rats thanks to maintenance of HRmax as well as of maximal stroke volume. Q preservation, coupled with a higher arterial O2 content, resulted in the acclimatized trained rats having the highest convective O2 transport and Vo2 max. These results show that ET attenuates beta-AR downregulation and preserves Q and Vo2 max after acclimatization, and support the idea that beta-AR downregulation partially contributes to the limitation of Vo2 max after acclimatization in rats.     

The effects of previous severe exercise upon the respiratory Vco2/Vo2 exchange ratio as a predictor of maximum oxygen uptake

The present study examined the effect of previous severe exercise upon (i) respiratory exchange during maximal exercise, and (ii) the respiratory Vco2/Vo2 exchange ratio (R) as a predictor of maximum oxygen uptake (Vo2max). Thirteen healthy males performed a progressive treadmill test to Vo2max: at rest (T1); after a 1 h run on the level treadmill at a speed corresponding 82.4 +/- 7.3% of their Vo2max (T2); after 1 h recovery (T3); and after 24 h recovery (T4). Respiratory gases were continuously monitored. No changes in average work Vo2, Vo2max or maximum heart rate were found between trials. Average work Vco2 was lower in T2 (2.055 +/- 0.093 1.min-1, p less than 0.001), T3 (2.080 +/- 0.087 1.min-1, p less than 0.001) and T4 (2.337 +/- 0.154 1.min-1, NS) compared with T1 (2.360 +/- 0.147 1.min-1). This resulted in lower average R values in T2 (0.81 +/- 0.02, p less than 0.001), T3 (0.83 +/- 0.02, p less than 0.001) and T4 (0.94 +/- 0.02, NS) in relation to T1 (0.95 +/- 0.02). Analysis of the %Vo2max/R relationship over the final 5 min of each test showed a shift to the left during T2 (p less than 0.001), T3 (p less than 0.001) and T4 (NS) compared with T1. As a result predictions of Vo2max based on R (Vo2max/R) were similar to recorded Vo2max in T1 (+ 0.6%) and T4 (+ 2.2%). But higher in T2 (+ 8.7%, p less than 0.001) and T3 (+ 6.9%, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

训练专一性对无氧阈测定的影响

本文对以上肢训练为主的15名优秀皮划艇运动员和以下肢训练为主的14名优秀中长跑运动员在两种常规负荷方式下的无氧阈及最大吸氧量进行了测定分析,以探讨训练专一性对无氧阈测定的影响。采用踏车式功量计和活动平板方式逐级递增负荷,通过与Apple Ⅱ_E辅助联机的Jaeger EOS自动分析系统,以通气和气体交换指标的变化,无创性地测定无氧阈和最大吸氧量。结果表明,训练专一性会影响无氧阈测定结果。欲测得最高的无氧阈值,实验室测试手段就应当尽量模拟训练时的运动形式。此外,能敏感地反映出运动训练专一性适应的是无氧阈时的吸氧量绝对值(1/min),而不是无氧阈的相对值(％Vo_2max)。     

Training-induced changes in skeletal muscle Na+-K+ pump number and isoform expression in rats with chronic heart failure.

The mechanisms responsible for the decrements in exercise performance in chronic heart failure (CHF) remain poorly understood, but it has been suggested that sarcolemmal alterations could contribute to the early onset of muscular fatigue. Previously, our laboratory demonstrated that the maximal number of ouabain binding sites (B(max)) is reduced in the skeletal muscle of rats with CHF (Musch TI, Wolfram S, Hageman KS, and Pickar JG. J Appl Physiol 92: 2326-2334, 2002). These reductions may coincide with changes in the Na(+)-K(+)-ATPase isoform (alpha and beta) expression. In the present study, we tested the hypothesis that reductions in B(max) would coincide with alterations in the alpha- and beta-subunit expression of the sarcolemmal Na(+)-K(+)-ATPase of rats with CHF. Moreover, we tested the hypothesis that exercise training would increase B(max) along with producing significant changes in alpha- and beta-subunit expression. Rats underwent a sham operation (sham; n = 10) or a surgically induced myocardial infarction followed by random assignment to either a control (MI; n = 16) or exercise training group (MI-T; n = 16). The MI-T rats performed exercise training (ET) for 6-8 wk. Hemodynamic indexes demonstrated that MI and MI-T rats suffered from severe left ventricular dysfunction and congestive CHF. Maximal oxygen uptake (Vo(2 max)) and endurance capacity (run time to fatigue) were reduced in MI rats compared with sham. B(max) in the soleus and plantaris muscles and the expression of the alpha(2)-isoform of the Na(+)-K(+)-ATPase in the red portion of the gastrocnemius (gastrocnemius(red)) muscle were reduced in MI rats. After ET, Vo(2 max) and run time to fatigue were increased in the MI-T group of rats. This coincided with increases in soleus and plantaris B(max) and the expression of the alpha(2)-isoform in the gastrocnemius(red) muscle. In addition, the expression of the beta(2)-isoform of the gastrocnemius(red) muscle was increased in the MI-T rats compared with their sedentary counterparts. This study demonstrates that CHF-induced alterations in skeletal muscle Na(+)-K(+)-ATPase, including B(max) and isoform expression, can be partially reversed by ET.     

Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study.

The aim of the present study was to establish fat oxidation rates over a range of exercise intensities in a large group of healthy men and women. It was hypothesised that exercise intensity is of primary importance to the regulation of fat oxidation and that gender, body composition, physical activity level, and training status are secondary and can explain part of the observed interindividual variation. For this purpose, 300 healthy men and women (157 men and 143 women) performed an incremental exercise test to exhaustion on a treadmill [adapted from a previous protocol (Achten J, Venables MC, and Jeukendrup AE. Metabolism 52: 747-752, 2003)]. Substrate oxidation was determined using indirect calorimetry. For each individual, maximal fat oxidation (MFO) and the intensity at which MFO occurred (Fat(max)) were determined. On average, MFO was 7.8 +/- 0.13 mg.kg fat-free mass (FFM)(-1).min(-1) and occurred at 48.3 +/- 0.9% maximal oxygen uptake (Vo(2 max)), equivalent to 61.5 +/- 0.6% maximal heart rate. MFO (7.4 +/- 0.2 vs. 8.3 +/- 0.2 mg.kg.FFM(-1).min(-1); P < 0.01) and Fat(max) (45 +/- 1 vs. 52 +/- 1% Vo(2 max); P < 0.01) were significantly lower in men compared with women. When corrected for FFM, MFO was predicted by physical activity (self-reported physical activity level), Vo(2 max), and gender (R(2) = 0.12) but not with fat mass. Men compared with women had lower rates of fat oxidation and an earlier shift to using carbohydrate as the dominant fuel. Physical activity, Vo(2 max), and gender explained only 12% of the interindividual variation in MFO during exercise, whereas body fatness was not a predictor. The interindividual variation in fat oxidation remains largely unexplained.     

DNA sequence variation in the promoter region of the VEGF gene impacts VEGF gene expression and maximal oxygen consumption

In its role as an endothelial cell proliferation and migration factor, vascular endothelial growth factor (VEGF) can affect peripheral circulation and therefore impact maximal oxygen consumption (Vo2 max). Because of the role of VEGF, and because variation in the VEGF gene has the ability to alter VEGF gene expression and VEGF protein level, we hypothesized that VEGF gene polymorphisms are related to VEGF gene expression in human myoblasts and Vo2 max before and after aerobic exercise training. We analyzed the effects of the VEGF -2578/-1154/-634 promoter region haplotype on VEGF gene expression by using a luciferase reporter assay in cultured human myoblasts and found that the AAG and CGC haplotypes resulted in significantly higher hypoxia-stimulated VEGF gene expression than the AGG and CGG haplotypes. Consistent with these results, we found that individuals with at least one copy of the AAG or CGC haplotype had higher Vo2 max before and after aerobic exercise training than did subjects with only the AGG and/or CGG haplotype. In conclusion, we found that VEGF -2578/-1154/-634 haplotype impacts VEGF gene expression in human myoblasts and is associated with Vo2 max. These results have potential implications for aerobic exercise training and may prove relevant in the study of pathological conditions that can be affected by angiogenesis, such as coronary artery disease and peripheral artery disease.     

