EFFECT OF PHYSICAL EXERCISE ON INCREASING THE MAXIMUM OXYGEN UPTAKE OF SKELETAL MUSCLE

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INTRODUCTION
Commonly used test index of anaerobic threshold (AT).Lactic acid is closely related to the dissociation of oxyhemoglobin (HbO 2 ).The body will experience an imbalance of oxygen supply and demand during heavy exercise.The status of skeletal muscle oxygen supply and consumption is an effective way to understand the status of body functions during exercise.The body's adaptation to different intensities of loads and mastering the training intensity, evaluating training effects, and judging sports fatigue have important reference values.Some scholars have proposed using near-infrared spectroscopy (NIRS) to measure oxygen supply and oxygen consumption in living tissues.Subsequently, some scholars conducted extensive research on the reliability and effectiveness of NIRS in testing muscle oxygen levels during exercise and have been confirmed. 1In this study, a continuous light three-wavelength system was used to test male juvenile rowers' skeletal muscle oxygen changes during the incremental load process.At the same time, we test the subjects' heart rate (Hb), blood lactate (BLa), and oxygen uptake (VO 2 ).This article uses NIRS to measure muscle oxygen to assess the feasibility of individual aerobic metabolism.

METHOD Object
We chose 22 healthy young male rowers from our school's water sports center.We are divided into two groups A and B, according to the level of exercise.Group A is the incredible group (n=12), including 5 first-level athletes and 7 second-level athletes.Group B is the general group (n=10).The professional training years of this group of athletes are less than 2 years.The primary conditions of the subjects are shown in Table 1.

Instruments and equipment
American MAX-II cardiopulmonary function meter, domestic YSI-23L blood lactate analyzer, portable three-wavelength muscle oxygen meter, German WLP-940 power bicycle, Finnish P-Lar heart rate monitor.

Methods and steps
We choose the right lateral femoral muscle to measure muscle oxygen content.In the experiment, the probe was placed longitudinally about 10 cm above the knee joint gap of the subject's right thigh. 2 At the same time, we make the axis of the light source and the detector parallel to the thigh. 3To prevent the influence of sweating, we put an ultra-thin transparent plastic between the skin and the detector and use a particular shading device to fix the detector on the skin of the detected area.This can avoid the interference of external light.
The experiment adopts a step-by-step increasing load power bicycle exercise.Start the formal test after 2 minutes of preparation activities.The initial load is 50W, 70 rpm, and the increment is 50W every 3 minutes.After the experiment reaches AT, it can be accelerated to 80-90 rpm to exhaustion.During the exercise, the skeletal muscle oxygen content, oxygen uptake (VO 2 ), and heart rate (HR) were measured at the end of each load level.10-15 seconds before the end of each load level, we take blood from the fingertips to determine the lactic acid content.Group A completes level 6 load, and group B completes level 5 load. 4

Modeling of personnel travel energy consumption
As early as the beginning of the last century, British scholar Gathcart and others started researching the energy consumption of personnel traveling.In the early 1960s, Goldman et al. studied the energy consumption of weight-bearing travel and obtained a regression model formula for energy consumption and travel speed, load, and rowing slope: Where E is energy consumption.V is the travel speed.L is negative weight.G is the rowing slope.They proposed an energy consumption model that includes the metabolic energy consumption of travel speed, slope, weight and body weight, and road coefficient: M is metabolic energy consumption.ƞ is the road coefficient.W b is the weight.Studies have shown that the applicable range of the model is various situations where the speed is more significant than 2.54km/h, the weight--bearing position is close to the human center of gravity, and the product of the weight and the speed is less than 100.The model for rowing is as follows: VO 2 is oxygen consumption.W b is body weight.V is the travel speed.For the convenience of comparison and application, the experimental research model also uses the power unit watt to represent the metabolic intensity of exercise energy.We apply the commonly used formula for oxygen uptake and power conversion: E is energy consumption.R is the respiratory volume.VO 2 is the oxygen uptake.Among them, R and VO 2 correspond to each other, they are the average of the R values recorded in the fourth minute of each speed stage.The article establishes a mathematical energy consumption model, and the specific analysis process is as follows: 1. Determine the variables that affect energy consumption (E).The essential variables that determine travel energy consumption are speed (V), gradient (G), and load ratio (L/W b ).However, the relationship between energy consumption and these variables, especially speed, is not a simple linear relationship.At the same time, various variables generally have cross-influences.We get 12 items such as to ensure that the relevant variables are not artificially omitted.2. Filter variables.We use the backward method to filter out the excess variables, and the standard is α ≥ 0.100.We then use the forward method to select model variables.The selection criteria is α ≥ 0.050.The selected variables are as follows:

