Selection of measurement frequencies for optimal extraction of tissue impedance model parameters

The results are presented of a study performed to determine the measurement frequencies that provide optimal extraction of tissue impedance model parameters from in vivo measured electrical impedance spectra. Measurement frequency sets that are logarithmic and quasi-linear, and frequency sets that produce angularly equidistant points on the Nyquist loci are used to test the parametric fitting algorithm that calculates R₀, R_∞, α and τ tissue parameters from complex impedance spectra. Simulated data, calculated in the presence of ≤5% measurement noise, and in vivo experiments indicate that the quality of the fitted parameters depends upon the selection of measurement frequencies. The results show that, if measurements are performed with a system that has a realistic measurement bandwidth, then, for the best estimation of: R₀, the measurement frequencies should include the decade from 100Hz-1 kHz; R_∞, the algorithm should not include frequencies under 1kHz; α and τ, the measurement frequencies should be equidistantly spaced on the Nyquist locus.     

Prior heavy knee extension exercise does not affect $$\dot{V}\hbox{O}_{2}$$ kinetics during subsequent heavy cycling exercise

This study examined the magnitude of the oxygen uptake slow component during heavy exercise when preceded by heavy knee extension (KE) exercise. Nine males (26.6 ± 1.7 years, ±SE) performed repeated bouts of heavy exercise, each lasting 6 min with 6 min of recovery. Cycling–cycling trials (CYC₁, CYC₂) involved step transitions to a workrate corresponding to 50% of the difference between peak and the lactate threshold (Δ 50%). During bilateral KE-cycling trails (KE, CYC₃), KE was performed at an intensity requiring twofold greater muscle activation relative to CYC₁ followed by a cycling transition to Δ 50%. was measured breath-by-breath and was modeled using three exponentials to determinate the amplitudes (A ₂′, A ₃′) and time constants (τ ₂, τ ₃) of the primary phase and SC. Electromyography (EMG) recorded from the vastus lateralis and medialis was averaged and reported relative to maximal voluntary contraction (%MVC). EMG was higher (p < 0.05) during KE (37.6 ± 8.1 %MVC) than CYC₁ (20.8 ± 1.9 %MVC), CYC₂ (21.6 ± 5.7 %MVC) and CYC₃ (19.8 ± 6.3 %MVC). The amplitude of the SC was lower (p < 0.05) in CYC₂ (197 ± 120 ml min⁻¹) and CYC₃ (163 ± 51 ml min⁻¹) compared to CYC₁ (325 ± 126 ml min⁻¹). No difference in SC was observed between CYC₂ and CYC₃. Although the activation of additional motor units during KE exercise reduced the amplitude of the SC, the decrease was similar to that observed following heavy cycling exercise. Thus, the activation of motor units in excess of those required for the activity does not alter the response during a subsequent bout of exercise.     

Kinetics of pulmonary \dot{V} \hbox{O}_{2} and femoral artery blood flow and their relationship during repeated bouts of heavy exercise

The mechanism that alters the pulmonary response to heavy-intensity exercise following prior heavy exercise has been frequently ascribed to an improvement in pre-exercise blood flow (BF) or O₂ delivery. Interventions to improve O₂ delivery have rarely resulted in a similar enhancement of However, the actual limb blood flow and dynamics in the second bout of repeated exercise remain equivocal. Seven healthy female subjects (21–32 years) performed consecutive 6-min (separated by 6 min of 10 W exercise) bilateral knee extension (KE) exercise in a semisupine position at a work rate halfway between the lactate threshold (LT) and peak. Femoral artery blood flow (FBF) was measured by Doppler ultrasound simultaneously with breath-by-breath each protocol being repeated at least four times for precise kinetic characterization. The effective time-constant (τ′) of the response was reduced following prior exercise (bout 1: 61.0 ±10.5 vs. bout 2: 51.6±9.0 s; mean ± SD; P<0.05), which was a result of a reduced slow component (bout 1: 16.0±8.0 vs. bout 2: 12.5±6.7 %; P<0.05) and an unchanged ‘primary’ τ. FBF was consistently faster than However, there was no bout-effect on τ′ FBF (bout 1: 28.2±12.0 vs. bout 2: 34.2±8.5 s). The relationship between the exercise-associated (i.e., ) and Δ FBF was similar between bouts, with a tendency (N.S: P>0.05) for to be increased during the transition to bout 2 rather than decreased, as hypothesized. The return of kinetics toward first order, therefore, was associated with an ‘appropriate’, not enhanced, BF to the working muscles. Whether a relative prior-hyperemia in bout 2 enables a more homogeneous intramuscular distribution of BF and/or metabolic response is unclear, however, these data are consistent with events more proximal to the exercise muscle in mediating the response during repeated heavy-intensity KE exercise.     

Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans

[(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , [(Q)\dot] \dot{Q} and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%_VT) and at 120% of [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (120%_Wmax). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(Q)\dot] \dot{Q} kinetics at 120%_Wmax. Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , \mathop Q ^· \mathop Q\limits^{ \cdot } and HHb data were fitted with traditional exponential models. τ₂ of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was longer (62.5 ± 20.9 s) at 120%_Wmax than at 80%_VT (27.8 ± 10.4 s). The τ₂ of [(Q)\dot] \dot{Q} kinetics was unaffected by exercise intensity and, at 120% of [(V)\dot]\textO_2max , \dot{V}{\text{O}}_{2\max } , it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%_Wmax than at 80%_VT (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%_Wmax. These results suggest that [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at the onset of exercise is not regulated/limited by muscle’s O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics observed during supramaximal exercise.     

Assessment of the effects of physical training in patients with chronic heart failure: the utility of effort-independent exercise variables

Traditionally, the effects of physical training in patients with chronic heart failure (CHF) are evaluated by changes in peak oxygen uptake (peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ). The assessment of peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , however, is highly dependent on the patients’ motivation. The aim of the present study was to evaluate the clinical utility of effort-independent exercise variables for detecting training effects in CHF patients. In a prospective controlled trial, patients with stable CHF were allocated to an intervention group (N = 30), performing a 12-week combined cycle interval and muscle resistance training program, or a control group (N = 18) that was matched for age, gender, body composition and left ventricular ejection fraction. The following effort-independent exercise variables were evaluated: the ventilatory anaerobic threshold (VAT), oxygen uptake efficiency slope (OUES), the [(V)\dot]_\textE /[(V)\dot]\textCO ₂ \dot{V}_{\text{E}} /\dot{V}{\text{CO}}_{ 2} slope and the time constant of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics during recovery from submaximal constant-load exercise (τ-rec). In addition to post-training increases in peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and peak [(V)\dot]_\textE , \dot{V}_{\text{E}} , , the intervention group showed significant within and between-group improvements in VAT, OUES and τ-rec. There were no significant differences between relative improvements of the effort-independent exercise variables in the intervention group. In contrast with VAT, which could not be determined in 9% of the patients, OUES and τ-rec were determined successfully in all patients. Therefore, we conclude that OUES and τ-rec are useful in clinical practice for the assessment of training effects in CHF patients, especially in cases of poor subject effort during symptom-limited exercise testing or when patients are unable to reach a maximal exercise level.     

Reproducibility of relationships between human ventilation, its components and oesophageal temperature during incremental exercise

For human exercise at intensities greater than ~70 to 85% of maximal levels of exertion, ventilation (V _E) increases proportionately to core temperature (T _C) following distinct T _C thresholds. This suggested T _C in humans could be a modulator of exercise-induced ventilation. This study tested the reproducibility of relationships between oesophageal temperature (T _oes), ventilation and its components during incremental exercise. On two nonconsecutive days, at an ambient temperature of 22.1±0.3°C and RH of 45±5%, seven untrained adult males of normal physique pedaled on a seated cycle ergometer in an incremental exercise protocol from rest to the point of exhaustion. In each exercise session, ventilatory equivalents for oxygen consumption and carbon dioxide production plus the components of V _E, tidal volume (V _T) and frequency of respiration (ƒ), were expressed as a function of T _oes. Results indicated the reproducibility criteria of Bland and Altman were met for the relationships between T _oes and both and as well as for relationships between T _oes and each of V _T and f. Intraclass correlation coefficients (R) for between-trial T _oes thresholds for (R=0.91, P<0.05) and (R=0.88, P<0.05) were also high and significant. In both trials, after T _oes increased by ~0.3°C, V _T demonstrated a distinct plateau point at a reproducible T _oes (R=0.93, P<0.05) and ƒ demonstrated a distinct and reproducible T _oes threshold (R=0.84, P<0.05). In conclusion, the results illustrate that for humans, ventilation has a significant and reproducible relationship with core temperature during incremental exercise.     

