Abstract
und:Research into key performance factors in trail running, particularly in vertical kilometer (VK) races, is crucial for effective training and periodization. However, recent studies on metabolic and cardiorespiratory responses during VK races, especially using field tests, are limited. Objectives:Therefore, the aim of this study is to evaluate the metabolic and cardiorespiratory responses during a VK field test, identifying differences based on sex and performance level, as well as key performance factors and their deterioration due to fatigue. Fifteen trained trail runners (ten males and five females, 19 to 38 years old) perform a VK race.Methods:The global physiological response is evaluated using the portable gas analyzer Cosmed K5 and the local response using near-infrared spectroscopy technology.Results: In gender comparisons, the ANCOVA test shows significant differences (p< 0.05) in the ventilation, tidal volume, expiratory time-to-inspiratory time ratio, inspiratory flow rate, end-tidal CO 2partial pressure, heart rate, oxygen pulse, and total hemoglobin. Additionally, the performance comparison reveals significant differences in the variables’ velocity, oxygen consumption, carbon dioxide production, ventilation, dead space-to-tidal volume ratio, total time of the breathing cycle, expiratory time-to-inspiratory time ratio, inspiratory duty cycle, expiratory fractions of CO 2, quadriceps saturation index, and VE/VCO 2ratio. Finally, the correlation analysis shows oxygen consumption (r =−0.80 mean;
oxygen pulse, and total hemoglobin. Additionally, the performance comparison reveals significant differences in the variables’ velocity, oxygen consumption, carbon dioxide production, ventilation, dead space-to-tidal volume ratio, total time of the breathing cycle, expiratory time-to-inspiratory time ratio, inspiratory duty cycle, expiratory fractions of CO 2, quadriceps saturation index, and VE/VCO 2ratio. Finally, the correlation analysis shows oxygen consumption (r =−0.80 mean; r =−0.72 peak), carbon dioxide production (r =−0.91 mean; r =−0.75 peak), expiratory time-to-inspiratory time ratio (r = 0.68 peak), ventilation (r =−0.58 mean), and quadriceps saturation index (r = 0.54 mean; r =−0.76 coefficient of variation) as the key performance factors in the VK race.Conclusions:Overall, the physiological analysis indicates the importance of local muscular adaptations and respiratory system capacity in this type of short-duration race. Keywords:field tests; physiological assessment; sport performance; portable devices; trail running 1. Introduction In recent years, an increase in the number of athletes participating in outdoor sports, such as trail running, has been observed. Within this sport, a wide variety of races with different durations can be identified. The investigation for key parameters in running performance, both road and trail, has progressively become a study aim for numerous researchers in the health and sports sciences field with regard to applying this knowledge to the formulation of training programs and periodization schedules for runners. Recent studies have identified multiple physiological and biomechanical variables correlated with trail running performance, including maximal aerobic speed (VO2max), sustained fraction of VO2max, time limit of maximal aerobic speed, running economy, knee extensor maximal isometric voluntary force, and its decline or sustainable running power [1,2]. These variables are directly involved in maintaining increased running paces throughout the entire race, so their improvement could minimize the substantial acid–base J. Funct. Morphol. Kinesiol.2024,9, 230.
J. Funct. Morphol. Kinesiol.2024,9, 230 2 of 15 imbalance that may compromise muscle contraction [2]. Additionally, it has been observed that these variables are related to the delay in muscle glycogen depletion during exercise, thus prolonging fatigue onset [3]. Furthermore, these variables are associated with an enhanced impact attenuation during the braking phase in downhill running, facilitated by the eccentric control on knee flexion, while in the propulsion phase, they contribute significantly to energy generation during running on steep slopes [1]. Due to the complexity of performance analysis in trail running races, recent studies have conducted investigations isolating uphill and downhill running to obtain more ap- plicable conclusions. The two main performance predictors in both uphill and downhill running, in order of importance, are maximal aerobic speed and maximum strength, which could help maintain a better stride frequency and length. Nevertheless, there are third and fourth predictors, which are less decisive but relevant, that differ depending on the inclination type: body mass index (BMI) in uphill running and leg stiffness in downhill running [4]. Muscle tone and stiffness remain constant throughout the race after the initial adjustment of running kinematics, regardless of speed and inclination [5], while BMI has shown an inverse correlation with running economy [6]. Amongst the trail running modalities, the most popular races are characterized by a short duration and high intensity, such as the vertical kilometer, where runners are required to overcome an approximately 1000 m vertical elevation along a 5000 m distance. Regarding the previously mentioned physiological and biomechanical parameters, except for maximal aerobic speed, these have limited predictive values for short-trail running performance [7]. In fact, it is more appropriate to consider other variables, such as muscle endurance (lower fatigue index in the concentric knee extension torque, which could restrict muscle recruitment and coordination pattern changes), running economy when at a 10% incline, and lipid metabolism at a 10 km/h speed, as performance factors for these running distances [7]. Likewise, analyzing specifically the vertical kilometer race performance, the limited scientific evidence has highlighted the importance of maintaining elevated levels of vertical mechanical power, metabolic
