Acute, vigorous and/or unaccustomed eccentric exercise can induce muscle injury and
inflammatory reactions, and oxidative stress, but also reduced muscle performance. For
this reason, many professional as well as amateur athletes, often consume nutritional
supplements such as antioxidants, anticipating to reduce inflammation and oxidative
stress after intense exercise.
The human gastrointestinal tract is inhabited by various microorganisms, called the gut
microbiome (GM). GM, among other things, contributes to the normal functioning of the
immune system, contributes to the production of short-chain fatty acids (SCFAs) and
vitamin synthesis as well as the digestion and absorption of food, protects against
enteropathogens and regulates inflammatory and redox responses. Recent evidence also
suggests that GM may be involved in athletic performance. In contrast, disruption of GM
composition (dysbiosis) is characterized by reduced diversity, reduced abundance of
health-promoting bacteria, and increased abundance of gram-negative and other pathogenic
bacteria and is associated with various metabolic diseases such as obesity, diabetes, and
various forms of cancer, systemic inflammation, oxidative stress and reduced performance.
Thus, the supplementation of several "biotics" has been emerged as a means to regulate
the GM in favor of health-promoting bacteria.
Postbiotics is defined as a "preparation of inanimate microorganisms and/or their
components that confers a health benefit on the host". Evidence suggests that
supplementation with postbiotics may regulate the GM, and consequently, strengthen the
immune system, reduce intestinal permeability, improve antioxidant mechanisms, as well as
accelerate recovery after exercise-induced inflammation, enhance adaptations to exercise,
and improve performance. However, the scientific data regarding the possible beneficial
effect of supplemental administration of postbiotics is limited. More research is needed,
in order to determine the role of postbiotics supplementation on GM composition and
function, exercise-induced inflammation and redox status, but also on performance after
intense exercise.
This study will investigate the potential of postbiotics supplementation to alter the GM
composition and affect the recovery of exercise-induced oxidative stress and performance
following intense, eccentrically biased acute exercise. The study will be cross-over,
randomized, double-blind, controlled, and will be conducted in two cycles. The
participants, will be primarily informed regarding the study procedures, as well as the
benefits and possible risks, and will sign an informed consent form for participation in
the study. Before the experimental procedure, they will be involved in a week of
familiarization to the evaluation tests and the exercise protocol, at a low intensity.
Participants will undergo baseline measurements: anthropometric characteristics (body
height, body mass, body mass index) via a stadiometer-scale (Stadiometer 208; Seca,
Birmingham, UK), body composition (amount of body fat, lean body mass, fat mass, bone
density) via by dual emission X-ray absorptiometry (DXA, GE-Healthcare, Lunar DPX NT,
Belgium), aerobic capacity (VO2max) via an automated online pulmonary gas analyzer (Vmax
Encore 29, BEBJO296, Yorba Linda, CA, USA) during a graded exercise protocol on a
treadmill (Stex 8025T, Korea), isokinetic strength (isometric, concentric and eccentric
torque of the knee extensors and knee flexors) on an isokinetic dynamometer (Cybex, HUMAC
NORM 360, Ronkonkoma, NY), and muscle power via the assessment of countermovement jump
(CMJ) via an optical measurement system (Optojump next, Microgate, USA). In addition, the
participants will record their diet via a 7-days recall before their participation in the
first experimental condition, and dietary data will be analyzed with ScienceFit Diet 200A
diet analysis program (Science Technologies, Athens, Greece), in order to estimate that
they do not consume nutrients that may affect muscle injury, inflammation and oxidative
stress (e.g. antioxidants, etc.). Participants will then be randomized in one of the two
conditions: i) Postbiotics supplementation (50mg/day of Heatkilled Lactobacillus
plantarum L-137, Immuno-LP20TM) for 4 weeks, or ii) placebo supplementation for 4 weeks.
Randomization of the conditions will be done by a software generating random integers
available on the internet (Random.org). Participants will then perform an exercise
protocol comprised of 45 min downhill running (-15% slope, ~70-75% VO2max) on a treadmill
followed by a time-trial (0% slope, ~95% VO2max) until exhaustion. Before the exercise
protocol, as well as 24 h, 48 h and 72 h after exercise, exercise-induced muscle damage
(EIMD) [delayed onset of muscle soreness (DOMS) via palpation of the knee extensors and
knee flexors on a scale of 1 to 10 (1 = no pain at all; 10 = extreme pain), and muscle
performance (CMJ, isometric, concentric and eccentric torque of the knee extensors and
knee flexors)], will be assessed. At the same time points, feces samples will be
collected for the analysis of GM composition and function, and GM metabolites, as well as
blood samples for the assessment of complete blood count (CBC), blood inflammatory status
(creatine kinase, tumor necrosis factor alpha, interleukin 6, C-reactive protein), gut
inflammatory status (lipopolysacharides-binding protein, zonulin), and blood redox status
[reduced glutathione (GSH), oxidized glutathione (GSSG), GSH/GSSG ratio, total
antioxidant capacity, catalase, protein carbonyls, uric acid, bilirubin). Furthermore,
metabolism (lactic acid) will be assessed before and 4 min following exercise by
analyzing capillary blood with a portable lactate analyzer (Lactate Plus, Nova
Biomedical, USA). Afterwards, the participants will receive the postbiotics supplement or
the placebo for 4 weeks, and will repeat the exercise protocol and measurements of EIMD,
CBC, blood inflammatory status, blood redox status and performance at the same
time-points. At the second cycle, participants will repeat the exact same procedures for
the remaining condition. Between cycles, a 14-days washout period will be applied.
Additionally, the 7-day diet recall from the first cycle, will be given to the
participants to follow the same diet before the experimental exercise protocol at the
second cycle.