O2 Min-1 Kg-1 Research Articles

Physical fitness assessment of a Venezuelan industrial direct labor force population

Introduction The purpose of this research is to evaluate the physical fitness variables of Venezuelan workers, taking into account exercise batteries or submaximal tests that have been little used in the industrial environment.Methods: A quantitative, descriptive, cross-sectional, epidemiological and field study was conducted in a Venezuelan population of industrial direct labor workers in bipedestation. The sample consisted of 185 workers (M: 136, W: 49) in the main industrial areas of the state of Aragua-Venezuela.Results: Results were obtained on the physical fitness of Venezuelan industrial direct labor workers presenting average results in both sexes. Calculations for obtaining HRmax and RAC in ml O2 min-1 kg-1 were taken into account.Conclusions: A population of industrial direct labor was observed, of low physical capacity with values associated with age (42.87 M-38.43W), physical wear and tear, poor physical fitness habits, poor dietary habits and decrease in muscle mass.

Evaluating Airflow Sensor Methods: Precision in IndirectCalorimetry.

This study assesses the impact of three volumetric gas flow measurement methods-turbine (fT); pneumotachograph (fP), and Venturi (fV)-on predictive accuracy and precision of expired gas analysis indirect calorimetry (EGAIC) across varying exercise intensities. Six males (Age: 38 ± 8 year; Height: 178.8 ± 4.2 cm; : 42 ± 2.8 mL O2 kg-1 min-1) and 14 females (Age = 44.6 ± 9.6 year; Height = 164.6 ± 6.9 cm; = 45 ± 8.6 mL O2 kg-1 min-1) were recruited. Participants completed physical exertion on a stationary cycle ergometer for simultaneous pulmonary minute ventilation ( ) measurements and EGAIC computations. Exercise protocols and subsequent conditions involved a 5-min cycling warm-up at 25 W min-1, incremental exercise to exhaustion ( ramp test), then a steady-state exercise bout induced by a constant Watt load equivalent to 80% ventilatory threshold (80% VT). A linear mixed model revealed that exercise intensity significantly affected measurements (p < 0.0001), whereas airflow sensor method (p = 0.97) and its interaction with exercise intensity (p = 0.91) did not. Group analysis of precision yielded a CV % = 21%; SEM = 5 mL O2 kg-1 min-1. Intra- and interindividual analysis of precision via Bland-Altman revealed a 95% confidence interval (CI) precision benchmark of 3-5 mL kg-1 min-1. Agreement among methods decreased at power outputs eliciting up to 150 L min-1, indicating a decrease in precision and highlighting potential challenges in interpreting biological variability, training response heterogeneity, and test-retest comparisons. These findings suggest careful consideration of airflow sensor method variance across metabolic cart configurations.

Energy expenditure and intensity of ritual jumping-dancing in male Maasai.

Traditional jumping-dance rituals performed by Maasai men involve prolonged physical exertion that may contribute significantly to overall physical activity level. We aimed to objectively quantify the metabolic intensity of jumping-dance activity and assess associations with habitual physical activity and cardiorespiratory fitness (CRF). Twenty Maasai men (18-37 years) from rural Tanzania volunteered to participate in the study. Habitual physical activity was monitored using combined heart rate (HR) and movement sensing over 3 days, and jumping-dance engagement was self-reported. A 1-h jumping-dance session resembling a traditional ritual was organized, during which participants' vertical acceleration and HR were monitored. An incremental, submaximal 8-min step test was performed to calibrate HR to physical activity energy expenditure (PAEE) and assess CRF. Mean (range) habitual PAEE was 60 (37-116) kJ day-1 kg-1 , and CRF was 43 (32-54) mL O2 min-1 kg-1 . The jumping-dance activity was performed at an absolute HR of 122 (83-169) beats·min-1 , and PAEE of 283 (84-484) J min-1 kg-1 or 42 (18-75)% when expressed relative to CRF. The total PAEE for the session was 17 (range 5-29) kJ kg-1 , ~28% of the daily total. Self-reported engagement in habitual jumping-dance frequency was 3.8 (1-7) sessions/week, with a total duration of 2.1 (0.5-6.0) h/session. Intensity during traditional jumping-dance activity was moderate, but on average sevenfold higher than habitual physical activity. These rituals are common, and can make a substantial contribution to overall physical activity in Maasai men, and thus be promoted as a culture-specific activity to increase energy expenditure and maintain good health in this population.

