Non-steady State Exercise Research Articles

Data repeatability for the Cosmed K4 b2 portable metabolic cart during non-steady state exercise

BACKGROUND: Portable metabolic carts are a popular tool to assess aerobic capacity and affirm many cardiorespiratory conditions. They may also measure strength training performance. Given their popularity and increased usage to assess strength training performance; their data accuracy and consistency are important to determine. OBJECTIVE: Measure Cosmed K4 b2 portable metabolic cart data repeatability from consecutive seated calf press workouts. METHODS: Fifteen women and twelve men did two workouts that began with a stationary cycling warm-up followed by calf presses. Gases were measured before the calf press portion of workouts to establish baseline VO2 and VCO2 values, as well as continually throughout and after the calf press protocol. Subjects were detached from the cart once gas values returned to baseline after workouts concluded. In addition to VO2 and VCO2, repeatability was quantified for: breaths per minute, tidal volume, ventilation, O2 uptake relative to body mass, expired O2 and CO2 fractions, percent fat and carbohydrate utilization, METS and total energy cost. Mean and peak values per variable were analyzed. Repeatability was assessed separately for male and female data, as well as with values pooled, by the following: intraclass correlation coefficients, eta squared, limits of agreement, coefficient of variation and smallest real difference percent. RESULTS: Per variable, repeatability values across workouts were low. Female intraclass correlation coefficient mean values were more repeatable for variables related to gas measurements, yet male data were generally more repeatable for those related to substrate usage. CONCLUSIONS: Results for some repeatability indices were influenced by measurement magnitude. Peak values were predictably less repeatable than those for mean values. Most smallest real differences percent scores are so high they were rendered irrelevant or meaningless to determine true differences among paired values. Results suggest low data repeatability that are likely appropriate and realistic for the exercise protocol, hardware and intensity examined.

Increased hip flexion gait as an exercise modality for individuals with obesity.

Exercise is a critical element for the management of body weight and improvement of quality of life of individuals with obesity. Due to its convenience and accessibility, running is a commonly used exercise modality to meet exercise guidelines. However, the weight-bearing component during high impacts of this exercise modality might limit the participation in exercise and reduce the effectiveness of running-based exercise interventions in individuals with obesity. The hip flexion feedback system (HFFS) assists participants in meeting specific exercise intensities by giving the participant specific increased hip flexion targets while walking on a treadmill. The resulting activity involves walking with increased hip flexion which removes the high impacts of running. The purpose of this study was to compare physiological and biomechanical parameters during an HFFS session and an independent treadmill walking/running session (IND). Heart rate, oxygen consumption (VO2), heart rate error, and tibia peak positive accelerations (PPA) were investigated for each condition at 40% and 60% of heart rate reserve exercise intensities. VO2 was higher for IND despite no differences in heart rate. Tibia PPAs were reduced during the HFFS session. Heart rate error was reduced for HFFS during non-steady state exercise. While demanding lower energy consumption compared to running, HFFS exercise results in lower tibia PPAs and more accurate monitoring of exercise intensity. HFFS might be a valid exercise alternative for individuals with obesity or individuals that require low-impact forces at the lower limbs.

Oxygen Uptake and Near Infrared Spectroscopy Responses during Heavy Intensity Pseudorandom Binary Sequence Exercise

