Diversity in athlete’s response to strength effort in normobaric hypoxia
Journal of Thermal Analysis and Calorimetry
Diversity in athlete's response to strength effort in normobaric hypoxia
Serum DSC study 0 1 2 3
Anna Michnik 0 1 2 3
Zofia Drzazga 0 1 2 3
Izabela Schisler 0 1 2 3
Stanisław Poprze˛ cki 0 1 2 3
Miłosz Czuba 0 1 2 3
Hypoxia 0 1 2 3
0 Department of Physiological and Medical Sciences, Department of Biochemistry, The Jerzy Kukuczka Academy of Physical Education in Katowice , ul. Mikołowska 72a, 40-065 Katowice , Poland
1 Department of Medical Physics, A. Chełkowski Institute of Physics, The Silesian Centre for Education and Interdisciplinary Research, University of Silesia in Katowice , ul. 75 Pułku Piechoty 1A, 41-500 Chorzow , Poland
2 & Anna Michnik
3 Department of Physiology, Institute of Sport , ul Trylogii 2/16, 01-982 Warsaw , Poland
The hypoxia may be used during exercise training sessions in humans with the aim of improving athletic performance. The effect of normobaric hypoxia strength training on thermal properties of blood serum has been evaluated in a group of 12 male and female athletes using differential scanning calorimetry (DSC). Each athlete was tested under normoxic and simulated hypoxic (4000 m, FiO2 = 13% and 5000 m, FiO2 = 11.3%) conditions during squats with a barbell (70% 1RM) exercise. A substantial inter-individual variation in the effects of hypoxia on serum DSC curves has been observed. The effect of exercising in normobaric hypoxia has been found greater for men than for the women. When the work intensity is high enough, the strength exercise in hypoxia can trigger an acute-phase response. Calorimetric and biochemical data have shown that men's exercising in hypoxia could increase the concentration of acute-phase proteins: haptoglobin and/or C-reactive protein. Our results suggest that 24-h period of rest is sufficient to return to the pre-exercise state after normoxic as well as hypoxic training session for both men and women. The recovery seems to be faster after the training in normobaric hypoxia conditions than in normoxia in the male but not in the female group of athletes.
Differential scanning calorimetry (DSC); Exercise; Human blood serum
The concept of altitude or hypoxic training is a common
practice since 40 years for improving sport performance.
During this time, several strategies of such training
regimens have been proposed, like ‘‘live high-train high’’
(LHTH), ‘‘live high-train low’’ (LH-TL) or ‘‘intermittent
hypoxic training’’ (IHT). Recently, most attention is given
to IHT that is considered the effective method of
developing aerobic [
] and anaerobic [
] capacity. In this
method, athletes live under normoxic conditions and train
in a natural hypobaric or simulated normobaric hypoxic
environment. The improvement in sport performance after
IHT is mostly associated with non-hematological adaptive
] to hypoxia. The results of our previous
] and other well-controlled studies [
that the improvements in aerobic capacity and endurance
performance are caused by muscular and systemic
adaptations, which are either absent or less developed after
training under normoxia. The systemic hypoxia during the
training process may cause more pronounced adaptive
changes in muscle tissues than after traditional endurance
training under normoxic conditions. These changes include
increased fiber cross-sectional area, skeletal muscle
mitochondrial density and elevated capillary-to-fiber ratio
Though the different hypoxic training methods have
gained popularity recently [
], scientific debate continues
into whether the hypoxic training has any performance
benefit for athletes [
]. A number of research projects
have failed to demonstrate the improvement in sea level
performance after IHT [
]. Further research is
necessary to explain the mechanisms involved in muscle
hypertrophy during resistance training under hypoxic
conditions. Moreover, it has been suggested that hypoxic
training sessions appear to require longer recovery periods
compared to normoxic training . The review published
by Flaherty et al. [
] provides an overview of potential
problems which an athlete may experience at altitude.
Some authors examined the effect of normobaric
hypoxia on maximal oxygen uptake (VO2max) and maximal
power Pmax output during the exercise. In acute hypoxia,
the decline of VO2max was observed [
]. The trained
athletes experienced greater reductions in VO2max while
exercising in acute hypoxic conditions compared to
untrained subjects. This is consistent with greater
pulmonary diffusion limitations to VO2max for trained than
untrained athletes during maximal exercise.
