Increasing Work Rate Research Articles

Determinants of Longitudinal Changes in Exercise Capacity in Patients with Independent Functioning on Hemodialysis.

Patients with chronic kidney disease reportedly have decreased muscle oxygen utilization, which most substantially decreases exercise capacity, followed by cardiac reserve. However, determinants of longitudinal changes in exercise capacity in patients on hemodialysis and the effects of long-term exercise interventions are unknown. This study was conducted to clarify these concerns. This was a prospective cohort study. Patients on hemodialysis that were not hospitalized were followed from baseline up to 2years, and cardiopulmonary exercise testing results, including peak oxygen uptake, peak work rate, heart rate reserve, and ventilatory equivalent for carbon dioxide slope, as well as implementation of exercise interventions were assessed. Based on the 2-year change in peak oxygen uptake, they were divided into improvement or declined groups. Forty-five patients who were not hospitalized completed the follow-up were analyzed. In the improvement group, the variation was determined by an increase in peak work rate, which is a peripheral factor (partial regression coefficient 0.08 [95% CI = 0.01 to 0.16]), while in the decline group, the variation was determined by a decrease in the ventilatory equivalent for carbon dioxide slope, which is a cardiac factor (partial regression coefficient = -0.12; 95% CI = -0.21 to -0.03). Moreover, exercise intervention was associated with the change in peak oxygen uptake (partial regression coefficient = 3.09; 95% CI = 1.45 to 4.72). Exercise intolerance even in patients on hemodialysis that were not hospitalized and stable progressed over time with deterioration of cardiac reserve, whereas exercise interventions were associated with improved exercise capacity through enhanced peripheral function. The results support the early measurement of cardiopulmonary or skeletal muscle reserve through cardiopulmonary exercise testing and the implementation of long-term exercise interventions based on the measurement results to address the potential deterioration in exercise capacity associated with reduced cardiac reserve, even in patients on hemodialysis that are asymptomatic and stable.

Identifying time-varying dynamics of heart rate and oxygen uptake from single ramp incremental running tests

Objective. The fact that ramp incremental exercise yields quasi-linear responses for pulmonary oxygen uptake ( V˙O2 ) and heart rate (HR) seems contradictory to the well-known non-linear behavior of underlying physiological processes. Prior research highlights this issue and demonstrates how a balancing of system gain and response time parameters causes linear V˙O2 responses during ramp tests. This study builds upon this knowledge and extracts the time-varying dynamics directly from HR and V˙O2 data of single ramp incremental running tests. Approach. A large-scale open access dataset of 735 ramp incremental running tests is analyzed. The dynamics are obtained by means of 1st order autoregressive and exogenous models with time-variant parameters. This allows for the estimates of time constant (τ) and steady state gain (SSG) to vary with work rate. Main results. As the work rate increases, τ-values increase on average from 38 to 132 s for HR, and from 27 to 35 s for V˙O2 . Both increases are statistically significant (p < 0.01). Further, SSG-values decrease on average from 14 to 9 bpm (km·h−1)−1 for HR, and from 218 to 144 ml·min−1 for V˙O2 (p < 0.01 for decrease parameters of HR and V˙O2 ). The results of this modeling approach are line with literature reporting on cardiorespiratory dynamics obtained using standard procedures. Significance. We show that time-variant modeling is able to determine the time-varying dynamics HR and V˙O2 responses to ramp incremental running directly from individual tests. The proposed method allows for gaining insights into the cardiorespiratory response characteristics when no repeated measurements are available.

Understanding optimal cadence dynamics: a systematic analysis of the power-velocity relationship in track cyclists with increasing exercise intensity.