Activities of daily living are characterized by continuous changes in exercise intensity and duration resulting in many abrupt changes in metabolic demand. The ability to readily meet these demands is described by the rate of adaptation in oxygen uptake measured at either the mouth (VO2p) or at the site of active muscle. Many studies have used a single step transition to assess this rate of adaptation. However, a continually changing exercise, such as a pseudorandom binary sequence (PRBS) protocol, provides more transition phases to analyze. We examined the VO2p and microvascular oxygenation responses using near infrared spectroscopy (NIRS) during PRBS exercise. Five healthy males (30 ± 6 yrs, 83.4 ± 20.9 kg, VO2pk, 38.9 ± 5.9 mL/kg/min; mean ± SD) completed a ramp exercise to fatigue for the determination of the lactate threshold (LT) and peak VO2p (VO2pk). Each bout of PRBS exercise transitioned from a baseline of 20 W to a WR corresponding to either 90% of LT (MOD, 100 ± 7 W)) or to a WR at 40% of the difference between LT and VO2pk (HVY, 173 ± 13 W). The PRBS exercise consisted of 30 units of 15 s that alternated between BSL and the higher WR in a pseudorandom pattern; the pattern was repeated 3 times. VO2p was measured breath-by-breath using a metabolic cart and interpolated to 1 s intervals. For each subject and WR, the 3 repetitions for each trial were ensembled averaged yielding a single 450 s response. Changes in hemoglobin oxygenation (deoxy-[Hb+Mb]) and total hemoglobin concentration ([THC]) were measured from the vastus lateralis (VL) using frequency-domain NIRS. Data were collected at 1 Hz and ensembled averaged to yield a single 450 s response. VO2p and deoxy-[Hb+Mb] responses were transformed into the frequency domain and analyzed using standard approaches and the mean-normalized gain (MNG). The harmonic amplitudes (Amph) for VO2p/WR were lower (p<0.05) during HVY at 0.0067 Hz (Mod, 56.9 ± 13.0 %; HVY, 49.3 ± 6.8 %), 0.011 Hz (Mod, 37.6 ± 17.0 %, HVY: 25.8 ± 5.7 %) and 0.013 Hz (Mod, 33.2 ± 12.8 %; HVY, 15.8 ± 10.2 %). The Amph for deoxy-[Hb+Mb]/WR were lower (p<0.05) for VO­2p/WR in HVY compared to MOD (Mod, 39.5 ± 6.0 %; HVY, 30.2 ± 3.9 %). MNG was also lower (p<0.05) for deoxy-[Hb+Mb]/WR in HVY compared to MOD (Mod, 77.4 ± 26.6 %; HVY, 47.3 ± 10.0 %). The VO2p and deoxy-[Hb+Mb] responses from a PRBS trial represent the responses to individual sinusoidal inputs at each frequency tested. The normalized Amph and MNG measured in the current study described the temporal dynamics of the variables of interest (i.e., VO2p and deoxy-[Hb+Mb]). The results of the current study showed a significant decrease in both normalized Amph and MNG for VO2p and deoxy-[Hb+Mb] suggesting that exercise performed above the LT results in a slowing of both the VO2p and microvascular deoxy-[Hb+Mb] responses. These findings are consistent with previous studies demonstrating a slowing of VO2p above the LT. Compared to studies using a single step protocol, responses to PRBS protocols include many transition periods to identify potential control mechanisms that are more discernable during non-steady state exercise.

Pulmonary hemodynamic and right ventricular responses to brief and prolonged exercise in middle-aged endurance athletes.

Right ventricular (RV) function is closely coupled to pulmonary arterial (PA) hemodynamics and is believed to decline with prolonged exercise. A linear pressure-flow relationship is thought to exist between PA pressures and increasing exercise intensity in athletes, yet a paucity of directly measured pulmonary hemodynamic data exists supporting this contention. We sought to describe the PA pressure, PA wedge pressure (PAWP), and RV functional responses to brief and prolonged exercise in endurance-trained athletes. Twenty-one healthy athletes (54 ± 5 yr) underwent right heart catheterization to assess pulmonary hemodynamics during graded, submaximal exercise. Measurements were made at rest and during three stages of steady-state, semiupright cycle ergometry at heart rates of 100 beats/min (EX1), 130 beats/min (EX2), and 150 beats/min (EX3). Five athletes completed an additional 34 min at 130 beats/min for a total exercise time of 60 min [prolonged exercise (PLG)]. PA pressures and PAWP increased significantly at EX1 without a further rise at EX2, EX3, or PLG. PAWP adjusted for absolute work rate demonstrated a significant decline as exercise intensity increased from EX1 to EX2. The resistance compliance time constant decreased at EX1 without further changes at EX2, EX3, and prolonged exercise. RV function did not decline during PLG. After an initial rise in PA pressure and PAWP during early, nonsteady-state exercise, values remained constant despite increases in exercise intensity and duration. These data indicate that in healthy, middle-aged endurance-trained athletes, the PA and pulmonary venous/left atrial compartments rapidly accommodate high conduit flows produced during intensive and prolonged exercise while maintaining RV function. NEW & NOTEWORTHY The right ventricular (RV)-pulmonary arterial (PA) circulatory unit has not been well studied during prolonged exercise, and this study provides an ecological approach that reflects a typical bout of endurance training integrating a transition from rest to exercise with successive increases in intensity, progressing to steady-state, sustained exercise. We demonstrated a remarkably constant response of the PA and PA wedge pressure during incremental, steady-state exercise and that no changes occur in pulmonary pressures throughout prolonged exercise, concomitant to a preservation of RV performance.

