Authors:Tatyana Dzimbova, Hristo Nikolov, Radoslav Mavrevski, Stefan Kapralov

Corresponding Author:
Assoc. prof. Tatyana Dzimbova, PhD
66 Ivan Michailov Str.
Blagoevgrad, 2700 Bulgaria

Study on professional football players – factors in recovery and preparation and performance markers during scheduled training session


Purpose. The purpose of the present study is to estimate if the athletes can satisfy their energy needs by diet, if they are well hydrated before training, and if the training is effective.

Methods. Ten players of the football team in the B professional league participated in the study (age 23.44 ± 5.98 years, weight 70.64 ± 4.57 kg, height 176.4 ± 7.35 cm; ±SD). Their body composition was analyzed with the Body Composition Analyzer IoI 353 and they completed food questionnaires. Blood lactate concentrations were determined using the biochemical analyzer BIOSEN – C Line, EKF Diagnostic. The heart rates of the subjects are recorded using the activePULS, MEDION AG. Data was processed using SPSS and Graphpad Prism software.

Results. According to the data obtained from the food questionnaires all subjects received the necessary amount of energy to fully meet their energy needs. From the multiple linear regression, it is seen that the highest value has the standardized coefficient in front of the carbohydrate intake which means that it has the greatest influence (about 65%) on total energy intake. The heart rates of participants in the study range from 78 to 90% of the predicted maximum, i.e., high intensity. Differences in blood lactate concentration before and after exercise are significant, evidence of effective performance on training.

Conclusions. We can conclude that according to the nutrition questionnaire the athletes received a sufficient amount of macronutrients and sufficient amount of energy for their training needs. The change in blood lactate concentrations and heart rate during training is indicative of the responsible attitude of the players, and therefore the target endurance is most likely to be achieved.

Applications in Sport. Reported methods could be a useful tool for coaches to track the recovery and preparation of the athletes in season and to evaluate their performance during a scheduled training session.

Keywords: football, food questionnaire, body composition analysis, blood lactate concentration, heart rate, training


Intensive training is a daily routine for elite athletes and is aimed at improving performance at a competition. Optimizing performance requires a balance between training and recovery. The diet is particularly important for supplying the body with the necessary nutrients for its day-to-day activities. For athletes, this is all the more important, as intensive training requires higher amounts of energy from food. In Bulgaria, the athletes themselves or with the help of the coach determine their diet, uses various supplements and nevertheless cannot meet their energy needs. Another important issue is the athlete’s hydration. Especially during the summer months, when ambient temperatures are around and above 30°C, it is important for athletes to recover water losses during daily intensive outdoor training. For an athlete to cope with the challenges of the upcoming training session, it is necessary to fully recover from the previous, have sufficient energy reserves and be well hydrated.

Several parameters are tracked during the training and we have focused on heart rate (HR) and blood lactate concentrations (BLC) as biomarkers widely used in elite athletes’ training to determine the effectiveness of the training. Maintaining a balance between heart rate and heart rate increase in response to growing energy needs, is crucial for a person to maintain their workout. This physiological parameter is proposed as a good marker for determining exercise intensity and is an easy method for observing training by athletes and coaches (3).

Blood lactate concentration is one of the most commonly measured parameters during an athletes’ performance testing. While elevated levels of lactate in the blood may be indicative of ischemia or hypoxia, it may be a “normal” physiological response to the athlete’s effort. In response to a maximum effort of 30-120 seconds, peak blood lactate concentrations of 15-25 mM can be observed. In response to the progressive, increasing load, the lactate concentration increases gradually at the beginning and then faster when the load becomes more intensive. The operating rate above which blood lactate concentration increases exponentially, the lactate threshold is a better prediction parameter than VO2max and is a better indicator of exercise intensity than heart rate; thus the lactate threshold is useful in determining the intensity of training (4). The combination of these two parameters – heart rate and blood lactate concentration – can be an excellent tool for tracking and controlling exercise stress (5-7). The objectives of this study are to determine:

  • Whether athletes are sufficiently recovered before training, especially hydration and energy needs are being met.
  • Whether the training is effective enough to enable the athlete to train the appropriate skills  
  • How biochemical and physiological tests can be used for such assessment.

