Study on professional football players – factors in recovery and preparation and performance markers during scheduled training session – United States Sports Academy Sports Journal

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

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

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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

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
  • 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
  • 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
  • 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

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

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

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.

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

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

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.

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

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

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.


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


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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