Background: This study aimed to investigate the changes in force-velocity (F/v) and power-velocity (P/v) relationships with increasing work rate up to maximal oxygen uptake and to assess the resulting alterations in optimal cadence, particularly at characteristic metabolic states. Methods: Fourteen professional track cyclists (9 sprinters, 5 endurance athletes) performed submaximal incremental tests, high-intensity cycling trials, and maximal sprints at varied cadences (60, 90, 120rpm) on an SRM bicycle ergometer. Linear and non-linear regression analyses were used to assess the relationship between heart rate, oxygen uptake (V.O2), blood lactate concentration and power output at each pedaling rate. Work rates linked to various cardiopulmonary and metabolic states, including lactate threshold (LT1), maximal fat combustion (FATmax), maximal lactate steady-state (MLSS) and maximal oxygen uptake (V.O2max), were determined using cadence-specific inverse functions. These data were used to calculate state-specific force-velocity (F/v) and power-velocity (P/v) profiles, from which state-specific optimal cadences were derived. Additionally, fatigue-free profiles were generated from sprint data to illustrate the entire F/v and P/v continuum. Results: HR, V.O2 demonstrated linear relationships, while BLC exhibited an exponential relationship with work rate, influenced by cadence (p < 0.05, η2 ≥ 0.655). Optimal cadence increased sigmoidally across all parameters, ranging from 66.18 ± 3.00rpm at LT1, 76.01 ± 3.36rpm at FATmax, 82.24 ± 2.59rpm at MLSS, culminating at 84.49 ± 2.66rpm at V.O2max (p < 0.01, η2 = 0.936). A fatigue-free optimal cadence of 135 ± 11rpm was identified. Sprinters and endurance athletes showed no differences in optimal cadences, except for the fatigue-free optimum (p < 0.001, d = 2.215). Conclusion: Optimal cadence increases sigmoidally with exercise intensity up to maximal aerobic power, irrespective of the athlete's physical condition or discipline. Threshold-specific changes in optimal cadence suggest a shift in muscle fiber type recruitment toward faster types beyond these thresholds. Moreover, the results indicate the need to integrate movement velocity into Henneman's hierarchical size principle and the critical power curve. Consequently, intensity zones should be presented as a function of movement velocity rather than in absolute terms.

High cadence cycling not high work rate, increases gait velocity post-exercise

ABSTRACT Gait velocity, or walking speed, has been referred to as the sixth vital sign, and research suggests that it is highly sensitive to change. Previous research has demonstrated the utility of cycling to improve gait parameters and in particular gait velocity in a variety of populations. However, it is unclear if the benefits from cycling to gait velocity stem from increased cadence, increased work rate, or the interaction between them. Therefore, the objective of the current research was to explicitly test the relationship between cycling work rate, cycling cadence, and gait velocity. 45 recreationally active young adults were randomly assigned to cycle at a normalised cadence and work rate, a higher cadence, or a higher work rate (CONTROL, FAST, HARD). All participants completed two ten-metre walk tests (10 MWT) pre- and post-cycling intervention. There was a significant interaction between group and time and post hoc comparisons showed that the FAST group walked significantly faster than the HARD group post-cycling. These results support the hypothesis that cycling at a cadence greater than the comfortable walking cadence, and not cycling at an increased work rate, increased gait velocity post-exercise for all members of our sample of healthy young adults.

What I see and what I feel: the influence of deceptive visual cues and interoceptive accuracy on affective valence and sense of effort during virtual reality cycling.

How we feel during exercise is influenced by exteroceptive (e.g., vision) and interoceptive (i.e., internal body signals) sensory information, and by our prior experiences and expectations. Deceptive visual cues about one's performance during exercise can increase work rate, without negatively impacting affective valence (good/bad responses) or perceived exertion. However, what is less understood is whether the perception of the exercise experience itself can be shifted, if work rate is held constant. Here we aimed to investigate whether deceptive vision-via illusory hills in a virtual reality (VR) cycling experience-alters affective valence and perceived exertion when physical effort is controlled. We also evaluated whether the accuracy with which one detects interoceptive cues influences the extent to which deceptive visual information can shift exercise experiences. A total of 20 participants (10 female; 30.2 ±11.2yrs) completed three VR cycling conditions each of 10-min duration, in a randomised, counterbalanced order. Pedal resistance/cadence were individualised (to exercise intensity around ventilatory threshold) and held constant across conditions; only visual cues varied. Two conditions provided deceptive visual cues about the terrain (illusory uphill, illusory downhill; resistance did not change); one condition provided accurate visual cues (flat terrain). Ratings of affective valence (Feeling Scale) and of perceived exertion (Borg's RPE) were obtained at standardised timepoints in each VR condition. Interoceptive accuracy was measured via a heartbeat detection test. Linear mixed effects models revealed that deceptive visual cues altered affective valence (f2 = 0.0198). Relative to flat terrain, illusory downhill reduced affective valence (Est = -0.21, p=0.003), but illusory uphill did not significantly improve affective valence (Est = 0.107, p=0.14). Deceptive visual cues altered perceived exertion, and this was moderated by the level of interoceptive accuracy (Condition-Interoception interaction, p=0.00000024, f2 = 0.0307). Higher levels of interoceptive accuracy resulted in higher perceived exertion in the illusory downhill condition (vs flat), while lower interoceptive accuracy resulted in lower perceived exertion in both illusory hill conditions (vs flat) and shifts of greater magnitude. Deceptive visual cues influence perceptual responses during exercise when physical effort does not vary, and for perceived exertion, the weighting given to visual exteroceptive cues is determined by accuracy with which interoceptive cues are detected. Contrary to our hypotheses, deceptive visual cues did not improve affective valence. Our findings suggest that those with lower levels of interoceptive accuracy experience most benefit from deceptive visual cues, providing preliminary insight into individualised exercise prescription to promote positive (and avoid negative) exercise experiences.