Investigation of the temporal and spectral characteristics of certain artifact signals and background bioelectric activity

Conclusions 1. The As of extrabrain origin caused by “winking,” “eye movement,” and “swallowing” are manifested significantly in the frequency range Δf=0.5−20 Hz at various points of the surface of a person's head and in the overwhelming majority of cases exceed the BBA level severalfold. In this case the times of occurrence of the AS at various points of the head surface differ insignificantly, and the form of the AS has a qualitatively identical character. 2. The AS caused by “winking” and “eye movements” consist of positive and negative components. The average duration of these components =0.46 sec with standard deviation σ_τ=0.084 sec. 3. The AS caused by “swallowing” in the frequency range 0.5–20 Hz has a “two-humped” character and an average duration =1.62 sec with σ_τ=0.27 sec. In the frequency range 20–500 Hz the corresponding AS are manifested by an increase of general bioelectricactivity, in which case τ_AS=1.65 sec, σ_τ=0.2 sec. The data obtained on the form of the AS and their duration make it possible to develop the structure of a quasi-optimal channel of their detection, in particular, with the use of postdetector optimization with respect to the duration of the AS. Such noise-immune channels can be realized for detecting each of the types of AS and the given set of AS. In this case worsening of the noise immunity of the channel detecting several types of AS compared with the corresponding ones for each of the types may prove to be negligible. Institute of Superhard Materials, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Meditsinskaya Tekhnika, No. 6, pp. 15–18, November–December, 1984.     

α2-Adrenoreceptor mediated sympathoinhibition of heart rate during acute hypoxia is diminished in conscious prostacyclin synthase deficient mice

Acute hypoxia increases ventilatory drive in conscious animals, resulting in tachycardia. Sustained hypoxia changes the initial chemoreflex ventilatory increase to secondary ventilatory depression, which then evokes a gradual secondary heart rate (HR) reduction. Prostacyclin (PGI₂) release is known to potentiate α₂-adrenoreceptor (α₂-AR) mediated inhibition of sympathoactivation during ischaemia and hypoxia. We examined whether α₂-AR mediated sympathoinhibition was responsible for limiting hypoxic heart rate increases during initial sympathoactivation, and subsequent secondary HR depression, and if PGI₂ is required for sympathoinhibition of HR. The responses of unrestrained PGI₂ synthase deficient (PGID) and wild type (WT) mice to acute hypoxia (10% O₂ for 30 min) were investigated by simultaneous telemetry, whole body plethysmography and open-flow respirometry. PGID mice exhibited potentiated (p < 0.007) after intraperitoneal vehicle injection (n = 8), but not so HR responses compared to WT mice during sustained hypoxia. Idazoxan (α₂-AR antagonist, i.p. bolus 3 mg/kg) pretreatment did not change hypoxic ventilatory response in either group, but significantly elevated hypoxic HR in WT mice only (p < 0.013). Sodium meclofenamate (cyclooxygenase inhibition, i.p. bolus 25 mg/kg) pretreatment eliminated the potentiated of PGID and caused significant basal hypotension that led to a transient hypertensive response to hypoxia. From these results, we suggest that α₂-AR activation is required for coupling HR to central inspiratory drive during acute hypoxia, and that PGI₂ is required to enhance the inhibition of sympathoactivation.     

Seasonal training and heart rate and blood pressure variabilities in young swimmers

To evaluate if changes in athletes’ physical fitness due to seasonal training are associated with changes in cardiovascular autonomic control, nine swimmers (three males and six females; aged 14–18 years) were evaluated before and after 5 months of training and competitions. Maximal oxygen consumption and ventilatory threshold were determined during a maximal test; heart rate (HR) and blood pressure (BP) variabilities’ power spectra were calculated at rest (supine and sitting positions) and in the recovery of two exercises at 25 and 80% pre-training At the end of the season: (a) and ventilatory threshold increased respectively by 12 and 34% (P<0.05); (b) at rest, HR decreased by 9 b min⁻¹ in both body positions, whereas BP decreased in supine position only by 17%. No change in low frequency (LF, 0.04–0.15 Hz) and high frequency (HF, 0.15–1.5 Hz) normalized powers and in LF/HF ratio of HR variability and in LF power of systolic BP variability was observed. In contrast, a significant increase in HF α-index (about 12 ms mmHg⁻¹) was found; (c) during recovery no change in any parameter was observed. Seasonal training improved exercise capacity and decreased resting cardiovascular parameters, but did not modify vagal and sympathetic spectral markers. The increase in α-index observed at rest after the season and expression of augmented baroreflex sensibility indicated however that HR vagal control could have been enhanced by seasonal training. These findings suggested that autonomic system might have played a role in short-term adaptation to training.     