Exploring relationships between oxygen consumption and biologger-derived estimates of heart rate in two warmwater piscivores.

Estimating metabolic rate in wild, free-swimming fish is inherently challenging. Here, we explored using surgically implanted heart rate biologgers to estimate metabolic rate in two warmwater piscivores, bowfin Amia calva (Linneaus 1766) and largemouth bass Micropterus salmoides (Lacepède 1802). Fish were surgically implanted with heart rate loggers, allowed to recover for 24 h, exposed to a netting and air exposure challenge, and then placed into respirometry chambers so that oxygen consumption rate (ṀO2 ) could be measured in parallel to heart rate (fH ) for a minimum of 20 h (ca. 20 estimates of ṀO2 ). Heart rate across the duration of the experiment (at 19°C) was significantly higher in largemouth bass (mean ± s.d., 45 ± 14 beats min-1 , range 18-86) than in bowfin (27 ± 9bpm, range 16-98). Standard metabolic rate was also higher in largemouth bass (1.06 ± 0.19 mg O2 kg-1 min-1 , range 0.46-1.36) than in bowfin (0.89 ± 0.17 mg O2 kg-1 min-1 , range 0.61-1.28). There were weak relationships between fH and ṀO2 , with heart rate predicting 28% of the variation in oxygen consumption in bowfin and 23% in largemouth bass. The shape of the relationship differed somewhat between the two species, which is perhaps unsurprising given their profound differences in physiology and life history, illustrating the need to carry out species-specific validations. Both species showed some potential for a role of fH in efforts to estimate field metabolic rates, although further validation experiments with a wider range of conditions (e.g., digestive states, swimming activity) would likely help improve the strength of the ṀO2 -fH relationship for use in field applications.

Factors correlated with running economy among elite middle‐ and long‐distance runners

Running economy (RE) at a given submaximal running velocity is defined as oxygen consumption per minute per kg body mass. We investigated RE in a group of 12 male elite runners of national class. In addition to RE at 14 and 18 km h−1 we measured the maximal oxygen consumption (VO2max) and anthropometric measures including the moment arm of the Achilles tendon (L Ach), shank and foot volumes, and muscular fascicle lengths. A 3‐D biomechanical movement analysis of treadmill running was also conducted. RE was on average 47.8 and 62.3 ml O2 min−1 kg−1 at 14 and 18 km h−1. Maximal difference between the individual athletes was 21% at 18 km h−1. Mechanical work rate was significantly correlated with VO2 measured in L min−1 at both running velocities. However, RE and relative work rate were not significantly correlated. L Ach was significantly correlated with RE at 18 km h−1 implying that a short moment arm is advantageous regarding RE. Neither foot volume nor shank volume were significantly correlated to RE. Relative muscle fascicle length of m. soleus was significantly correlated with RE at 18 km h−1. Whole body stiffness and leg stiffness were significantly correlated with L Ach indicating that a short moment arm coincided with high stiffness. It is concluded that a short L Ach is correlated with RE. Probably, a short L Ach allows for storage of a larger amount of elastic energy in the tendon and influences the force–velocity relation toward a lower contraction velocity.

Sex And Fiber-type Differences: Vascular ATP-sensitive K + (K ATP ) Channels Support Critical Speed And Interstitial PO 2