To meet these goals, several specific tasks need to be implemented:

  • Measuring anthropometric indicators and body composition using an impedance analyzer, analyzing all available information obtained from the analyzer;
  • Conduct a nutrition study with a special questionnaire assessing the total energy value of the athlete’s diet and the amounts of the individual macronutrients – carbohydrates, proteins and fats;
  • Measuring the blood lactate concentration before and immediately after workout to determine the difference that will provide information on the intensity of training;
  • Measuring the heart rate of the athletes during a training session, specifying the minimum and maximum pulse frequencies, and the average pulse frequency for the training.
  • Determine any correlations between the measured parameters in order to find certain dependencies that will serve as a starting point for the subsequent planning of effective coaching strategies.



Ten main players of the football team of the B professional league of Bulgaria participate in the study, with the exception of the goalkeepers, as their training is different (age 23.44 ± 5.98 years, weight 70.64 ± 4.57 kg, height 176.4 ± 7.35 cm; ±SD). The study was conducted in mid-August 2018 during the active competition season. On that day, football players had a scheduled training session in the afternoon (at 6:00 pm). Anthropometric measurements were carried out in the morning of the same day (9:00 a,m.) at the Center for functional research in sports and kinesiotherapy – SWU “Neofit Rilski” in Blagoevgrad. Prior to the testing, participants were asked to refrain from physical exercise, food, and fluid intake. Each participant in the study signed an informed consent form and the study was approved by the South-West University “Neofit Rilski” Research Ethics Committee.

Determination of body composition

Determination of body composition was performed using the Body Composition Analyzer, model IoI 353. The device presents not only analyzed results for body composition but also energy expenditure. The participants of the study were dressed with clothes as light as possible and they took off socks before the measurement. From these results we used the Body Mass Index (BMI), Total Body Water (TBW), Basal Metabolite Rate (BMR) and Total Energy Expenditure (TEE). TBW consists of intracellular and extracellular water. In healthy adults, body water is 45-65% of body weight, although it varies between individuals. This indicator may serve as an indication for the athlete’s body hydration. BMR are the calories needed to maintain vital functions of the human body at rest, such as heartbeat, neural transmissions, body temperature regulation, and so on. BMR is proportional to Soft Lean Mass (SLM), since fat is a source of energy, and SLM consumes calories. So, even if the weight is the same for two people, the one who has a high value of SLM shows a larger BMR. TEE (total energy expenditure) is the sum of the basal metabolism and calories required for daily activity and is generally calculated by multiplying BMR with PAL (Physical Activity Level). In our case, this indicator does not include the energy needed to conduct a training session. This energy can be calculated for each player using BMR and the relevant Metabolic Equivalent of Task (MET) (2).

Determination of the energy value of the usual diet of the players

Determination of the energy value of the usual diet is done using pre-prepared food questionnaires. Taru at el. (8) have published a simple questionnaire, which we modified for the conditions in Bulgaria. Each person fills in a pre-encoded questionnaire that automatically calculates the total amount of kilocalories that a person normally consumes, and respectively the amount of carbohydrates, proteins and fats commonly found on the player’s menu.


The training session was a standard workout for speed endurance included in the players’ training schedule. The duration is 90 minutes. The training consists of three parts as follows:

Preparatory part – 20 minutes

1. Three laps evenly running;

2. Total-developing exercises;

3. Special-preparatory exercises;

4. Passing the ball between three or four in motion;

5. Passing the ball in pairs (with increasing and decreasing distance).

Basic part

1. Special squares – three squares 10 x 10 m by six players (Figure 1a)

2. Special 20 x 20 m square – three teams of six players, each team consists of three players. (Figure 1b).

3. Bilateral game – tournament, three teams each against each.

Closing part

1. Light running;

2. Stretching.

Figure 1. Exercises from the main part of the training

Figure 1

Determination of lactate concentration in arterial blood

Blood lactate concentrations are determined by the biochemical analyzer BIOSEN – C Line of the German company EKF Diagnostic. Determination is based on electrochemical measurement with a chip sensor. The sample is aspirated and injected automatically. L-lactate, which is converted by enzyme immobilized on the chip sensor to pyruvate forms hydrogen peroxide. It releases free electrons that generate an electrical current that is recorded by an electrode on the device. The resulting electrical signal is proportional to the pyruvate concentration in the sample. Samples are taken before the training and after the basic part of the training session.

Determination of heart rate during exercise

During exercise, the heart rates of the subjects are recorded using the activePULS of the German company MEDION AG. The capabilities of the apparatus are measurements in the range of 30-240 beats per minute. Each set of the device is programmed in advance for the respective player. Programming includes setting gender, age, height, weight. Players are instructed to put their watch in the Stopwatch mode before the start of the training, and at the end, they turned it off. Throughout the training, heart rate is measured and the data was analyzed later in the laboratory. The device allows us to determine the minimum and maximum heart rate during exercise, and the average heart rate for the entire training.

