Biomechanical, physiological and anthropometrical predictors of performance in recreational runners.

Background: The maximal running speed (VMAX) determined on a graded treadmill test is well-recognized as a running performance predictor. However, few studies have assessed the variables that predict VMAX in recreationally active runners. Methods: We used a mathematical procedure combining Fick's law and metabolic cost analysis to verify the relation between (1) VMAX versus anthropometric and physiological determinants of running performance and, (2) theoretical metabolic cost versus running biomechanical parameters. Linear multiple regression and bivariate correlation were applied. We aimed to verify the biomechanical, physiological, and anthropometrical determinants of VMAX in recreationally active runners. Fifteen recreationally active runners participated in this observational study. A Conconi and a stead-steady running test were applied using a heart rate monitor and a simple video camera to register the physiological and mechanical variables, respectively. Results: Statistical analysis revealed that the speed at the second ventilatory threshold, theoretical metabolic cost, and fat-mass percentage confidently estimated the individual running performance as follows: VMAX = 58.632 + (-0.183 * fat percentage) + (-0.507 * heart rate percentage at second ventilatory threshold) + (7.959 * theoretical metabolic cost) (R2 = 0.62, p = 0.011, RMSE = 1.50 km.h-1). Likewise, the theoretical metabolic cost was significantly explained (R2 = 0.91, p = 0.004, RMSE = 0.013 a.u.) by the running spatiotemporal and elastic-related parameters (contact and aerial times, stride length and frequency, and vertical oscillation) as follows: theoretical metabolic cost = 10.421 + (4.282 * contact time) + (-3.795 * aerial time) + (-2.422 * stride length) + (-1.711 * stride frequency) + (0.107 * vertical oscillation). Conclusion: Critical determinants of elastic mechanism, such as maximal vertical force and vertical and leg stiffness were unrelated to the metabolic economy. VMAX, a valuable marker of running performance, and its physiological and biomechanical determinants can be effectively evaluated using a heart rate monitor, treadmill, and a digital camera, which can be used in the design of training programs to recreationally active runners.

Effects of acute and multi-day low-dose sodium bicarbonate intake on high-intensity endurance exercise performance in male recreational cyclists.

PURPOSE: This study aimed to compare the effects of acute and multi-day low-dose sodium bicarbonate (SB) intake on high-intensity endurance exercise performance. METHODS: In a randomized, double-blind, cross-over design, twelve recreational male cyclists (age: 31.17 ± 4.91 years; V ˙ O2peak: 47.98 ± 7.68 ml·kg-1·min-1) completed three endurance performance tests following acute SB (ASB, 0.2 g·kg-1 SB), multi-day SB (MSB, 0.2 g·kg-1·day-1 SB for four days), and placebo (PLA) intake. The high-intensity endurance performance was assessed with a cycling exercise test, wherein participants cycled on a bicycle ergometer at 95% of the predetermined anaerobic threshold for 30 min, followed by a time-to-exhaustion test at 110% of the anaerobic threshold. Data were analyzed using one-way and two-way repeated-measures ANOVA. RESULTS: Significant main effects of supplementation protocol were evident in pre-exercise bicarbonate concentrations (F = 27.93; p < 0.01; partial eta squared (η2) = 0.72; false discovery rate (FDR)-adjusted p value = 0.001). Prior to performance test, blood bicarbonate concentrations were significantly higher in MSB (25.78 ± 1.63 mmol·L-1 [95% CI 26.55-28.44] (p < 0.001; FDR-adjusted p value = 0.001)) and ASB (27.49 ± 1.49 mmol·L-1 [95% CI 24.75-26.81] (p < 0.001; FDR-adjusted p value = 0.007)) compared to PLA (23.75 ± 1.40 mmol·L-1 [95% CI 22.86 to 24.64]). Time-to-exhaustion increased in MSB (54.27 ± 9.20 min [95% CI 48.43-60.12]) compared to PLA (49.75 ± 10.80 min [95% CI 42.89-56.62]) (p = 0.048); however, this increase in MSB did not reach the significance threshold of 1% FDR (FDR-adjusted p value = 0.040). No significant difference was noted in exhaustion times between ASB (51.15 ± 8.39 min [95% CI 45.82-56.48]) and PLA (p > 0.05). CONCLUSION: Both acute and multi-day administration of low-dose SB improves buffering system in cyclists; nevertheless, neither intervention demonstrates sufficient efficacy in enhancing high-intensity endurance performance.