Angermann et al. [
] have reported that VO2max and Pmax
were affected differently by acute normobaric hypoxia
corresponding to 3200 m. Their another important finding
was that athletes with high muscle capillarity and high
muscle mitochondrial density are more susceptible to
hypoxia. According to the results of Ofner et al. [
participants with higher VO2max in normoxia demonstrated
a more pronounced reduction of this parameter in hypoxia
in absolute terms as well as relative to Pmax (r = - 0.76,
p \ 0.05). Lately, meta-regression analysis conducted by
MacInnis et al. [
] on 105 independent groups of
participants (n = 21 958 subjects from 80 different studies)
showed that VO2max decreases as altitude increases and
that the decrease is greater in individuals with higher
aerobic capacities. There are, however, studies, where a
significant increase in VO2max has been observed after IHT,
e.g., in well-trained cyclists and basketball players [
In current study, athletes were exposed to normobaric
hypoxia only during exercise sessions. In this situation, the
potentially negative effects related to the exposure to high
altitude could be avoided. The exercises performed in
normoxia and normobaric hypoxia at simulated altitudes of
4000 and 5000 m above the sea level were separated by
7 days. The effect of hypoxia was evaluated using
differential scanning calorimetry (DSC) method. Blood serum
profiles of temperature heat capacity changes were
analyzed and compared for athlete’s performed squats with a
barbell in normoxia and in a hypoxic training cycle.
The modern DSC was shown recently as valuable,
harmless tool for disease diagnosis. This method enables to
distinguish any slight differences between thermodynamic
parameters of cancer and non-cancer diseases and norm
]. Our earlier DSC studies [
] of athlete’s
serum indicate that this technique may be also applied in
sports medicine to support sports training.
Materials and methods
Participants of the experiment
Twelve active students of the Academy of Physical
Education practicing strength sports participated in a research
experiment, including 6 males (mean ± SD: age
24.1 ± 1.0 year, mass 82.9 ± 15.2 kg, high
175.5 ± 7.5 cm and BMI 25.6 ± 3.8 kg m-2) and 6 females
(mean ± SD: age 24.5 ± 1.5 year, mass 67.6 ± 13.2 kg,
high 162.5 ± 2.5 cm, and BMI 24.9 ± kg m-2). All athletes
were informed about the purpose and the nature of the
research before giving their written consent to participate in
the experiment. The studies were performed in accordance
with the ethical standards of the responsible committee on
human experimentation (institutional and national) and with
Declaration of Helsinki. The study protocol was approved by
the Ethics Committee of the Jerzy Kukuczka Academy of
Physical Education in Katowice (Certificate of approval No.
Initially, the maximal load 1RM (1-repetition maximum)
was measured in normoxic and hypoxic (4000 and 5000 m
above the sea level) conditions using the device Myotest
with test Half-Squat Profile. The exercise test was carried
out in: (1) normoxic conditions (NORM), corresponding to
the level of the sea and fraction of inspired oxygen 21%,
(2) normobaric hypoxia HYP4—4000 m above the sea
level where the oxygen content was 13%, (3) normobaric
hypoxia HYP5—5000 m above the sea level where the
oxygen content was 11.3%. All tests were performed in
normobaric hypoxia chamber. Normobaric hypoxia
conditions were obtained with the climate system
LOSHYP_1/3 NU (LOVOGEN SYSTEMS, Germany). The
experiment comprised three stages in a 7-day interval. The
participants of our experiment performed squats with a
barbell with individual weight (70% 1RM) in each
environmental condition. They performed 10 sets of 10–12
repetitions with 5-min rest period between sets.
Participants entered the exercise test after a 24-h rest period.
Blood serum samples
Blood samples from each participant were obtained at
approximately the same time of the day under experimental
(normoxic or hypoxic) condition. Blood were collected at
four time points: at rest (before the exercise—‘‘be’’), 3 min
after the exercise (‘‘ae’’), after 1 h (‘‘r1h’’) and 24 h
(‘‘r24h’’) of passive recovery. In normoxia and in HYP5
blood was collected from only 10 participants. Samples
were obtained in a seated position from antecubital vein
using Vacutainer system to draw blood into 2 9 4 mL
tubes containing no additives. Serum was obtained by
centrifugation at 3500 rpm for 10 min, (4 C). Blood
samples were assayed for albumin, a1-, a2-, b- and
cglobulins. Serum from one tube was used to separate and to
assay the contents of the major serum protein fractions
using the device Minicap the Sebia capillary
electrophoresis system and Minicap Protein (E) 6 kit. Serum
samples were stored at - 20 C before analysis. For DSC
experiment, serum was diluted 20-fold with distilled
degassed water. The pH value of the diluted samples has
been within the range 6.5–7.0.