Data processing

To model the TEI’s dependence on carbohydrate, fat, and protein intake, a multiple least-squares linear regression analysis was performed. To determine the degree of impact of the different factor variables, the corresponding standardized regression coefficients were also calculated. The regression analysis is based on the statistical software package SPSS Statistics 20. GaphpadPrism was used for determining the correlations between the measured BLC and HR.


A major problem for Bulgaria is that there are no developments related to field biochemical tests of athletes. This study is a part of a planned in-depth study of various biochemical parameters during exercise in various sports, and preliminary results for football players are presented here.

Players’ anthropometric data was measured in the morning before the training and presented in Table 1. As can be seen from Table 1, the age, weight and height of the players varies, which is common to this type of sport. Various skills are needed in the different positions in the football game, so the body of the players is different.

Table 1. Data of the participants in the study

Table 1

As shown in Table 1,  all players are within the normal range of the BMI score (18.5-25.4, SD ± 1.01). The BMI is generally not used in trained athletes, as in sports where muscle mass is higher, and so this indicator can be misleading. Athletes with well-developed muscles usually fall into the group of people with high body mass, even in some cases they are in the obese category first and even second degree. Footballers are athletes with a high lean body mass (LBM), where too much muscle is not an advantage, as the extra weight will be an obstacle for 90 minutes to running faster. Therefore, BMI of the subjects is a reliable and fair indicator of weight relative to height but perhaps does not account for LBM.

From the data obtained from IoI 353, we use total body water (TBW). Although it varies from person to person, from 36.6 to 48.6 kilograms, the tendency is that the mass of body water is at the upper limit and, in some cases, exceeds it slightly. This indicator shows, first, that players have enough muscle mass, which has a higher percentage of water compared to fat, and, on the other hand, they are also well hydrated for training despite the intense training sessions and high ambient temperatures (temperature of the air at the time of the study is about 32°C).

The other two indicators we use from IoI 353 are basal metabolic rate (BMR) and total energy expenditure (TEE). These two indicators serve as a starting point for our assessment of whether a person’s usual diet is able to meet their daily energy needs and provide the energy needed to conduct the planned training session. Together with the nutrition questionnaire, which gives information on the total intake of energy from food and drink, the amount of macronutrients in the food can be determined by analyzing the energy availability that is important for the health and performance of the athlete. Individual BMR and TEE vary considerably from person to person, because their age and body size are crucial for their determination. Since the team consists of players of different ages and sizes BMR varies from 1484 to 1820 kJ and TEE, respectively, from 2285 to 2803 kJ. The individual differences are presented in Figure 2:

Figure 2. Individual BMR and TEE.

Figure 2

The nutrition questionnaire makes it possible to calculate the total energy intake with the food by the players and to estimate the amount of carbohydrates, proteins and fats they eat. From the analysis of the results of the questionnaire (Table 2), the following conclusions can be drawn: The energy costs during a training session calculated according to the Physical Activity Compendium (6) for each individual player are in the range of 371-425 kJ / 90 minutes. The differences between total energy intake and TEE are within the range 1068.71 – 2920.71 kJ, which is well above the energy requirements of the training. Consequently, according to the questionnaire, the players receive the necessary amount of energy to fully meet their energy costs.

It is noteworthy that the players include the most carbohydrates in their menu, with the average ratio of macronutrients being 77/10/13 – carbohydrates / fats / proteins. This diet provides enough energy to meet energy needs, as carbohydrates are the most comfortable source of energy for the body. The recommended intake of carbohydrates (1) in this type of physical activity is 8-10 g / kg body weight, with only four of the studied group are taking less of this amount. The recommended protein intake for this type of sport ranges from 1.4-1.7 g / kg of weight, with all but two players consuming less than 0.88 g and 0.40 g / kg of weight respectively. Fat intake should be such as to meet energy needs. Typically, the intake of fat is about 1 g / kg body weight, with all subjects receiving fewer fats below 1 g / kg body weight, as they receive the energy they need from the large amounts of carbohydrates they consumed.

Of the sufficient amount of energy, as well as the fact that football players report eating fruit and vegetables in meals, it can be concluded that their usual food satisfies their micronutrient needs – vitamins and minerals. Another proof of this is the mineral analyzer data, which is found in all norms and near the upper limit.

From the analysis of the players’ diet, it can be concluded that all players take the necessary amount of energy to meet their needs during a training session.