Evaluation of the ratio of mean square inertia radii of branched and linear macromolecules from intrinsic viscosity measurements

A method for the evaluation of the ratio of the mean square inertia radii \documentclass{article}\pagestyle{empty}\begin{document}$ (\overline {R^2 } )^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern‐\nulldelimiterspace} 2}} $\end{document} of branched (b) and linear (1) molecules \documentclass{article}\pagestyle{empty}\begin{document}$ g[\eta ] = {{(\overline {R_{\rm b}^2 } )_{[\eta ]} } \mathord{\left/ {\vphantom {{(\overline {R_{\rm b}^2 } )_{[\eta ]} } {(\overline {R_{\rm l}^{\rm 2} } }}} \right. \kern‐\nulldelimiterspace} {(\overline {R_{\rm l}^{\rm 2} } }})_{[\eta ]} $\end{document} from intrinsic viscosity measurements is proposed. The evaluation is based on the solution of the equation: where erf \documentclass{article}\pagestyle{empty}\begin{document}$ x = \frac{2}{{\sqrt \pi }}\int\limits_0^{\rm x} {{\rm e}^{ ‐ t^2 } } {\rm d}t $\end{document}; a is the exponent in the Mark-Kuhn-Houwink relation [η₁] = KM^a, ε = (2a?1)/3 and ?(a) is the shielding function, tabulated by Debye and Bueche. The method is used for the evaluation of g[η] in Θ- and in good solvents from experimental data published in the literature. The results show that it is possible to find the dimensions of branched molecules from intrinsic viscosity measurements in good solvents using the above formula. These results are obtained by the analysis of changes of the macromolecular dimensions in different solvents and in part by the results of second virial coefficient measurements of different polymers.     

Energy cost and energy sources of a ballet dance exercise in female adolescents with different technical ability

This study evaluated energy cost and energy sources of a ballet exercise (grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level (n = 13) and high-level (n = 12). The overall energy requirement of dance exercise (VO_2eq) was obtained by adding the amount of VO₂ during exercise above resting (aerobic source or VO_2ex) to the VO₂ up to the fast component of recovery (anaerobic alactic source or VO_2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or ) of recovery. VO_2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg⁻¹ in low-level and high-level groups, respectively. VO_2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO_2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO_2al and 12 ± 1% for . In high-level group the remaining fractions were: 18 ± 2 % for VO_2al and 4 ± 1% for . Between two groups, significant differences were found in VO_2ex (P < 0.01), (P < 0.01), and VO_2al (P < 0.05). IAT was 55 and 60% of for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to      

Effects of aerobic fitness on oxygen uptake kinetics in heavy intensity swimming

This study aimed to characterise both the [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics within constant heavy-intensity swimming exercise, and to assess the relationships between [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics and other parameters of aerobic fitness, in well-trained swimmers. On separate days, 21 male swimmers completed: (1) an incremental swimming test to determine their maximal oxygen uptake ([(V)\dot]\textO_2max ) (\dot{V}{\text{O}}_{2\max } ) , first ventilatory threshold (VT), and the velocity associated with [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (v[(V)\dot]\textO_2max ) (v\dot{V}{\text{O}}_{2\max } ) and (2) two square-wave transitions from rest to heavy-intensity exercise, to determine their [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics. All the tests involved breath-by-breath analysis of freestyle swimming using a swimming snorkel. [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was modelled with two exponential functions. The mean values for the incremental test were 56.0 ± 6.0 ml min⁻¹ kg⁻¹, 1.45 ± 0.08 m s⁻¹; and 42.1 ± 5.7 ml min⁻¹ kg⁻¹ for [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } , v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } and VT, respectively. For the square-wave transition, the time constant of the primary phase (τ_p) averaged 17.3 ± 5.4 s and the relevant slow component (A′_sc) averaged 4.8 ± 2.9 ml min⁻¹ kg⁻¹ [representing 8.9% of the end-exercise [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (%A′_sc)]. τ_p was correlated with v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } (r = −0.55, P = 0.01), but not with either [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} (r = 0.05, ns) or VT (r = 0.14, ns). The %A′_sc did not correlate with either [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} (r = −0.14, ns) or v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } (r = 0.06, ns), but was inversely related with VT (r = −0.61, P < 0.01). This study was the first to describe the [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics in heavy-intensity swimming using specific swimming exercise and appropriate methods. As has been demonstrated in cycling, faster [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics allow higher aerobic power outputs to be attained. The slow component seems to be reduced in swimmers with higher ventilatory thresholds.     

