EQOL Journal (2022) 14(1): 49-53
Serum creatine-kinase and extended breastfeeding: Case study
Ksenija Bubnjević
Bojana Mar
Dušan Stupar
Dragan Grujičić
Received: 14
April, 2022 DOI: 10.31382/eqol.220606
Accepted: 2
June, 2022
© The Author(s) 2022. This article is published with open access.
The World Health Organization recommends infants
should be exclusively breastfed for the first six
months of life. Various factors can affect the
maintenance of lactation. Increased physical activity
and stress are thought to negatively affect
breastfeeding success. The aim of this case study
was to examine the effect of high serum creatine-
kinase (CK) values and the success of breastfeeding
after sports competition. It is assumed that
continuous aerobic exercise is a stress for the body
that can have a negative impact on lactation and
extended breastfeeding. Methods. The level of acute
muscle damage (AC) was measured before and after
the competition in order to confirm continuous
exposure to aerobic exercise. Results. After the
competition, elevated serum creatine-kinase levels
were noted. Prolactin and TSH values remained
within optimal values. Conclusion. Several months
of preparation for the competition had an impact on
increasing acute muscle damage (AC) after the
competition. No negative effect of continuous
aerobic exercise on breastfeeding success was
observed in this case study.
Keywords aerobic physical exercise prolactin
extended breastfeeding.
The World Health Organization recommends
extended breastfeeding for the first six months of
a newborn`s life, and even longer (WHO, 2020;
Kramer, & Kakuma, 2012). Breastfeeding is
considered the healthiest diet and excludes giving
infants water (Almroth, Mohale, & Latham, 2000;
Dewey, 2001). Although many positive effects of
extended breastfeeding are known, it is still a
problem for many mothers (Pérez-Escamilla,
2020). Only a small percentage of women manage
to maintain lactation during the first months after
giving birth (Binns, Lee, & Low, 2016; Yuliarti,
2010). It is believed that stress, increased physical
activity, chronic diseases, as well as some other
lesser-known factors can cause a low milk supply
during breastfeeding. In as many as 80% of cases,
due to chronic stress, there is a reduced oxytocin
secretion, which is responsible for milk
production. (Yuliarti, 2010). There are few studies
that have investigated the impact of continuous
aerobic exercise during breastfeeding (Bubnjević,
Ugarković, and Kovačević, 2020). It has not been
sufficiently researched how high-intensity
exercise affects the possibility of breastfeeding,
especially extended breastfeeding.
There are various ways to describe the training
load of physical exercise. One of the indicators is
the appearance of creatine kinase in the blood
(CK), (Anugweje, & Okonko, 2012). This serum
marker indicates acute skeletal muscle fibre
damage (Mougios, 2007). According to the
experiences of some researchers, there are no
unique markers that would be a reliable indicator
of transient muscle damage and overtraining.
(Marić, 2018). Although researchers recommend
University of Educons, Faculty of Sport and
Psychology, Novi Sad, Serbia
Serbian Armed Forces, 1
Training Centre,
Sombor, Serbia
EQOL Journal (2022) 14(1): 49-53
measuring more than one marker, CK can be
considered one of the best indicators because it enters
the circulation and is the result of muscle metabolism
(Brancaccio, Lippi, & Maffulli, 2010; Nigro et al.,
1983). Also, one of the markers used as an indirect
marker of muscle damage is the aspartate
aminotransferase (AST), (Brancaccio, Lippi, &
Maffulli, 2010; Paulsen et al., 2012). If the values of
AST are increased, chronic muscle injury can be
suspected, but then the value of alanine
aminotransferase (ALT) is also increased, (Nathwani,
Pais, Reynolds, & Kaplowitz, 2005). A number of
parameters used to investigate possible stress caused
by high training load certainly better describe a
possible problem. Also, the analysis of the
composition and quality of breast milk would be a
reliable indicator of the impact of physical exercise
on lactation, but in this case it was not easily feasible.
A study on a larger number of female respondents
who regularly train some aerobic sport would
certainly contribute to the research. However, since
few women have the ability to breastfeed
successfully, this case study was sufficient to show
the individual impact of continuous aerobic exercise
on lactation success and extended breastfeeding.
Case study
In this case study, an analysis of data collected before
and after a triathlon competition (long triathlon) was
performed. The respondent (35 years old; BMI 18.5
kg/m2) competed in several aerobic sports before her
first pregnancy. Apart from thyroid disease, she had
no other health problems. Two weeks after giving
birth, she continued with training (running) of light to
moderate intensity. She increased her training load
gradually (running - about 5-7 trainings per week /
about 60-70 km). After a year, she included
swimming (once or twice a week) and cycling (once
to three times a week) in her training program. With
enough rest and proper nutrition, the respondent
continued to breastfeed successfully at the request of
the child, and after the sixth month she introduced
solid foods into the child`s diet and continued to
breastfeed 3-6 times a day. After 15 months of giving
birth, she participated in a long triathlon in Austria
(St. Pölten, May 22, 2016).
It is believed that taking part in a long triathlon
requires several months of training and possible
disruption of the conditions for successful
breastfeeding. Monitoring and control of parameters
before and after the competition will show whether
great physical exertion after continuous aerobic
physical exercise can affect lactation and thus the
possibility of breastfeeding. The following
parameters were measured: KKS, prolactin, TSH,
FT4, ferritin, AST/OT, CK, direct and indirect
bilirubin (3 days before competition). Body
composition monitoring was performed for seven
days, as well as one day after the competition. Quality
control of breast milk was not performed.
