Validity and Reliability of Ventilatory and Blood Lactate Thresholds in Well-Trained Cyclists

Estimation of ventilatory thresholds during exercise using respiratory wearable sensors

Ventilatory thresholds (VTs) are key physiological parameters used to evaluate physical performance and determine aerobic and anaerobic transitions during exercise. Current assessment of these parameters requires ergospirometry, limiting evaluation to laboratory or clinical settings. In this work, we introduce a wearable respiratory system that continuously tracks breathing during exercise and estimates VTs during ramp tests. We validate the respiratory rate and VTs predictions in 17 healthy adults using ergospirometry analysis. In addition, we use the wearable system to evaluate VTs in 107 recreational athletes during ramp tests outside the laboratory and show that the mean population values agree with physiological variables traditionally used to exercise prescription. We envision that respiratory wearables can be useful in determining aerobic and anaerobic parameters with promising applications in health telemonitoring and human performance.

Setting sail for Paris 2024: Retrospective analysis of world-class ILCA 7 Olympic sailors' cardiorespiratory fitness (2015-2020)

The aim of this retrospective analysis was to provide a more comprehensive understanding of the cardiorespiratory profile of world-class ILCA-7 sailors (n = 3, all males), through a longitudinal evaluation offering real-world data on physiological profile and exercise intensity domains. The cardiopulmonary exercise testing (CPET) was performed by the same researchers using the same equipment during the study. Assessments took place twice a year, aligning with major international competition preparations. Participants trained and competed at the same sailing club in Split, Croatia, under consistent supervision from the same team throughout the study, winning a total of 21 medals at major international competitions. The recordedV ̇ O 2 peak ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{peak}}}}$ ranged from 51.7 ± 1.6 to 61.9 ± 3.0 mL min-1 kg-1, respectively. Similarly, peak power output varied from 352 ± 10 to 426 ± 34 W. The changes in physiological responses at the ventilatory thresholds were proportional to the changes in peak cardiorespiratory fitness capacity. Interestingly, the oxygen pulse measured in 2015 was 25 ± 1 mL O2 beat-1. Over the subsequent 6 years, the O2 pulse marginally increased and appeared to stabilize at 27 ± 1 mL O2 beat-1 in 2020, when these athletes were 32 ± 3 years old. This work offers a broader understanding of world-class Olympic sailors' cardiorespiratory fitness, going beyond the standard assessment of peakV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ to incorporate an analysis of ventilatory thresholds. While a direct link between cardiorespiratory fitness and competitive success remains ambiguous, the importance of a well-rounded aerobic capacity for excellence in ILCA-7 sailing class is evident. HIGHLIGHTS: What is the central question of this study? What are the temporal changes in the physiological profiles of three world-class ILCA-7 sailors? What is the main finding and its importance? Data on oxygen pulse adjustments suggest the involvement of compensatory cardiovascular mechanisms, likely associated with the isometric and quasi-isometric contractions inherent in ILCA-7 sailing. This is evidenced by the absence of an age-related increase in oxygen pulse, a phenomenon often observed in endurance athletes throughout their competitive careers.

Relative pedaling forces are low during cycling

We quantified and compared the mechanical force demands relative to the maximum dynamic force (MDF) of 11 cyclists when pedaling at different intensities (ventilatory threshold, maximum lactate steady state, respiratory compensation point, and maximal aerobic power), cadences (free, 40, 60 and 80 rpm), and all-out resisted sprints. Relative force demands (expressed as %MDF) progressively increased with higher intensities (p < 0.001) and lower cadences (p < 0.001). Notwithstanding, relative force demands were low (<54 % MDF) for all conditions, even during the so-called 'torque training'. These results might be useful when programming on-bike resistance training to improve torque production capacity.

Inter-day reliability of heart rate complexity and variability metrics in healthy highly active younger and older adults

PURPOSE

To investigate the inter-day reliability of time-domain, frequency-domain, and nonlinear HRV metrics in healthy highly active younger and older adults. The study also assessed the effect of age on the HRV metrics.

METHODS

Forty-four older adults (34 M, 10F; 59 ± 5 years;V ˙ O 2peak  = 40.9 ± 7.6 ml kg-1 min-1) and twenty-two younger adults (16 M, 6F; 22 ± 4 years;V ˙ O 2peak  = 47.2 ± 12.8 ml kg-1 min-1) attended the laboratory. Visit one assessed aerobic fitness through an exercise test. In visits two and three, participants completed a 30-min supine RR interval measurement to derive the HRV metrics.

RESULTS

The younger group (YG) and older group (OG) demonstrated poor to good day-to-day relative and absolute reliability for all HRV metrics (OG, ICCs = 0.33 to 0.69 and between day CVs = 3.8 to 29.2%; YG, ICCs = 0.37 to 0.93 and between day CVs = 3.5 to 36.5%). There was a significant reduction in ApEn (P < 0.001), SampEn (P = 0.031), RMSSD (P < 0.001), SDNN (P < 0.001), LF power (P < 0.001) and HF power (P < 0.001), HRV metrics with ageing. There was no significant effect of age the complexity metrics DFA α1 (P = 0.107), α2 (P = 0.147) and CI-8 (P = 0.493).

CONCLUSION

HRV metrics are reproducible between days in both healthy highly active younger and older adults. There is a decline in linear and nonlinear HRV metrics with age, albeit there being no age-related change in the nonlinear metrics, DFA α1, α2 and CI-8.

Heat stress increases carbohydrate oxidation rates and oxygen uptake during prolonged load carriage exercise

Military missions are conducted in a multitude of environments including heat and may involve walking under load following severe exertion, the metabolic demands of which may have nutritional implications for fueling and recovery planning. Ten males equipped a military pack loaded to 30% of their body mass and walked in 20°C/40% relative humidity (RH) (TEMP) or 37°C/20% RH (HOT) either continuously (CW) for 90 min at the first ventilatory threshold or mixed walking (MW) with unloaded running intervals above the second ventilatory threshold between min 35 and 55 of the 90 min bout. Pulmonary gas, thermoregulatory, and cardiovascular variables were analyzed following running intervals. Final rectal temperature (MW: p < 0.001, g = 3.81, CW: p < 0.001, g = 4.04), oxygen uptake, cardiovascular strain, and energy expenditure were higher during HOT trials (p ≤ 0.05) regardless of exercise type. Both HOT trials elicited higher final carbohydrate oxidation (CHOox) than TEMP CW at min 90 (HOT MW: p < 0.001, g = 1.45, HOT CW: p = 0.009, g = 0.67) and HOT MW CHOox exceeded TEMP MW at min 80 and 90 (p = 0.049, g = 0.60 and p = 0.024, g = 0.73, respectively). There were no within-environment differences in substrate oxidation indicating that severe exertion work cycles did not produce a carryover effect during subsequent loaded walking. The rate of CHOox during 90 minutes of load carriage in the heat appears to be primarily affected by accumulated thermal load.

The Effects of a Carbohydrate Hydrogel System for the Delivery of Bicarbonate Mini-Tablets on Acid-Base Buffering and Gastrointestinal Symptoms in Resting Well-trained Male Cyclists

BACKGROUND

A new commercially available sodium bicarbonate (SB) supplement claims to limit gastrointestinal (GI) discomfort and increase extracellular buffering capacity. To date, no available data exists to substantiate such claims. Therefore, the aim of this study was to measure blood acid-base balance and GI discomfort responses following the ingestion of SB using the novel "Bicarb System" (M-SB). Twelve well-trained male cyclists completed this randomised crossover designed study. Maximal oxygen consumption was determined in visit one, whilst during visits two and three participants ingested 0.3 g∙kg-1 BM SB using M-SB (Maurten, Sweden) or vegetarian capsules (C-SB) in a randomised order. Finger prick capillary blood samples were measured every 30 min for pH, bicarbonate (HCO3-), and electrolytes (potassium, chloride, calcium, and sodium), for 300 min. Visual analogue scales (VAS) were used to assess GI symptoms using the same time intervals.

RESULTS

Peak HCO3- was 0.95 mmol∙L-1 greater following M-SB (p = 0.023, g = 0.61), with time to peak HCO3- achieved 38.2 min earlier (117 ± 37 vs. 156 ± 36 min; p = 0.026, r = 0.67) and remained elevated for longer (p = 0.043, g = 0.51). No differences were observed for any electrolytes between the conditions. Aggregated GI discomfort was reduced by 79 AU following M-SB (p < 0.001, g = 1.11), with M-SB reducing stomach cramps, bowel urgency, diarrhoea, belching, and stomach-ache compared to C-SB.

CONCLUSIONS

This is the first study to report that M-SB can increase buffering capacity and reduce GI discomfort. This presents a major potential benefit for athletes considering SB as an ergogenic supplement as GI discomfort is almost eliminated. Future research should determine if M-SB is performance enhancing.

Reliability and validity of a non-linear index of heart rate variability to determine intensity thresholds

Exercise intensity distribution is crucial for exercise individualization, prescription, and monitoring. As traditional methods to determine intensity thresholds present limitations, heart rate variability (HRV) using DFA a1 has been proposed as a biomarker for exercise intensity distribution. This index has been associated with ventilatory and lactate thresholds in previous literature. This study aims to assess DFA a1's reliability and validity in determining intensity thresholds during an incremental cycling test in untrained healthy adults. Sixteen volunteers (13 males and 3 females) performed two identical incremental cycling stage tests at least 1 week apart. First and second ventilatory thresholds, lactate thresholds, and HRV thresholds (DFA a1 values of 0.75 and 0.5 for HRVT1 and HRVT2, respectively) were determined in heart rate (HR), relative oxygen uptake (VO2rel), and power output (PO) values for both tests. We used intraclass correlation coefficient (ICC), change in mean, and typical error for the reliability analysis, and paired t-tests, correlation coefficients, ICC, and Bland-Altman analysis to assess the agreement between methods. Regarding reliability, HRV thresholds showed the best ICCs when measured in PO (HRVT1: ICC = .87; HRVT2: ICC = .97), comparable to ventilatory and lactate methods. HRVT1 showed the strongest agreement with LA 2.5 in PO (p = 0.09, r = .93, ICC = .93, bias = 9.9 ± 21.1), while HRVT2 reported it with VT2 in PO (p = 0.367, r = .92, ICC = .92, bias = 5.3 ± 21.9). DFA a1 method using 0.75 and 0.5 values is reliable and valid to determine HRV thresholds in this population, especially in PO values.