Cardiac Acoustic Biomarkers in Patients with Heart Failure during Cardiopulmonary Exercise Testing: An Exploratory Study.

Objective Exercise therapy as part of cardiac rehabilitation is one of the most effective treatments for patients with chronic heart failure (HF). The anaerobic threshold (AT) determined by an exhaled gas analysis during cardiopulmonary exercise testing (CPX) is used to prescribe the appropriate level of exercise therapy. However, CPX using an exhaled gas analysis is not widely performed because of its cost, complexity, and the need for skilled staff. Therefore, a simpler and inexpensive method for determining AT without respiratory gas measurements is required in patients with HF. The present study elucidated the relationship between the AT determined by the CPX ventilatory method (CPX-AT) and the AT determined by cardiac acoustic biomarkers (CABs), which are measured by acoustic cardiography (CAB-AT), in HF patients. Methods Patients underwent symptom-limited ramp CPX twice using a cycle ergometer. The ATs determined from the exhaled gas analysis were identified by three independent physicians. CABs, including S1 and S2 intensities (peak-to-peak amplitudes), electromechanical activation time (EMAT) defined as the time interval from the Q wave onset on electrocardiography to the first heart sound (S1), heart rate (HR), and other parameters, were collected during CPX. Patients Forty patients with HF were included in this study. Results A significant correlation (R=0.70; p<0.001) was found between CPX-AT and CAB-AT, using the double product of S1 intensity and heart rate. CAB-AT using S1 intensity also showed a significant correlation with CPX-AT (R=0.71; p<0.001). Conclusion The present study suggests a possible new method for determining AT without respiratory gas measurements in patients with HF.

Revisiting the clinical utilization of cardiopulmonary exercise testing in Saudi Arabia after 2 decades: A cross-sectional study.

OBJECTIVES: To assess the prevalence of cardiopulmonary exercise testing (CPET) usage and identify barriers among major hospitals and medical centers in Saudi Arabia. We also aim to compare these findings with data from nearly 2 decades ago. METHODS: In this cross-sectional study, 70 major hospitals and medical centers were contacted, and 52 (74.2%) responded. The participants involved in this study were healthcare providers proficient in carrying out CPET from different specialties. The survey comprised 21 items covering CPET utilization, exercise mode characteristics, common protocols, types of patients or disorders, and barriers to not carrying out CPET. RESULTS: The majority (n=37; 71.9%) of the centers reported a lack of CPET utilization. Of the 15 centers that used CPET, only 11 carried out regular CPET. Cardiac-related conditions were the most commonly referred clinical cases (n=7), followed by pulmonary conditions and cardiopulmonary fitness. The common barriers to carrying out CPET have remained unchanged compared to 2 decades ago - that is, the lack of equipment or trained technicians. However, there has been a 14.1% increase in the utilization of CPET and a 10.1% increase in the use of treadmill mode compared to a survey carried out 2 decades ago. CONCLUSION: Although CPET utilization has increased over 2 decades, this still falls below the desired benchmark. This highlights the need for collaborative efforts among policymakers, and healthcare institutions to address barriers and improve CPET integration into clinical practice.

Effect of Acute Altitude Exposure on Anaerobic Threshold Assessed by a Novel Electrocardiogram-Based Method.