Table 2. Results of the food questionnaire

Table 2

To determine the effect of carbohydrate (C), fat (F), and protein intake (P) on total energy intake (TEI), multiple linear least squares regression was made using the SPSS software package. To determine the influence of the various independent (factor) variables C, F and P on the dependent TEI variable, the standardized regression coefficients of the multiple linear regression are taken into account. They are derived from the regression coefficients. Standardized coefficients are interpreted by character but are comparable and in absolute value. The most influential factor is the one whose standardized coefficient of regression is greatest.

The equation for multiple linear regression is:

ТЕI =  a + b*(C*4) + c*(F*9) + d*(P*4)

Table 3. Results from multiple linear regression

Table 3

From the above table it is seen that the highest value has the standardized coefficient b, in front of the carbohydrate intake which it means that it has the greatest influence (about 65%) on TEI.

At the second stage of the work, a field test was conducted during training. Prior to the exercise, the first blood samples were taken to provide information about the BLC prior to loading. Individual heart rate monitors were place during training and players are instructed to switch them on immediately before the start of the training. The tool measures the duration of the exercise and the HR throughout the training, and the software determines the minimum, maximum and average HR, as well as the period during which this HR is maintained. The minimum and maximum frequencies in all subjects are maintained for only a few seconds, with the minimum heart rate at the beginning of the measurement period, and the maximum is during the basic part of the exercise when the player is struggling to take the ball. High intensity training tends to improve endurance. There are separate factors such as medical conditions, prescription medications, and general exercises that affect the maximum heart rate of a person. Most people have one to two minutes in maximum HR, highly trained athletes may have more. There are 5 heart rate zones according to the heart rate: 50-59% and 60-69% of maximum HR – a moderate intensity zones, 70-79% of maximum HR – a moderate to vigorous intensity zone (75% of maximum HR and above is considered vigorous intensity), 80-89% and 90% + of maximum HR – a vigorous or high intensity zones.

Table 4. Individual values ​​of the heart rate of the subjects under study

Table 4

As can be seen from the table, individuals begin the training with HR values ​​around the lower limit. During training for a few seconds at the peak load, their HR repeatedly exceeds the maximum. For most of the training, the HR of participants in the study range from 78.13 to 90.05 % of the maximum value, meaning that they exercise at high intensity. Maintaining such a high HR indicates that football players are actively involved in training, and training will result in improved endurance, which is the main goal of the training session.

Whether the training was effective can also be determined by the BLC. The second blood sample is collected before the start of the final part of the training, with the players one leaving football field on the sign of the coach and the blood is taken immediately to prevent the lactate from being metabolized. In high-trained athletes, this happens very quickly, which would vitiate the result. The results obtained are presented in Table 5.

Table 5. Individual concentrations of lactate in the blood of the players

Table 5

Some of the players, on the advice of the coach, warm up in the stadium’s gym, so the values ​​ of their BLC exceed 2 mol/L. As can be seen from the table, differences in BLC before and after exercise are significant, which new evidence of effective performance training is and that it is able to develop the desired quality of football players, namely endurance. It is noticeable that two of the players have a small difference in BLC before and after exercise, 4.51 mol/L and 4.27 mol/L respectively. Since the HR of the same players is in the intensive effort zone, respectively 78.13 and 83.99 % of the maximum HR, perhaps the small change is due to the larger amount of red muscle fibers that work in aerobic mode and produce less lactate.

No correlation can be found between heart rate and lactate concentration (Pearson`s correlation coefficient r = -0.16, p value = 0.65) because the latter strongly depends on the type of muscle fibers of the respective player. Despite the intensity of exercise, people with a higher percentage of red muscle fibers use glucose and fat as an aerobic fuel (oxidative phosphorylation), so their BLC do not increase.


In conclusion, it can be said that according to the nutrition questionnaires, completed by the participants in the study, they receive a sufficient amount of macronutrients and energy for their training needs; and it can be assumed that they in turn had a sufficient quantity of vitamins and minerals. The change in blood lactate concentrations and heart rate during training is indicative of the correctly conducted high intensity training, the effort made by the players, and therefore the target endurance quality was most likely to be achieved.


Reported methods could be a useful tool for coaches to track the recovery and preparation of the athletes in season and to evaluate their performance during scheduled training session. This methodology allows determining the intensity of the training not only in football, but in different types of sports. Knowledge and skills were developed to use different biochemical parameters to improve their training programs.


The study was conducted with the financial support of a project RP B7/18 of SWU “N. Rilski”


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