Glibenclamide (GLI), prescribed to Type II diabetes patients, enhances insulin release by inhibiting pancreatic KATP channels. KATP channels support maximal aerobic capacity (V̇O2max) and blood flow during treadmill running in male rats. Whether high-intensity exercise tolerance (i.e. critical speed, CS) and muscle O2 delivery-utilization matching (interstitial PO2, PO2is) is impaired, and whether sex differences exist in KATP function, are unknown. PURPOSE We hypothesized that systemic inhibition of KATP channels via GLI would decrease V̇O2max and CS, while local inhibition would decrease contracting PO2is and blood flow within fast-twitch oxidative (mixed gastrocnemius (MG)) and slow-twitch oxidative (soleus (SOL)) muscles with females (F and F+OVX) expressing the greatest reduction. METHODS: Male (n=12), female (n=10, proestrus) and ovariectomized female (F+OVX; n=12) Sprague-Dawley rats with and without GLI (10 mg kg-1 in DMSO i.p.). V̇O2max and CS were assessed using state-of-the art techniques on a motorized treadmill. PO2is was determined, before and after GLI superfusion (5 mg kg-1), via phosphorescence quenching (G4) in the exposed MG and SOL muscles during electrically-induced contractions and blood flow by fluorescent-labeled microspheres (15 μm). RESULTS: GLI decreased V̇O2max in female (71.5 ± 1.0 vs 67.9 ± 1.5) and F+OVX (76.8 ± 1.4 vs 74.4 ± 1.4; p<0.05 for both) but not males (81.5 ± 2.0 vs 80.8 ± 2.0 mL O2 min-1 kg-1; p>0.05). CS was reduced equivalently in all groups (8-11%; p<0.05). GLI reduced MG blood flow (female: 49 ± 9 vs 34 ± 5; male: 50 ± 5 vs 35 ± 4) and PO2is (female: 7.3 ± 0.5 vs 6.1 ± 0.5; male: 8.9 ± 1.1 vs 7.2 ± 0.5), but not SOL, of female and male rats (p<0.05). Conversely, in F+OVX, PO2is was reduced in the SOL (14.5 ± 1.5 vs 10.2 ± 1.1; p<0.05), but not MG. CONCLUSION: These data support the role of vascular KATP channels in exercise tolerance (i.e. CS) by matching O2 delivery-utilization with ovariectomy shifting KATP channel effects from fast- to slow-twitch muscles. Supported by NIH Grants: HL108328 and F31HL145981

The relationships between age and running performance variables in master runners.

Peak aerobic capacity (V̇O2peak) declines with age, but running economy (RE) may not. We evaluated VO2peak and RE in master runners and determined whether age is associated with these measures. In a cross-sectional study, runners completed two running tests within four weeks of a goal race of 10-26.2 miles. Subjects ran for five min at 88% of predicted maximum heart rate, approximating a marathon-intensity effort (MIE), then performed a V̇O2peak test. Running economy in the MIE was measured using oxygen cost with body mass scaled allometrically (alloV̇O2); energy cost (EC), determined using caloric equivalents; and percent of V̇O2peak (%V̇O2peak). Pearson's correlations were used to determine relationships between age and running performance variables. Runners (n = 31, 13 females; mean age 54.9 ± 8.4 years) had a mean VO2peak of 52.5 ± 7.9 ml O2 kg-1 min-1. Age was significantly correlated with V̇O2peak (r = - 0.580, p = 0.001) and alloV̇O2 (r = - 0.454, p = 0.034). Age was related to EC in females (r = 0.649, p = 0.042) and MIE V̇O2 in males (r = - 0.600, p = 0.039). In this population, age was negatively associated with V̇O2peak and alloV̇O2. Females showed a positive relationship between age and EC, while males had a negative correlation between age and MIE V̇O2. Aerobic capacity declines with age, but there may be sex differences in age-related alterations to submaximal running.

Pelagic shrimp play dead in deep oxygen minima.

Pelagic crustaceans are arguably the most abundant group of metazoans on Earth, yet little is known about their natural behavior. The deep pelagic shrimp Hymenopenaeus doris is a common decapod that thrives in low oxygen layers of the eastern Pacific Ocean. When first observed in situ using a remotely operated vehicle, most specimens of H. doris appeared dead due to inactivity and inverted orientation. Closer inspection revealed that these animals were utilizing small, subtle shifts in appendage position to control their orientation and sink rate. In this mode, they resembled molted shrimp exoskeletons. We hypothesize that these shrimp may avoid capture by visually-cued predators with this characteristic behavior. The low metabolic rates of H. doris (0.55–0.81 mg O2 kg-1 min-1) are similar to other deep-living shrimp, and also align with their high hypoxia tolerance and reduced activity. We observed similar behavior in another deep pelagic decapod, Petalidium suspiriosum, which transiently inhabited Monterey Canyon, California, during a period of anomalously warm ocean conditions.