DSC measurements were taken on the VP DSC MicroCal
instrument (Northampton, MA) in the temperature range
20–100 C with the heating rate 1 C min-1. A constant
pressure of about 1.8 atm was exerted on the liquids in the
cells. The calorimetric data were corrected for the
instrumental baseline water–water. DSC curves were normalized
for the gram mass of protein, and next a linear baseline was
subtracted. An apparent excess specific heat capacity Cpex
(J C-1 g-1) versus temperature ( C) has been plotted.
The following parameters of observed DSC transitions
have been determined: temperatures of local peak maxima
Tm (m = 1, 2, 3), excess specific heat capacities at these
temperatures Cpm, the enthalpy (DH) of serum
denaturation (calculated as the area under the endothermic peak,
expressed in J g-1) and the width of peak in its half-height
Statistical analysis was performed using the Statistica 13
software. For all measures, descriptive statistics were
calculated. The Shapiro–Wilk test was used to check the
normality of distributions of the studied variables. The
homogeneity of variances in analyzed groups was verified
by Leven’s test. Student’s t test was used to compare the
mean values between the two independent groups (men and
women). Analysis of variance (ANOVA) with the period of
training cycle as a repeated measure and the group or
training conditions as categorical variables was used. If
repeated measures ANOVA was statistically significant,
Tukey’s post-hoc test was applied. The level of statistical
significance was set at p \ 0.05, results with p \ 0.1 were
interpreted as tendencies.
Pearson’s correlation coefficients were found to describe
the relationships between biochemical and thermodynamic
blood serum parameters.
DSC curves of blood serum acquired before a training in
normoxia have been averaged in the men and women
groups of participants. Such mean DSC melting profiles for
both groups are shown in Fig. 1. The observed complex
endothermic transition represents the weighted sum of heat
capacity changes connected with the thermal denaturation
of the individual proteins within serum thus serum DSC
curves give information about the thermodynamic stability
of the most abundant serum proteins. Similar curves were
presented and discussed by us earlier for aqueous solutions
of serum derived from male amateur cyclists [
athletes who performed CrossFit [
]. The intensities of
three visible local maxima (T1, Cp1), (T2, Cp2), (T3, Cp3)
have been found correlated with the level of: (1) albumin
fatless fraction and a-2 globulins, (2) a-1- and
a-2-globulins, (3) b-and c-globulins, respectively. Thus, an increase
or decrease in component peaks intensity may be linked to
changes in various protein fractions.
The shapes of the blood serum heat capacity profiles
presented in this and earlier works [
] for athletes
serum diluted with distilled water (pH 6.5–7.0) are
distinctly different from serum/plasma profiles reported for
healthy persons where the final pH of solutions was in the
range 7.2–7.5 [
]. The main origin of discussed
differences is probably the thermal denaturation profile of
fatty acid-free fraction of albumin. DSC transition
representing unfolding of unligated albumin was shown much
sharper in buffer (pH 7.2) than in water (pH 6.5) solution
(see Fig. 1a in Ref. [
]). The advantage of DSC profiles
observed for aqueous serum solutions (with pH below the
physiological value) is the separation of contributions from
albumin and haptoglobin.
The comparison of serum DSC curves shown in Fig. 1
indicates differences in the relation of component peaks
observed for men and women participated in our study. The
Cp3/Cp1 ratio is significantly higher (p = 0.02) for women
(1.60 ± 0.19) than for men (1.27 ± 0.17). This ratio
reflects to some extent globulins to albumin proportion in
serum. Data shown in Table 1 indicate that there are no
meaningful differences in the mean level of globulins
fractions between male and female participants. At the
beginning of the experiment, the mean level of albumins
and A/G ratio were higher for men than for women but
differences were not statistically significant, probably due
to a small number of participants and a great individual
variability, which was observed in our experiment. In
hypoxic conditions the opposite tendency in A/G changes
was observed depending on gender: an increase in the A/
G ratio for women and its decrease for men in comparison
Figures 2 and 3 illustrate mean DSC curves of serum
taken before the exercise (‘‘be’’), after the exercise (‘‘ae’’),
after an hour of rest (‘‘r1h’’) and 24 h of rest (‘‘r24h’’) in a
group of men at NORM and in a group of women at
simulated hypoxic conditions 5000 m (FiO2 = 11.3%),
respectively. In both figures, only the curve after 1 h of rest
clearly stands out from the others. Thus, it can be supposed
that the effect of strength exercise is reflected in the serum
with a delay. So, it is better visible in DSC curves after a
short recovery period than immediately after the effort.