Background: Acute altitude has a relevant impact on exercise physiology and performance. Therefore, the positive impact on the performance level is utilized as a training strategy in professional as well as recreational athletes. However, ventilatory thresholds (VTs) and lactate thresholds (LTs), as established performance measures, cannot be easily assessed at high altitudes. Therefore, a noninvasive, reliable, and cost-effective method is needed to facilitate and monitor training management at high altitudes. High Alt Med Biol. 25:94-99, 2024. Methods: In a cross-sectional setting, a total of 14 healthy recreational athletes performed a graded cycling exercise test at sea level (Munich, Germany: 512 m/949 mbar) and high altitude (Zugspitze: 2,650 m/715 mbar). Anaerobic thresholds (ATs) were assessed using a novel method based on beat-to-beat repolarization instability (dT) detected by Frank-lead electrocardiogram (ECG) monitoring. The ECG-based ATs (ATdT°) were compared to routine LTs assessed according to Dickhuth and Mader. Results: After acute altitude exposure, a decrease in AT was detected using a novel ECG-based method (ATdT°: 159.80 ± 52.21 W vs. 134.66 ± 34.91 W). AtdT° levels correlated significantly with LTDickhuth and LTMader, at baseline (rDickhuth/AtdT° = 0.979; p < 0.001) (rMader/AtdT° = 0.943; p < 0.001), and at high altitude (rDickhuth/AtdT° = 0.969; p < 0.001) (rMader/AtdT° = 0.942; p < 0.001). Conclusion: Assessment of ATdT is a reliable method to detect performance alterations at altitude. This novel method may facilitate the training management of athletes at high altitudes.

Development of deep-learning models for real-time anaerobic threshold and peak VO2 prediction during cardiopulmonary exercise testing.

AIMS: Exercise intolerance is a clinical feature of patients with heart failure (HF). Cardiopulmonary exercise testing (CPET) is the first-line examination for assessing exercise capacity in patients with HF. However, the need for extensive experience in assessing anaerobic threshold (AT) and the potential risk associated with the excessive exercise load when measuring peak oxygen uptake (peak VO2) limit the utility of CPET. This study aimed to use deep-learning approaches to identify AT in real time during testing (defined as real-time AT) and to predict peak VO2 at real-time AT. METHODS AND RESULTS: This study included the time-series data of CPET recorded at the Department of Cardiovascular Medicine, Kyushu University Hospital. Two deep neural network models were developed to: (i) estimate the AT probability using breath-by-breath data and (ii) predict peak VO2 using the data at the real-time AT. The eligible CPET contained 1472 records of 1053 participants aged 18-90 years and 20% were used for model evaluation. The developed model identified real-time AT with 0.82 for correlation coefficient (Corr) and 1.20 mL/kg/min for mean absolute error (MAE), and the corresponding AT time with 0.86 for Corr and 0.66 min for MAE. The peak VO2 prediction model achieved 0.87 for Corr and 2.25 mL/kg/min for MAE. CONCLUSION: Deep-learning models for real-time CPET analysis can accurately identify AT and predict peak VO2. The developed models can be a competent assistant system to assess a patient's condition in real time, expanding CPET utility.

Cardiopulmonary exercise testing can be used to evaluate the condition of patients with heart failure during exercise. Developed deep-learning models can accurately predict a patient's anaerobic threshold in real time and peak oxygen uptake. The models can be used by clinicians for more objective and accurate assessments in real time, expanding the utility of cardiopulmonary exercise testing.

Reproducibility (reliability and agreement) of ventilatory threshold and peak responses during cardiopulmonary exercise test in people with stroke.

BACKGROUND: A cardiopulmonary exercise test (CPET) is used to determine the ventilatory thresholds and to directly assess cardiorespiratory capacity. However, its reproducibility should be tested in people with stroke as sequelae imposed by the stroke may induce important variations among and within each subject, affecting the reproducibility of the physiological responses to CPET. PURPOSE: This cross-sectional repeated measures study design aims to determine the reproducibility of anaerobic threshold (AT), respiratory compensation point (RCP), and maximal cardiorespiratory capacity assessed during a CPET in people with stroke. METHODS: Twenty-eight subjects with hemiparesis after stroke aging 60 ± 13 years were submitted to two treadmill CPETs with identical protocols. DATA ANALYSIS: The reproducibility of heart rate (HR) and oxygen consumption (VO2) obtained at AT, RCP, and peak effort was evaluated by systematic error (paired t-test); reliability (ICC and 95% confidence interval); and agreement (typical error and coefficient of variation). RESULTS: There were no systematic errors for HR and VO2assessed at AT, RCP, and peak effort (p > 0,05). Reliability was high for these variables during CPET (ICCs > 0.93). Agreement was good for all variables. Typical errors for HR and VO2 assessed at AT, RCP, and peak effort were, respectively, 7, 7, and 8 bpm, and 1.51, 1.44, and 1.57 ml.kg-1.min-1. Coefficients of variation assessed at AT, RCP, and peak effort were, respectively, 5.7, 5.1, and 6.0% for HR and 8.7, 7.3, and 7.5% for VO2. CONCLUSIONS: HR and VO2 measured at AT, RCP, and peak effort during a treadmill CPET present good reproducibility in people with stroke, showing high reliability and good agreement.