The effect of increasing work rate amplitudes from a common metabolic baseline on the kinetic response of V̇O2p, blood flow, and muscle deoxygenation.

A step-transition in external work rate (WR) increases pulmonary O2 uptake (V̇O2p) in a monoexponential fashion. While the rate of this increase, quantified by the time constant (τ), has frequently been shown to be similar between multiple different WR amplitudes (ΔWR), the adjustment of O2 delivery to the muscle (via blood flow; BF), a potential regulator of V̇O2p kinetics, has not been extensively studied. To investigate the role of BF on V̇O2p kinetics, ten participants performed step-transitions on a knee-extension ergometer from a common baseline WR (3 W) to: 24, 33, 45, 54, and 66 W. Each transition lasted 8 min and was repeated 4-6 times. Volume turbinometry and mass spectrometry, Doppler ultrasound, and near-infrared spectroscopy were used to measure V̇O2p, BF, and muscle deoxygenation (deoxy[Hb+Mb]), respectively. Like transitions were ensemble-averaged and phase II V̇O2p, BF, and deoxy[Hb+Mb] were fit with a monoexponential non-linear least squares regression equation. With increasing ΔWR, τV̇O2p became larger at the higher ΔWRs (p < 0.05), while τBF did not change significantly, and the mean response time (MRT) of deoxy[Hb+Mb] became smaller. These findings that V̇O2p kinetics become slower with increasing ΔWR, while BF kinetics are not influenced by ΔWR, suggest that O2 delivery could not limit V̇O2p in this situation. However, the speeding of deoxy[Hb+Mb] kinetics with increasing ΔWR does imply that the O2 delivery-to-O2 utilization of the microvasculature decreases at higher ΔWRs. This suggests that the contribution of O2 delivery and O2 extraction to V̇O2 in the muscle change with increasing ΔWR.

Exercise systolic blood pressure indexed to work rate predicts future risk of incident stroke