Hypoxic conditions modify the difference between ‘‘r1h’’
and ‘‘be’’ DSC curves. It decreases with increasing
simulated altitude for men while for women the opposite
tendency has occurred. Moreover, a slight increase in Cp1, the
intensity of peak corresponding mainly to unligated
albumin, can be observed directly after the exercise for men
(see Fig. 2) but not for the women (see Fig. 3). Similar
finding refers to the training in other conditions also (data
Fig. 2 Mean DSC curves of serum taken before exercise (solid line),
after exercise (dot line), after an hour of rest (dash line) and 24 h of
rest (dash–dot line) in a group of men in normoxic conditions
Fig. 3 Mean DSC curves of serum taken before exercise (solid line),
after exercise (dot line), after an hour of rest (dash line) and 24 h of
rest (dash–dot line) in a group of women at simulated hypoxic
The set of mean DSC curves for women’s serum after
the exercise in NORM, HYP4 and HYP5, shown in Fig. 4,
suggests that the direct effect of exercise performed by
women does not depend on training conditions. Practically,
there are no changes connected with hypoxic conditions in
comparison with NORM in presented mean melting
41.3 ± 3.1
2.6 ± 0.9
5.5 ± 1.1
10.0 ± 1.7
12.1 ± 2.3
1.39 ± 0.16
44.7 ± 2.9
2.1 ± 0.2
5.1 ± 0.8
9.0 ± 0.9
11.1 ± 2.4
1.65 ± 0.21
45.1 ± 2.7
2.0 ± 0.3
5.4 ± 0.6
9.3 ± 1.1
12.9 ± 1.9
1.53 ± 0.09
43.2 ± 4.2
2.4 ± 0.5
7.2 ± 2.3
10.2 ± 1.3
12.0 ± 2.1
1.39 ± 0.29
profiles of post-exercise woman’s serum. Generally, the
mean response of women to hypoxia seems to be hardly
Unlike, the set of mean curves presented in Fig. 5 for
post-exercise men’s serum indicates clear changes
connected with hypoxic conditions. A significant increase in
Cp2 intensity with increasing altitude is well visible,
especially in HYP5. A characteristic, sharp peak giving the
main contribution to the local maximum (T2, Cp2) comes
from haptoglobin (Hp), the acute-phase protein belonging
to a-2 globulins fraction. The thermal denaturation profile
of Hp has been shown in the Supplement to [
Garbett et al. Even at relatively low concentration in
serum, haptoglobin gives a significant, specific contribution
to the serum denaturation DSC profile [
]. The level of
this acute-phase protein (APP) may increase in any
inflammatory process (infection, extreme stress, burns,
major crush injury, etc.). In particular, intensive increase in
Cp2 value in response to hypoxic conditions has been
observed for two men who performed 10 series of 12 squats
with 90-kg barbells (the largest weight, because the man
who was going to do this with 120-kg barbell did not finish
the task). Probably, in the case of these two men exercise in
hypoxia was enough to produce exercise-induced
acutephase response that resulted in marked increase in serum
concentration of haptoglobin. The elevated value of Cp2
has been observed for these athletes also before the
exercise in HYP5 conditions, 7 days after the training in HYP4.
It suggests keeping up an elevated level of Hp due to the
earlier exhaustive exercises in hypoxia, what is in
agreement with a dynamics of Hp concentration changes in
It should be said, that substantial inter-individual
variation in the effects of hypoxia on men’s response to
exercising has been observed. Figure 6 illustrates quite
different trend of post-exercise serum DSC profile changes
associated with increasing altitude than the average one
shown in Fig. 5. For this athlete the most significant
change concerns the first local maximum (T1, Cp1).
Although this maximum is connected mainly with
unligated albumin, the observed increase in Cp1 can not be
explain by an increase in the level of this most abundant
serum protein in this case. The post-exercise concentration
of albumin in serum of said man was 47.0 g L-1 in
normoxia, 46.9 g L-1 in HYP4 and 43.3 g L-1 in HYP5.