A retrospective analysis of the association of effort-independent cardiopulmonary exercise test variables with postoperative complications in patients who underwent elective colorectal surgery.

PURPOSE: This study aimed to investigate the association of effort-independent variables derived from the preoperative cardiopulmonary exercise test (CPET) with 30-day postoperative complications after elective colorectal surgery. METHODS: A multicenter (n=4) retrospective explorative study was performed using data of patients who completed a preoperative CPET and underwent elective colorectal surgery. The preoperative slope of the relation between minute ventilation and carbon dioxide production (VE/VCO2-slope) and the oxygen uptake efficiency slope (OUES), as well as 30-day postoperative complications, were assessed. Multivariable logistic regression analyses and receiver operating characteristic (ROC) curves were used to investigate the prognostic value of the relationship between these preoperative CPET-derived effort-independent variables and postoperative complications. RESULTS: Data from 102 patients (60.1% males) with a median age of 72.0 (interquartile range 67.8-77.4) years were analyzed. Forty-four patients (43.1%) had one or more postoperative complications (of which 52.3% general and 77.3% surgical complications). Merely 10 (9.8%) patients had a general complication only. In multivariate analysis adjusted for surgical approach (open versus minimally invasive surgery), the VE/VCO2-slope (odds ratio (OR) 1.08, confidence interval (CI) 1.02-1.16) and OUES (OR 0.94, CI 0.89-1.00) were statistically significant associated with the occurrence of 30-day postoperative complications. CONCLUSION: The effort-independent VE/VCO2-slope and OUES might be used to assist in future preoperative risk assessment and could especially be of added value in patients who are unable or unwilling to deliver a maximal cardiorespiratory effort. Future research should reveal the predictive value of these variables individually and/or in combination with other prognostic (CPET-derived) variables for postoperative complications. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov NCT05331196.

The Interpretation of Standard Cardiopulmonary Exercise Test Indices of Cardiac Function in Chronic Kidney Disease.

BACKGROUND AND AIMS: As there is growing interest in the application of cardiopulmonary exercise test (CPX) in chronic kidney disease (CKD), it is important to understand the utility of conventional exercise test parameters in quantifying the cardiopulmonary fitness of patients with CKD. Merely extrapolating information from heart failure (HF) patients would not suffice. In the present study, we evaluated the utility of CPX parameters such as the peak O2-pulse and the estimated stroke volume (SV) in assessing the peak SV by comparing with the actual measured values. Furthermore, we compared the anaerobic threshold (AT), peak circulatory power, and ventilatory power with that of the measured values of the peak cardiac power (CPOpeak) in representing the cardiac functional reserve in CKD. We also performed such analyses in patients with HF for comparison. METHOD: A cross sectional study of 70 asymptomatic male CKD patients [CKD stages 2-5 (pre-dialysis)] without primary cardiac disease or diabetes mellitus and 25 HF patients. A specialized CPX with a CO2 rebreathing technique was utilized to measure the peak cardiac output and peak cardiac power output. The peak O2 consumption (VO2peak) and AT were also measured during the test. Parameters such as the O2-pulse, stroke volume, arteriovenous difference in O2 concentration [C(a-v)O2], peak circulatory power, and peak ventilatory power were all calculated. Pearson's correlation, univariate, and multivariate analyses were applied. RESULTS: Whereas there was a strong correlation between the peak O2-pulse and measured peak SV in HF, the correlation was less robust in CKD. Similarly, the correlation between the estimated SV and the measured SV was less robust in CKD compared to HF. The AT only showed a modest correlation with the CPOpeak in HF and only a weak correlation in CKD. A stronger correlation was demonstrated between the peak circulatory power and CPOpeak, and the ventilatory power and CPOpeak. In HF, the central cardiac factor was the predominant determinant of the standard CPX-derived surrogate indices of cardiac performance. By contrast, in CKD both central and peripheral factors played an equally important role, making such indices less reliable markers of cardiac performance per se in CKD. CONCLUSION: The results highlight that the standard CPX-derived surrogate markers of cardiac performance may be less reliable in CKD, and that further prospective studies comparing such surrogate markers with directly measured cardiac hemodynamics are required before adopting such markers into clinical practice or research in CKD.