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): 1) The CircM network, Linköping University 2) The Swedish Stroke Association. Background Hypertension is a major risk factor for stroke. Exaggerated peak systolic blood pressure (SBP) during exercise is associated with increased risk of hypertension in normotensive subjects, whereas low, rather than high, peak exercise SBP predicts cardiovascular and all-cause mortality. Purpose We aimed to study the risk of incident fatal and non-fatal stroke in relation to absolute and work rate indexed exercise SBP, in patients referred for exercise testing. Methods We cross-linked clinical data from 14,428 bicycle ergometer exercise tests with data from the National Patient Registry and the Registry of Prescribed Medications up until December 2019. Subjects with a history of cerebrovascular disease were excluded, as well as subjects with submaximal tests, a drop in SBP during exercise, or with missing SBP data at the end of exercise. Baseline comorbidity was defined as diagnosis of, or treatment for, hypertension, diabetes, hyperlipidemia, and coronary artery disease (CAD). Work rate indexed SBP response (SBP/Watt-slope) was calculated as the increase in SBP during exercise divided by the increase in work rate. We applied Cox regression to calculate hazard ratios (HR) with 95% confidence intervals (95% CI) for the risk of incident stroke in association to peak SBP and the SBP/Watt-slope. We used absolute values as well the upper limit of normal (≥2 Z scores) of a recently published reference population, with reference equation including age, sex, SBP at rest, Wmax (for SBP peak only) and height (for SBP/W-slope only). Analyses were adjusted for age, sex, and baseline comorbidity. Results In total, 7,946 subjects (54% male, age 55±13 years) were included, with baseline comorbidity of hypertension (28%), diabetes (7%), hyperlipidemia (16%), and CAD (13%). During a median follow-up of 8.4 years (inter quartile range 5.8-11.5), 3.1% developed ischemic (2.2%) or hemorrhagic (1.0%) stroke. There were positive associations to future stroke with absolute peak exercise SBP (HR: 1.08 [1.03 – 1.13] per 10 mmHg increase) and with SBP/Watt-slope (HR: 1.09 [1.05 – 1.14] per 1 mmHg/10 Watt increase), but not after adjustment for sex, age and baseline comorbidity. However, having a SBP/Watt-slope ≥2 Z scores was associated with an increased risk for stroke (HR: 1.56 [1.08 – 2.25)] after adjustment for baseline comorbidity, whereas an adjusted SBP peak ≥2 Z scores was not (HR: 0.62 [0.32 – 1.21]). Conclusion A workload-indexed SBP response (SBP/Watt-slope) above the upper limit of normal may help to identify subjects with no history of cerebrovascular disease at risk of future stroke. In contrast, the absolute exercise SBP response to exercise does not add substantial information to the risk estimation above age, sex, and baseline comorbidity.

Does saddle height influence knee frontal-plane biomechanics during stationary cycling?

IntroductionCycling is a common modality for rehabilitation and exercise. However, there is a lack of information in the literature on the effects of saddle height adjustments on internal peak knee abduction moment, which is an important loading variable for the medial compartment of tibiofemoral joint for patients with knee osteoarthritis. The purpose of this study was to examine effects of saddle height on frontal-plane biomechanics of the knee during cycling. MethodsFourteen recreational cyclists (age: 57.1 ± 6.37 years) performed 2-min bouts of cycling at three saddle heights of 40°, 30° and 20° knee extension angle at bottom crank position, at two workrates of 80 and 120 W. Three-dimensional kinematic, kinetic, and electromyography data were collected and analyzed using a 3 × 2 (height × workrate) analysis of variance (ANOVA). ResultsThere were no changes in internal knee abduction moment across saddle heights. Increases in saddle height from 40° to both 30° and 20° reduced the knee extension moment (d = 0.3 and 0.4, respectively, P = 0.012). Increases in workrate increased both knee abduction and extension moments (η2p = 0.75 and 0.88, respectively, P < 0.001 for both). ConclusionsIncreased knee extension moment with decreased saddle height is likely to indicate increased knee joint load.

Cerebral Oxygenation Dynamics During Incremental Exercise: Comparison of Arm Cranking and Leg Cycling.

This study aimed to compare cerebral oxyhemoglobin (O2Hb) levels during incremental exercise by cycling vs. arm cranking in 12 healthy adult men aged 20.8±0.2years old. O2Hb was measured by near-infrared spectroscopy. Regions of interest included the left and right prefrontal cortices (LtPFC and RtPFC, respectively), the left and right premotor cortices (LtPMC and RtPMC, respectively), and the supplementary motor area (SMA) bilaterally. After 4 min of rest, 4 min of warm-up was performed by using ergometer followed by incremental exercise (increasing work rate by 5W/min for arm cranking and 20W/min for cycling exercise). All values were averaged every tenth of the participant's exercise time period from beginning of incremental exercise to end point. At the middle exercise intensity (50% exercise time), the averaged O2Hb values obtained at all regions of interest seemed to be higher during arm cranking exercise as compared to cycling; however, there were no significant differences between two types of exercise. At the end point of incremental exercise (100% exercise time), the O2Hb obtained at all regions of interest was significantly higher during arm cranking exercise compared to cycling (LtPFC 0.081±0.019 vs. -0.001±0.013mM·cm, RtPFC 0.076±0.021 vs. 0.018±0.015mM·cm, SMA 0.012±0.040 vs. 0.040±0.016mM·cm; arm cranking vs. cycling; p<0.05, respectively). We conclude that exercise-induced cerebral oxygenation is greater with arm cranking than with leg cycling.