The influence of acute and 23 days of intermittent hypoxic exposures on the exercise-induced forehead sweating response

The effect of acute and 23 days of intermittent exposures to normobaric hypoxia on the forehead sweating response during steady-state exercise was investigated. Eight endurance athletes slept in a normobaric hypoxic room for a minimum of 8 h per day at a simulated altitude equivalent to 2,700 m for 23 days (sleep high–train low regimen). Peak oxygen uptake and peak work rate (WR_peak) were determined under normoxic (20.9%O₂) and hypoxic (13.5%O₂) conditions prior to (pre-IHE), and immediately after (post-IHE) the intermittent hypoxic exposures (IHE). Also, each subject performed three 30-min cycle-ergometry bouts: (1) normoxic exercise at 50% WR_peak attained in normoxia (control trial; CT); (2) hypoxic exercise at 50% WR_peak attained in hypoxia (hypoxic relative trial; HRT) and (3) hypoxic exercise at the same absolute work rate as in CT (hypoxic absolute trial; HAT). Exposure to hypoxia induced a 33 and 37% decrease (P < 0.001) in pre-IHE and post-IHE, respectively. Despite similar relative oxygen uptake during HAT pre-IHE and post-IHE, the ratings of perceived whole-body exertion decreased substantially (P < 0.05) post-IHE. Pre-IHE the sweat secretion on the forehead was greater (P < 0.01) in the HAT (2.60 (0.80) mg cm⁻² min⁻¹) compared to the other two trials (CT = 1.87 (1.09) mg cm⁻² min⁻¹; HRT = 1.57 (0.82) mg cm⁻² min⁻¹) despite a similar exercise-induced elevation in body temperatures, resulting in an augmented (P < 0.01) gain of the sweating response The augmented and during the HAT were no longer evident post-IHE. Thus, it appears that exercise sweating on the forehead is potentiated by acute exposure to hypoxia, an effect which can be abolished by 23 days of intermittent hypoxic exposures.     

Metabolic and cardiovascular responses during sub-maximal exercise in humans after 14 days of head-down tilt bed rest and inactivity

f _H, SV, [Hb], C_aO₂, O₂, MAP and R _P were measured in 10 young subjects at rest and during exercise at 50, 100 and 150 W before and after 14 days of head-down tilt bed rest (HDTBR) and of ambulatory (AMB) control period. f _H was 18 and 8% higher after HDTBR and AMB, respectively. SV dropped by 15% both after HDTBR and AMB, whereas did not change. After HDTBR, C_aO₂ decreased at rest (−8%) and at 50 W (−5%), whereas O₂ did not change; MAP was 14 and 6% lower at rest and at 100 W and R _P decreased by 23% only at rest. Changes in f _H and SV were larger after HDTBR than after AMB. These results show that, notwhistanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.     

Interaction of heart and arterial system

We have studied the interrelation of left ventricle and arterial system in the anesthetized open-thorax cat. The ventricle was characterized by its pump function graph, relating mean ventricular pressure ( ) and mean aortic flow ( ). The pump function graph was determined by means of an artificial periphery and on a beat-to-beat basis. The periphery was characterized by relating mean aortic pressure ( ) and mean flow. Mean aortic and mean left ventricular pressure could be related over a wide range of values by a proportionality factor . In a series of five separate experiments a value of a=1.72±0.14 (mean±SD) was found. This simplified relation allows direct comparison of apparent source resistance (i.e., slope of pump function graph), (R_s), and peripheral resistance (R_p). It was also found experimentally that total external power ( ) could be calculated from mean aortic pressure and mean flow as well as from mean left ventricular pressure and mean flow (thus from the pump function graph) by . The value of c=1.16±0.12 (mean±SD, n=4). Maximum external power was predicted for . In six different cats R_p/R_s ratio in the working point (i.e., mean left ventricular pressure and mean flow when the normal periphery loaded the heart) was found to be R_p/R_s=2.63±0.92. This value could not be shown to differ from that in the point where maximal external power was found, i.e., R_p/R_s=1.81±0.08 (n=6).     

