Raphael Knaier

University of Basel | UNIBAS · Department Sport Exercise and Health

Purpose: This study examines age- and sex-related physiological differences in cardiopulmonary exercise testing (CPET) between children and adults, focusing on ventilatory thresholds (VT) and oxygen uptake efficiency slope and plateau (OUES; OUEP). Methods: The cross-sectional analysis comprised 24 children (7–11 years), 20 moderately- trained (MTA...

To define training zones, ventilatory thresholds (VTs) are commonly established by cardiopulmonary gas-exchange analysis during incremental exercise tests. Portable near-infrared spectroscopy (NIRS) devices have emerged as a potential tool for detecting these thresholds by monitoring muscle oxygenation. This study evaluated the accuracy of NIRS mea...

Coronary artery disease (CAD) remains a leading cause of death worldwide and imposes a substantial socioeconomic burden on healthcare. Improving risk stratification in clinical practice could help to combat this burden. As amino acids are biologically active metabolites whose involvement in CAD remains largely unknown, this study investigated assoc...

Aims To investigate how physical activity (PA) volume, intensity, duration, and fragmentation are associated with the risk of all-cause and cardiovascular disease mortality. To produce centile curves for PA volume and intensity representative of US adults. Methods This study is based on the observational 2011-2014 National Health and Nutrition Exa...

Objective: To (1) establish extensive physiological profiles of highly trained CrossFit® athletes using gold-standard tests and (2) investigate which physiological markers best correlate with CrossFit Open performance. Methods: This study encompassed 60 participants (30 men and 30 women), all within the top 5% of the CrossFit Open, including 7 Cro...

Background To investigate whether quantifying both the absolute and relative intensity of physical activity (PA) improves understanding of age, sex, and occupation-related differences in PA in healthy adults aged 20–89. Methods In the cross-sectional COmPLETE study, participants (N = 460, 48% women, age 55 [IQR 37, 71]) wore accelerometers for up...

Purpose The objective was to investigate if performing a sub-peak or supra-peak verification phase following a ramp test provides additional value for determining 'true' maximum oxygen uptake (V˙\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs...

Background: Gait changes with aging have been investigated, but few studies have examined a wide range of gait parameters across the adult lifespan. This study aimed to investigate gait differences across age groups stratified by sex. Methods: This cross-sectional study included 629 healthy, normal-weight (i.e., BMI < 30 kg/m 2) participants from S...

Objective: To 1) establish extensive physiological profiles of highly-trained CrossFit athletes using gold-standard tests and 2) investigate which physiological markers best correlate with CrossFit Open performance. Methods: This study encompassed sixty participants (30 males and 30 females), all within the top 5% of the CrossFit Open, including 7...

Purpose: Accelerometer-assessed physical activity (PA) can be summarised using cut-point-free or population-specific cut-point-based outcomes. We aimed to: 1) examine the interrelationship between cut-point-free (intensity gradient [IG] and average acceleration [AvAcc]) and cut-point-based accelerometer metrics, 2) compare the association between c...

Introduction Well-trained staff is needed to interpret cardiopulmonary exercise tests (CPET). We aimed to examine the accuracy of machine learning-based algorithms to classify exercise limitations and their severity in clinical practice compared to expert consensus using patients presenting at a pulmonary clinic. Methods This study included 200 hi...

Background Current recommendations for physical exercise include information about the frequency, intensity, type, and duration of exercise. However, to date, there are no recommendations on what time of day one should exercise. The aim was to perform a systematic review with meta-analysis to investigate if the time of day of exercise training in i...

Objectives: To compare the association between cardiorespiratory fitness (CRF) and cut-point-free accelerometer metrics (intensity gradient [IG] and average acceleration [AvAcc]) to that with traditional metrics in healthy adults aged 20 to 89 years and patients with heart failure, and 2) provide age-, sex-, and CRF-related reference values for hea...

Background Accelerometry has gained increasing popularity and yields numerous physical activity (PA) outcomes (Rowlands et al., 2019). These include traditional cut-point-based (i.e. light, moderate, and vigorous PA) and cut-point-free metrics (i.e. intensity gradient [IG] and average acceleration [AvAcc]). IG reflects the intensity distribution o...

Patients recovering from COVID-19 often report symptoms of exhaustion, fatigue and dyspnoea and present with exercise intolerance persisting for months post-infection. Numerous studies investigated these sequelae and their possible underlying mechanisms using cardiopulmonary exercise testing. We aimed to provide an in-depth discussion as well as an...

Background: Cardiovascular health scores, such as Life's Simple 7 from the American Heart Association, and the assessment of arterial properties are independently used to determine cardiovascular risk. However, evidence of their association remains scarce, especially in healthy, middle-aged to older populations. Methods: A healthy sample of the...