Data processing
The data are all expressed as mean±standard deviation.We use SPSS10.0statistical software.The article uses unary regression to analyze the relationship between muscle oxygen and lactate, oxygen uptake, and heart rate. 5The aerobic capacity of the two groups of athletes was compared by independent-sample t-test, and P<0.05 indicated a significant difference.

Comparison of aerobic exercise capacity of the two groups of athletes
It can be seen from Table 2 that the physiological indicators of the athletes in group A are higher than those in group B (P<0.01).This shows that there are very significant differences in the aerobic exercise capacity of the two groups of athletes.

Muscle oxygen changes during increasing load
Under the encouragement of group A athletes, 10 people completed the 6th load, and 2 athletes completed the 6th load for 2 minutes.In the statistics, we calculate according to the 6-level load.Seven athletes in Group B completed the 5th load, and 3 athletes completed the 5th load for 2 minutes.In the statistics, we all calculate according to the 5-level load.Figure 1 and Figure 2 are typical examples of measured muscle oxygen changes when a rowing athlete in each A and B group completes the 6th and 5th load. 6The relative change of oxygenated hemoglobin content (HbO 2 ) in the figure represents the change of muscle oxygen.
In Figures 1 and 2, the abscissa is time. 7 The relationship between end-load muscle oxygen density and lactate, oxygen uptake, and heart rate It can be seen from Table 3 that when the athletes in Group A increase their load, the decrease in muscle oxygen content is synchronized with the increase in lactate, oxygen uptake, and heart rate.Statistical analysis showed that muscle oxygen was highly negatively correlated with lactate, oxygen uptake, and heart rate.
From Table 4, the decrease in muscle oxygen content of the athletes in group B increases in synchronization with the increase in lactate, oxygen uptake, and heart rate.

The relationship between muscle oxygen changes and oxygen uptake
This experiment shows that the change in muscle oxygen at the end of each level is highly negatively correlated with oxygen uptake.Peripheral muscle oxygen dynamics reflect system oxygen uptake.The study found that the delay time of oxygen uptake (30±8s) was significantly longer than the delay time of deoxygenation (10±3s).The local oxygen ionization increases faster than the oxygen uptake.On the contrary, increased local perfusion and increased oxygen delivery do not match the metabolic tissue rate.This shows that the increase in the body's oxygen consumption increases the body's demand for oxygen, and then the oxygen uptake increases.

The relationship between muscle oxygen changes and blood lactate changes
In this experiment, the change in muscle oxygen at the end of each load level was highly negatively correlated with blood lactate.The slight decrease of muscle oxygen at a low load is consistent with the slow increase of lactate.When the load is large, the muscle oxygen drops rapidly, and an inflection point appears, which is consistent with the inflection point of the increase of lactic acid.Some scholars believe that when the exercise intensity is high, various acidic metabolites inside and outside the muscle cells increase, lactic acid begins to accumulate, and the increase of PaCO 2 and H + concentration promotes the rapid separation of O 2 and hemoglobin.Therefore, reduced hemoglobin increases, and oxygenated   hemoglobin decreases.Some scholars have found in experiments that the femoral venous oxygen partial pressure (PaO 2 ) has only a tiny change from moderate-intensity to high-intensity exercise.Still, the oxygen capacity decreases significantly with the increase in intensity. 8

Figure 1 .
Figure 1.Muscle oxygen changes of a rowing athlete in group A during the 6-level load exercise.

Figure 2 .
Figure 2. Muscle oxygen changes of a rowing athlete in Group B during the 5-level load exercise.

Table 1 .
Basic information of subjects.

Table 2 .
Comparison of aerobic exercise performance indexes of athletes in groups A and B.

Table 4 .
Muscle oxygen, lactate, oxygen uptake, and heart rate test results of athletes in group B during incremental exercise.