Cardiorespiratory fitness is impaired and predicts mid-term postoperative survival in patients with abdominal aortic aneurysm disease.

What is the central question of this study? To what extent cardiorespiratory fitness is impaired in patients with abdominal aortic aneurysmal (AAA) disease and corresponding implications for postoperative survival requires further investigation. What is the main finding and its importance? Cardiorespiratory fitness is impaired in patients with AAA disease. Patients with peak oxygen uptakeof <13.1ml O2 kg-1 min-1 and ventilatory equivalent for carbon dioxide at anaerobic threshold ≥34 are associated with increased risk of postoperative mortality at 2 years. These findings demonstrate that cardiorespiratory fitness can predict mid-term postoperative survival in AAA patients, which may help to direct care provision. Preoperative cardiopulmonary exercise testing is a standard assessment of cardiorespiratory fitness (CRF) and risk stratification. However, to what extent CRF is impaired in patients undergoing surgical repair of abdominal aortic aneurysm (AAA) disease and the corresponding implications for postoperative outcome requires further investigation. We measured CRF during an incremental exercise test to exhaustion using online respiratory gas analysis in patients with AAA disease (n=124, aged 72±7years) and healthy sedentary control subjects (n=104, aged 70±7years). Postoperative survival was examined for association with CRF, and threshold values were calculated for independent predictors of mortality. Patients who underwent preoperative cardiopulmonary exercise testing before surgical repair had lower CRF [age-adjusted mean difference of 12.5mlO2 kg-1 min-1 for peak oxygen uptake ( ), P<0.001versus control subjects]. After multivariable analysis, both and the ventilatory equivalent for carbon dioxide at anaerobic threshold ( ) were independent predictors of mid-term postoperative survival (2years). Hazard ratios of 5.27 (95% confidence interval 1.62-17.14, P=0.006) and 3.26 (95% confidence interval 1.00-10.59, P=0.049) were observed for <13.1mlO2 kg-1 min-1 and ≥ 34, respectively. Thus, CRF is lower in patients with AAA, and those with a <13.1mlO2 kg-1 min-1 and ≥ 34 are associated with a markedly increased risk of postoperative mortality. Collectively, our findings demonstrate that CRF can predict mid-term postoperative survival in AAA patients, which may help to direct care provision.

Energy expenditure after spinal cord injury in people with motor-complete tetraplegia or motor-complete paraplegia.

Cross-sectional. This study aimed to describe and compare VO2 and energy expenditure at rest (REE) and during standardized sedentary, non-exercise physical activity, and exercise activities, in people with motor-complete tetraplegia (C5-C8). Further, REE and energy expenditure (EE) for the different activities were compared to data from a reference group of people with motor-complete paraplegia (T7-T12). Sweden. The sample of people with motor-complete tetraplegia consisted of 26 adults (seven women) with SCI, C5-C8 AIS A-B. REE and EE for the different activities were measured with indirect calorimetry. The results were further compared to people with motor-complete paraplegia. Resting VO2 was 2.57 ml O2 kg-1 min-1, 2.54 for men and 2.60 for women. The VO2 or activity energy expenditure related to body weight increased three to four times during non-exercise physical activity compared to sedentary activities for the people with motor-complete tetraplegia, and up to six times during exercise activity. No significant differences were seen in resting or sedentary activity VO2 between the people with motor-complete tetraplegia and those with motor-complete paraplegia. Activities of daily life revealed no or small differences in VO2, except for setting a table, while the people with tetraplegia had ∼50% lower VO2 during exercise activities. Non-exercise physical activities of daily life may be significant for increasing total daily EE in people with motor-complete tetraplegia. This might act to motivate the individual, and might be clinically important when designing adapted lifestyle intervention programs for the target group.

Energy expenditure in people with motor-complete paraplegia.