A Five-Week Periodized Carbohydrate Diet Does Not Improve Maximal Lactate Steady-State Exercise Capacity and Substrate Oxidation in Well-Trained Cyclists compared to a High-Carbohydrate Diet

There is a growing interest in studies involving carbohydrate (CHO) manipulation and subsequent adaptations to endurance training. This study aimed to analyze whether a periodized carbohydrate feeding strategy based on a daily training session has any advantages compared to a high-carbohydrate diet in well-trained cyclists. Seventeen trained cyclists (VO2peak = 70.8 ± 6.5 mL·kg-1·min-1) were divided into two groups, a periodized (PCHO) group and a high-carbohydrate (HCHO) group. Both groups performed the same training sessions for five weeks. In the PCHO group, 13 training sessions were performed with low carbohydrate availability. In the HCHO group, all sessions were completed following previous carbohydrate intake to ensure high pre-exercise glycogen levels. In both groups, there was an increase in the maximal lactate steady state (MLSS) (PCHO: 244.1 ± 29.9 W to 253.2 ± 28.4 W; p = 0.008; HCHO: 235.8 ± 21.4 W to 246.9 ± 16.7 W; p = 0.012) but not in the time to exhaustion at MLSS intensity. Both groups increased the percentage of muscle mass (PCHO: p = 0.021; HCHO: p = 0.042) and decreased the percent body fat (PCHO: p = 0.021; HCHO: p = 0.012). We found no differences in carbohydrate or lipid oxidation, heart rate, and post-exercise lactate concentration. Periodizing the CHO intake in well-trained cyclists during a 5-week intervention did not elicit superior results to an energy intake-matched high-carbohydrate diet in any of the measured outcomes.

Analysis of Course of Changes in Blood Lactate Concentration in Response to Graded Exercise Test and Modified Wingate Test in Adolescent Road Cyclists

BACKGROUND

The purpose of this study was to analyze the course of changes in the blood lactate (BL) concentration in response to the graded exercise test (GXT) and the modified Wingate test (MWT).

METHODS

This study involved 23 male highly trained road cyclists (age: 16.2 ± 1.1 years; experience: 5.0 ± 2.1 years; VO2max 59.0 ± 3.5 mL × kg-1 × min-1). The analysis of BL concentration was conducted using an enzymatic-amperometric electrochemical technique.

RESULTS

Our study provided the following information: (i) peak BL concentration in response to GXT (12.86 ± 2.32 mmol × L-1) and MWT (12.85 ± 1.47 mmol × L-1) is expected around the third minute after the completion of the trial; (ii) 60 min is not a sufficient period for BL concentration to return to resting values after GXT; (iii) post-GXT BL removal during the 60 min period is unsteady (3-20 min: -2.6 ± -0.6% × min-1; 20-60 min: -1.6 ± -0.3% × min-1; p-value for comparison < 0.01), whereas post-MWT BL removal during the 12 min period appears to be constant (3-6 min: -2.4 ± -5.6% × min-1, 6-9 min: -2.6 ± -1.8 % × min-1; 9-12 min: -3.1 ± -2.1 % × min-1; p-value for all comparisons < 0.01).

CONCLUSIONS

When aiming to obtain valuable data regarding the course of changes in BL concentration during the post-exertion period, it is essential to consider the number of measurements and the time points in sample collection for analysis.

A comparative analysis of mathematical methods for detecting lactate thresholds using muscle oxygenation data during a graded cycling test

Objective. Threshold determination for improving training and sports performance is important for researchers and trainers, who currently use different methods for determining lactate, ventilatory or muscle oxygenation (SmO2) thresholds. Our study aimed to compare the identification of the intensity at the first and second thresholds using lactate and SmO2data by different mathematical methods in different muscles during a graded cycling test.Approach. Twenty-six cyclists (15 males and 11 females; 23 ±6 years, 1.71 ± 0.09 m, 64.3 ± 8.8 Kg and 12 ± 3 training hours per week) performed a graded test on the cycle ergometer. Power output and saturation of muscle oxygen in four muscles (vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior) were measured, along with systemic lactate concentration.Main Results. Our results showed that any method was reliable for determining the first muscle oxygenation threshold (MOT1) when comparing the lactate threshold in any muscle. However, the best method for determining the second muscle oxygenation threshold (MOT2) was the Exp-Dmax (p< 0.01; ICC = 0.79-0.91) in all muscles. In particular, the vastus lateralis muscle showed the highest intraclass correlation coefficient (ICC = 0.91, CI95% [0.81, 0.96]). However, results varied per sex across all muscles analyzed.Significance. Although the first muscle oxygenation threshold could not be determined using mathematical methods in all the muscles analyzed, the Exp-Dmax method presented excellent results in detecting the second systemic threshold in the vastus lateralis.

Assessing Acute Responses to Exercises Performed Within and at the Upper Boundary of Severe Exercise Domain

Purpose: The highest work-rate that provides maximal oxygen uptake (V ˙ O 2 m a x ) may be one of the best exercise stimuli to yield both V ˙ O 2 m a x and lactate accumulation. The aim of this study was to analyze physiological and metabolic acute responses of an exercise modality performed at the upper boundary of the severe exercise domain, and compare those responses with exercise modalities applied within the severe exercise domain. Method: Ten trained male cyclists participated in this study. The V ˙ O 2 m a x , corresponding power output (POVO2max), and the highest work-rate that provides the V ˙ O 2 m a x (IHIGH) were determined by constant work-rate exercises. Cyclists performed three high-intensity interval training (HIIT) strategies as follows; HIIT-1: 4-6 × 3-min at 95% of POVO2max with 1:1 (workout/rest ratio); HIIT-2: 16-18 × 1-min at 105% of POVO2max with 1:1; HIIT-3: 4-7 × 1-2-min at the IHIGH with 1:2. Capillary blood samples were analyzed before, immediately after HIIT sessions, and at the first, third, and fifth minutes of recovery periods. Lactate difference between the highest lactate response and resting status was considered as the peak lactate response for each HIIT modality. Results: Time spent at V ˙ O 2 m a x was greater at HIIT-1 and HIIT-3 (272 ± 127 and 208 ± 111 seconds, respectively; p = 0.155; effect size = 0.43) when compared to the HIIT-2 (~26 seconds; p < 0.001), while there was a greater lactate accumulation at HIIT-3 (~16 mmol·L-1) when compared to HIIT-1 and HIIT-2 (12 and 14 mmol·L-1, respectively; p < 0.001). Conclusions: In conclusion, HIIT-3 performed at IHIGH was successful to provide time spent at V ˙ O 2 m a x with a greater lactate accumulation in a single session.

Exercise evaluation with metabolic and ventilatory responses and blood lactate concentration in mice

This study aimed to clarify the differential exercise capacity between 2-month-old and 10-month-old mice using an incremental running test. Metabolic and ventilatory responses and blood lactate concentration were measured to evaluate exercise capacity. We examined whether incremental running test results reflected metabolic and ventilatory responses and blood lactate concentration observed during the steady-state running test. Metabolic response significantly declined with age, whereas ventilatory response was similar between the groups. A low-intensity/moderate exercise load of 10/min in an incremental running test was performed on both mice for 30 min. They showed a characteristic pattern in ventilatory response in 10-month mice. The results of incremental running tests didn't necessarily reflect the steady-state metabolic and ventilatory responses because some parameters showed an approximation and others did not in incremental and steady-state tests, which changed with age. Our study suggests metabolic and ventilatory responses depending on age and provides basic knowledge regarding the objective and quantitative assessment of treadmill running in an animal model.

Test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests in highly trained cross-country skiers

PURPOSE

Laboratory tests are commonly performed by cross-country (XC) skiers due to the challenges of obtaining reliable performance indicators on snow. However, only a few studies have reported reliability data for ski-specific test protocols. Therefore, this study examined the test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests.

METHODS

Thirty-nine highly trained XC skiers (26 men and 13 women, age: 22 ± 4 years, V̇O2max : 70.1 ± 4.5 and 58.8 ± 4.4 mL·kg-1 ·min-1 , respectively) performed two test trials within 6 days of a diagonal V̇O2max test, n = 27; skating graded exercise test to assess the second lactate threshold (LT2 ), n = 27; 24-min double poling time trial (24-min DP, n = 25), double poling sprint test (SprintDP1 , n = 27), and 1-min self-paced skating sprint test (Sprint1-min , n = 26) using roller skis on a treadmill, and an upper-body strength test (UB-ST, n = 27) to assess peak power (Ppeak ) with light, medium, and heavy loads. For each test, the coefficient of variation (CV), intraclass correlation coefficient (ICC), and minimal detectable change (MDC) were calculated.

RESULTS

V̇O2max demonstrated good-to-excellent reliability (CV = 1.4%; ICC = 0.99; MDC = 112 mL·min-1 ), whereas moderate-to-excellent reliability was found for LT2 (CV = 3.1%; ICC = 0.95). Performance during 24-min DP, SprintDP1 , and Sprint1-min showed good-to-excellent reliability (CV = 1.0%-2.3%; ICC = 0.96-0.99). Absolute reliability for UB-ST Ppeak was poor (CV = 4.9%-7.8%), while relative reliability was excellent (ICC = 0.93-0.97) across the loads.

CONCLUSION

In highly trained XC skiers, sport-specific aerobic and sprint performance tests demonstrated high test-retest reliability, while neuromuscular performance for the upper body was less reliable. Using the presented protocols, practitioners can assess within- and between-season changes in relevant performance indicators.