knee extension torque, which could restrict muscle recruitment and coordination pattern changes), running economy when at a 10% incline, and lipid metabolism at a 10 km/h speed, as performance factors for these running distances [7]. Likewise, analyzing specifically the vertical kilometer race performance, the limited scientific evidence has highlighted the importance of maintaining elevated levels of vertical mechanical power, metabolic power (oxygen consumption and carbon dioxide production interaction), and vertical velocity throughout the entire race duration, regardless of the slope [8]. Regarding performance differences based on sex, it is well known that men tend to outperform women by approximately 10–30%, depending on the strength demands of the sport event. The largest differences are found in short-duration events that require significant amounts of strength and power. Men, due to higher testosterone secretion from adolescence, have greater muscle mass and strength, providing them with a competitive advantage in such short events [9,10]. However, this difference appears to decrease to about 1–3% in ultra-endurance events [11]. Despite this, there is still no scientific literature investigating sex-based performance differences in short-trail running events, such as the vertical kilometer. Technological advancements have developed novel noninvasive portable devices that enable the real-time assessment of cardiorespiratory responses and hemodynamic skeletal muscle behavior during exercise. These devices facilitate the monitoring of the heart, respiratory system, and muscular physiological adaptability to changes in exercise intensity. Moreover, analyzing the ventilatory response to exercise, the ability of the trail runner to maintain metabolic power during the race could be assessed. This metabolic power, as a performance factor [8], is dependent on the VO2and VCO2by reflecting the amount of oxygen consumed by the muscle, which could serve as an indicator of skeletal muscle oxidative capacity during exercise [12]. They also allow for the measurement of local oxygenation responses (delivery vs. consumption) in the skeletal muscle microcircu- lation, providing real-time data on changes in oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and the tissue saturation index [13]. The evaluation of skeletal muscle oxy- genation using near-infrared spectroscopy (NIRS) depends on several key factors such as blood flow, hematocrit levels, muscle capillarity, muscle tissue metabolic state, mitochon-
the measurement of local oxygenation responses (delivery vs. consumption) in the skeletal muscle microcircu- lation, providing real-time data on changes in oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and the tissue saturation index [13]. The evaluation of skeletal muscle oxy- genation using near-infrared spectroscopy (NIRS) depends on several key factors such as blood flow, hematocrit levels, muscle capillarity, muscle tissue metabolic state, mitochon- drial density, oxidative capacity, and alterations in hemoglobin dissociation curves [14].
J. Funct. Morphol. Kinesiol.2024,9, 230 3 of 15 This technology enables the analysis of the arteriovenous oxygen difference in athletes, which plays a critical role in their oxidative capacity and endurance performance [15]. It serves as an indicator of oxygen delivery and consumption in skeletal muscle tissue, which are dependent on multiple factors such as enzymatic activity, mitochondrial density, and capillary density [15]. The number of recent publications in the endurance training field where NIRS technique is used has undergone an exponential increase in last years. These studies have revealed that NIRS is useful for stablishing training intensity zones based on the threshold breakpoints determination [13]. Furthermore, NIRS is able to determine the performance in short-length endurance events, being a reliable indicator of critical velocity and critical power, and may predict the exhaustion time during severe full-body exercise (like cycling and running above critical power) [13]. In particular, the application of NIRS in trail running allows for more sensitive control of exercise intensity compared to traditional parameters such as the heart rate [16]. Moreover, NIRS is less affected by changes in tem- perature, humidity, hydration, emotional state, altitude, and day hour [12]. Nevertheless, despite the mentioned advantages and portability, there are still few studies that use this technology in the trail running context. Considering the current publications, the majority of vertical kilometer trail running research has been conducted on a lab treadmill, while a few have been carried out via field tests. Consequently, the purpose of this study is to analyze metabolic and cardiorespiratory responses, both global and local, during a vertical kilometer field test using a portable gas analyzer and NIRS technology. The results of such physiological analysis in field tests could reveal crucial data for their application in training and for preparing these particular types of tests. The primary objective is to observe the full-body metabolic and cardiorespiratory responses during an extremely short endurance-trail running event, aiming to identify differences based on performance level and sex, as well as to infer diverse performance factors in a real vertical kilometer field test. As a secondary objective, we aim to