The present descriptive clinical and laboratory study is cross-sectional in design. The primary aim is to describe and compare resting energy expenditure (REE) and energy expenditure (EE) during different standardized sedentary, non-exercise and exercise activities in people with motor-complete paraplegia (Th7 to Th12.). A secondary aim was to compare men and women. Thirty-eight adults (10 women) with SCI, T7-T12 AIS A-B, were recruited. All the data were collected through indirect calorimetry. REE was measured in supine for 30 min after 8 h of overnight fasting. Activity energy expenditure (AEE) for activities was measured for seven minutes during sedentary, non-exercise physical activity (NEPA) and exercise activities. AEE increased four to eight times when engaging in NEPA compared to that in sedentary activities. Men had significantly higher resting oxygen uptake compared to women, 0.19 vs 0.15 l min-1 (P=0.005), REE per 24 h, 1286 vs 1030 kcal (P=0.003) and EE during weight-bearing activities. However, these became nonsignificant after adjustment for body weight and speed of movement, with a mean resting oxygen uptake of 2.47 ml O2 per kg min-1 for the whole group (women 2.43 and men 2.57 ml O2 kg-1 min-1, P=0.49). NEPA increases AEE up to eight times compared to sedentary activities. Gender differences in oxygen uptake during both rest and weight-bearing activities were diminished after adjustment for body weight. The mean resting oxygen uptake for the whole group was 2.47 ml O2 kg-1 min-1. These results highlight the importance, especially of NEPA, for increasing total daily EE in the target population.

Intrinsic and extrinsic influences on standard metabolic rates of three species of Australian otariid.

The study of marine mammal energetics can shed light on how these animals might adapt to changing environments. Their physiological potential to adapt will be influenced by extrinsic factors, such as temperature, and by intrinsic factors, such as sex and reproduction. We measured the standard metabolic rate (SMR) of males and females of three Australian otariid species (two Australian fur seals, three New Zealand fur seals and seven Australian sea lions). Mean SMR ranged from 0.47 to 1.05 l O2 min-1, which when adjusted for mass was from 5.33 to 7.44 ml O2 min-1 kg-1. We found that Australian sea lion mass-specific SMR (sSMR; in millilitres of oxygen per minute per kilogram) varied little in response to time of year or moult, but was significantly influenced by sex and water temperature. Likewise, sSMR of Australian and New Zealand fur seals was also influenced by sex and water temperature, but also by time of year (pre-moult, moult or post-moult). During the moult, fur seals had significantly higher sSMR than at other times of the year, whereas there was no discernible effect of moult for sea lions. For both groups, females had higher sSMR than males, but sea lions and fur seals showed different responses to changes in water temperature. The sSMR of fur seals increased with increasing water temperature, whereas sSMR of sea lions decreased with increasing water temperature. There were no species differences when comparing animals of the same sex. Our study suggests that fur seals have more flexibility in their physiology than sea lions, perhaps implying that they will be more resilient in a changing environment.

Reproducibility of incremental maximal cycle ergometer tests in healthy recreationally active subjects.

Testing of the ventilatory threshold (VT) and maximal oxygen uptake (VO2 peak) is relevant for the evaluation of a range of training studies, clinical trials and cross-sectional studies. Due to a possible learning effect, a familiarization test is often performed to increase test reproducibility. However, limited research has investigated this learning effect and reproducibility of maximal exercise testing. The most appropriate ways to determine VT and VO2 peak are not clear, and this study evaluated two approaches (V-slope and a combined method) for the determination of VT and five time-averaging intervals (60, 30, 15, 10 and 5s) for the determination of VO2 peak to compare test results and reproducibility. Thirteen recreational triathletes completed three identical incremental maximal cycle ergometer tests. The initial workload was 75 and 100 watt (W) for women and men, respectively, and the workload was increased by 4W/10s thereafter. No familiarization test was performed. VO2 peak increased significantly as the time-averaging interval became shorter (e.g. 5-s interval 48·7 versus 60-s interval 44·8ml O2 kg-1 min-1 ; overall P<0·001). All test results were similar for the three test rounds, indicating that repeated testing was not associated with any learning effect. The different VT measuring methods (CV 7·6 versus 7·7%, P=0·58) and VO2 peak time-averaging intervals (CV 3·7-4·4%, P=0·99) did not influence test reliability. The reproducibility of VT and VO2 peak was not affected by measuring methods and time-averaging intervals. However, the time-averaging intervals significantly affect the absolute VO2 peak values. Furthermore, no learning effect of maximal cycle ergometer testing was observed.