The respiratory Vco2/Vo2 exchange ratio during maximum exercise and its use as a predictor of maximum oxygen uptake

The purpose of this study was to define carefully the dynamic relationship between oxygen uptake (as % Vo2max) and the respiratory Vco2/Vo2 exchange ratio (R) during maximum progressive treadmill exercise in trained and untrained men, and to determine if this relationship could be used to predict Vo2max. Respiratory gases were continuously monitored and the %Vo2max/R time profile calculated at 15 sec intervals over the final 5 min of each test. Young sedentary men (controls, n = 122) and over-60y sedentary men (n = 30) shared the same %Vo2max/R relationship but the latter group had lower R values at Vo2max (1.06 +/- 0.03 vs 1.08 +/- 0.03, p less than 0.01) than controls. Endurance trained men (n = 45) had a lower %Vo2max/R relationship and higher R at Vo2max (1.11 +/- 0.02, p less than 0.001), team athletes (n = 98) had a lower %Vo2max/R relationship but lower R at Vo2max (1.06 +/- 0.03, p less than 0.001) and the weight trained (n = 19) had a higher %Vo2max/R relationship and lower R at Vo2max (1.01 +/- 0.02, p less than 0.001) all compared to controls. From the %Vo2max/R time profile, the following formulae were devised for the estimation of Vo2max (Vo2maxR): Young Sedentary, Vo2maxR = Vo2R (3.000-1.874 R); Over-60y Sedentary, Vo2maxR = Vo2R (3.457-2.345 R); Endurance Trained, Vo2max = Vo2R (1.980-0.912 R); Team Athletes, Vo2maxR = Vo2R (2.805-1.726 R); Weight Trained, Vo2maxR = Vo2R (4.236-3.191 R).(ABSTRACT TRUNCATED AT 250 WORDS)     

Aerobic and resistance exercise sequence affects excess postexercise oxygen consumption

Excess postexercise oxygen consumption (EPOC) may describe the impact of previous exercise on energy metabolism. Ten males completed Resistance Only, Run Only, Resistance-Run, and Run-Resistance experimental conditions. Resistance exercise consisted of 7 lifts. Running consisted of 25 minutes of treadmill exercise. Vo(2) was determined during treadmill exercise and after each exercise treatment. Our findings indicated that treadmill exercise Vo(2) was significantly higher for Resistance-Run compared with Run-Resistance and Resistance Only at all time intervals. At 10 minutes postexercise, Vo(2) was greater for Resistance Only and Run-Resistance than for Resistance-Run. At 20 and 30 minutes, Vo(2) following Resistance Only was significantly greater than following Run Only. In conclusion, EPOC is greatest following Run-Resistance; however, treadmill exercise is more physiologically difficult following resistance exercise. Furthermore, the sequence of resistance and treadmill exercise influences EPOC, primarily because of the effects of resistance exercise rather than the exercise combination. We recommend performing aerobic exercise before resistance exercise when combining them into 1 exercise session.     

Greater rate of decline in maximal aerobic capacity with age in endurance-trained than in sedentary men.

To determine the relation between habitual endurance exercise status and the age-associated decline in maximal aerobic capacity [i.e., maximal O(2) consumption (Vo(2 max))] in men, we performed a well-controlled cross-sectional laboratory study on 153 healthy men aged 20-75 yr: 64 sedentary and 89 endurance trained. Vo(2 max) (ml. kg(-1). min(-1)), measured by maximal treadmill exercise, was inversely related to age in the endurance-trained (r = -0.80) and sedentary (r = -0.74) men but was higher in the endurance-trained men at any age. The rate of decline in Vo(2 max) with age (ml. kg(-1). min(-1)) was greater (P < 0.001) in the endurance-trained than in the sedentary men. Whereas the relative rate of decline in Vo(2 max) (percent decrease per decade from baseline levels in young adulthood) was similar in the two groups, the absolute rate of decline in Vo(2 max) was -5.4 and -3.9 ml. kg(-1). min(-). decade(-1) in the endurance-trained and sedentary men, respectively. Vo(2 max) declined linearly across the age range in the sedentary men but was maintained in the endurance-trained men until approximately 50 yr of age. The accelerated decline in Vo(2 max) after 50 yr of age in the endurance-trained men was related to a decline in training volume (r = 0.46, P < 0.0001) and was associated with an increase in 10-km running time (r = -0.84, P < 0.0001). We conclude that the rate of decline in maximal aerobic capacity during middle and older age is greater in endurance-trained men than in their sedentary peers and is associated with a marked decline in O(2) pulse.     