Correlation properties of heart rate variability to assess the first ventilatory threshold and fatigue in runners

PURPOSE

The short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA-a1) of heart rate variability (HRV) has shown potential to delineate the first ventilatory threshold (VT1). The aims of this study were to investigate the accuracy of this method for VT1 determination in runners using a consumer grade chest belt and to explore the effects of acute fatigue.

METHODS

We compared oxygen uptake (V̇O2) and heart rate (HR) at gas exchange VT1 to V̇O2 and HR at a DFA-a1 value of 0.75. Gas exchange and HRV data were obtained from 14 individuals during a treadmill run involving two incremental ramps. Agreement was assessed using Bland-Altman analysis and linear regression.

RESULTS

Bland-Altman analysis between gas exchange and HRV V̇O2 and HR at VT1 during the first ramp showed a mean (95% limits of agreement) bias of -0.5 (-6.8 to 5.8) ml∙kg-1∙min-1, and -0.9 (-12.2 to 10.5) beats∙min-1, with R2 of 0.83 and 0.56, respectively. During the second ramp, the differences were -7.3 (-18.1 to 3.5) ml∙kg-1∙min-1 and -12.3 (-30.4 to 5.9) beats∙min-1, with R2 of 0.62 and 0.43, respectively.

CONCLUSION

A chest-belt derived DFA-a1 of 0.75 is closely related to gas exchange VT1, with the variability in accuracy at an individual level being similar to gas exchange methods. This suggests this to be a useful method for exercise intensity demarcation. The altered relationship during the second ramp indicates that DFA-a1 is only able to accurately demarcate exercise intensity thresholds in a non-fatigued state, but also opens opportunities for fatigue-based training prescription.

Association Among Different Aerobic Threshold Markers and FATmax in Men With Obesity

Purpose: This work studies the interrelation of the first ventilatory threshold (VT1), the heart rate inflection point (HRIP), and the exercise intensity at which blood lactate started to accumulate (LIAB) or increased 1 mmol∙L-1 above baseline (LT+1.0); and examinee their association with the exercise intensity eliciting maximal fat oxidation (FATmax). Methods: Eighteen young men with obesity performed an incremental-load exercise test on a treadmill after overnight fasting. Gas exchange, heart rate, and blood lactate concentration were recorded. Linear regression analysis was used to determine the association among FATmax and AeT markers. A standard error of estimate (SEE) ≤9 beats∙min-1 and the concordance correlation coefficient (CCC) were used to examine the accuracy of different AeT for predicting FATmax heart rate. Results: The FATmax occurred at 36±7%VO2peak before the HRIP (41±6%VO2peak), LIAB (42±10%VO2peak), LT+1.0 (61±9%VO2peak) and VT1 (40±7%VO2peak). Furthermore, the HRIP (R2= 0.71; SEE= 6 beats∙min-1; CCC=0.77), VT1 (R2= 0.76; SEE= 5 beats∙min-1; CCC=0.84) and LIAB (R2= 0.77; SEE= 5 beats∙min-1; CCC=0.85) were strongly associated to FATmax and showed an acceptable estimation error for predicting FATmax heart rate. Otherwise, LT+1.0 showed a moderate correlation with FATmax, a low accuracy for predicting FATmax HR (R2= 0.57; SEE= 7 beats∙min-1; CCC=0.66) and a poor agreement with the rest of AeT markers (Bias: +20%VO2peak). Conclusion: The HRIP, LIAB and VT1 did not perfectly captured the FATmax, however, these could be exchanged for predicting the FATmax heart rate in men with obesity. Moreover, the LT+1.0 should not be used for AeT or FATmax assessment in men with obesity.

Comparing the reliability of muscle oxygen saturation with common performance and physiological markers across cycling exercise intensity

Introduction

Wearable near-infrared spectroscopy (NIRS) measurements of muscle oxygen saturation (SmO2) demonstrated good test-retest reliability at rest. We hypothesized SmO2 measured with the Moxy monitor at the vastus lateralis (VL) would demonstrate good reliability across intensities. For relative reliability, SmO2 will be lower than volume of oxygen consumption (V̇O2) and heart rate (HR), higher than concentration of blood lactate accumulation ([BLa]) and rating of perceived exertion (RPE). We aimed to estimate the reliability of SmO2 and common physiological measures across exercise intensities, as well as to quantify within-participant agreement between sessions.

Methods

Twenty-one trained cyclists completed two trials of an incremental multi-stage cycling test with 5 min constant workload steps starting at 1.0 watt per kg bodyweight (W·kg-1) and increasing by 0.5 W kg-1 per step, separated by 1 min passive recovery intervals until maximal task tolerance. SmO2, HR, V̇O2, [BLa], and RPE were recorded for each stage. Continuous measures were averaged over the final 60 s of each stage. Relative reliability at the lowest, median, and highest work stages was quantified as intraclass correlation coefficient (ICC). Absolute reliability and within-subject agreement were quantified as standard error of the measurement (SEM) and minimum detectable change (MDC).

Results

Comparisons between trials showed no significant differences within each exercise intensity for all outcome variables. ICC for SmO2 was 0.81-0.90 across exercise intensity. ICC for HR, V̇O2, [BLa], and RPE were 0.87-0.92, 0.73-0.97, 0.44-0.74, 0.29-0.70, respectively. SEM (95% CI) for SmO2 was 5 (3-7), 6 (4-9), and 7 (5-10)%, and MDC was 12%, 16%, and 18%.

Discussion

Our results demonstrate good-to-excellent test-retest reliability for SmO2 across intensity during an incremental multi-stage cycling test. V̇O2 and HR had excellent reliability, higher than SmO2. [BLa] and RPE had lower reliability than SmO2. Muscle oxygen saturation measured by wearable NIRS was found to have similar reliability to V̇O2 and HR, and higher than [BLa] and RPE across exercise intensity, suggesting that it is appropriate for everyday use as a non-invasive method of monitoring internal load alongside other metrics.

Heart Rate Variability-Derived Thresholds for Exercise Intensity Prescription in Endurance Sports: A Systematic Review of Interrelations and Agreement with Different Ventilatory and Blood Lactate Thresholds

BACKGROUND

Exercise intensities are prescribed using specific intensity zones (moderate, heavy, and severe) determined by a 'lower' and a 'higher' threshold. Typically, ventilatory (VT) or blood lactate thresholds (LT), and critical power/speed concepts (CP/CS) are used. Various heart rate variability-derived thresholds (HRVTs) using different HRV indices may constitute applicable alternatives, but a systematic review of the proximity of HRVTs to established threshold concepts is lacking.

OBJECTIVE

This systematic review aims to provide an overview of studies that determined HRVTs during endurance exercise in healthy adults in comparison with a reference VT and/or LT concept.

METHODS

A systematic literature search for studies determining HRVTs in healthy individuals during endurance exercise and comparing them with VTs or LTs was conducted in Scopus, PubMed and Web of Science (until January 2022). Studies claiming to describe similar physiological boundaries to delineate moderate from heavy (HRVTlow vs. VTlow and/or LTlow), and heavy from severe intensity zone (HRVThigh vs. VThigh and/or LThigh) were grouped and their results synthesized.

RESULTS

Twenty-seven included studies (461 participants) showed a mean difference in relative HR between HRVTlow and VTlow of - 0.6%bpm in weighted means and 0.02%bpm between HRVTlow and LTlow. Bias between HR at HRVTlow and VTlow was 1 bpm (limits of agreement (LoA): - 10.9 to 12.8 bpm) and 2.7 bpm (LoA: - 20.4 to 25.8 bpm) between HRVTlow and LTlow. Mean difference in HR between HRVThigh and VThigh was 0.3%bpm in weighted means and 2.9%bpm between HRVThigh and LThigh while bias between HR at HRVThigh and VThigh was - 4 bpm (LoA: - 17.9 to 9.9 bpm) and 2.5 bpm (LoA: - 12.1 to 17.1 bpm) between HRVThigh and LThigh.

CONCLUSION

HRVTlow seems to be a promising approach for the determination of a 'lower' threshold comparable to VTlow and potentially for HRVThigh compared to VThigh, although the latter needs further empirical evaluation. LoA for both intensity zone boundaries indicates bias of HRVTs on an individual level. Taken together, HRVTs can be a promising alternative for prescribing exercise intensity in healthy, male athletes undertaking endurance activities but due to the heterogeneity of study design, threshold concepts, standardization, and lack of female participants, further research is necessary to draw more robust and nuanced conclusions.

Peak performance and cardiometabolic responses of modern US army soldiers during heavy, fatiguing vest-borne load carriage

INTRODUCTION

Physiological limits imposed by vest-borne loads must be defined for optimal performance monitoring of the modern dismounted warfighter.

PURPOSE

To evaluate how weighted vests affect locomotion economy and relative cardiometabolic strain during military load carriage while identifying key physiological predictors of exhaustion limits.

METHODS

Fifteen US Army soldiers (4 women, 11 men; age, 26 ± 8 years; height, 173 ± 10 cm; body mass (BM), 79 ± 16 kg) performed four incremental walking tests with different vest loads (0, 22, 44, or 66% BM). We examined the effects of vest-borne loading on peak walking speed, the physiological costs of transport, and relative work intensity. We then sought to determine which of the cardiometabolic indicators (oxygen uptake, heart rate, respiration rate) was most predictive of task failure.

RESULTS

Peak walking speed significantly decreased with successively heavier vest loads (p < 0.01). Physiological costs per kilometer walked were significantly higher with added vest loads for each measure (p < 0.05). Relative oxygen uptake and heart rate were significantly higher during the loaded trials than the 0% BM trial (p < 0.01) yet not different from one another (p > 0.07). Conversely, respiration rate was significantly higher with the heavier load in every comparison (p < 0.01). Probability modeling revealed heart rate as the best predictor of task failure (marginal R², 0.587, conditional R², 0.791).

CONCLUSION

Heavy vest-borne loads cause exceptional losses in performance capabilities and increased physiological strain during walking. Heart rate provides a useful non-invasive indicator of relative intensity and task failure during military load carriage.