Fitness as a determinant of oxygen uptake response to constant-load exercise

Summary Exercise performed above the lactate threshold (Θ _La) produces a slowly-developing phase of oxygen uptake ( ) kinetics which elevates above that predicted from the sub-Θ _La -work rate relationship. This phenomenon has only been demonstrated, to date, in subjects who were relatively homogeneous with respect to fitness. This investigation therefore examined whether this behaviour occurred at a given absolute or whether it was a characteristic of supra-Θ _La exercise in a group of subjects with over a threefold range ofΘ _La (990–3000 ml O₂·min⁻¹) and peak (1600–5260 ml O₂·min⁻¹). Twelve healthy subjects performed: 1) exhausting incremental cycle ergometer exercise for estimation ofΘ _La ( ) and peak , and 11) a series of constant-load tests above and below for determination of the profile and efficiency of work. During all tests expired ventilation, and carbon dioxide production were monitored breath-by-breath. The efficiency of work determined during incremental exercise (28.1±0.7%, ,n=12) did not differ from that determined during sub- constant-load exercise (27.4±0.5%,p>0.05). For constant-load exercise, rose above that predicted, from the sub- -work rate relationship, for all supra- work rates. This was evident above 990 ml O₂·min⁻¹ in the least fit subject but only above 3000 ml O₂·min⁻¹ in the fittest subject. As a consequence the efficiency of work was reduced from 27.4±0.5% for sub- exercise to 22.6±0.4% (p<0.05) at the lowest supra- work rate (i.e. +20 W, on average). The efficiency of work generally decreased further at the higher supra- work rates. We conclude that the response to constant-load exercise includes an additional slow phase of the kinetics for all exercise intensities above irrespective of the fitness of the subject. Consequently, measurements of the aerobic efficiency of work during constant-load exercise must rigorously constrain the exercise intensity to the sub- domain. Supported by grants from the John D. and Catherine T. Mac-Arthur Foundation, USPHS RR 00865-15, and NIH HL 07694-01     

Evaluation of the Oxycon Mobile metabolic system against the Douglas bag method

The aim of this study was to evaluate two versions of the Oxycon Mobile portable metabolic system (OMPS1 and OMPS2) in a wide range of oxygen uptake, using the Douglas bag method (DBM) as criterion method. The metabolic variables [(V)\dot]\textO₂ , [(V)\dot]\textCO₂ , \dot{V}{\text{O}}_{2} , \dot{V}{\text{CO}}_{2} , respiratory exchange ratio and [(V)\dot]_\textE \dot{V}_{\text{E}} were measured during submaximal and maximal cycle ergometer exercise with sedentary, moderately trained individuals and athletes as participants. Test–retest reliability was investigated using the OMPS1. The coefficients of variation varied between 2 and 7% for the metabolic parameters measured at different work rates and resembled those obtained with the DBM. With the OMPS1, systematic errors were found in the determination of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(V)\dot]\textCO₂ . \dot{V}{\text{CO}}_{2} . At submaximal work rates [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} was 6–14% and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} 5–9% higher than with the DBM. At [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } both [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} were slightly lower as compared to DBM (−4.1 and −2.8% respectively). With OMPS2, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} was determined accurately within a wide measurement range (about 1–5.5 L min⁻¹), while [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} was overestimated (3–7%). [(V)\dot]_\textE \dot{V}_{\text{E}} was accurate at submaximal work rates with both OMPS1 and OMPS2, whereas underestimations (4–8%) were noted at [(V)\dot]\textO_2max . \dot{V}{\text{O}}_{2\max } . The present study is the first to demonstrate that a wide range of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} can be measured accurately with the Oxycon Mobile portable metabolic system (second generation). Future investigations are suggested to clarify reasons for the small errors noted for [(V)\dot]_\textE \dot{V}_{\text{E}} and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} versus the Douglas bag measurements, and also to gain knowledge of the performance of the device under applied and non-laboratory conditions.     