Physical workload and cardiopulmonary parameters in relation to individual capacity of bulk waste workers - a cross-sectional field-study.

PURPOSE: Waste collection is considered particularly heavy work, although no previous study has yet investigated the strain of bulk waste collection. The aim of this study is to determine the workload of bulk waste workers in practice. METHOD: We conducted a cross-sectional field-study. Fourteen male volunteers from the bulk waste collection of the municipal sanitation department in Hamburg, Germany, were included. Performance was determined by cardiopulmonary exercise testing under laboratory conditions. During the shift, each worker was accompanied by a researcher, and heart rate (HR) was recorded under field conditions using an HR watch with a belt system. We examined mean HR, relative heart rate (RHR), relative aerobic strain (RAS), calculated oxygen uptake ([Formula: see text])  and individual ventilatory threshold 1 (VT1) as parameters of workload during their daily work. RESULTS: During the shift, HR was scaled: 102 bpm (SD 10.2), RHR: 36.9%, [Formula: see text]: 1267 ml/min (SD 161), RAS: 49.4% (SD 9.3), and [Formula: see text] in relation to VT1: 75% (SD 18.5). There was no significant difference between oxygen consumption during the main task of lifting and carrying bulky waste and the individual [Formula: see text] at VT1. CONCLUSION: Although the burden of the main task of lifting and carrying bulky waste is very high (at VT1 for more than 3 h), interruptions from other tasks or formal breaks spread the burden over the entire shift. The total workload exceeded most recommendations in the literature across the different work periods. However, the total burden remains below VT1, the only parameter that takes individual endurance performance into account. We recommend again VT1 as an individual upper limit for prolonged occupational work.

Comparison of intradialytic continuous and interval training on hemodynamics and dialysis adequacy: A crossover randomized controlled trial.

AIM: Circulating blood volume (BV) during exercise changes depending on the intensity and duration, and post-exercise hypotension is observed after continuous exercise. We investigated the safety and efficacy of both interval and continuous IDE at anaerobic threshold (AT) levels with respect to hemodynamic stability and dialysis efficiency. METHODS: In this crossover randomized controlled trial, 16 patients on haemodialysis were subjected to three trial arms, including non-IDE, interval-IDE, and continuous-IDE arms. Systolic blood pressure (SBP), BV, and ultraviolet absorbance - an indicator of dialysis efficiency - were continuously measured, and each change was compared between the three arms by two-way analysis of variance. RESULTS: Continuous IDE decreased SBP from post-exercise to the end of dialysis compared with baseline (pre 142.8 ± 19.0 vs. post 127.5 ± 24.5 mmHg, p = .02), whereas interval IDE maintained better SBP levels post-exercise (pre 139.9 ± 17.1 vs. post 140.1 ± 15.8 mmHg, p = 1.0) than continuous IDE (non-IDE 133.2 ± 19.9 vs. interval 140.1 ± 15.8 vs. continuous 127.5 ± 24.5 mmHg, p = .04). Moreover, interval IDE caused less tiredness and few symptoms (p < .05), despite reaching higher intensity than continuous IDE (p = .001). The BV of each IDE arm decreased during exercise and recovered post-exercise to the same level as non-IDE. Ultraviolet absorbance was not different between each arm (p = .16). CONCLUSION: AT-level interval IDE maintains better hemodynamic stability from post-exercise to the end of dialysis and may represent a novel approach that can be effectively performed with fewer symptoms.

Dysregulation of ventilation at day and night time in heart failure.