Thus, an increase in unligated fraction of albumin may be
suggested. The collected biochemical data have shown a
slight increase in a2- and b-globulins occurred for
considered example in hypoxic conditions. The most
significant increase has been observed in c-globulins
concentration: from 11.8 g L-1 in normoxia to 13.3 g L-1
in HYP4 and 14.0 g L-1 in HYP5. DSC curves shown in
Fig. 6 indicate that the levels of immunoglobulins, which
give a contribution to the peak with maximum (T3, Cp3), do
not rise. Because the c-globulin fraction includes also
C-reactive protein (CRP), the overall increase in
c-globulins level may be due to an increase in this acute-phase
protein. According to Supplemental Fig. 1 presented by
Garbett et al. [
], CRP thermal denaturation transition
takes place in the temperature range 50–68 C. So, the
increase in Cp1 intensity in hypoxic conditions, visible in
Fig. 6, may be partly explained by the increase in CRP
concentration in serum. It has been concluded that strength
exercising in hypoxia could elevate the level of acute-phase
proteins (Hp and/or CRP) in the group of men.
All mean DSC curves corresponding to pre-exercise
serum and after 24 h of rest (an examples can be seen in
Figs. 2, 3) are very similar. So, our results indicate that
hypoxic training sessions do not require longer recovery
periods compared to normoxic training. The 24 h period of
rest is sufficient to return to the pre-exercise state for both
men and women. However, some differences between men
and women can be observed after the short 1-h rest
depending on the hypoxic conditions. In a group of men
differences between serum DSC curves before the exercise
and after 1 h of rest decline with altitude increase. In
normobaric hypoxia at a simulated altitude of 5000 m
mean DSC curves before the exercise, after 1 h of rest and
after 24 h of rest are practically the same (data not shown).
These results suggest that for men the recovery after
hypoxic training session is faster than after the normoxic
The opposite effect of hypoxia on differences between
DSC curves after 1 h of rest and before the exercise can be
observed for women. Differential curves shown in Fig. 7
indicate that these differences increase with increasing
altitude in the female group. The clear minimum in the
temperature range 50–60 C, accompanied by the
maximum in the temperature range 70–80 C is well visible for
women who trained in HYP5 conditions. As no significant
changes have been found in mean values of albumin as
well as globulins levels between ‘‘be’’ and ‘‘r1h’’ periods
for women in our study, the shape of the described HYP5
differential curve does not result from changes of these
proteins concentration. The suggested explanation may be
connected with changes in the proportion of different
albumin forms: unligated and carrying different ligands.
Various forms of albumin unfold in different temperature
ranges, e.g., the denaturation of fatty acid-free albumin
molecules proceeds in much lower temperatures than the
denaturation of non-defatted albumin [
]. The decline
of unligated form to increase the ligands bounded form of
albumin 1 h after the completion of the exercise in HYP5
training can explain the shape of curves shown in Fig. 7. It
is worth noting that at HYP4 conditions differential curves
for men and women are very similar.
The analysis of the level of serum proteins fractions as
well as thermodynamic parameters describing serum
thermal transition has shown that most of these parameters are
practically independent of the stage of training cycle
(‘‘be’’, ‘‘ae’’, ‘‘r1h’’ and ‘‘r24h’’) and hypoxic conditions
(NORM, HYP4, HYP5). Exceptions are a2-globulins level
and Cp2 value in the male participants group. Mean values
of a2-globulins concentration in serum of athletes are
shown in Fig. 8 at different times of the normoxic and
hypoxic training cycle. Similar dependences for Cp2 values
are presented in Fig. 9. A marked increase in a2-globulins
level as well as Cp2 with simulated extreme altitude is well
visible for male athletes. Statistical analysis showed
significant differences between a2-globulins concentrations in
NORM, HYP4 and HYP5 conditions (p = 0.04) while for
Cp2 parameter only the tendency was found (p = 0.07). A
slight increase in the mean a2-globulins concentration is
also noticeable after the exercise for men as well as for
women in all training conditions. Results of ANOVA with
the period of training cycle as a repeated measure indicate
that a2-globulins concentrations changes are statistically
significant in NORM (p = 0.01) and in HYP5 (p = 0.003)
conditions. The post hoc Tukey’s test pointed to
‘‘ae’’ 7 ‘‘r1h’’ (p = 0.006) difference in NORM and
‘‘be’’ 7 ‘‘ae’’ (p = 0.01), ‘‘ae’’ 7 ‘‘r1h’’ (p = 0.006),
‘‘ae’’ 7 ‘‘r24h’’ (p = 0.008) differences in HYP5.