Real-time extraction of tissue impedance model parameters for electrical impedance spectrometer

This paper presents a new algorithm for real-time extraction of tissue electrical impedance model parameters from in vivo electrical impedance spectroscopic measurements. This algorithm was developed as a part of a system for muscle tissue ischemia measurements using electrical impedance spectroscopy. An iterative least square fitting method, biased with a priori knowledge of the impedance model was developed. It simultaneously uses both the real and imaginary impedance spectra to calculate tissue parameters R0, R infinity, alpha and tau. The algorithm was tested with simulated data, and during real-time in vivo ischemia experiments. Experimental results were achieved with standard deviations of sigma R0 = 0.80%, sigma R infinity = 0.84%, sigma alpha = 0.72%, and sigma tau = 1.26%. On a Pentium II based PC, the algorithm converges to within 0.1% of the results in 17 ms. The results show that the algorithm possesses excellent parameter extraction capabilities, repeatability, speed and noise rejection.     

Living high–training low: effect on erythropoiesis and maximal aerobic performance in elite Nordic skiers

The “living high–training low” model (Hi–Lo) may improve aerobic performance in athletes, and the main mechanism of this improvement is thought to be augmented erythropoiesis. A positive effect of Hi–Lo has been demonstrated previously by using altitudes of 2,000–3,000 m. Since the rate of erythropoiesis is altitude-dependent, we tested whether a higher altitude (3,500 m) during Hi–Lo increases erythropoiesis and maximal aerobic performance. Nordic skiers trained for 18 days at 1,200 m, while sleeping at 1,200 m in ambient air (control group, n = 5) or in hypoxic rooms (Hi–Lo, n = 6; 3 × 6 days at simulated altitudes of 2,500, 3,000 and finally 3,500 m, 11 h day⁻¹). Measurements were done before, during (blood samples only) and 2 weeks after the intervention (POST). Maximal aerobic performance was examined from and time to exhaustion (T _exh) at (minimum speed associated with ), respectively. Erythropoietin and soluble transferrin receptor responses were higher during Hi–Lo, whereas reticulocytes did not change. In POST (vs. before): hematological parameters were similar to basal levels, as well as red blood cell volume, being 2.68 ± 0.83 l (vs. 2.64±0.54 l) in Hi–Lo and 2.62±0.57 l (vs. 2.87 ± 0.59 l) in controls. At that time, neither nor T _exh were improved by Hi–Lo, being non-significantly decreased by 2.0% (controls) and 3.7% (Hi–Lo). The present results suggest that increasing the altitude up to 3,500 m during Hi–Lo stimulates erythropoiesis but does not confer any advantage for maximal O₂ transport.     

A prediction equation for indirect assessment of anaerobic threshold in male distance runners

Summary The predictability of anaerobic threshold (AT) from maximal aerobic power, distance running performance, chronological age, and total running distance achieved on the treadmill (TRD) was investigated in a sample of 53 male distance runners, 17–23 years of age. The dependent variable was oxygen uptake ( ) at which AT was detected (i. e., @AT). A regression analysis of the data indicated @AT could be predicted from the following four measurements with a multipleR=0.831 and a standard error of the estimate of 2.66 ml · min⁻¹ · kg⁻¹: (67.9±5.7 ml · min⁻¹ · kg⁻¹), 1,500-m running performance (254.5±14.2 s), TRD (6.82±1.13 km), and age (19.4±2.2 years). When independent variables were limited to (X ₁) and 1,500-m running performance (X ₂) for simpler assessment, a multipleR=0.806 and a standard error of the estimate of 2.76 ml · min⁻¹ · kg⁻¹ were computed. A useful prediction equation with this predictive accuracy was considered to be @AT= 0.386X₁−0.128X₂+57.11. To determine if the prediction equation developed for the 53 male distance runners could be generalized to other samples, cross-validation of the equation was tested, using 21 different distance runners, 17–22 years of age. A high correlation (R=0.927) was obtained between @AT predicted from the above equation and directly measured @AT. It is concluded that the generalized equation may be applicable to young distance runners for indirect assessment of @AT. This study was supported by grants from The Descente Foundation for the Promotion of Sports Science, awarded to K. Tanaka