The respondent successfully completed the first long
triathlon for about 06:00. The air temperature ranged
from about 12 degrees (start of the race - 07h) to 25
degrees, which could have caused dehydration. After
the competition, the respondent received an infusion
for preventive reasons. Breastfeeding was established
after one hour.
The KKS analysis showed the good health
condition of the respondent before and after the
competition. The measured biochemical values (in
two measurements) were within the reference values.
Blood analysis showed that there were no indications
of possible anaemia, infection or dehydration.
Prolactin, which is primarily related to lactation, but
can also indicate the existence of stress, was within
the reference values. AST values that were within the
reference values (up to 40 U/I) before the competition
increased significantly after the competition. CK
values also ranged within pre-competition reference
values (26-140 U/I). After the competition, the results
of the measured CK values showed that there was
severe acute muscle damage (115 U/I in the first
measurement; 1445 U/I in the second measurement).
No major changes in thyroid hormone (TSH) were
observed (Table 1). Biochemical results were
measured by SPFT laboratory method in the same
laboratory. The body composition values in both
measurements showed slight differences. The muscle
mass values were within the reference values, while
the percentage of adipose tissue was slightly reduced
(9.6% - 9.4%).
EQOL Journal (2022) 14(1): 49-53
Table 1. Blood biochemistry
Bilirubin total
up to 20.1
Bilirubin direct
up to 7
up to 40
M (38-174); F (26-140)
0.27-4.20 mU/I
M (86-324); F (102-496)
*Free T4
M (10.6-28.3); F (6.6-26)
* Missed the second measurement.
Prolonged overtraining can lead to the development
of chronic stress. On the other hand, moderate daily
aerobic physical activity is recommended to maintain
good health (WHO). A study that investigated the
effects of yoga during lactation shows a positive
effect on prolactin secretion, a calm mom and
breastfeeding success (Wildan, & Primasari, 2011).
Although continuous aerobic exercise has a positive
effect, it can negatively affect the secretion of
oxytocin, and thus the possibility of breastfeeding.
Also, it is considered that the psychological factor is
most responsible for the success of breastfeeding
(Yuliarti, 2010). The mother`s commitment proved to
be very important (Brew, 2003). During several
months of breastfeeding, periods are expected when
there may be a loss of interest and cessation of
breastfeeding due to the impending crisis (Wildan, &
Primasari, 2011). Exercise is thought to reduce stress
and the possible development of postpartum
depression (Currie, Rich, & McMahon, 2004). Some
studies point out that the problem of breastfeeding
when it comes to top female athletes has been
insufficiently researched. How to maintain lactation
during the competition period is something that
definitely worries many athletes.
In addition to the necessary commitment of the
mother, proper nutrition is also very important, as
well as enough rest (Brew, 2003; Nedelec, Mathieu et
al., 2018). Breastfeeding women burn an additional
500 kcal per day. After intensive training, it is
necessary to get enough protein (Morton, Robert
W., et al., 2018). Although the respondent had lower
BMI values, a lower percentage of adipose tissue did
not negatively affect the possibility of breastfeeding.
The success of breastfeeding in this case study can be
explained by establishing a proper breastfeeding
rhythm and getting adequate rest.
Increased CK marker values, which were recorded
after the second measurement, can be explained by
the respondent`s physical fitness levels (Brancaccio,
Lippi, & Maffulli, 2010). TSH and prolactin values
show that there was no chronic stress during several
months of training and breastfeeding. The largest
changes in serum were observed after the second
measurement in the CK and ALT values. Increased
CK values indicate the resulting acute damage that is
probably proportional to the duration and intensity of
muscle contractions, and which also depends on
muscle sensitivity. The ALT (alanine
aminotransferase) indirect marker confirms the
resulting acute muscle damage. The highest CK
marker values are recorded about 24 hours after the
end of physical activity, and can be maintained from
48 to 72 hours after exercise. CK values measured can
be attributed to gender, physical fitness levels, and
increased fatigue (Brancaccio, Lippi, & Maffulli,
2010; Anugweje, & Okonko, 2012). In this case
study, there was no negative impact of sports
competition on establishing lactation and
breastfeeding after the triathlon competition. Also,
great physical effort did not pose a problem to easier
and faster recovery of the organism because the
respondent participated in the next competition only
7 days later (long triathlon). Sports and competition
EQOL Journal (2022) 14(1): 49-53
regime did not have a negative impact on extended
A review of the available scientific literature so far
has shown that female athletes are not sufficiently
informed about the possibilities of sports training
during the period of extended breastfeeding. Also, no
data have been reported describing the impact of
continuous aerobic exercise on breastfeeding success
as measured by confirmation of physical exertion and
a measured marker of acute serum muscle damage
(CK). Based on the results obtained from this study,
it can be assumed that continuous aerobic exercise
will not have a negative impact on the success of
extended breastfeeding if a healthy diet, enough rest,
proper hydration and optimal training load are
included in the daily lifestyle. Further research is
needed on the different types and intensities of
physical exercise on the possibility of breastfeeding
during the first six months and after that period.
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How to cite this article:
Bubnjević, K., Marić, B., Stupar, D., & Grujičić, D. (2022). Serum
creatine-kinase and extended breastfeeding: Case study.
Exercise and Quality of Life, 14(1), 49-53.
Bubnjević, Ksenija, et al. "Serum creatine-kinase and extended
breastfeeding: Case study." Exercise and Quality of Life 14.1
(2022): 49-53.
Bubnjević, Ksenija, Bojana Marić, Dušan Stupar, and Dragan Grujičić.
"Serum creatine-kinase and extended breastfeeding: Case
study." Exercise and Quality of Life 14, no. 1 (2022): 49-53.