The anaerobic threshold: 50+ years of controversy.

The anaerobic threshold (AT) remains a widely recognized, and contentious, concept in exercise physiology and medicine. As conceived by Karlman Wasserman, the AT coalesced the increase of blood lactate concentration ([La- ]), during a progressive exercise test, with an excess pulmonary carbon dioxide output ( ). Its principal tenets were: limiting oxygen (O2 ) delivery to exercising muscle→increased glycolysis, La- and H+ production→decreased muscle and blood pH→with increased H+ buffered by blood [HCO3- ]→increased CO2 release from blood→increased and pulmonary ventilation. This schema stimulated scientific scrutiny which challenged the fundamental premise that muscle anoxia was requisite for increased muscle and blood [La- ]. It is now recognized that insufficient O2 is not the primary basis for lactataemia. Increased production and utilization of La- represent the response to increased glycolytic flux elicited by increasing work rate, and determine the oxygen uptake ( ) at which La- accumulates in the arterial blood (the lactate threshold; LT). However, the threshold for a sustained non-oxidative contribution to exercise energetics is the critical power, which occurs at a metabolic rate often far above the LT and separates heavy from very heavy/severe-intensity exercise. Lactate is now appreciated as a crucial energy source, major gluconeogenic precursor and signalling molecule but there is no ipso facto evidence for muscle dysoxia or anoxia. Non-invasive estimation of LT using the gas exchange threshold (non-linear increase of versus ) remains important in exercise training and in the clinic, but its conceptual basis should now be understood in light of lactate shuttle biology.

Near-infrared spectroscopy measures of sternocleidomastoid blood flow during exercise and hyperpnoea.

What is the central question of this study? How does sternocleidomastoid blood flow change in response to increasing ventilation and whole-body exercise intensity? What is the main finding and its importance? Sternocleidomastoid blood flow increased with increasing ventilation. For a given ventilation, sternocleidomastoid blood flow was lower during whole-body exercise compared to resting hyperpnoea. These findings suggest that locomotor muscle work exerts an effect on respiratory muscle blood flow that can be observed in the sternocleidomastoid. Respiratory muscle work influences the distribution of blood flow during exercise. Most studies have focused on blood flow to the locomotor musculature rather than the respiratory muscles, owing to the complex anatomical arrangement of respiratory muscles. The purpose of this study was to examine how accessory respiratory (i.e. sternocleidomastoid, and muscles in the intercostal space) muscle blood flow changes in response to locomotor muscle work. Seven men performed 5min bouts of constant load cycling exercise trials at 30%, 60% and 90% of peak work rate in a randomized order, followed by 5min bouts of voluntary hyperpnoea (VH) matching the ventilation achieved during each exercise (EX) trial. Blood-flow index (BFI) of the vastus lateralis, sternocleidomastoid (SCM) and seventh intercostal space (IC) were estimated using near-infrared spectroscopy and indocyanine green and expressed relative to resting levels. BFISCM was greater during VH compared to EX (P=0.002) and increased with increasing exercise intensity (P=0.036). BFISCM reached 493±219% and 301±215% rest during VH and EX at 90% peak work rate, respectively. BFIIC increased to 242±178% and 210±117% rest at 30% peak work rate during VH and EX, respectively. No statistically significant differences in BFIIC were observed with increased work rate during VH or EX (both P>0.05). Moreover, there was no observed difference in BFIIC between conditions (P>0.05). BFISCM was lower for a given minute ventilation during EX compared to VH, suggesting that accessory respiratory muscle blood flow is influenced by whole-body exercise.

Knee joint biomechanics of patients with unilateral total knee arthroplasty during stationary cycling