Background Grip strength is used to estimate whole-body strength for health surveillance purposes. Explosive strength is considered important, yet economic measures able to detect early deterioration of neuromuscular capabilities are lacking. Whether handgrip maximum rate of force development (GRFD) or whole-body strength tests are better predictor...

Purpose There is no convincing evidence for the idea that a high power output at the maximal lactate steady state (PO_MLSS) and a high fraction of 𝑉˙O2max at MLSS (%𝑉˙O2_MLSS) are decisive for endurance performance. We tested the hypotheses that (1) %𝑉˙O2_MLSS is positively correlated with the ability to sustain a high fraction of 𝑉˙O2max for a giv...

Background Individuals with a higher lifelong cardiorespiratory fitness show better vascular health with aging. Studies on fitness-related effects on endothelial function either analyzed samples with a narrow age-range or incompletely assessed endothelial responsiveness. This study aims to assess the impact of cardiorespiratory fitness on the assoc...

Background Endothelial dysfunction represents a diagnostic marker to differentiate disease severity in chronic heart failure (CHF) patients. Retinal vessel phenotyping was applied in CHF patients as it has been acknowledged as a sensitive diagnostic tool to quantify microvascular health and overall cardiovascular risk. Methods The central retinal...

Coronary artery disease (CAD) remains the leading cause of death worldwide. Expanding patients' metabolic phenotyping beyond clinical chemistry investigations could lead to earlier recognition of disease onset and better prevention strategies. Additionally, metabolic phenotyping, at the molecular species level, contributes to unravel the roles of m...

Objective: The aim of this study was to analyze whether V̇O2-kinetics during cardiopulmonary exercise testing (CPET) is a useful marker for the diagnosis of heart failure (HF) and to determine which V̇O2-kinetic parameter distinguishes healthy participants and patients with HF. Methods: A total of 526 healthy participants and 79 patients with HF be...

Background: For valid accelerometer‑assessed physical activity (PA) data, several methodological aspects should be considered. We aimed to 1) visualize the applicability of absolute accelerometer cut‑offs to classify PA intensity, 2) verify recommendations to measure PA over 7 days by examining inter‑day variability and reactivity, 3) examine sea...

A flattening of the oxygen uptake-work rate relationship at severe exercise indicates the achievement of maximum oxygen uptake [Formula: see text]. Unfortunately, a distinct plateau [Formula: see text] at [Formula: see text]is not found in all participants. The aim of this investigation was to critically review the influence of research methods and...

Introduction: Diurnal variations in physical performance can affect athletes' success in competitive sports depending on whether the time of peak performance concurs with the time of competition. The purpose of this systematic review was to investigate the diurnal variation in maximum endurance and strength performance. Methods: The databases Pu...

Retinal vessel phenotype is predictive for cardiovascular outcome. This cross-sectional population-based study aimed to quantify normative data and standard operating procedures for static and dynamic retinal vessel analysis. We analysed central retinal arteriolar (CRAE) and venular (CRVE) diameter equivalents, as well as retinal endothelial functi...

As ageing is a major risk factor for the development of non-communicable diseases, extending healthspan has become a medical and societal necessity. Precise lipid phenotyping that captures metabolic individuality could support healthspan extension strategies. This study applied ‘omic-scale lipid profiling to characterise sex-specific age-related di...

Objectives: Brachial arterial low flow-mediated constriction (L-FMC) and flow-mediated dilation (FMD) are ultrasound-based biomarkers that emerge into scientific and clinical practice indicating cardiovascular effects of medical and lifestyle-based treatment beyond classical risk factors. This study is the first to provide reference values and to...

Objective This study compared the robustness of a V˙O2-plateau definition and a verification-phase protocol to day-to-day and diurnal variations in determining the true V˙O2max. Further, the additional value of a verification-phase was investigated. Methods Eighteen adults performed six cardiorespiratory fitness tests at six different times of the...

Background Aging and changing age demographics represent critical problems of our time. Physiological functions decline with age, often ending in a systemic process that contributes to numerous impairments and age-related diseases including heart failure (HF). We aimed to analyze whether differences in composite measures of physiological function [...

Purpose: Cardiopulmonary exercise testing (CPET) is an important measurement in clinical practice, and its primary outcome, maximal oxygen uptake (V˙O2peak), is inversely associated with morbidity and mortality. The purposes of this study are to provide CPET reference values for maximal and submaximal parameters across the adult age spectrum of a...