training and for preparing these particular types of tests. The primary objective is to observe the full-body metabolic and cardiorespiratory responses during an extremely short endurance-trail running event, aiming to identify differences based on performance level and sex, as well as to infer diverse performance factors in a real vertical kilometer field test. As a secondary objective, we aim to examine the impact of these performance factors on fatigue in this running modality. We hypothesized that physiological adaptation would differ based on sex and the training level of the subjects, with men and more highly trained runners achieving superior values in cardiovascular, respiratory, and local muscular parameters during the test. 2. Materials and Methods 2.1. Experimental Design This cross-sectional study involved each runner performing a vertical kilometer field test. A vertical kilometer is characterized by a maximum distance of 5 km with a positive elevation gain of 1000 m. In our case, the selected field test was 20% shorter than an official vertical kilometer, consisting of a continuous ascent over a distance of 4.64 km, with a positive elevation gain of 835 m (Figure). Despite the differences from the official race, the physiological response to continuous uphill running is expected to be very similar.J. Funct. Morphol. Kinesiol. 2024, 9, x FOR PEER REVIEW 4 of 17 Figure 1. Vertical kilometer track. 2.2. Participants Fifteen trained trail runners participated in this study (ten males and five females). The inclusion criteria required that each participant had been training regularly in trail running for more than 3 years, was accustomed to training and competing in vertical kilometer events, agreed to participate voluntarily, and signed an informed consent form. The exclusion criteria included having experienced any musculoskeletal injuries within the past year, currently having a febrile illness or infection, or presenting any pathological condition at the time of the study. The runners were recruited through contact with coaches from the Aragón Trail Running Federation. Prior to the experiment, all subjects were informed about the objectives, benefits, and risks of the research. All of them signed an informed consent form. The experimental protocol was approved
a febrile illness or infection, or presenting any pathological condition at the time of the study. The runners were recruited through contact with coaches from the Aragón Trail Running Federation. Prior to the experiment, all subjects were informed about the objectives, benefits, and risks of the research. All of them signed an informed consent form. The experimental protocol was approved by the University Ethics Committee (Ref. 005-19/20). All procedures fulfilled the Declaration of Helsinki requirements. 2.3. Measurements 2.3.1. Portable Gas Analyzer Data The participants were equipped with a portable gas analyzer (Cosmed K5, Rome, Italy) during the entire route to collect central metabolic and cardiorespiratory data breath by breath with a turbine flowmeter connected to an adjustable face mask. The gas analyzer was attached to the runner’s back with a harness, with the weight of the entire system being 900 g. All data were collected in the device recorder for subsequent analysis. The calibration process of the K5 system was performed before each test with a 3 L calibration syringe for the turbine. O 2 and CO 2 sensors were calibrated to the ambient air conditions (20.93% O 2; 0.03% CO 2), along with delay calibration, according to the manufacturer’s instructions. Before the VK test, the metabolic rate was determined during a 10 min standing trial. During the entire VK track, the following variables were assessed: velocity; VO 2; VCO2; minute ventilation (VE); respiratory rate (RR); tidal volume (TV); dead space- to-tidal volume ratio (VD/TV); inspiration time (IT); expiration time (ET); total time of respiratory cycle (TotalT); expiratory time-to-inspiratory time ratio (ET/IT); relationship between inspiratory time and the total time of respiratory cycle, or inspiratory duty cycle (IT/TotalT); relationship between tidal volume and inspiratory time, or inspiratory flow rate (TV/IT); expiratory fractions of O 2 (FEO2); expiratory fractions of CO 2 (FECO2); fraction of inspired oxygen (FIO 2), end-tidal O 2 partial pressure (PETO 2); end-tidal CO 2 partial pressure (PETCO 2); respiratory exchange ratio (RER); heart rate (HR); relationship between oxygen uptake and heart rate, or oxygen pulse (VO 2/HR); VE/VO 2 ratio; and VE/VCO 2 ratio. The portable