Pulmonary O2 uptake kinetics as a determinant of high-intensity exercise tolerance in humans

Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.     

Measurement of maximum oxygen consumption in Guinea fowl Numida meleagris indicates that birds and mammals display a similar diversity of aerobic scopes during running

Judgement of exercise performance in birds has been hampered by a paucity of data on maximal aerobic capacity. We measured the maximal rate of oxygen consumption (Vo2,max) in running guinea fowl Numida meleagris, a bird that has been used in several previous studies of avian running. Mean Vo2,max during level treadmill running was 97.5+/-3.7 mL O(2) kg(-1) min(-1) (mean+/-SEM, N=5). Vo2,max was on average 6% higher when the birds ran uphill compared with the value during level running (paired t-test, P=0.041, N=5). The mean basal rate of oxygen consumption (Vo2,bmr) of the same individuals was 7.9+/-0.5 mL O(2) kg(-1) min(-1). Mean factorial aerobic scope based on individually measured values of Vo2,max and Vo2,bmr was 13.2+/-0.6 (mean+/-SEM, N=5). This value was considerably lower than the factorial aerobic scope previously measured during running in Rhea americana, a large flightless ratite. The difference in factorial scope between these two running birds likely reflects the effects of body size as well as size-independent differences in the ability to deliver and use oxygen. These data confirm a previous prediction that birds have a diversity of factorial aerobic scopes similar to that exhibited by mammals.     

The role of exercise intensity in the bone metabolic response to an acute bout of weight-bearing exercise

We compared the effects of exercise intensity (EI) on bone metabolism during and for 4 days after acute, weight-bearing endurance exercise. Ten males [mean ± SD maximum oxygen uptake (Vo(2max)): 56.2 ± 8.1 ml·min(-1)·kg(-1)] completed three counterbalanced 8-day trials. Following three control days, on day 4, subjects completed 60 min of running at 55%, 65%, and 75% Vo(2max). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH(2)-terminal propeptides of procollagen type 1 (P1NP), osteocalcin (OC), bone-alkaline phosphatase (ALP)], osteoprotegerin (OPG), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate (PO(4)), and cortisol were measured during and for 3 h after exercise and on four follow-up days (FU1-FU4). At 75% Vo(2max), β-CTX was not significantly increased from baseline by exercise but was higher compared with 55% (17-19%, P < 0.01) and 65% (11-13%, P < 0.05) Vo(2max) in the first hour postexercise. Concentrations were decreased from baseline in all three groups by 39-42% (P < 0.001) at 3 h postexercise but not thereafter. P1NP increased (P < 0.001) during exercise only, while bone-ALP was increased (P < 0.01) at FU3 and FU4, but neither were affected by EI. PTH and cortisol increased (P < 0.001) with exercise at 75% Vo(2max) only and were higher (P < 0.05) than at 55% and 65% Vo(2max) during and immediately after exercise. The increases (P < 0.001) in OPG, ACa, and PO(4) with exercise were not affected by EI. Increasing EI from 55% to 75% Vo(2max) during 60 min of running resulted in higher β-CTX concentrations in the first hour postexercise but had no effect on bone formation markers. Increased bone-ALP concentrations at 3 and 4 days postexercise suggest a beneficial effect of this type of exercise on bone mineralization. The increase in OPG was not influenced by exercise intensity, whereas PTH was increased at 75% Vo(2max) only, which cannot be fully explained by changes in serum calcium or PO(4) concentrations.     

Is running performance enhanced with creatine serum ingestion?

Runners Advantage (RA) creatine (Cr) serum has been marketed to increase running performance. To test this claim, cross-country runners completed baseline testing (BASE), an outdoor 5,000-m run followed by treadmill Vo(2)max testing on the same day. Subjects repeated testing after ingesting 5 ml of RA (n = 13) containing 2.5 g of Cr or placebo (n = 11). Heart rate (HR), rating of perceived exertion (RPE), and run time were recorded. With RA (56.48 +/- 8.93 ml.kg(-1.)min(-1)), Vo(2)max was higher (p = 0.01) vs. BASE (54.07 +/- 9.36 ml.kg(-1.)min(-1)), yet the magnitude of the increase was within the coefficient of variation of Vo(2)max. No effect of RA on maximal HR was exhibited, yet Vco(2)max and duration of incremental exercise were significantly higher (p < 0.025) vs. BASE. Vo(2)max was similar in PL (58.85 +/- 6.67 ml.kg(-1).min(-1)) and BASE (57.28 +/- 7.22 ml.kg(-1.)min(-1)). With RA, the 5,000-m time was unchanged, and RPE was lower (p < 0.025) vs. BASE. These data do not support the ergogenic claims of RA in its current form and dose.     