Improved Estimation of Exercise Intensity Thresholds by Combining Dual Non-Invasive Biomarker Concepts: Correlation Properties of Heart Rate Variability and Respiratory Frequency

Identifying exercise intensity boundaries has been shown to be important during endurance training for performance enhancement and rehabilitation. Unfortunately, even though surrogate markers show promise when assessed on a group level, substantial deviation from gold standards can be present in each individual. The aim of this study was to evaluate whether combining two surrogate intensity markers improved this agreement. Electrocardiogram (ECG) and gas exchange data were obtained from 21 participants who performed an incremental cycling ramp to exhaustion and evaluated for first (VT1) and second (VT2) ventilatory thresholds, heart rate (HR) variability (HRV), and ECG derived respiratory frequency (EDR). HRV thresholds (HRVT) were based on the non-linear index a1 of a Detrended Fluctuation Analysis (DFA a1) and EDR thresholds (EDRT) upon the second derivative of the sixth-order polynomial of EDR over time. The average of HRVT and EDRT HR was set as the combined threshold (Combo). Mean VT1 was reached at a HR of 141 ± 15, HRVT1 at 152 ± 14 (p < 0.001), EDRT1 at 133 ± 12 (p < 0.001), and Combo1 at 140 ± 13 (p = 0.36) bpm with Pearson's r of 0.83, 0.78, and 0.84, respectively, for comparisons to VT1. A Bland-Altman analysis showed mean biases of 8.3 ± 7.9, -8.3 ± 9.5, and -1.7 ± 8.3 bpm, respectively. A mean VT2 was reached at a HR of 165 ± 13, HRVT2 at 167 ± 10 (p = 0.89), EDRT2 at 164 ± 14 (p = 0.36), and Combo2 at 164 ± 13 (p = 0.59) bpm with Pearson's r of 0.58, 0.95, and 0.94, respectively, for comparisons to VT2. A Bland-Altman analysis showed mean biases of -0.3 ± 8.9, -1.0 ± 4.6, and -0.6 ± 4.6 bpm, respectively. Both the DFA a1 and EDR intensity thresholds based on HR taken individually had moderate agreement to targets derived through gas exchange measurements. By combining both non-invasive approaches, there was improved correlation, reduced bias, and limits of agreement to the respective corresponding HRs at VT1 and VT2.

Investigating the roles of exercise intensity and biological sex on postexercise alterations in cardiac function

The term exercise-induced cardiac fatigue (EICF) has typically been used to describe a transient reduction in cardiac function following prolonged-strenuous exercise. Recent evidence demonstrates that EICF can occur following only 45 min of high-intensity exercise when assessed using exercising stress echocardiography. This investigation sought to examine whether sprint intervals (SIT; 6 × 30 s Wingate tests), or 90-min moderate-cycling with sprint intervals (MIX; 90 min with 1 × 30 s Wingate test every 15 min) would cause greater EICF than 90 min (CON) or 3 h (LONG) moderate-cycling assessed using stress echocardiography, with a secondary aim to interrogate sex differences in EICF. Seventeen participants (M: 9, F: 8) underwent three cycling sessions with stress-echocardiography performed before-and-after each condition at a target heart rate (HR) of 100 beats·min^-1, with the CON testing occurring at the mid-point of the 3 h LONG condition. For all conditions, measures of left ventricular (LV) systolic [stroke volume, ejection fraction (EF), peak longitudinal strain, isovolumetric contraction time, S') and diastolic (E/A, E', isovolumetric relaxation time, longitudinal strain rate) function were reduced after exercise (all P < 0.05). In the right ventricle (RV), systolic function was reduced (tricuspid annular plane systolic excursion, S', peak longitudinal strain and strain rate) following all conditions, and fractional area change was reduced to the greatest degree following SIT (condition × time, P = 0.01). Females demonstrated lesser impairments in LV EF, and elastance (ESP/ESV) compared with males (P < 0.05). Markers of EICF occurred similarly following all cycling loads, suggesting the functional changes may be due to altered loading conditions and reduced stress-echocardiography workload. However, males experienced greater cardiac alterations in some measures, likely due to greater changes in postexercise loading conditions.NEW & NOTEWORTHY This investigation sought to determine the role of exercise intensity on the magnitude of exercise-induced cardiac fatigue using stress echocardiography to maintain loading conditions, with a secondary purpose of assessing sex differences. Unexpectedly, it was found that all cycling loads elicited the same magnitude of functional alteration, which likely represents a common response to exercise and stress echocardiography, rather than intrinsic cardiac impairment. Males demonstrated greater alterations than females, likely due to sex differences in postexercise hemodynamics.

Use of Streptococcus salivarius K12 in supporting the mucosal immune function of active young subjects: A randomised double-blind study

Introduction

Upper respiratory tract infections (URTI) are the most common illnesses affecting athletes, causing absences from training and competition. Salivary immunoglobulin A (sIgA) is the main immune factor in saliva, and a consistent association between low concentrations of sIgA and an increased incidence of URTIs has been reported. The oral probiotic Streptococcus salivarius K12 has been suggested to have the potential to improve oral diseases and mucosal barrier function. However, the effects of this probiotic on active young subjects performing a high-intensity training (HIT) program have not been investigated.

Methods

Active young students were randomised into a treated group (S. salivarius K12) and a control (placebo) group and asked to take the product daily for 30 days. After this period, participants performed a graded exercise test and five HIT sessions, all within 3 days. They were also asked to complete the Wisconsin Upper Respiratory Symptom Survey daily to monitor URTI's presence. Before and after the 30 days, and at 0h, 24h and 72h after the last training session, saliva samples were collected to quantify sIgA level, secretion rate, and flow. The effect of S. salivarius K12 intake on these parameters was tested using an ANOVA for repeated measures.

Results

Twenty (M = 14, F = 6) young subjects (23.5 ± 2.3 years old) participated in the study. The total accumulated training load (sRPE) in the supplementation period was similar in the two groups (treated: 4345 ± 3441 AU; control: 4969 ± 4165 AU; p > 0.05). Considering both sIgA level and secretion rate, significant time (F_(4,15) = 3.38; p = 0.037; F_(4,15) = 6.00; p = 0.004) and time×group interactions (F_(4,15) = 2.49; p = 0.049; F_(4,15) = 5.01; p = 0.009) were reported, with the treated group showing higher sIgA levels at 72h post-exercise and increased secretion rate both at 0h and 72h. The number of URTI episodes was similar in the treated and control groups (χ² = 1.83; p > 0.05).

Conclusion

This study demonstrates that relatively short-term S. salivarius K12 supplementation increased sIgA level and secretion in healthy subjects performing a demanding exercise-training programme composed of HIT sessions.

Factors Determining the Agreement between Aerobic Threshold and Point of Maximal Fat Oxidation: Follow-Up on a Systematic Review and Meta-Analysis on Association

Regular exercise at the intensity matching maximal fat oxidation (FAT_max) has been proposed as a key element in both athletes and clinical populations when aiming to enhance the body's ability to oxidize fat. In order to allow a more standardized and tailored training approach, the connection between FAT_max and the individual aerobic thresholds (AerT) has been examined. Although recent findings strongly suggest that a relationship exists between these two intensities, correlation alone is not sufficient to confirm that the intensities necessarily coincide and that the error between the two measures is small. Thus, this systematic review and meta-analysis aim to examine the agreement levels between the exercise intensities matching FAT_max and AerT by pooling limits of agreement in a function of three parameters: (i) the average difference, (ii) the average within-study variation, and (iii) the variation in bias across studies, and to examine the influence of clinical and methodological inter- and intra-study differences on agreement levels. This study was registered with PROSPERO (CRD42021239351) and ClinicalTrials (NCT03789045). PubMed and Google Scholar were searched for studies examining FAT_max and AerT connection. Overall, 12 studies with forty-five effect sizes and a total of 774 subjects fulfilled the inclusion criteria. The ROBIS tool for risk of bias assessment was used to determine the quality of included studies. In conclusion, the overall 95% limits of agreement of the differences between FAT_max and AerT exercise intensities were larger than the a priori determined acceptable agreement due to the large variance caused by clinical and methodological differences among the studies. Therefore, we recommend that future studies follow a strict standardization of data collection and analysis of FAT_max- and AerT-related outcomes.

Is Maximal Lactate Accumulation Rate Promising for Improving 5000-m Prediction in Running?

Endurance running performance can be predicted by maximal oxygen uptake (V̇O2max), the fractional utilisation of oxygen uptake (%V̇O2max) and running economy at lactate threshold (REOBLA). This study aims to assess maximal lactate accumulation rate (ċLamax) in terms of improving running performance prediction in trained athletes. Forty-four competitive female and male runners/triathletes performed an incremental step test, a 100-m sprint test and a ramp test to determine their metabolic profile. Stepwise linear regression was used to predict 5000-m time trial performance. Split times were recorded every 200-m to examine the ‘finishing kick’. Females had a slower t5k and a lower V̇O2max, ċLamax, ‘finishing kick’ and REOBLA. Augmenting Joyner’s model by means of ċLamax explained an additional 4.4% of variance in performance. When performing the same analysis exclusively for males, ċLamax was not included. ċLamax significantly correlated with %V̇O2max (r=-0.439, p=0.003) and the ‘finishing kick’ (r=0.389, p=0.010). ċLamax allows for significant (yet minor) improvements in 5000-m performance prediction in a mixed-sex group. This margin of improvement might differ in middle-distance events. Due to the relationship to the ‘finishing kick’, ċLamax might be related to individual pacing strategies, which should be assessed in future research.