Effect Of Whey Protein Hydrolysate On Adaptation To Endurance Training In Well-trained Runners

PURPOSE: To compare intake of whey protein hydrolysate (WB) in connection to each exercise session with intake of carbohydrate on adaptation to endurance training in runners. METHODS: 24 well-trained endurance runners (Age 30±9 yrs, VO2max 61±4 ml O2 min-1 kg-1) participated in a block randomized controlled intervention trial including a six weeks running program. Half of the runners ingested WB before (0.3 g kg-1) and WB+carbohydrate (0.3 g protein kg-1 + 1 g carbohydrate kg-1) after each exercise session (PRO). The others ingested isocaloric carbohydrate before and after exercise (CAR). Muscle biopsies were obtained before and after the first training session. Before and two days after the intervention period post-absorptive muscle biopsies were obtained and VO2max and 6k performance were tested. Diet was controlled before tests and four days food diary was obtained in the beginning and end of the intervention period. RESULTS: Improvements were observed in 6k-run performance test (25±1 sec, p<0.01) and VO2max (0.07±0.01 L O2/min, p<0.05) compared to baseline, but no intervention interaction was observed Western plot analysis showed group difference in adaptations in Cyt C (PRO 19±8%, CAR -17±13%, p<0.05). Tendencies towards similar adaption pattern were observed for other mitochondrial targets (VDAC, PHB1, SDHA, intervention interaction p<0.1). mRNA expression of mitochondrial PGC1-α was acutely enhanced after the first running session (0hr post-exercise 339±27% and 2 hr post-exercise 651±25%, p<0.01), but not influenced by intervention beverages. No time or intervention interaction was observed before and after the intervention period in mRNA PGC1-α expression. Daily protein intake excluding intervention beverages was not different between groups. CONCLUSIONS: Ingestion of whey protein hydrolysate before and whey protein hydrolysat plus carbohydrate after each exercise session compared to isocaloric carbohydrate intake did not influence adaptions in 6k performance and VO2max after six weeks of running training. Intake of whey protein seems to have a positive influence on mitochondrial adaptions in well-trained runners and might be beneficial for performance in a longer perspective. Supported by Arla Foods Ingredients Group P/S, Ministry of Culture Committee on Sports Research & Team Denmark.

TRPV4 Induces Warm‐Defense Responses in Non‐Genetically Modified Rats

TRPV4 is a warmth sensitive channel, suggested to act as a thermosensor but with no thermoregulatory role described in vivo (sensitive to temperatures in vitro at the range of ~24 ‐ 34ºC). Thus, we aimed at investigating which thermoeffectors are affected by TRPV4 activation in rats. To this end, we measured core body temperature (Tc), oxygen consumption and heat loss index (HLI) in male rats (290‐320g) under different ambient temperatures (Ta) after the intravenous blockade of this channel with HC‐067047. Moreover the preferred ambient temperature was assessed: i) after thermal stimulation combined with the intravenous blockage of TRPV4 with HC‐067047; and ii) after topical application of agonist RN‐1747. HC‐067047 caused an increase on Tc at Ta of 26 and 30°C (~0.65°C; p&lt;0.05), but not at 22 and 32°C. At 26°C, HC‐067047‐induced hyperthermia was accompanied by increase in oxygen consumption (1.24 ± 0.2 mL O2 kg‐¹ min‐¹ more than the controls; p&lt; 0.05), but no difference on HLI was observed. Furthermore, rats chemically stimulated with TRPV4 agonist leaned towards colder Tas (29°C for controls and 21°C for agonist‐treated; p&lt; 0.05) and the cold‐seeking behaviour after thermal stimulation (28‐31°C) was inhibited by TRPV4 antagonist (24°C for controls and 28°C for antagonist‐treated; p&lt; 0.05). Our results suggest, for the first time, that TRPV4 channel is involved in the recruitment of behavioural and autonomic warmth defense responses in order to regulate Tc. Financial Support: FAPESP

Disrupted flow sensing impairs hydrodynamic performance and increases the metabolic cost of swimming in the yellowtail kingfish,Seriola lalandi