Application of Critical Power in Sport

The critical power (CP) is mathematically defined as the power-asymptote of the hyperbolic relationship between power output and time-to-exhaustion. Physiologically, the CP represents the boundary between the steady-state and nonsteady state exercise intensity domains and therefore may provide a more meaningful index of performance than other well-known landmarks of aerobic fitness such as the lactate threshold and the maximal O2 uptake. Despite the potential importance to sports performance, the CP is often misinterpreted as a purely mathematical construct which lacks physiological meaning and only in recent years has this concept begun to emerge as valid and useful technique for monitoring endurance fitness. This commentary defines the basic principles of the CP concept, outlines its importance to high-intensity exercise performance, and provides an overview of the current methods available for its assessment. Interventions including training, pacing and prior exercise can be used to alter the parameters of the power-time relationship. A future challenge lies in optimizing such interventions in order to positively affect the parameters of the power-time relationship and thereby enhance sports performance in specific events.

Non-linear cardiac output dynamics during ramp-incremental cycle ergometry

Published literature asserts that cardiac output (Q(.) = V(.) >O(2)x1/C((a-v))O(2)) increases as a linear function of oxygen uptake with a slope of approximately 5-6 during constant work rate exercise. However, we have previously demonstrated that C((a-v))O(2) has a linear relationship as a function of V(.)O(2) during progressively increasing work rate incremental exercise. Therefore, we hypothesized that Q(.) may indeed have a non-linear relationship with respect to V(.)O(2) during incremental, non-steady state exercise. To investigate this hypothesis, we performed five maximal progressive work rate exercise studies in healthy human subjects. Q(.) was determined every minute during exercise using measured breath-by-breath V(.) >O(2), and arterial and pulmonary artery measurements of PO(2), hemoglobin saturation, and content. Q(.) was plotted as a function of V(.) >O(2) and the linear and non-linear (first order exponential and hyperbolic) fits determined for each subject. Tests for linearity were performed by assessing the significance of the quadratic terms added to the linear relation using least squares estimation in linear regression. Linearity was inadequate in all cases (group P<0.0001). We conclude that cardiac output is a non-linear function of V(.)O(2 )during ramp-incremental exercise; the pattern of non-linearity suggests that while the kinetics of Q(.) > are faster than those of V(.) >O(2) they progressively slow as work rate (and V(.) >O(2)) increases.