Effects of Alternating Unilateral vs. Bilateral Resistance Training on Sprint and Endurance Cycling Performance in Trained Endurance Athletes: A 3-Armed, Randomized, Controlled, Pilot Trial

ABSTRACT

Ji, S, Donath, L, and Wahl, P. Effects of alternating unilateral vs. bilateral resistance training on sprint and endurance cycling performance in trained endurance athletes: A 3-armed, randomized, controlled, pilot trial. J Strength Cond Res 36(12): 3280-3289, 2022-Traditional preparatory resistance training for cyclists mainly relies on simultaneous bilateral movement patterns. This lack of movement specificity may impede transfer effects to specific aerobic and anaerobic requirements on the bike. Hence, this study investigated the effects of resistance training in alternating unilateral vs. simultaneous bilateral movement pattern on strength and anaerobic as well as aerobic cycling performance indices. Twenty-four trained triathletes and cyclists (age: 31.1 ± 8.1 years; V̇ o2 max: 57.6 ± 7.1 ml·min -1 ·kg -1 ) were randomly assigned to either an alternating unilateral (AUL), a simultaneous bilateral (BIL) training group or a control group (CON). Ten weeks of resistance training (4 × 4-10 repetition maximum) were completed by both training groups, although CON maintained their usual training regimen without resistance training. Maximal strength was tested during isometric leg extension, leg curl, and leg press in both unilateral and bilateral conditions. To compare the transfer effects of the training groups, determinants of cycling performance and time to exhaustion at 105% of the estimated anaerobic threshold were examined. Maximal leg strength notably increased in both training groups (BIL: ∼28%; AUL: ∼27%; p < 0.01) but not in CON (∼6%; p > 0.54). A significant improvement in cycling time trial performance was also observed in both training groups (AUL: 67%; BIL: 43%; p < 0.05) but not for CON (37%; p = 0.43). Bilateral group exhibited an improved cycling economy at submaximal intensities (∼8%; p < 0.05) but no changes occurred in AUL and CON (∼3%; p > 0.24). While sprint cycling performance decreased in CON (peak power: -6%; acceleration index: -15%; p < 0.05), improvement in favor of AUL was observed for acceleration abilities during maximal sprinting (20%; d = 0.5). Our pilot data underpin the importance of resistance training independent of its specific movement pattern both for improving the endurance cycling performance and maximal leg strength. Further research should corroborate our preliminary findings on whether sprint cycling benefits favorably from AUL resistance training.

Improved Oxygen Uptake Efficiency Parameters Are Not Correlated with VO2peak or Running Economy and Are Not Affected by Omega-3 Fatty Acid Supplementation in Endurance Runners

Peak oxygen uptake (VO_2peak) is one of the most reliable parameters of exercise capacity; however, maximum effort is required to achieve this. Therefore, alternative, and repeatable submaximal parameters, such as running economy (RE), are needed. Thus, we evaluated the suitability of oxygen uptake efficiency (OUE), oxygen uptake efficiency plateau (OUEP) and oxygen uptake efficiency at the ventilatory anaerobic threshold (OUE@VAT) as alternatives for VO_2peak and RE. Moreover, we evaluated how these parameters are affected by endurance training and supplementation with omega-3 fatty acids. A total of 26 amateur male runners completed a 12-week endurance program combined with omega-3 fatty acid supplementation or medium-chain triglycerides as a placebo. Before and after the intervention, the participants were subjected to a treadmill test to determine VO_2peak, RE, OUE, OUEP and OUE@VAT. Blood was collected at the same timepoints to determine eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in erythrocytes. OUE correlated moderately or weakly with VO_2peak (R² = 0.338, p = 0.002) and (R² = 0.226, p = 0.014) before and after the intervention, respectively. There was a weak or no correlation between OUEP, OUE@VAT, VO_2peak and RE despite steeper OUE, increased OUEP and OUE@VAT values in all participants. OUE parameters cannot be treated as alternative parameters for VO_2peak or RE and did not show changes following supplementation with omega-3 fatty acids in male amateur endurance runners.

Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis

Supplementation with Citrulline (Cit) has been shown to have a positive impact on aerobic exercise performance and related outcomes such as lactate, oxygen uptake (VO₂) kinetics, and the rate of perceived exertion (RPE), probably due to its relationship to endogenous nitric oxide production. However, current research has shown this to be controversial. The main objective of this systematic review and meta-analysis was to analyze and assess the effects of Cit supplementation on aerobic exercise performance and related outcomes, as well as to show the most suitable doses and timing of ingestion. A structured literature search was carried out by the PRISMA^® (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and PICOS guidelines in the following databases: Pubmed/Medline, Scopus, and Web of Science (WOS). A total of 10 studies were included in the analysis, all of which exclusively compared the effects of Cit supplementation with those of a placebo group on aerobic performance, lactate, VO₂, and the RPE. Those articles that used other supplements and measured other outcomes were excluded. The meta-analysis was carried out using Hedges’ g random effects model and pooled standardized mean differences (SMD). The results showed no positive effects of Cit supplementation on aerobic performance (pooled SMD = 0.15; 95% CI (−0.02 to 0.32); I², 0%; p = 0.08), the RPE (pooled SMD = −0.03; 95% CI (−0.43 to 0.38); I², 49%; p = 0.9), VO₂ kinetics (pooled SMD = 0.01; 95% CI (−0.16 to 0.17); I², 0%; p = 0.94), and lactate (pooled SMD = 0.25; 95% CI (−0.10 to 0.59); I², 0%; p = 0.16). In conclusion, Cit supplementation did not prove to have any benefits for aerobic exercise performance and related outcomes. Where chronic protocols seemed to show a positive tendency, more studies in the field are needed to better understand the effects.

Validity and Reliability of the Leomo Motion-Tracking Device Based on Inertial Measurement Unit with an Optoelectronic Camera System for Cycling Pedaling Evaluation

Background: The use of inertial measurement sensors (IMUs), in the search for a more ecological measure, is spreading among sports professionals with the aim of improving the sports performance of cyclists. The kinematic evaluation using the Leomo system (TYPE-R, Leomo, Boulder, CO, USA) has become popular. Purpose: The present study aimed to evaluate the reliability and validity of the Leomo system by measuring the angular kinematics of the lower extremities in the sagittal plane during pedaling at different intensities compared to a gold-standard motion capture camera system (OptiTrack, Natural Point, Inc., Corvallis, OR, USA). Methods: Twenty-four elite cyclists recruited from national and international cycling teams performed two 6-min cycles of cycling on a cycle ergometer at two different intensities (first ventilatory threshold (VT1) and second ventilatory threshold (VT2)) in random order, with a 5 min rest between intensity conditions. The reliability and validity of the Leomo system versus the motion capture system were evaluated. Results: Both systems showed high validity and were consistently excellent in foot angular range Q1 (FAR (Q1)) and foot angular range (FAR) (ICC-VT1 between 0.91 and 0.95 and ICC-VT2 between 0.88 and 0.97), while the variables leg angular range (LAR) and pelvic angle showed a modest validity (ICC-VT1 from 0.52 to 0.71 and ICC-VT2 between 0.61 and 0.67). Compared with Optitrack, Leomo overestimated all the variables, especially the LAR and pelvic angle values, in a range between 12 and 15°. Conclusions: Leomo is a reliable and valid tool for analyzing the ranges of motion of the cyclist’s lower limbs in the sagittal plane, especially for the variables FAR (Q1) and FAR. However, its systematic error for FAR and Pelvic Angle values must be considered in sports performance analysis.

Fractal Correlation Properties of Heart Rate Variability as a Biomarker for Intensity Distribution and Training Prescription in Endurance Exercise: An Update

While established methods for determining physiologic exercise thresholds and intensity distribution such as gas exchange or lactate testing are appropriate for the laboratory setting, they are not easily obtainable for most participants. Data over the past two years has indicated that the short-term scaling exponent alpha1 of Detrended Fluctuation Analysis (DFA a1), a heart rate variability (HRV) index representing the degree of fractal correlation properties of the cardiac beat sequence, shows promise as an alternative for exercise load assessment. Unlike conventional HRV indexes, it possesses a dynamic range throughout all intensity zones and does not require prior calibration with an incremental exercise test. A DFA a1 value of 0.75, reflecting values midway between well correlated fractal patterns and uncorrelated behavior, has been shown to be associated with the aerobic threshold in elite, recreational and cardiac disease populations and termed the heart rate variability threshold (HRVT). Further loss of fractal correlation properties indicative of random beat patterns, signifying an autonomic state of unsustainability (DFA a1 of 0.5), may be associated with that of the anaerobic threshold. There is minimal bias in DFA a1 induced by common artifact correction methods at levels below 3% and negligible change in HRVT even at levels of 6%. DFA a1 has also shown value for exercise load management in situations where standard intensity targets can be skewed such as eccentric cycling. Currently, several web sites and smartphone apps have been developed to track DFA a1 in retrospect or in real-time, making field assessment of physiologic exercise thresholds and internal load assessment practical. Although of value when viewed in isolation, DFA a1 tracking in combination with non-autonomic markers such as power/pace, open intriguing possibilities regarding athlete durability, identification of endurance exercise fatigue and optimization of daily training guidance.

Constant power threshold—predicting maximal lactate steady state in recreational cyclists

Introduction

Prolonged time trials proved capable of precisely estimating anaerobic threshold. However, time trial studies in recreational cyclists are missing. The aim of the present study was to evaluate accuracy and viability of constant power threshold, which is the highest power output constantly maintainable over time, for estimating maximal lactate steady state in recreational athletes.

Methods

A total of 25 recreational athletes participated in the study of whom 22 (11 female, 11 male) conducted all constant load time trials required for determining constant power threshold 30 min and 45 min, which is the highest power output constantly maintainable over 30 min and 45 min, respectively. Maximal lactate steady state was assessed subsequently from blood samples taken every 5 min during the time trials.

Results

Constant power threshold over 45 min (175.5 ± 49.6 W) almost matched power output at maximal lactate steady state (176.4 ± 50.5 W), whereas constant power threshold over 30 min (181.4 ± 51.4 W) was marginally higher (P = 0.007, d = 0.74). Interrelations between maximal lactate steady state and constant power threshold 30 min and constant power threshold 45 min were very close (R2 = 0.99, SEE = 8.9 W, Percentage SEE (%SEE) = 5.1%, P < 0.001 and R2 = 0.99, SEE = 10.0 W, %SEE = 5.7%, P < 0.001, respectively).

Conclusions

Determination of constant power threshold is a straining but viable and precise alternative for recreational cyclists to estimate power output at maximal lactate steady state and thus maximal sustainable oxidative metabolic rate.