Heart failure (HF) is characterized by an increase in ventilatory response to exercise of multifactorial aetiology and by a dysregulation in the ventilatory control during sleep with the occurrence of both central and obstructive apnoeas. In this setting, the study of the ventilatory behaviour during exercise, by cardiopulmonary exercise testing, or during sleep, by complete polysomnography or simplified nocturnal cardiorespiratory monitoring, is of paramount importance because of its prognostic value and of the possible effects of sleep-disordered breathing on the progression of the disease. Moreover, several therapeutic interventions can significantly influence ventilatory control in HF. Also, rest daytime monitoring of cardiac, metabolic, and respiratory activities through specific wearable devices could provide useful information for HF management. The aim of the review is to summarize the main studies conducted at Centro Cardiologico Monzino on these topics.

Lactate thresholds and role of nitric oxide in male rats performing a test with forced swimming to exhaustion.

The present study assessed a complex of biochemical parameters at the anaerobic threshold (AT) in untrained male Wistar rats with different times to exhaustion (Tex ) from swimming. The first group of rats was randomly divided into six subgroups and subjected to a swimming test to exhaustion without a load or with a load of 2%-10% of body weight (BW). In the first group, we established that for untrained rats, the load of 4% BW in the swimming to exhaustion test was optimal for endurance assessment in comparison with other loads. The second group of rats went through a preliminary test with swimming to exhaustion at 4% BW and was then divided into two subgroups: long swimming time (LST, Tex > 240 min) and short swimming time (SST, Tex < 90 min). All rats of the second group performed, for 6 days, an experimental training protocol: swimming for 20 min each day with weight increasing each day. We established that the AT was 3% BW in SST rats and 5% BW in LST rats. The AT shifted to the right on the lactate curve in LST rats. Also, at the AT in the LST rats, we found significantly lower levels of blood lactate, cortisol, and NO.

Determinants of Anaerobic Threshold at Each Stage of Renal Dysfunction in Patients With Heart Disease.

Patients with heart disease have a low anaerobic threshold (AT), and the determinants of AT may differ, depending on the severity of renal dysfunction. This study aimed to verify the determinants of AT for each stage of renal function in patients with heart disease. We consecutively enrolled 250 patients with heart disease who underwent cardiopulmonary exercise testing in our institution. The patients were divided into 3 groups by their estimated glomerular filtration rate (eGFR): <45, 45 to 59, and ≥60 ml/min/1.73 m2. A multivariate linear regression analysis was performed to evaluate the independent determinants of AT for each group. In total, 201 patients were analyzed. AT decreased with the deterioration of renal function (eGFR <45, 10.9 ± 2.1 vs eGFR 45 to 59, 12.4 ± 2.5 vs eGFR ≥60, 14.0 ± 2.6 ml/min/kg, p <0.001). In the eGFR <45 group, left ventricular ejection fraction and hemoglobin were significantly associated with AT (ß = 0.427, p = 0.006 and ß = 0.488, p = 0.002, respectively). In the eGFR 45 to 59 and ≥60 groups, ΔPETO2 (end-tidal oxygen partial pressure from rest to AT) showed a significant association with AT (ß = 0.576, p <0.001 and ß = 0.308, p = 0.003, respectively). The determinants of AT depended on the stage of renal dysfunction in patients with heart disease. In conclusion, in the eGFR <45 group, the determinants of AT were left ventricular ejection fraction and hemoglobin, whereas in the eGFR 45 to 59 and eGFR ≥60 groups, the determinant of AT was ΔPETO2.

Functional and Morphological Adaptations in the Heart of Children Aged 12-14 Years following Two Different Endurance Training Protocols.

This study investigated the cardiac functional and the morphological adaptations because of two endurance training protocols. Untrained children (N = 30, age: 12-14 years) were divided into three groups (N = 10/group). The first group did not perform any session (CONTROL), the second performed ventilatory threshold endurance training (VTT) for 12 weeks (2 sessions/week) at an intensity corresponding to the ventilatory threshold (VT) and the third (IT) performed two sessions per week at 120% of maximal oxygen uptake (VO2max). Two other sessions (30 min running at 55-65% of VO2max) per week were performed in VVT and IT. Echocardiograms (Left Ventricular end Diastolic Diameter, LVEDd; Left Ventricular end Diastolic Volume, LVEDV; Stroke Volume, SV; Ejection Fraction, EF; Posterior Wall Thickness of the Left Ventricle, PWTLV) and cardiopulmonary ergospirometry (VO2max, VT, velocity at VO2max (vVO2max), time in vVO2max until exhaustion (Tlim) was conducted before and after protocols. Significant increases were observed in both training groups in LVEDd (VTT = 5%; IT = 3.64%), in LVEDV (VTT = 23.7%; ITT = 13.6%), in SV (VTT = 25%; IT = 16.9%) but not in PWTLV and EF, after protocols. No differences were noted in the CONTROL group. VO2max and VT increased significantly in both training groups by approximately 9% after training. Our results indicate that intensity endurance training does not induce meaningful functional and morphological perturbations in the hearts of children.