Aerobic Energy Contribution during High Intensity Exercise

LANGUAGE NOTE | Document text in English; abstract also in Chinese.The review focuses on the aerobic energy contribution during high intensity cycling exercise. It is erroneous to assume that the energy demands of an exercise task can be met exclusively by either aerobic or anaerobic sources. During peak oxygen uptake determination, especially during the latter portions of the incremental exercise test, the anaerobic energy stores are also taxed. Not surprising, during maximal exercise of a short duration, there is also energy supplementation from aerobic energy sources. However, for a test to be considered predominantly anaerobic, the aerobic contribution to the test must be kept minimal. The quantification of aerobic contribution to a maximal exercise performance is difficult because the mechanical efficiency (ME) during a non-steady state exercise task remains speculative. Nevertheless extreme ME values for cycling have been proposed to provide a general scope of the estimated values. In adults, assumptions about oxygen uptake lag time, the size and role of the stored oxygen stores, which are taken into account also affect the magnitude to the aerobic contribution. Equivalent data on young people are insecure and greater research attention in this area is advised.本文著重介紹了大強度自行車運動中的有氧供能。如果認為運動中機體所需能量僅以某一能源系統，有氧系統或無氧系統供能是不正確的。在逐級遞增負荷測定最大攝氧量的運動中，尤其在測試的後階段，無氧系統參與供能。而在短時間的最大強度運動中，有氧供能也佔有一定的比例。即使進行無氧運動，在測試中仍能發現有低比例有氧供能。很難確定有氧系統在最大強度運動中的供能量為多少，因為不穩定狀態下的運動其供能效率仍不十分明確。但對於踏車運動中最高供能效率有一估計值範圍。對於成年人，攝氧量的延遲時間以及氧的儲存量的多少將影響最大有氧供能的比例。而在青少年中：有關這方面的資料較為缺乏，有待進一步的研究。

The relationship between heart rate and oxygen uptake during non-steady state exercise

In this study the validity of using heart rate (HR) responses to estimate oxygen uptake ([Vdot]O2) during varying non-steady state activities was investigated. Dynamic and static exercise engaging large and small muscle masses were studied in four different experiments. In the first experiment, 16 subjects performed an interval test on a cycle ergometer, and 12 subjects performed a field test consisting of various dynamic leg exercises. Simultaneous HR and [Vdot]O2 measurements were made. Linear regression analyses revealed high correlations between HR and [Vdot]O2 during both the interval test (r= 0.90±0.07) and the field test (r= 0.94±0.04). In the second experiment, 14 non-wheelchair-bound subjects performed both an interval wheelchair test on a motor driven treadmill, and a wheelchair field test consisting of dynamic and static arm exercise. Significant relationships were found for all subjects during both the interval test (r = 0.91±0.06) and the field test (r= 0.86±0.09). During non-steady state exercise using both arms and legs in a third experiment, contradictory results were found. For 11 of the 15 subjects who performed a field test consisting of various nursing tasks no significant relationship between HR and [Vdot]O2 was found (r= 0.42±0.16). All tasks required almost the same physiological strain, which induced a small range in data points. In a fourth experiment, the influence of a small data range on the HR-[Vdot]O2 relationship was investigated: five subjects performed a field test that involved both low and high physiological strain, non-steady state arm and leg exercise. Significant relationships were found for all subjects (r = 0.86±0.04). Although the r-values found in this study were less than under steady state conditions, it can be concluded that [Vdot]O2 may be estimated from individual HR-[Vdot]O2 regression lines during non-steady state exercise.

Continuous Estimation of CO2 Production during Exercise

A new method was developed for continuous isotopic estimation of human whole body CO2 rate of appearance (Ra) during non-steady state exercise. The technique consisted of a breath-by-breath measurement of 13CO2 enrichment (E) and a real-time fuzzy logic feedback system which controlled NaH13CO3 infusion rate to achieve an isotopic steady state. Ra was estimated from the isotope infusion rate and body 13CO2 enrichment which was equal to E at the isotopic steady state. During a non-steady state incremental cycle exercise (5 w/min or 10 w/min), NaH13CO3 infusion rate was successfully increased by the action of feedback controller so as to keep E constant.