Validity of Detrended Fluctuation Analysis of Heart Rate Variability to determine intensity thresholds in professional cyclists

BACKGROUND

The evaluation of performance in endurance athletes and the subsequent individualization of training is based on the determination of individual physiological thresholds during incremental tests. Gas exchange or blood lactate analysis are usually implemented for this purpose, but these methodologies are expensive and invasive. The short-term scaling exponent alpha 1 of detrended Fluctuation Analysis (DFA-α1) of the Heart Rate Variability (HRV) has been proposed as a non-invasive methodology to detect intensity thresholds.

PURPOSE

The aim of this study is to analyse the validity of DFA-α1 HRV analysis to determine the individual training thresholds in elite cyclists and to compare them against the lactate thresholds.

METHODOLOGY

38 male elite cyclists performed a graded exercise test to determine their individual thresholds. HRV and blood lactate were monitored during the test. The first (LT1 and DFA-α1-0.75, for lactate and HRV, respectively) and second (LT2 and DFA-α1-0.5, for lactate and HRV, respectively) training intensity thresholds were calculated. Then, these points were matched to their respective power output (PO) and heart rate (HR).

RESULTS

There were no significant differences (p > 0.05) between the DFA-α1-0.75 and LT1 with significant positive correlations in PO (r = 0.85) and HR (r = 0.66). The DFA-α1-0.5 was different against LT2 in PO (p = 0.04) and HR (p = 0.02), but it showed significant positive correlation in PO (r = 0.93) and HR (r = 0.71).

CONCLUSIONS

The DFA1-a-0.75 can be used to estimate LT1 non-invasively in elite cyclists. Further research should explore the validity of DFA-α1-0.5.

An Index of Non-Linear HRV as a Proxy of the Aerobic Threshold Based on Blood Lactate Concentration in Elite Triathletes

A non-linear index of heart rate (HR) variability (HRV) known as alpha1 of Detrended Fluctuation Analysis (DFA a1) has been shown to change with increasing exercise intensity, crossing a value of 0.75 at the aerobic threshold (AT) in recreational runners defining a HRV threshold (HRVT). Since large volumes of low-intensity training below the AT is recommended for many elite endurance athletes, confirmation of this relationship in this specific group would be advantageous for the purposes of training intensity distribution monitoring. Nine elite triathletes (7 male, 2 female) attended a training camp for diagnostic purposes. Lactate testing was performed with an incremental cycling ramp test to exhaustion for the determination of the first lactate threshold based on the log–log calculation method (LT1). Concurrent measurements of cardiac beta-to-beat intervals were performed to determine the HRVT. Mean LT1 HR of all 9 participants was 155.8 bpm (±7.0) vs. HRVT HR of 153.7 bpm (±10.1) (p = 0.52). Mean LT1 cycling power was 252.3 W (±48.1) vs. HRVT power of 247.0 W (±53.6) (p = 0.17). Bland–Altman analysis showed mean differences of −1.7 bpm and −5.3 W with limits of agreement (LOA) 13.3 to −16.7 bpm and 15.1 to −25.6 W for HR and cycling power, respectively. The DFA a1-based HRVT closely agreed with the LT1 in a group of elite triathletes. Since large volumes of low-intensity exercise are recommended for successful endurance performance, the fractal correlation properties of HRV show promise as a low-cost, non-invasive option to that of lactate testing for identification of AT-related training boundaries.

Determination of second lactate threshold using near-infrared spectroscopy in elite cyclists

The use of near-infrared spectroscopy could be an interesting alternative to other invasive or expensive methods to estimate the second lactate threshold. Our objective was to compare the intensities of the muscle oxygen saturation breakpoint obtained with the Humon Hex and the second lactate threshold in elite cyclists. Ninety cyclists performed a maximal graded exercise test. Blood capillary lactate was obtained at the end of steps and muscle oxygenation was continuously monitored. There were no differences (p>0.05) between muscle oxygen oxygenation breakpoint and second lactate threshold neither in power nor in heart rate, nor when these values were relativized as a percentage of maximal aerobic power or maximum heart rate. There were also no differences when men and women were studied separately. Both methods showed a highly correlation in power (r=0.914), percentage of maximal aerobic power (r=0.752), heart rate (r=0.955), and percentage of maximum heart rate (r=0.903). Bland-Altman resulted in a mean difference of 0.05±0.27 W·kg-1, 0.91±4.93%, 0.63±3.25 bpm, and 0.32±1.69% for power, percentage of maximal aerobic power, heart rate and percentage of maximum heart rate respectively. These findings suggest that Humon may be a non-invasive and low-cost alternative to estimate the second lactate threshold intensity in elite cyclists.

Novel Computerized Method for Automated Determination of Ventilatory Threshold and Respiratory Compensation Point

Introduction: The ventilatory threshold (named as VT₁) and the respiratory compensation point (named as VT₂) describe prominent changes of metabolic demand and exercise intensity domains during an incremental exercise test.

Methods: A novel computerized method based on the optimization method was developed for automatically determining VT₁ and VT₂ from expired air during a progressive maximal exercise test. A total of 109 peak cycle tests were performed by members of the US astronaut corps (74 males and 35 females). We compared the automatically determined VT₁ and VT₂ values against the visual subjective and independent analyses of three trained evaluators. We also characterized VT₁ and VT₂ and the respective absolute and relative work rates and distinguished differences between sexes.

Results: The automated compared to the visual subjective values were analyzed for differences with t test, for agreement with Bland–Altman plots, and for equivalence with a two one-sided test approach. The results showed that the automated and visual subjective methods were statistically equivalent, and the proposed approach reliably determined VT₁ and VT₂ values. Females had lower absolute O₂ uptake, work rate, and ventilation, and relative O₂ uptake at VT₁ and VT₂ compared to men (p ≤ 0.04). VT₁ and VT₂ occurred at a greater relative percentage of their peak VO₂ for females (67 and 88%) compared to males (55 and 74%; main effect for sex: p < 0.001). Overall, VT₁ occurred at 58% of peak VO_2, and VT₂ occurred at 79% of peak VO₂ (p < 0.0001).

Conclusion: Improvements in determining of VT₁ and VT₂ by automated analysis are time efficient, valid, and comparable to subjective visual analysis and may provide valuable information in research and clinical practice as well as identifying exercise intensity domains of crewmembers in space.

Grey Zone: A Gap Between Heavy and Severe Exercise Domain

ABSTRACT

Ozkaya, O, Balci, GA, As, H, Cabuk, R, and Norouzi, M. Grey zone: A gap between heavy and severe exercise domain. J Strength Cond Res 36(1): 113-120, 2022-The aim of this study was to determine a critical threshold (CT) interpreted as "the highest exercise intensity where V̇o2 can be stabilized before reaching 95% of V̇o2max (V̇o2peak)" and compare it with commonly used anaerobic threshold indices. Ten well-trained male cyclists volunteered for this study. Ventilatory threshold (VT) was determined from incremental tests. Multisession constant-load trials were performed to reveal V̇o2max. Mathematically modeled critical power (CP) was estimated through the best individual fit parameter method. Maximal lactate steady state (MLSS) was detected by 30-minute constant-load exercises. The individual CT load of each cyclist was tested by constant-load exercises to exhaustion with +15 W intervals until minimal power output to elicit V̇o2peak. The results showed that work rate corresponding to CT (329.5 ± 41.5 W) was significantly greater than that of the MLSS (269.5 ± 38.5 W; p = 0.000), VT (279.6 ± 33 W; p = 0.000), and CP (306.3 ± 39.4 W; p = 0.000), and CP overestimated both VT and MLSS (p = 0.000). There was no significant V̇o2 difference between the 10th and 30th minute of MLSS and MLSS + 15 W exercise (0.36-0.13 ml·min-1·kg-1; p = 0.621). Exercising V̇o2 response of MLSS + 15 W could not exceed the level of 95% V̇o2max (57.02 ± 3.87 ml·min-1·kg-1 and 87.2 ± 3.1% of V̇o2max; p = 0.000), whereas V̇o2 responses greater than 95% of V̇o2max were always attained during exercises performed at CT + 15 W (64.52 ± 4.37 ml·min-1·kg-1 and 98.6 ± 1% of V̇o2max; p > 0.05). In conclusion, this study indicates that there is a "grey zone" between heavy and severe exercise domain. This information may play a key role in enhancing athletic performance by improving the quality of training programs.

A Reappraisal of Ventilatory Thresholds in Wheelchair Athletes With a Spinal Cord Injury: Do They Really Exist?

The ventilatory threshold (VT) separates low- from moderate-intensity exercise, the respiratory compensation point (RCP) moderate- from high-intensity exercise. Both concepts assume breakpoints in respiratory data. However, the objective determination of the VT and RCP using breakpoint models during upper-body modality exercise in wheelchair athletes with spinal cord injury (SCI) has received little attention. Therefore, the aim of this study was to compare the fit of breakpoint models (i.e., two linear regression lines) with continuous no-breakpoint models (i.e., exponential curve/second-order polynomial) to respiratory data obtained during a graded wheelchair exercise test to exhaustion. These fits were compared employing adjusted R², and blocked bootstrapping was used to derive estimates of a median and 95% confidence intervals (CI). V̇O₂-V̇CO₂ and V̇E/V̇O₂-time data were assessed for the determination of the VT, and V̇CO₂-V̇E and V̇E/V̇CO₂-time data for the determination of the RCP. Data of 9 wheelchair athletes with tetraplegia and 8 with paraplegia were evaluated. On an overall group-level, there was an overlap in the adjusted R² median ± 95% CI between the breakpoint and the no-breakpoint models for determining the VT (V̇O₂-V̇CO₂: 0.991 ± 0.003 vs. 0.990 ± 0.003; V̇E/V̇O₂-time: 0.792 ± 0.101 vs. 0.782 ± 0.104, respectively) and RCP (V̇E-V̇CO₂: 0.984 ± 0.004 vs. 0.984 ± 0.004; V̇E/V̇CO₂-time: 0.729 ± 0.064 vs. 0.691 ± 0.063, respectively), indicating similar model fit. We offer two lines of reasoning: (1) breakpoints in these respiratory data exist but are too subtle to result in a significant difference in adjusted R² between the investigated breakpoint and no-breakpoint models; (2) breakpoints do not exist, as has been argued previously.