Is Stryd critical power a meaningful parameter for runners?

Stryd is a foot pod that reliably estimates running power. Our objectives were to examine the efficacy of the website-generated Stryd critical power (CPSTRYD) as a meaningful parameter for runners. 20 runners performed their regular training while wearing Stryd for a minimum of 6 weeks to generate CPSTRYD. Runners completed laboratory graded exercise testing, and outdoor 1500 m and 5000 m time trails. CPSTRYD was most similar to the second ventilatory threshold (VT2) or the onset of blood lactate accumulation (OBLA) and is highly predictive of running performance. Stryd ground contact time (GCT) was a predictor of performance when comparing runners at the same submaximal treadmill speed. CPSTRYD generated from outdoor running is equivalent to that calculated using an established CP model. However, variance between different methods of CP estimation must be a consideration for runners and coaches. Stryd offers meaningful data for runners including a realistic estimate of CP.

Revisiting cardiac output estimated noninvasively from oxygen uptake during exercise: an exploratory hypothesis-generating replication study.

Stringer et al. [J Appl Physiol (1985) 82: 908-912, 1997] developed a method from invasive data to estimate cardiac output during incremental exercise testing based on Fick's principle. The authors proposed that the arterio-mixed venous oxygen content difference increases linearly with percentage of maximal O2 consumption. We hypothesized an S-shaped pattern in the published data and calculated the inflection point of this curve and of the standard resting oxygen dissociation curve. Using a partial F test, we compared the linear model with a third-order polynomial model, which showed a better fit to the data [F(2,101) = 9.5, P < 0.001]. This finding was reproduced in a dataset published by Åstrand et al. in 1964 [F(2, 122) = 10.6, P < 0.001]. The inflection point of the curve coincided with the lactate acidosis threshold [first ventilatory threshold (VT1)] as measured by Stringer et al. (VT1 at 50% and inflection point at 56% [95% CI, 52.9 to 60.7] of maximal O2 consumption). The inflection point of the standard resting oxygen dissociation curve was calculated at a partial pressure of 21.5 mmHg and a saturation of 36%, matching the "critical capillary Po2" concept of Stringer et al. (21.2 mmHg). We conclude that the arterio-mixed venous oxygen content difference increases in an S-shaped manner with percentage of maximal oxygen consumption and that the inflection point of this curve may correspond to VT1 and that of the in vivo oxygen dissociation curve. Further research is needed to confirm these findings and improve the method.NEW & NOTEWORTHY In 1997, Stringer, Hansen, and Wasserman developed a method for estimating cardiac output during incremental exercise testing. They observed that the arterio-mixed venous oxygen content difference increases linearly with the percentage of maximal O2 consumption. This increase may be better modelled by an S-shaped function, the inflection point of which may be related to the first ventilatory threshold and the inflection point of the oxygen dissociation curve. This finding may help to improve the method.

Relationship of maximum walking speed with peak oxygen uptake and anaerobic threshold in male patients with heart failure.