Stationary cycling is typically recommended following total knee arthroplasty (TKA) operations. However, knee joint biomechanics during cycling remains mostly unknown for TKA patients. Biomechanical differences between the replaced and non-replaced limb may inform applications of cycling in TKA rehabilitation. The purpose of this study was to examine the knee joint biomechanics of TKA patients during stationary cycling. Fifteen TKA participants cycled at 80 revolutions per minute and workrates of 80 W and 100 W while kinematics (240 Hz) and pedal reaction forces using a pair of instrumented pedals (1200 Hz) were collected. A 2x2 (limb × workrate) repeated measures ANOVA was run with an alpha of 0.05. Peak knee extension moment (KEM, p = 0.034) and vertical pedal reaction force (p = 0.038) were significantly reduced in the replaced limbs compared to non-replaced limbs by 21.3% and 5.3%, respectively. Peak KEM did not change for TKA patients with the increased workrate (p = 0.750). However, both peak hip extension moment (p = 0.009) and ankle plantarflexion moment (p = 0.017) increased due to increased workrate. Patients following TKA showed similar decreases in peak KEM and vertical pedal reaction force in their replaced compared to non-replaced limbs, as previously seen in gait. Patients of TKA may rely on their hip and ankle extensors to increases in workrate. Increasing intensity by 20 W did not exacerbate any inter-limb differences for peak KEM and vertical PRF.

Differences in joint power distribution in high and low lactate threshold cyclists.

The biomechanical differences between cyclists with a high compared with a low blood lactate threshold (HLT; 80% VO2max vs LLT, 70% VO2max) have yet to be completely described. We hypothesize that HLT cyclists reduce the stress placed on the knee extensor muscles by increasing the relative contribution from the hip joint during high-intensity cycling. Sixteen well-trained endurance athletes, with equally high VO2max while cycling and running completed submaximal tests during incremental exercise to identify lactate threshold ([Formula: see text]) while running and cycling. Subjects were separated into two groups based on % VO2max at LT during cycling (high; HLT: 80.2 ± 2.1% VO2max; n = 8) and (LLT: 70.3 ± 2.9% VO2max; n = 8; p < 0.01). Absolute and relative joint specific powers were calculated from kinematic and pedal forces using inverse dynamics while cycling at intensities ranging from 60-90% VO2max for between group comparisons. There was no difference between HLT and LLT in [Formula: see text] (p > 0.05) while running. While cycling in LLT, knee joint absolute power increased with work rate (p < 0.05); however, in HLT no changes in knee joint absolute power occurred with increased work rate (p > 0.05). The HLT generated significantly greater relative hip power compared with the LLT group at 90% VO2max (p < 0.05). These data suggest that HLT cyclists exhibit a greater relative hip contribution to power output during cycling at 90% VO2max. These observations support the theory that lactate production during cycling can be reduced by spreading the work rate between various muscle groups.

Sweat Electrolytes: Influence Of Environment, Sex And Exercise Intensity

Sweat rate and electrolyte loss are highly variable among individuals; but sources of intra-individual variability due to test conditions remain to be quantified. PURPOSE: To determine the impact of exercise intensity and environment on sweat electrolyte losses in men and women. METHODS: Twenty adult women and men completed two sessions during summer months: 3 x 20 min intermittent cycling beginning at low intensity (50/75 Watts) with 25 W increases in work rate under hot-humid (35oC, 60%RH) or hot-dry (35oC, 20%RH) conditions. Whole body sweat rate, regional sweat [Na+] and [K+] were obtained at each work rate. Sweat was acquired via Opsite (Brisson method) on the scapula. Electrolytes were measured using Horiba LAQUAtwin Ion meters. RESULTS: Sweat rate and [Na+] was significantly higher (p<0.001) due to increased RH in the heat and incremental changes in exercise intensity. Compared to low exercise intensity, sweat [Na+] increased by 26 (72%) and 39 mmol (108%) with successive 25W increases, similar in relative magnitude to sweat rate increases of 0.4 l/min (67%) and 0.6 l/min (100%) compared to low exercise intensity. However, [Na+] difference due to greater %RH of environment (60% vs. 20%RH) was only 7.7 mmol (14%) higher for all bouts combined. Sweat [K+] was not different (p=0.4) based on environment, but significantly higher (p=0.003) under low intensity exercise compared to higher work rates (6.9±1.9 > 6.0±1.4 mmol). When work rate was matched (75W) under humid conditions, no differences between men and women were observed in sweat rate (0.8 ± 0.3 l/min) or sweat sodium (49.2 ± 17.2 vs. 52.7 ± 30.0 mmol, respectively). CONCLUSION: At matched low intensity exercise, sex differences in sweat sodium and rate were not observed. Intra-individual variability in sweat sodium is influenced more by modest incremental changes (25 W) in exercise intensity than the ambient humidity in hot conditions. Sweat testing of athletes using field techniques should carefully consider the intensity of the training session to accurately translate results. Supported by a grant from The Coca-Cola Company