Biological variation of venous acid-base status measurands in athletes

BACKGROUND

Analysis of acid-base status (ABS) is requested in a wide range of clinical scenarios, including in the assessment of athletes' performance and follow up, but there is a lack of high-quality biological variation (BV) data. The aims of this study were to estimate the BV of ABS related parameters in athletes and to evaluate if variables related to exercise may influence the estimates.

MATERIAL AND METHODS

Eleven samples from 30 triathletes were drawn, on a monthly basis. The samples were measured for pH, pCO₂, bicarbonate, base excess, TCO₂, Ca²⁺ and lactate. A CV-ANOVA was performed to calculate within-subject (CV_I) estimates and a linear mixed model was applied to analyze the effect of the folowing variables on the BV; health status, sampling interval, intensity and duration of the exercise.

RESULTS

For all ABS parameters except for lactate, higher CV_I estimates were found in athletes than what have been reported for the general population. No significant effect of the exercise and sampling related variables were observed, except for Ca²⁺.

CONCLUSION

This difference founds in ABS parameters between athletes and the general population could be explained by the physiological stress during exercise. Laboratories attending this population could use these BV estimates to establish quality goals.

Respiratory Activity during Exercise: A Feasibility Study on Transition Point Estimation Using Impedance Pneumography

The current diagnostic procedures for assessing physiological response to exercise comprise blood lactates measurements, ergospirometry, and electrocardiography. The first is not continuous, the second requires specialized equipment distorting natural breathing, and the last is indirect. Therefore, we decided to perform the feasibility study with impedance pneumography as an alternative technique. We attempted to determine points in respiratory-related signals, acquired during stress test conditions, that suggest a transition similar to the gas exchange threshold. In addition, we analyzed whether or not respiratory activity reaches steady states during graded exercise. Forty-four students (35 females), practicing sports on different levels, performed a graded exercise test until exhaustion on cycloergometer. Eventually, the results from 34 of them were used. The data were acquired with Pneumonitor 2. The signals demonstrated that the steady state phenomenon is not as evident as for heart rate. The results indicated respiratory rate approaches show the transition point at the earliest (more than 6 min before the end of the exercise test on average), and the tidal volume ones at the latest (less than 5 min). A combination gave intermediate findings. The results showed the impedance pneumography appears reasonable for the transition point estimation, but this should be further studied with the reference.

Aerobic Threshold Identification in a Cardiac Disease Population Based on Correlation Properties of Heart Rate Variability

An index of heart rate (HR) variability correlation properties, the short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA a1) has shown potential to delineate the first ventilatory threshold (VT1). This study aims to extend this concept to a group of participants with cardiac disease. Sixteen volunteers with stable coronary disease or heart failure performed an incremental cycling ramp to exhaustion PRE and POST a 3-week training intervention. Oxygen uptake (VO₂) and HR at VT1 were obtained from a metabolic cart. An ECG was processed for DFA a1 and HR. The HR variability threshold (HRVT) was defined as the VO₂, HR or power where DFA a1 reached a value of 0.75. Mean VT1 was reached at 16.82 ± 5.72 mL/kg/min, HR of 91.3 ± 11.9 bpm and power of 67.8 ± 17.9 watts compared to HRVT at 18.02 ± 7.74 mL/kg/min, HR of 94.7 ± 14.2 bpm and power of 73.2 ± 25.0 watts. Linear relationships were seen between modalities, with Pearson’s r of 0.95 (VO₂), 0.86 (HR) and 0.87 (power). Bland–Altman assessment showed mean differences of 1.20 mL/kg/min, 3.4 bpm and 5.4 watts. Mean peak VO₂ and VT1 did not change after training intervention. However, the correlation between PRE to POST change in VO₂ at VT1 with the change in VO₂ at HRVT was significant (r = 0.84, p < 0.001). Reaching a DFA a1 of 0.75 was associated with the VT1 in a population with cardiac disease. VT1 change after training intervention followed that of the HRVT, confirming the relationship between these parameters.

Hypoxic and Hyperoxic Breathing as a Complement to Low-Intensity Physical Exercise Programs: A Proof-of-Principle Study

Inflammation is an adaptive response to both external and internal stimuli including infection, trauma, surgery, ischemia-reperfusion, or malignancy. A number of studies indicate that physical activity is an effective means of reducing acute systemic and low-level inflammation occurring in different pathological conditions and in the recovery phase after disease. As a proof-of-principle, we hypothesized that low-intensity workout performed under modified oxygen supply would elicit a "metabolic exercise" inducing a hormetic response, increasing the metabolic load and oxidative stress with the same overall effect expected after a higher intensity or charge exercise. Herein, we report the effect of a 5-week low-intensity, non-training, exercise program in a group of young healthy subjects in combination with the exposure to hyperoxia (30% and 100% pO₂, respectively) or light hypoxia (15% pO₂) during workout sessions on several inflammation and oxidative stress parameters, namely hemoglobin (Hb), redox state, nitric oxide metabolite (NOx), inducible nitric oxide synthase (iNOS), inflammatory cytokine expression (TNF-α, interleukin (IL)-6, IL-10), and renal functional biomarkers (creatinine, neopterin, and urates). We confirmed our previous reports demonstrating that intermittent hyperoxia induces the normobaric oxygen paradox (NOP), a response overlapping the exposure to hypoxia. Our data also suggest that the administration of modified air composition is an expedient complement to a light physical exercise program to achieve a significant modulation of inflammatory and immune parameters, including cytokines expression, iNOS activity, and oxidative stress parameters. This strategy can be of pivotal interest in all those conditions characterized by the inability to achieve a sufficient workload intensity, such as severe cardiovascular alterations and articular injuries failing to effectively gain a significant improvement of physical capacity.

Comparison of Aerobic Capacity Changes as a Result of a Polarized or Block Training Program among Trained Mountain Bike Cyclists

This study compared the effectiveness of a block training program and a polarized training program in developing aerobic capacity in twenty trained mountain bike cyclists. The cyclists were divided into two groups: the block training program group (BT) and the polarized training program group (PT). The experiment lasted 8 weeks. During the experiment, the BT group alternated between 17-day blocks consisting of dominant low-intensity training (LIT) and 11-day blocks consisting of sprint interval training (SIT), and high-intensity interval training (HIIT), while the PT group performed SIT, HIIT, and LIT simultaneously. Before and after the experiment, the cyclists performed incremental tests during which maximal oxygen uptake (VO₂max), maximal aerobic power (Pmax), power achieved at the first ventilatory threshold (P_VT1), and at the second ventilatory threshold (P_VT2) were measured. VO₂max increased in BT group (from 3.75 ± 0.67 to 4.00 ± 0.75 L∙min^-1) and PT group (from 3.66 ± 0.73 to 4.20 ± 0.89 L∙min^-1). In addition, Pmax, P_VT1, and P_VT2 increased in both groups to a similar extent. In conclusion, the polarized training program was more effective in developing the VO₂max compared to the block program. In terms of developing other parameters characterizing the cyclists' aerobic capacity, the block and polarized program induced similar results.

Real-Time Estimation of Aerobic Threshold and Exercise Intensity Distribution Using Fractal Correlation Properties of Heart Rate Variability: A Single-Case Field Application in a Former Olympic Triathlete

A non-linear heart rate variability (HRV) index based on fractal correlation properties called alpha1 of Detrended Fluctuation Analysis (DFA-alpha1), has been shown to change with endurance exercise intensity. Its unique advantage is that it provides information about current absolute exercise intensity without prior lactate or gas exchange testing. Therefore, real-time assessment of this metric during field conditions using a wearable monitoring device could directly provide a valuable exercise intensity distribution without prior laboratory testing for different applied field settings in endurance sports. Until of late no mobile based product could display DFA-alpha1 in real-time using off the shelf consumer products. Recently an app designed for iOS and Android devices, HRV Logger, was updated to assess DFA-alpha1 in real-time. This brief research report illustrates the potential merits of real-time monitoring of this metric for the purposes of aerobic threshold (AT) estimation and exercise intensity demarcation between low (zone 1) and moderate (zone 2) in a former Olympic triathlete. In a single-case feasibility study, three practically relevant scenarios were successfully evaluated in cycling, (1) estimation of a HRV threshold (HRVT) as an adequate proxy for AT using Kubios HRV software via a typical cycling stage test, (2) estimation of the HRVT during real-time monitoring using a cycling 6 min stage test, (3) a simulated 1 h training ride with enforcement of low intensity boundaries and real-time HRVT confirmation. This single-case field evaluation illustrates the potential of an easy-to-use and low cost real-time estimation of the aerobic threshold and exercise intensity distribution using fractal correlation properties of HRV. Furthermore, this approach may enhance the translation of science into endurance sports practice for future real-world settings.

A qualitative scale of the 6-minute race test to evaluate maximum aerobic speed in physically active people from 18 to 25 years

[Purpose] To create a qualitative scale for the 6-minute race test in physically active participants from 18 to 25 years old. [Participants and Methods] The sample was 299 healthy participants (254 males and 45 females). All the participants were instructed to perform the greatest possible distance in the 6-minute race test. To evaluate the reliability of the 6-minute race test, 30 participants performed the 6-minute race test for a second time. The variable was distance in meters. The qualitative scale was constructed with the percentiles <25, 50, 75, 90 and >90 for the criteria poor, fair, good, very good and excellent, respectively; the reliability was calculated with the coefficient of variation, intra-class correlation coefficient and the standard error of the mean. [Results] In the 6-minute race test, the mean was 1,607 and 1,364 meters for males and females, respectively. The coefficient of variation=4.08%, intra-class correlation coefficient=0.93 and standard error of the mean=11.46. [Conclusion] The creation of the qualitative scale of the 6-minute race test allows us to evaluate and classify the level and increase of maximum aerobic speed in physically active participants from 18 to 25 years old.