The yellowtail kingfish, Seriola lalandi, shows a distribution of anaerobic and aerobic (red and pink) muscle fibres along the trunk that is characteristic of active pelagic fishes. The athletic capacity of S. lalandi is also shown by its relative high standard metabolic rate and optimal (i.e. least cost) swimming speed. To test the hypothesis that lateral line afferent information contributes to efficient locomotion in an active pelagic species, the swimming performance of S. lalandi was evaluated after unilateral disruption of trunk superficial neuromasts (SNs). Unilaterally disrupting the SNs of the lateral line impaired both swimming performance and energetic efficiency. The critical swimming speed (U(crit); mean ± s.d., N=12) for unilaterally SN-disrupted fish was 2.11±0.96 fork lengths (FL) s(-1), which was significantly slower than the 3.66±0.19 FL s(-1) U(crit) of sham SN-disrupted fish. The oxygen consumption rate (mg O(2) kg(-1) min(-1)) of the unilaterally SN-disrupted fish in a speed range of 1.0-2.2 FL s(-1) was significantly greater than that of the sham SN-disrupted fish. The least gross cost of transport (GCOT; N=6) for SN-disrupted fish was 0.18±0.06 J N(-1) m(-1), which was significantly greater than the 0.11±0.03 J N(-1) m(-1) GCOT for sham SN-disrupted fish. The factorial metabolic scope (N=6) of the unilaterally SN-disrupted fish (2.87±0.78) was significantly less than that of sham controls (4.14±0.37). These data show that an intact lateral line is important to the swimming performance and efficiency of carangiform swimmers, but the functional mechanism of this effect remains to be determined.

Lazy or old: mitochondria decline in vivo in human muscle similarly with inactivity and age

Here we tested the role of lifestyle vs. age using innovative noninvasive tools to measure key mitochondrial functional properties in vivo. Mitochondrial coupling (ATP/O2 or P/O), and phosphorylation capacity (ATPmax) were assessed in human vastus lateralis muscle (VL). Oxidative capacity was biochemically assessed in vitro from biopsies taken from the same site as the in vivo measures. The chronic activity level was measured using a physical activity questionnaire, VO2max test (active >40 ml O2 kg-1 min-1) and verified using a triaxial accelerometer. Subjects were screened to be healthy and disease free and were on average 30 yrs old for the active (n=9) and sedentary (n=18) subjects and 68 yrs old for the elderly (n=30). Mitochondrial coupling in active controls (2.3+0.20, mean+SE) agreed with well-coupled mitochondria (2.3–2.5) but both sedentary (P/O=1.41+0.09) and elderly groups (P/O=1.69+0.11) were substantially uncoupled. Similarly, active subjects had a higher ATPmax (1.11+0.08 mM ATP/sec) than sedentary (0.67+0.03) or aged groups (0.61+0.04). Oxidative capacity was reduced in both groups by 25% relative to active adults. These results demonstrate that mitochondrial properties in vivo drop substantially in sedentary adults and the old. Thus inactivity may be as important as age in the mitochondrial decline found in the elderly. Supported by NIH AG 030226, AR 41928, RC2AG036606, 1P30 DK072476.

Metabolism of normothermic woodchucks during prolonged fasting

The energy metabolism of hibernators has not been characterized for normothermic fasting, and our goal was to quantify oxidative fuel selection of non-hibernating woodchucks Marmota monax during prolonged food deprivation. Indirect calorimetry and nitrogen excretion measurements were used to assess changes in metabolic rate (VO2), fuel selection and composition of nitrogen wastes, as well as seasonal differences. For reference, matching experiments were also performed on rabbits. The results show that woodchucks have a higher metabolic rate in summer (271 micromol O2 kg(-1) min(-1)) than in spring (200 micromol O2 kg(-1) min(-1)) and that fasting-induced metabolic depression is only possible in summer (-25% in 14 days). The metabolic rate of rabbits is high at all times (383 micromol O2 kg(-1) min(-1)), but they show a more rapid depression in response to fasting (-32% in 7 days). Woodchucks have a naturally low reliance on proteins in the fed state (accounting for 8% VO2) in spring; 17% VO2 in summer; vs 28% VO2 in rabbits) and are able to decrease it even further during fasting (spring, 5% VO2); summer, 6% VO2; vs 20% VO2 in rabbits). This study shows that, apart from their notorious capacity for hibernation, woodchucks are particularly well adapted for normothermic fasting. Their ability to cope with prolonged food deprivation is based on a series of integrated responses eliciting deep metabolic depression and a rapid change in fuel selection to spare limited protein reserves. Information presently available on prolonged fasting suggests that such an ability for metabolic depression, possibly down to minimal levels still compatible with normothermic life, may be common among mammals. In contrast, the extreme protein sparing demonstrated in woodchucks is a unique metabolic feature of fasting champions.