Aerobic Exercise Training And Ventilation-cardiac Output Ratio In Interstitial Lung Disease And Pulmonary Hypertension

Aerobic exercise training has been shown to elicit physiological changes in cardiorespiratory capacity in people with advanced lung disease such as pulmonary hypertension (PH) and interstitial lung disease (ILD), despite impaired pulmonary ventilation (VE) and perfusion. PURPOSE: To examine whether aerobic exercise training alters the VE/Qt ratio in subjects with PH or ILD. METHODS: Twelve people with ILD (5 men and 8 women; age 56.83 ± 8.26 years; BMI 28.83± 5.01) and 17 females with PH (age 55± 8.88 years; BMI 29.97± 7.89 kg/m2) participated in the study. All subjects were enrolled in the National Institutes of Health Exercise Therapy for Advanced Lung Disease Trial [ClinicalTrials.gov identifier NCT00678821]. All subjects underwent cardiopulmonary exercise testing (CPET) with bioelectrical impedance measure of cardiac output (Qt) before and after 10 weeks of supervised vigorous treadmill walking, 30-45 minutes per session, 3 times per week (24-30 sessions). RESULTS: VE, Qt, and VE/Qt increased with CPET work stage before and after training. There was a significant increase in peak work rate after training in both groups (PH before 106±48.36 watts, after 133±64.12 watts p=0.002; ILD before 135±57.04 watts, after 180±77.35 watts p=0.001). There were no significant differences in peak VE, peak Qt, and peak VE/Qt before and after training in either group. Similarly, significant differences were not observed at rest or at the anaerobic threshold.CONCLUSION: Aerobic exercise training does not appear to have an effect on the ventilation-cardiac output ratio in these subjects with PH or ILD.

Time Control Model for Increasing Work Rate to High-Pressure Tube

The work of the fuel engine is based on the fuel entering and expelling high-pressure tubing. The intermittent work of the fuel entering and expelling will lead to the change of pressure in the high-pressure tubing. This paper established the time control model to carry out the research. For the first question, we made the fuel entry period and injection period equal to 100ms. Because of , the volume of the high-pressure tubing remained constant, and the fuel mass into the high-pressure tubing was equal to the fuel mass ejected from the high-pressure tubing. The density time control model was established under the condition of mass conservation, and the opening time of each time was obtained to be 0.275ms. For the second question, we set the pressure increase after each fuel entry in the adjustment process to be equal. Due to , we obtained the new density value of the high-pressure tubing, and substituted the density and time model to obtain the opening time of each one-way valve.

A Rapidly Incremented Tethered-Swimming Maximal Protocol for Cardiorespiratory Assessment of Swimmers.

Incremental exercise testing is the standard means of assessing cardiorespiratory capacity of endurance athletes. While the maximal rate of oxygen consumption is typically used as the criterion measurement in this regard, two metabolic breakpoints that reflect changes in the dynamics of lactate production/consumption as the work rate is increased are perhaps more relevant for endurance athletes from a functional standpoint. Exercise economy, which represents the rate of oxygen consumption relative to performance of submaximal work, is also an important parameter to measure for endurance-athlete assessment. Ramp incremental tests comprising a gradual but rapid increase in work rate until the limit of exercise tolerance is reached are useful for determining these parameters. This type of test is typically performed on a cycle ergometer or treadmill because there is a need for precision with respect to work-rate incrementation. However, athletes should be tested while performing the mode of exercise required for their sport. Consequently, swimmers are typically assessed during free-swimming incremental tests where such precision is difficult to achieve. We have recently suggested that stationary swimming against a load that is progressively increased (incremental tethered swimming) can serve as a "swim ergometer" by allowing sufficient precision to accommodate a gradual but rapid loading pattern that reveals the aforementioned metabolic breakpoints and exercise economy. However, the degree to which the peak rate of oxygen consumption achieved during such a protocol approximates the maximal rate that is measured during free swimming remains to be determined. In the present article, we explain how this rapidly incremented tethered-swimming protocol can be employed to assess the cardiorespiratory capacity of a swimmer. Specifically, we explain how assessment of a short-distance competitive swimmer using this protocol revealed that his rate of oxygen uptake was 30.3 and 34.8 mL∙min-1∙kg-1BM at his gas-exchange threshold and respiratory compensation point, respectively.