Training Load and Performance Impairments in Professional Cyclists During COVID-19 Lockdown

Purpose: The COVID-19 outbreak has challenged professional athletes’ training and competition routines in a way not seen before. This report aims to inform about the changes in training volume and intensity distribution and their effects on functional performance due to a 7-week home-confinement period in professional road cyclists from a Union Cycliste Internationale Pro Team. Methods: A total of 18 male professional cyclists (mean [SD] age = 24.9 [2.8] y, body mass = 66.5 [5.6] kg, maximal aerobic power = 449 [39] W; 6.8 [0.6] W/kg) were monitored during the 10 weeks before the lockdown (outdoor cycling) and the 7-week lockdown (indoor cycling turbo trainer). Data from the mean maximal power output (in watts per kilogram) produced during the best 5-minute and best 20-minute records and the training intensity distributions (weekly volumes at power-based training zones) were collected from WKO5 software. Results: Total training volume decreased 33.9% during the lockdown (P < .01). Weekly volumes by standardized zones (Z1 to Z6) declined between 25.8% and 52.2% (effect size from 0.83 to 1.57), except for Z2 (P = .38). There were large reductions in best 5-minute and best 20-minute performance (effect size > 1.36; P < .001) with losses between 1% and 19% in all the cyclists. Conclusions: Total indoor volumes of 12 hours per week, with 6 hours per week at low intensity (Z1 and Z2) and 2 hours per week at high intensity over the threshold (Z5 and Z6), were insufficient to maintain performance in elite road cyclists during the COVID-19 lockdown. Such performance declines should be considered to enable a safe and effective return to competition.

Modified Talk Test: a Randomized Cross-over Trial Investigating the Comparative Utility of Two "Talk Tests" for Determining Aerobic Training Zones in Overweight and Obese Patients

BACKGROUND

To validate the traditional talk test (TTT) and an alternative talk test (ATT; using a visual analog scale) in overweight/obese (OW-OB) patients and to establish its accuracy in determining the aerobic training zones.

METHODS

We recruited 19 subjects aged 34.9 ± 6.7 years, diagnosed with overweight/obesity (BMI 31.8 ± 5.7). Every subject underwent incremental cycloergometric tests for maximal oxygen consumption, and TTT in a randomized order. At the end of each stage during the TTT, each subject read out loud a 40 words text and then had to identify the comfort to talk in two modalities: TTT which consisted in answering "Yes," "I don't know," or "No" to the question Was talking comfortable?, or ATT through a 1 to 10 numeric perception scale (visual analog scale (VAS)). The magnitude of differences was interpreted in comparison to the smallest worthwhile change and was used to determine agreement.

RESULTS

There was an agreement between the power output at the VAS 2-3 of ATT and the power output at the ventilatory threshold 1 (VT1) (very likely equivalent; mean difference - 1.3 W, 90% confidence limit (CL) (- 8.2; 5.6), percent chances for higher/similar/lower values of 0.7/99.1/0.2%). Also, there was an agreement between the power output at the VAS 6-7 of ATT and the power output at the ventilatory threshold 2 (VT2) (very likely equivalent; mean difference 11.1 W, 90% CL (2.8; 19.2), percent chances for higher/similar/lower values of 0.0/97.6/2.4%).

CONCLUSIONS

ATT is a tool to determine exercise intensity and to establish aerobic training zones for exercise prescription in OW-OB patients.

Stability of Heart Rate at Physiological Thresholds Between Temperate and Heat Stress Environments in Endurance-Trained Males

Many endurance athletes perform specific blocks of training in hot environments in "heat stress training camps." It is not known if physiological threshold heart rates measured in temperate conditions are reflective of those under moderate environmental heat stress. A total of 16 endurance-trained cyclists and triathletes performed incremental exercise assessments in 18°C and 35°C (both 60% relative humidity) to determine heart rates at absolute blood lactate and ventilatory thresholds. Heart rate at fixed blood lactate concentrations of 2, 3, and 4 mmol·L-1 and ventilatory thresholds were not significantly different between environments (P > .05), despite significant heat stress-induced reductions in power output of approximately 10% to 17% (P < .05, effect size = 0.65-1.15). The coefficient of variation for heart rate at these blood lactate concentrations (1.4%-2.9%) and ventilatory thresholds (2.3%-2.7%) between conditions was low, with significant strong positive correlations between measurements in the 2 environments (r = .92-.95, P < .05). These data indicate heart rates measured at physiological thresholds in temperate environments are reflective of measurements taken under moderate environmental heat stress. Therefore, endurance athletes embarking on heat stress training camps can use heart rate-based thresholds ascertained in temperate environments to prescribe training under moderate environmental heat stress.

Relationship between functional threshold power, ventilatory threshold and respiratory compensation point in road cycling

BACKGROUND

The purpose of this study was to assess the relationship between power output and relative power output at the functional threshold power, ventilatory threshold and respiratory compensation point in road cyclists.

METHODS

Forty-six road cyclists (age 38 ± 9 years; height 177 ± 9 cm; body mass 71.4 ± 8.6 kg; body mass index 22.7 ± 2.2 kg·m-1; fat mass 7.8 ± 4%, VO2max 61.1 ± 9.1 ml·min-1·kg-1) performed a graded exercise test in which power output and relative power output at the ventilatory landmarks were identified. Functional threshold power was established as 95% of the power output during a 20-minute test.

RESULTS

Power output and relative power output at the functional threshold power were higher than at the ventilatory threshold (p < 0.001). There were very large to near perfect correlations for power output (95% CI for r from 0.71 to 0.9) and relative power output (95% CI for r from 0.79 to 0.93) at the functional threshold power and respiratory compensation point. Mean bias in power ouput and relative power output measured at RCP compared with FTP was not significant (mean bias 95% CI from -7 to 10 W and - 0.1 to 0.1 W/kg, respectively).

CONCLUSIONS

Power output and relative power output at the functional threshold power are higher than at the ventilatory threshold. Power output and relative power output at the functional threshold power and respiratory compensation point are strongly related, but caution is required when using both concepts indistinctly.

Exercise alters cardiac function independent of acute systemic inflammation in healthy men

Acute elevations in inflammatory cytokines have been demonstrated to increase aortic and left ventricular stiffness and reduce endothelial function in healthy subjects. As vascular and cardiac functions are often transiently reduced following prolonged exercise, it is possible that cytokines released during exercise may contribute to these alterations. The a priori aims of this study were to determine whether vaccine-induced increases in inflammatory cytokines would reduce vascular and left ventricular function, whether vascular alterations would drive cardiac impairments, and whether this would be potentiated by moderate exercise. In a randomized crossover fashion, 16 male participants were tested under control (CON) and inflammatory (INF) conditions, wherein INF testing occurred 8 h following administration of an influenza vaccine. On both days, participants underwent measures of echocardiography performed during light cycling (stress-echocardiography), carotid-femoral pulse wave velocity (cf-PWV), and superficial femoral flow-mediated dilation (FMD) before and after cycling for 90 min at ∼85% of their first ventilatory threshold. IL-6 increased significantly (Δ1.9 ± 1.3 pg/mL, P < 0.001), whereas TNFα was nonsignificantly augmented (Δ0.05 ± 0.11 pg/mL, P = 0.09), 8 h following vaccination. Vascular function was unaltered following cycling or inflammation (all P > 0.05). The use of echocardiography during light cycling revealed cardiac alterations traditionally expected to occur only with greater exercise loads, with reduced systolic (e.g., longitudinal strain CON: Δ3.3 ± 4.4%, INF: Δ1.7 ± 2.7%, P = 0.002) and diastolic function (e.g., E/A ratio CON: Δ-0.32 ± 0.34 a.u., INF:Δ-0.25 ± 0.27 a.u., P = 0.002) following cycling, independent of inflammation. The vaccine reduced stroke volume (SV) (main effect of condition P = 0.009) before-and-after cycling. These findings indicate that reduced cardiac function following exercise occurs largely independent of additional inflammatory load.NEW & NOTEWORHTHY This experimental investigation sought to determine the role of inflammation on the occurrence of cardiovascular alterations following exercise. Despite successfully stimulating systemic inflammation via vaccination, vascular and cardiac functions were largely unaltered. Prolonged exercise itself reduced cardiac function assessed via echocardiography performed during light exercise stress. This demonstrates a potential advantage to using stress-echocardiography for measuring exercise-induced cardiac fatigue, as typical resting measures following similar exercise exposures commonly suggest no effect.

Physiological Determinants of Ultramarathon Trail-Running Performance

CONTEXT

The physiological determinants of ultramarathon success have rarely been assessed and likely differ in their contributions to performance as race distance increases.

PURPOSE

To examine predictors of performance in athletes who completed either a 50-, 80-, or 160-km trail race over a 20-km loop course on the same day.

METHODS

Measures of running history, aerobic fitness, running economy, body mass loss, hematocrit alterations, age, and cardiovascular health were examined in relation to race-day performance. Performance was defined as the percentage difference from the winning time at a given race distance, with 0% representing the fastest possible time.

RESULTS

In the 50-km race, training volumes, cardiovascular health, aerobic fitness, and a greater loss of body mass during the race were all related to better performance (all P < .05). Using multiple linear regression, peak velocity achieved in the maximal oxygen uptake test (β = -11.7, P = .002) and baseline blood pressure (β = 3.1, P = .007) were the best performance predictors for the men's 50-km race (r = .98, r2 = .96, P < .001), while peak velocity achieved in the maximal oxygen uptake test (β = -13.6, P = .001) and loss of body mass (β = 12.8, P = .03) were the best predictors for women (r = .94, r2 = .87, P = .001). In the 80-km race, only peak velocity achieved in the maximal oxygen uptake test predicted performance (β = -20.3, r = .88, r2 = .78, P < .001). In the 160-km race, there were no significant performance determinants.

CONCLUSIONS

While classic determinants of running performance, including cardiovascular health and running fitness, predict 50-km trail-running success, performance in longer-distance races appears to be less influenced by such physiological parameters.