This retrospective observational study aimed to examine the relationships of maximum walking speed (MWS) with peak oxygen uptake (peak VO2) and anaerobic threshold (AT) obtained by cardiopulmonary exercise testing (CPX) in patients with heart failure. The study participants were 104 consecutive men aged ≥ 20 years who had been hospitalized or had undergone outpatient care at our hospital for heart failure between February 2019 and January 2023. MWS was measured in a 5-m section with a 1-m run-up before and after the course. Multivariable analysis was used to examine the association between MWS and peak VO2 and AT by CPX. The Pearson correlation coefficient showed that MWS was positively correlated with percent-predicted peak VO2 and percent-predicted AT (r = 0.463, p < 0.001; and r = 0.485, p < 0.001, respectively). In the multiple linear regression analysis employing percent-predicted peak VO2 and percent-predicted AT as the objective variables, only MWS demonstrated a significant positive correlation (standardized ß: 0.471, p < 0.001 and 0.362, p < 0.001, respectively). Multiple logistic regression analyses, using an 80% cutoff in percent-predicted peak VO2 and AT, revealed that only MWS was identified as a significant factor in both cases (odds ratio [OR]: 1.239, 95% confidence interval [CI]: 1.071-1.432, p = 0.004 and OR: 1.469, 95% CI: 1.194-1.807, p < 0.001, respectively). MWS was correlated with peak VO2 and AT in male patients with heart failure. The MWS measurement as a screening test for exercise tolerance may provide a simple means of estimating peak VO2 and AT in heart failure patients.

A Physiological Anchor for the Perception of Effort.

This is a two-part study to determine one or more reliable physiological anchors for perception of effort. The purpose of Study 1 was to compare ratings of perceived exertion (RPE) at the ventilatory threshold (VT) in running, cycling, and upper body exercise with the premise that if RPE at VT did not differ across exercise modes, VT might provide a unique set of physiological inputs for perception of effort. For 27 participants, values for VT and for RPE at VT (Borg 6 to 20 scale) averaged 9.4 km⋅h-1 (SD = 0.7) and 11.9 km⋅h-1 (SD = 1.4) respectively in running, 135 W (SD = 24) and 12.1 W (SD = 1.6) in cycling, and 46 W (SD = 5) and 12.0 W (SD = 1.7) in upper body exercise. RPE did not differ, suggesting that VT may anchor effort perception. In Study 2, 10 participants performed cycle ergometer exercise for 30 minutes at their VT (M = 101 W, SD = 21), at their maximal lactate steady state (M = 143 W, SD = 22), and at their critical power (CP; M = 167 W, SD = 23). Mean end-exercise RPE were 12.1 (SD = 2.1), 15.0 (SD = 1.9), and 19.0 (SD = 0.5), respectively. The very close clustering of RPE during exercise at CP hints that the confluence of physiological responses at CP may (also) serve as a determinant in perception of effort.

Cardiorespiratory Fitness in Individuals Post-stroke: Reference Values and Determinants.

OBJECTIVE: To provide reference values of cardiorespiratory fitness for individuals post-stroke in clinical rehabilitation and to gain insight in characteristics related to cardiorespiratory fitness post stroke. DESIGN: A retrospective cohort study. Reference equations of cardiopulmonary fitness corrected for age and sex for the fifth, 25th, 50th, 75th, and 95th percentile were constructed with quantile regression analysis. The relation between patient characteristics and cardiorespiratory fitness was determined by linear regression analyses adjusted for sex and age. Multivariate regression models of cardiorespiratory fitness were constructed. SETTING: Clinical rehabilitation center. PARTICIPANTS: Individuals post-stroke who performed a cardiopulmonary exercise test as part of clinical rehabilitation between July 2015 and May 2021 (N=405). MAIN OUTCOME MEASURES: Cardiorespiratory fitness in terms of peak oxygen uptake (V˙O2peak) and oxygen uptake at ventilatory threshold (V˙O2-VT). RESULTS: References equations for cardiorespiratory fitness stratified by sex and age were provided based on 405 individuals post-stroke. Median V˙O2peak was 17.8[range 8.4-39.6] mL/kg/min and median V˙O2-VT was 9.7[range 5.9-26.6] mL/kg/min. Cardiorespiratory fitness was lower in individuals who were older, women, using beta-blocker medication, and in individuals with a higher body mass index and lower motor ability. CONCLUSIONS: Population specific reference values of cardiorespiratory fitness for individuals post-stroke corrected for age and sex were presented. These can give individuals post-stroke and health care providers insight in their cardiorespiratory fitness compared with their peers. Furthermore, they can be used to determine the potential necessity for cardiorespiratory fitness training as part of the rehabilitation program for an individual post-stroke to enhance their fitness, functioning and health. Especially, individuals post-stroke with more mobility limitations and beta-blocker use are at a higher risk of low cardiorespiratory fitness.