Isometric Exercise with Large Muscle Mass Improves Redox Balance and Blood Pressure in Hypertensive Adults.

The aim of this study was to investigate the hemodynamic, oxidative stress (OS), and nitric oxide (NO) responses to a submaximal isometric exercise session (IES) involving large muscle mass. Fourteen hypertensive (HTG: age = 35.9 ± 8.1 yr, height = 1.73 ± 0.10 m, total body mass = 78.0 ± 15.8 kg) and 10 normotensive (NTG: age = 41.1 ± 9.4 yr, height = 1.71 ± 0.12 m, total body mass = 82.3 ± 22.4 kg) participants performed two experimental sessions in the leg press and bench press: (i) control session and (ii) 8 sets × 1 min contraction at 30% maximal voluntary isometric contraction with 2-min rest interval. Blood pressure (BP) was measured at rest and during 60 min postexercise. Blood samples were collected at rest, immediately after the session, and 60 min postexercise. NO was obtained through the Griess reaction method. OS parameters were analyzed using commercial kits. A repeated-measures ANOVA with Bonferroni post hoc test was used to analyze all dependent variables. A significant decrease in systolic BP was observed only for HTG at 45 and 60 min postexercise (baseline vs 45 min: P = 0.03, Δ% = 4.44%; vs 60 min: P = 0.018, Δ% = 5.58%). NO increased immediately postexercise only for HTG (P = 0.008, Δ% = 16.44%). Regarding OS parameters, thiobarbituric acid reactive substances presented a significant reduction 60 min after the IES for NTG and HTG; catalase increased in both groups. The data showed that only 8 min of IES with a large muscle mass elicits an elevated pro-oxidant activity leading to a greater NO bioavailability, increases antioxidant reaction, and consequently reduces BP in hypertensive patients.

Mechanisms of improved exercise capacity following respiratory muscle training in athletes with cervical spinal cord injury.

Mechanisms of improved exercise capacity following respiratory muscle training in athletes with cervical spinal cord injury.

Diffuse correlation spectroscopy and frequency-domain near-infrared spectroscopy for measuring microvascular blood flow in dynamically exercising human muscles

In the last 20 yr, near-infrared diffuse correlation spectroscopy (DCS) has been developed for providing a noninvasive estimate of microvascular blood flow (BF) as a BF index (BFi) in the human skin, muscle, breast, brain, and other tissue types. In this study, we proposed a new motion correction algorithm for DCS-derived BFi able to remove motion artifacts during cycling exercise. We tested this algorithm on DCS data collected during cycling exercise and demonstrated that DCS can be used to quantify muscle BFi during dynamic high-intensity exercise. In addition, we measured tissue regional oxygen metabolic rate (MRO2i) by combining frequency-domain multidistance near-infrared spectroscopy (FDNIRS) oximetry with DCS flow measures. Recreationally active subjects (n = 12; 31 ± 8 yr, 183 ± 4 cm, 79 ± 10 kg) pedaled at 80-100 revolutions/min until volitional fatigue with a work rate increase of 30 W every 4 min. Exercise intensity was normalized in each subject to the cycling power peak (Wpeak). Both rectus femoris BFi and MRO2i increased from 15% up to 75% Wpeak and then plateaued to the end of the exercise. During the recovery at 30 W cycling power, BFi remained almost constant, whereas MRO2i started to decrease. The BFi/MRO2i plateau was associated with the rising of the lactate concentration, indicating the progressive involvement of the anaerobic metabolism. These findings further highlight the utility of DCS and FDNIRS oximetry as effective, reproducible, and noninvasive techniques to assess muscle BFi and MRO2i in real time during a dynamic exercise such as cycling.NEW & NOTEWORTHY To the best of our knowledge, this study is the first to demonstrate that diffuse correlation spectroscopy in combination with frequency-domain near-infrared spectroscopy can monitor human quadriceps microvascular blood flow and oxygen metabolism with high temporal resolution during a cycling exercise. The optically measured parameters confirm the expected relationship between blood flow, muscle oxidative metabolism, and lactate production during exercise.