Vasodilatation, oxygen delivery and oxygen consumption in rat hindlimb during systemic hypoxia: roles of nitric oxide.

We have investigated the relationship between O2 delivery (DO2) and O2 consumption (VO2) in hindlimb muscle of anaesthetised rats during progressive systemic hypoxia. Since muscle vasodilatation that occurs during hypoxia is nitric oxide (NO) dependent, we examined the effects of the NO synthase (NOS) inhibitor nitro-L-arginine methyl ester (L-NAME). In control rats (n = 8), femoral vascular conductance (FVC) increased at each level of hypoxia. Hindlimb DO2 decreased with the severity of hypoxia, but muscle VO2 was maintained until the critical DO2 value (DO2,crit) was reached at 0.64 +/- 0.06 ml O2 min-1 kg-1; below this VO2 declined linearly with DO2. This is a novel finding for the rat but is comparable to the biphasic relationship seen in the dog. In another group of rats (n = 6), L-NAME caused hindlimb vasoconstriction and attenuated the hypoxia-evoked increases in FVC DO2 was so low after L-NAME administration that VO2 was dependent on DO2 at all levels of hypoxia. In a further group (n = 8), femoral blood flow and DO2 were restored after L-NAME by infusion of the NO donor sodium nitroprusside (20 g x kg(-1) x min(-1). Thereafter, hypoxia-evoked increases in FVC were fully restored. Nevertheless, DO2,crit was increased relative to control (0.96 +/- 0.07 ml O2 min(-1) x kg(-1), P < 0.01). As NOS inhibition limited the ability of muscle to maintain VO2 during hypoxia, we propose that hypoxia-induced dilatation of terminal arterioles, which improves tissue O2 distribution, is mediated by NO. However, since the hypoxia-evoked increase in FVC was blocked by L-NAME but restored by the NO donor, we propose that the dilatation of proximal arterioles is dependent on tonic levels of NO, rather than mediated by NO.

Human skeletal muscle mitochondrial capacity.

Under aerobic work, the oxygen consumption and major ATP production occur in the mitochondria and it is therefore a relevant question whether the in vivo rates can be accounted for by mitochondrial capacities measured in vitro. Mitochondria were isolated from human quadriceps muscle biopsies in yields of approximately 45%. The tissue content of total creatine, mitochondrial protein and different cytochromes was estimated. A number of activities were measured in functional assays of the mitochondria: pyruvate, ketoglutarate, glutamate and succinate dehydrogenases, palmitoyl-carnitine respiration, cytochrome oxidase, the respiratory chain and the ATP synthesis. The activities involved in carbohydrate oxidation could account for in vivo oxygen uptakes of 15-16 mmol O2 min-1 kg-1 or slightly above the value measured at maximal work rates in the knee-extensor model of Saltin and co-workers, i.e. without limitation from the cardiac output. This probably indicates that the maximal oxygen consumption of the muscle is limited by the mitochondrial capacities. The in vitro activities of fatty acid oxidation corresponded to only 39% of those of carbohydrate oxidation. The maximal rate of free energy production from aerobic metabolism of glycogen was calculated from the mitochondrial activities and estimates of the DeltaG or ATP hydrolysis and the efficiency of the actin-myosin reaction. The resultant value was 20 W kg-1 or approximately 70% of the maximal in vivo work rates of which 10-20% probably are sustained by the anaerobic ATP production. The lack of aerobic in vitro ATP synthesis might reflect termination of some critical interplay between cytoplasm and mitochondria.