RATE OF CO2 PRODUCTION (RaCO2) AND ESTIMATES OF ENERGY EXPENDITURE (EE) IN WRESTLING PRACTICE 271

To test the reliability of a method of estimating EE during non-steady state exercise, we measured RaCO2 during a 2-h wrestling practice. Breath samples were collected before (B) and every 10 min for 2-h after a single oral dose of 1-3C-bicarbonate (45 μmol/kg, 99%) in trained wrestlers (n=11, weight 67±14 kg). Subjects participated in two similarly conducted practices that differed only in that carbohydrate (CHO) was ingested every 20 min during one session (average: 24 g/h). Studies were also done without oral tracer. For each study of each subject, a pooled sample(P) was constructed using a 1-ml aliquot of every 10-min breath sample. RaCO2 (mmol/kg/2 hr) was calculated using the tracer dose and the isotope enrichment (IE,%) of P and B. EE (kcal/2 hr) was estimated assuming a ratio of 1.0 for VCO2/RaCO2 in trained athletes during exercise (J Appl Physiol 75:70-75, '93), and an RQ of 0.85. Means±SD were:Table Studies without tracer showed minimal (<0.1%) change in background13 C with or without CHO treatment. The correlation coefficient for EE of the two practice sessions was 0.66 (p<0.05). Conclusion: RaCO2 appears to be reliable for estimating EE in non-steady state sports such as wrestling, and may be useful in accounting for relative changes in EE during training when studying the effects of treatment interventions.

Cardiac Output Determination during Progressive Exercise in Cystic Fibrosis

Cardiac output (Q) determination using the equilibrium CO2-rebreathe indirect Fick technique (Equil) to estimate mixed venous PCO2 (Pv-CO2) has been validated during steady state (SS) exercise in subjects with lung disease. A modification of the exponential method using a low concentration of CO2 with an exponential rise in PEt-CO2 (Ex) during rebreathing to estimate Pv-CO2 has been validated during nonsteady state exercise. The purpose of the present study was to validate the Ex method in subjects with lung disease. Q was measured by Ex at every second work load during Prog. Q was measured after 5 min of SS exercise by both Ex and Equil. Arterial PCO2 was estimated from PEtCO2. There was no significant difference in the Q-VO2 relationship during Prog exercise between the combined control and mild (FEV1 > 70%) CF subjects or the moderate and severe CF subjects. Q can be determined in the nonsteady state using the exponential CO2-rebreathe indirect Fick technique in subjects with CF, allowing for noninvasive examination of cardiopulmonary interaction during exercise at a wide range of work loads.

Transition from Exercise to Rest: Ventilatory and Arterial Blood Gas Responses

The mechanisms leading to rapid changes in arterial blood gas values soon after exercise ends have not been well established. To further study these phenomena, we exercised seven normal male volunteers to exhaustion on a cycle ergometer with a 25-W/min ramped protocol measuring arterial blood gas values, and breath-by-breath gas exchange from rest to exercise and through 15 minutes of recovery. Arterial PO2 (PaO2) increased from 108 mm Hg at peak exercise to 125 mm Hg at 2 minutes of recovery. There was a smaller rise in calculated alveolar PO2 (PAO2) from 121 to 128 mm Hg over the same period. Arterial PCO2 (PaCO2) fell from 35.0 mm Hg to 31.9 mm Hg. The gas exchange ratio R rose from 1.21 to 1.52, after having peaked at 1.68 at 1 minute. The alveolar-arterial O2 gradient (P[A-a]O2) fell from 12.3 mm Hg at peak exercise to 3.2 mm Hg at 2 minutes. Following exercise, the rise in R is related to a more rapid fall in O2 uptake than in CO2 output, and the fall in P(A-a)O2 is probably related to improved V/Q relationships and to a rise in mixed venous PO2. We conclude that the rise in PaO2 in the recovery period after progressive nonsteady state exercise is due to several factors, including a fall in P(A-a)O2 and a rise in PAO2 due primarily to an elevation of R and also to a fall in PaCO2.

Comparison of Cardiorespiratory Responses During Steady-State and Nonsteady-State Exercise Tests In Patients with Left Ventricular Dysfunction

Comparison of Cardiorespiratory Responses During Steady-State and Nonsteady-State Exercise Tests In Patients with Left Ventricular Dysfunction

Leg exchange of amino acids during exercise in patients with arterial insufficiency.