A large similarity which is evident in the course of
changes shown in Figs. 8 and 9 for a2-globulins
concentrations and Cp2 parameter, respectively, indicates that our
DSC results are in accordance with biochemical data. A
very high, statistically significant correlation has been
found between the Cp2 intensity and a2-globulins levels.
The highest one (Pearson’s correlation coefficient
r = 0.94) has occurred for men after exercise.
Among proteins from a2-globulins fraction, especially
important when interpreting the DSC results, is
haptoglobin. As haptoglobin is an acute-phase protein, any
inflammatory process (infection, extreme stress, burns,
major crush injury, etc.) may significantly increase the
levels of plasma haptoglobin. It has been reported that the
inflammatory symptoms experienced after high intensity
exercise are similar to those seen during chronic disease
]. An increase in serum APPs (CRP, Hp, serum amyloid
A) after prolonged exercise was reported in humans
] and animals (mice, dogs) [
]. Since Hp is an
extremely potent antioxidant [
], Chen et al. [
suggested that elevated Hp expression level may
potentially play a protective role reducing the oxidative stress
during the exercise.
Recent studies indicate that high levels of plasma Hp is
advantageous in patients with acute respiratory distress
]. The relationship between VO2max and Cp2
intensity has been suggested by us recently [
]. In current
study, in particular intensive increase in Cp2 value
connected with an increase in a2-globulins in response to
hypoxic conditions has been observed for two men
repeated bouts of exercise with the largest weight. The reduced
ability of fitter elite athletes to train at altitude due to
limitations in their pulmonary gas exchange system at high
work rates [
] may be considered as the cause of such
observation. It is in agreement with finding that highly
trained endurance athletes suffer more severe gas exchange
impairments during acute exposure to hypoxia than
untrained individuals [
]. Unfortunately, we do not have
the VO2max values for athletes participated in this study.
In athletes, the changes in serum DSC at rest and after
exercise could be an important training tool for coaches
and clinicians. The scope of these changes depends of the
training load during the exercise and a level of hypoxia.
Additionally, we also observed a varied change in the
recovery period after different training sessions (different
level of hypoxia) in the study. DSC results suggests that
this method can be used as a marker of assessing fatigue
during weekly training program (microcycle) to
individualized training loads. The fatigue induction during sport
training is the first rule of the training adaptation process to
improve athlete performance by stimulating organism
functions. The balance between stress and recovery factors
defines the quality of the training program, and observation
of this state is necessary for effective training process and
prevents overtraining. The results of this study indicate the
need for more individualized programming of the training.
The time has come not only for personalized medicine, but
also for personalized training, which provides athletes
safety and success.
It is believed that intermittent hypoxic training IHT would
potentiate greater performance improvements compared to
similar training at sea level. The effectiveness of hypoxic
training to improve performance, however, varied among
different sports [
]. Increased hypoxic stress at altitude
facilitates key physiological adaptations within the athlete
and could increase the training stimulus. However, it is
widely accepted that prolonged exposure to extreme
altitude is detrimental for muscle structure. Moreover, hypoxia
impairs O2 delivery, which decreases one’s maximal
oxygen uptake VO2max relative to normoxia. Highly trained
subjects seem to suffer more under hypoxic conditions than
untrained people. Generally, an individual response to the
altitude should be expected, and our results confirm this
A substantial inter-individual variability has been
observed in the effects of hypoxia on DSC curves of
athlete’s serum. The exhaustive exercise in hypoxia has
induced probably an acute-phase response in some cases.
Particularly, in mail group an increase in haptoglobin and/
or C-reactive protein concentrations in serum has occurred
due to the intensive hypoxic training. The effect of
exercising in normobaric hypoxia at a simulated altitude of
4000 and 5000 m has been found greater for men than for
the women. Some opposite trends have emerged depending
on gender, e.g., an increase in albumin/globulin ratio for
women and a decrease in this ratio for men at 5000 m in
comparison with normoxia. Our results indicate also that
hypoxic training sessions do not require longer recovery
periods compared to normoxic training. The recovery
process after the men’s training in simulated normobaric
hypoxia has been suggested to be even faster than in
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