Markers of inflammation are inversely associated with VO2 max in asymptomatic men.

We investigated whether markers of inflammation, including a cytokine (IL-6), acute-phase reactants [C-reactive protein (CRP) and fibrinogen], and white blood cell (WBC) count are associated with maximal O(2) consumption (Vo(2 max)) in men without coronary heart disease (CHD). In asymptomatic men (n = 172, 51 +/- 9.3 yr old), Vo(2 max) was measured during a symptom-limited graded treadmill exercise test. Physical activity level was assessed by a standardized questionnaire. IL-6 and CRP were measured by immunoassays, fibrinogen by the Clauss method, and WBC count with a Coulter counter. IL-6 and CRP were logarithmically transformed to reduce skewness. Multivariable regression was used to assess whether markers of inflammation were associated with Vo(2 max) after adjustment for age, body mass index, CHD risk factors, and lifestyle variables (physical activity level, percent body fat, and alcohol intake). Vo(2 max) was 34.5 ml.kg(-1).min(-1) (SD 6.1). Log IL-6 (r = -0.38, P < 0.001), log CRP (r = -0.40, P < 0.001), fibrinogen (r = -0.42, P < 0.001), and WBC count (r = -0.22, P = 0.004) were each correlated with Vo(2 max). In separate multivariable linear regression models that adjusted for age, body mass index, CHD risk factors, and lifestyle variables, log IL-6 [beta-coeff = -1.66 +/- 0.63 (SE), P = 0.010], log CRP [beta-coeff = -0.99 +/- 0.33 (SE), P = 0.003], fibrinogen [beta-coeff = -1.51 +/- 0.44 (SE), P = 0.001], and WBC count [beta-coeff = -0.52 +/- 0.30 (SE), P = 0.088] were each inversely associated with Vo(2 max). In conclusion, higher circulating levels of IL-6, CRP, and fibrinogen are independently associated with lower Vo(2 max) in asymptomatic men.     

Physiologic responses during indoor cycling

During the last decade, there has been active interest in indoor cycling (e.g., spinning) as a method of choreographed group exercise. Recent studies have suggested that exercise intensity during indoor cycling may be quite high and may transiently exceed Vo2max. This study sought to confirm these findings, as the apparent high intensity of indoor cycling has implications for both the efficacy and the risk of indoor cycling as an exercise method. Twenty healthy female students performed an incremental exercise test to define Vo2max and performed 2 videotaped indoor exercise classes lasting 45 minutes and 35 minutes. Vo2, heart rate (HR), and rating of perceived exertion (RPE) were measured during the indoor cycling classes, with Vo2 data integrated in 30-second intervals. The mean %Vo2max during the indoor cycling classes was modest (74 +/- 14% Vo2max and 66 +/- 14%Vo2max, respectively). However, 52% and 35% of the time during the 45- and 35-minute classes was spent at intensities greater than the ventilatory threshold (VT). The HR response indicated that 35% and 38% of the session time was above the HR associated with VT. In 10 of the 40 exercise sessions, there were segments in which the momentary Vo2 exceeded Vo2max observed during incremental testing, and the cumulative time with exercise intensity greater than Vo2max ranged from 0.5 to 14.0 minutes. It can be concluded that although the intensity of indoor cycling in healthy, physically active women is moderate, there are frequent observations of transient values of Vo2 exceeding Vo2max, and a substantial portion of the exercise bouts at intensities greater than VT. As such, the data suggest that indoor cycling must be considered a high-intensity exercise mode of exercise training, which has implications for both efficacy and risk.     