Purpose: To determine age-dependent cutoff values for secondary exhaustion criteria for a general population free of exercise limiting chronic conditions; to describe the percentage of participants reaching commonly-used exhaustion criteria during a cardiopulmonary exercise test (CPET); and to analyze their oxygen uptake at the respective criteria...

OBJECTIVE: This study assessed the validity of a consumer activity wristband, a smartphone, and a research-grade accelerometer to measure steps in a free-living setting. APPROACH: Thirty healthy adults were equipped with two Garmin Vivofit (non-dominant wrist), one iPhone SE (right pants pocket), three ActiGraph wGT3X+ (two on the hip, one on the...

Time-of-day effects in strength performance have been extensively investigated due to their relevance in competitive sports. However, most studies use large measurement intervals making it difficult to monitor potential performance changes throughout the day. Furthermore, previous studies have exclusively focused on how the time of day affects stre...

Background: Cardiovascular (CV) diseases including heart failure are the leading causes of morbidity, with age being the primary risk factor. The combination of age-related organic functional impairment and reduced physical fitness can drastically impact an individual's healthspan. One's lifespan can potentially be prolonged by the preservation or...

In competitive sports any substantial individual differences in diurnal variations in maximal performance are highly relevant. Previous studies have exclusively focused on how the time of day affects performance and disregarded the maximal individual diurnal variation of performance. Thus, the aims of this study were (1) to investigate the maximum...

BACKGROUND: Wrist-worn accelerometers are increasingly used in epidemiological studies to record physical activity. The accelerometer data are usually only analyzed if the convention for compliant wear time is met (i.e. ≥ 10 h per day) but the algorithms to detect wear time have been developed based on data from hip-worn devices only and have not b...

Purpose: The aim was to determine the minimum maximum oxygen uptake (V˙O2max) criteria cut-offs in highly trained athletes (i.e., maximum RER [RERmax], maximum HR [HRmax], maximum RPE [RPEmax], and maximum blood lactate concentration [BLmax]) necessary to determine maximum oxygen uptake (V˙O2max) during cardiopulmonary exercise tests (CPET), by ba...

PURPOSE: To examine the validity of popular smartphone accelerometer applications and a consumer activity wristband compared to a widely-used research accelerometer while assessing the impact of the phone's position on the accuracy of step detection. METHODS: Twenty volunteers from two different age groups (Group A: 18-25 years, n=10; Group B 45...

INTRODUCTION: Activity trackers can increase physical activity among unmotivated inactive individuals. Commercial PA monitors, such as activity wristbands and smartwatches, and especially smartphones with their various applications have increasingly gained popularity in recent years and are most commonly used for PA assessment today . The fact that...

BACKGROUND: Activity trackers have been shown to motivate inactive individuals to become more physically active. In recent years, especially wrist-worn activity trackers have increasingly gained popularity because of their greater wearing comfort compared to hip-worn devices, while the thereby improved wear-time compliance is indispensable for an a...

BACKGROUND: Sports competitions often take place in the late evening to reach a broad audience, although this is not the time of peak performance for most athletes. In a previous study, we showed that light can improve cycling performance in a positive dose-response relationship in athletes. Aim: The aim of this study was to assess the effect of di...

Abbreviations: VO2max: maximum oxygen uptake; 95% CI: 95% confidence interval; SD: standard deviation.

PURPOSE: To assess which type of evening light exposure has the greatest effect on reaction time and maximum handgrip strength. These were pre-specified secondary outcomes in a trial which primarily investigated the influence of light on cycling performance. METHODS: Seventy-four male athletes were allocated at random to either bright light (BRI...

Many sports competitions take place during television prime time, a time of the day when many athletes have already exceeded their time of peak performance. We assessed the effect of different light exposure modalities on physical performance and melatonin levels in athletes during prime time. Seventy-two young, male elite athletes with a median (i...

Introduction: The concentration of lactate is still the most important parameter in performance diagnostic. Lactate concentration depends on glycogen, test protocol and art of movement. The influence of blood volume is still not reported yet. Material and method: 30 healthy and athletic male adults were examined. On one day a stress test (cycle erg...

Light has a stimulating effect on physical performance if scheduled according to the chronotype, but dose-dependent effects on performance have not yet been examined. Three groups of healthy men (25.1 ± 3.1 years) were exposed to light for different durations in a parallel group design before a 40-min time-trial. In each group, subjects were expose...

Purpose: The maximum oxygen uptake (VO2max) is depending on cardiac and hematological parameters. So far, blood volume and cardiac output had rarely been measured. The aim of this study was to investigate the influence of directly measured cardiac output and blood volume on VO2max in healthy subjects. Methods: 30 healthy males (age: 24±2 years, BMI...