Intermittent claudication is associated with adaptation in muscle metabolism. This study has evaluated the metabolism of amino acids at rest and during non-steady state exercise in patients with arterial insufficiency of at least six months duration in comparison with matched control individuals. The exchange of amino acids were measured during two periods of acute exercise; one initial exercise period with a standardized work load and exercise time and a second exercise period which continued until further exercise was impossible due to pain in the patients and exhaustion in the controls. The maximum blood flow was reduced by 40% in the patients but the maximum oxygen uptake per unit power developed was almost the same in patients and controls. The patients had significantly lower concentrations of glutamine, lysine and taurine at rest compared with the controls. The exchange of amino acids across the resting leg did not differ between the two groups. Exercise increased the efflux of amino acids in both patients and controls. The efflux of glutamine (896 +/- 205 vs. 48 +/- 359 nmol/100 ml/min/watt) was higher in the patients compared to the controls at the first exercise period with inverse changes in the opposite direction of asparagine (149 +/- 105 vs. 799 +/- 121 and 27 +/- 70 vs. 633 +/- 334 nmol/100 ml/min/watt at the first and second exercise, respectively. Alanine release did not differ between the groups. The complementary patterns of glutamine and asparagine during hypoxic exercise in the patients may reflect the fact that these amino acids share a common carrier system. The similarity in the efflux of non-metabolized amino acids, such as methionine, phenylalanine, tyrosine and 3-methylhistidine, indicated that muscle hypoxia in claudication patients did not promote net degradation of either globular or myofibrillar proteins, although exercise increased the efflux of 3-methylhistidine three- to fourfold in both patients and control individuals (from 1 +/- 0.4 to 4 +/- 1.8 and from 0 +/- 0.7 to 6 +/- 2.5 nmol/100 ml/min/watt, respectively). The exercise-induced alterations in leg exchange of amino acids were restored within 10-20 min following exercise regardless of hypoxia. The results demonstrate that patients with arterial insufficiency have altered intermediary metabolism of amino acids during exercise. However, muscle hypoxia in such patients does not seem to promote a negative protein balance or induce serious alterations in cell membrane integrity.

Intraerythrocyte and plasma lactate concentrations during exercise in humans.

The purpose of this study was to examine plasma and intraerythrocyte lactate concentrations during graded exercise in humans. Seven adult volunteers performed a maximum O2 uptake (VO2max) test on a cycle ergometer. Plasma and intraerythrocyte lactate concentrations (mmol . L-1 of plasma or cell water) were determined at rest, during exercise, and at 15-min post-exercise. The results show that plasma and intraerythrocyte lactate concentrations were not significantly different from each other at rest or moderate (less than or equal to 50% VO2max) exercise. However, the plasma concentrations were significantly increased over the intraerythrocyte levels at 75% and 100% VO2max. The plasma to red cell lactate gradient reached a mean (+/- SE) 1.7 +/- 0.4 mmol . L-1 of H2O at exhaustion, and was linearly (r = 0.84) related to the plasma lactate concentration during exercise. Interestingly, at 15-min post-exercise the direction of the lactate gradient was reversed, with the mean intraerythrocyte concentration now being significantly increased over that found in the plasma. These results suggest that the erythrocyte membrane provides a barrier to the flux of lactate between plasma and red cells during rapidly changing blood lactate levels. Furthermore, these data add to the growing body of research that indicates that lactate is not evenly distributed in the various water compartments of the body during non-steady state exercise.

Breath-by-Breath Measurement of Respiratory Gas Exchange Using On-Line Analog Computation

Study of transient changes in pulmonary oxygen uptake (Vo2) and carbon dioxide elimination (Vco2,) is becoming increasingly important in attempts to explore the dynamic behavior of the overall gas exchange system in response to physiological stimuli such as exercise. A method is described for accurate on-line computation and recording of breath-by-breath Vo2, Vco2 and respiratory exchange ratio (R) using fast-response transducers for expiratory flow, O2 and CO2 concentrations in conjunction with an analog computer. Special procedures for time alignment of flow and concentration signals, treatment of inspired-expired PH2O differences in respired gas, and computation of true R are described. The accuracy of the method was studied under steady and non-steady state exercise conditions, Vo2 and Vco2 values being in good agreement with those obtained by the conventional Douglas bag technique.