expiratory fractions of O 2 (FEO2); expiratory fractions of CO 2 (FECO2); fraction of inspired oxygen (FIO 2), end-tidal O 2 partial pressure (PETO 2); end-tidal CO 2 partial pressure (PETCO 2); respiratory exchange ratio (RER); heart rate (HR); relationship between oxygen uptake and heart rate, or oxygen pulse (VO 2/HR); VE/VO 2 ratio; and VE/VCO 2 ratio. The portable gas analyzer system was also equipped with a strap to monitor the HR and a GPS sensor to track the position and speed. The mean values and those associated with maximum intensity effort (whether peak or minimum, depending on the analyzed variable) of all the parameters recorded during Figure 1.Vertical kilometer track. The itinerary included a combination of trail segments and forest track sections, with a moderate level of technical difficulty. The test was conducted under the most standardized
J. Funct. Morphol. Kinesiol.2024,9, 230 4 of 15 conditions possible, aiming for a consistent temperature between 20 and 30 degrees Celsius. Due to the restriction on eating or drinking during the test, which was imposed using the gas analyzer, all participants were instructed to consume carbohydrates during the meal prior to the test to ensure full glycogen stores, as well as to maintain a good level of hydration in anticipation of dehydration during the test. Furthermore, no participant was allowed to consume caffeine or other supplements with ergogenic effects prior to the test. 2.2. Participants Fifteen trained trail runners participated in this study (ten males and five females). The inclusion criteria required that each participant had been training regularly in trail running for more than 3 years, was accustomed to training and competing in vertical kilometer events, agreed to participate voluntarily, and signed an informed consent form. The exclusion criteria included having experienced any musculoskeletal injuries within the past year, currently having a febrile illness or infection, or presenting any pathological condition at the time of the study. The runners were recruited through contact with coaches from the Aragón Trail Running Federation. Prior to the experiment, all subjects were informed about the objectives, benefits, and risks of the research. All of them signed an informed consent form. The experimental protocol was approved by the University Ethics Committee (Ref. 005-19/20). All procedures fulfilled the Declaration of Helsinki requirements. 2.3. Measurements 2.3.1. Portable Gas Analyzer Data The participants were equipped with a portable gas analyzer (Cosmed K5, Rome, Italy) during the entire route to collect central metabolic and cardiorespiratory data breath by breath with a turbine flowmeter connected to an adjustable face mask. The gas analyzer was attached to the runner’s back with a harness, with the weight of the entire system being 900 g. All data were collected in the device recorder for subsequent analysis. The calibration process of the K5 system was performed before each test with a 3 L calibration syringe for the turbine. O2and CO2sensors were calibrated to the ambient air conditions (20.93% O2; 0.03% CO2), along with
with a harness, with the weight of the entire system being 900 g. All data were collected in the device recorder for subsequent analysis. The calibration process of the K5 system was performed before each test with a 3 L calibration syringe for the turbine. O2and CO2sensors were calibrated to the ambient air conditions (20.93% O2; 0.03% CO2), along with delay calibration, according to the manufacturer’s instructions. Before the VK test, the metabolic rate was determined during a 10 min standing trial. During the entire VK track, the following variables were assessed: velocity; VO2; VCO2; minute ventilation (VE); respiratory rate (RR); tidal volume (TV); dead space-to-tidal volume ratio (VD/TV); inspiration time (IT); expiration time (ET); total time of respiratory cycle (TotalT); expiratory time-to-inspiratory time ratio (ET/IT); relationship between inspiratory time and the total time of respiratory cycle, or inspiratory duty cycle (IT/TotalT); relationship between tidal volume and inspiratory time, or inspiratory flow rate (TV/IT); expiratory fractions of O2(FEO2); expiratory fractions of CO2(FECO2); fraction of inspired oxygen (FIO2), end-tidal O2partial pressure (PETO2); end-tidal CO2partial pressure (PETCO2); respiratory exchange ratio (RER); heart rate (HR); relationship between oxygen uptake and heart rate, or oxygen pulse (VO2/HR); VE/VO2ratio; and VE/VCO2ratio. The portable gas analyzer system was also equipped with a strap to monitor the HR and a GPS sensor to track the position and speed. The mean values and those associated with maximum intensity effort (whether peak or minimum, depending on the analyzed variable) of all the parameters recorded during the VK test were evaluated. The variability of all variables was assessed using the coeffi- cient of variation (CV) calculation in order to be able to analyze the ability to adapt their physiological response to changes in the terrain incline in order to maintain the fastest pacing possible within each runner’s personal capabilities. 2.3.2. Near-Infrared Spectroscopy (NIRS) Data A portable NIRS device (Moxy Monitor, Fortiori Design LLC, Hutchinson, MN, USA) was positioned on each runner’s right vastus lateralis (12 cm above the patellar proximal border) and 3–5 cm laterally to the thigh midline to monitor the peripheral tissue oxy-
the fastest pacing possible within each runner’s personal capabilities. 2.3.2. Near-Infrared Spectroscopy (NIRS) Data A portable NIRS device (Moxy Monitor, Fortiori Design LLC, Hutchinson, MN, USA) was positioned on each runner’s right vastus lateralis (12 cm above the patellar proximal border) and 3–5 cm laterally to the thigh midline to monitor the peripheral tissue oxy-
Description
This study evaluates metabolic and cardiorespiratory responses during a VK field test.