Cardiac parasympathetic regulation: respective associations with cardiorespiratory fitness and training load

The objective of this study was to establish the separate associations between parasympathetic modulations of the heart [evaluated through heart rate (HR) variability (HRV) indexes and postexercise HR recovery (HRR) indexes] with cardiorespiratory fitness and training load. We have measured cardiorespiratory fitness through peak oxygen consumption (Vo2 max) and estimated weekly training load with the Baecke sport score in 55 middle-aged individuals (30.8 +/- 1.8 yr, body mass index 24.5 +/- 0.4 kg/m2). HRV indexes were analyzed at rest under controlled breathing, and HRR was estimated from HR curve fitting after maximal exercise or from measurements of the number of beats recovered at 60 s after exercise. Multiple linear regressions were used to investigate the separate relationships between vagal-related HRV indexes and Vo2 max and Baecke scores. On the basis of their Vo2 max and Baecke scores, subjects were classified as fit or unfit and as low trained (LT) or moderately trained (MT), which yielded four groups: UnfitLT, UnfitMT, FitLT, and FitMT. Vagal-related HRV indexes were positively correlated with Vo2 max (P < 0.05) but not with Baecke scores. In contrast, HRR indexes were related to Baecke scores (P < 0.05) but not with Vo2 max. FitLT and FitMT had significantly higher (P < 0.05) normalized vagal-related HRV indexes than UnfitLT and UnfitMT, but HRR did not change. Moderate training was associated with significantly lower HRR indexes both in UnfitMT and FitMT compared with UnfitLT and FitLT, but there was no difference in vagal-related HRV indexes. These results indicate that vagal-related HRV indexes are related more to cardiorespiratory fitness, whereas HRR appears to be better associated with training load.     

Comparative study of field and laboratory tests for the evaluation of aerobic capacity in soccer players

The purpose of this study was to evaluate the maximal oxygen uptake (Vo(2)max) values in soccer players as assessed by field and laboratory tests. Thirty-five elite young soccer players were studied (mean age 18.1 +/- 1.0 years, training duration 8.3 +/- 1.5 years) in the middle of the playing season. All subjects performed 2 maximal field tests: the Yo-Yo endurance test (T(1)) for the estimation of Vo(2)max according to normogram values, and the Yo-Yo intermittent endurance test (T(2)) using portable telemetric ergospirometry; as well as 2 maximal exercise tests on the treadmill with continuous (T(3)) and intermittent (T(4)) protocols. The estimated Vo(2)max values of the T(1) test (56.33 ml.kg(-1).min(-1)) were 10.5%, 11.4%, and 13.3% (p < or = 0.05) lower than those of the T(2) (62.96 ml.kg(-1).min(-1)), T(3) (63.59 ml.kg(-1).min(-1)) and T(4) (64.98 ml.kg(-1).min(-1)) tests, respectively. Significant differences were also found between the intermittent exercise protocols T(1) and T(3) (p < or = 0.001) and the continuous exercise protocols T(2) and T(4) (p < or = 0.001). There was a high degree of cross correlation between the Vo(2)max values of the 3 ergospirometric tests (T(2) versus T(3), r = 0.47, p < or = 0.005; T(2) versus T(4), r = 0.59, p < or = 0.001; T(3) versus T(4) r = 0.79, p < or = 0.001). It is necessary to use ergospirometry to accurately estimate aerobic capacity in soccer players. Nevertheless, the Yo-Yo field tests should be used by coaches because they are easy and helpful tools in the training program setting and for player follow-up during the playing season.     

Classification of Genes and Putative Biomarker Identification Using Distribution Metrics on Expression Profiles

Background

Identification of genes with switch-like properties will facilitate discovery of regulatory mechanisms that underlie these properties, and will provide knowledge for the appropriate application of Boolean networks in gene regulatory models. As switch-like behavior is likely associated with tissue-specific expression, these gene products are expected to be plausible candidates as tissue-specific biomarkers.

Methodology/Principal Findings

In a systematic classification of genes and search for biomarkers, gene expression profiles (GEPs) of more than 16,000 genes from 2,145 mouse array samples were analyzed. Four distribution metrics (mean, standard deviation, kurtosis and skewness) were used to classify GEPs into four categories: predominantly-off, predominantly-on, graded (rheostatic), and switch-like genes. The arrays under study were also grouped and examined by tissue type. For example, arrays were categorized as ‘brain group’ and ‘non-brain group’; the Kolmogorov-Smirnov distance and Pearson correlation coefficient were then used to compare GEPs between brain and non-brain for each gene. We were thus able to identify tissue-specific biomarker candidate genes.

Conclusions/Significance

The methodology employed here may be used to facilitate disease-specific biomarker discovery.