Repeated Bout Effect and Indirect Biomarkers After Eccentric Exercise Induced Muscle Damage
Phase: NA
Conditions: Exercise Induced Muscle Damage
Sponsor: Vassilis Paschalis

 
1 
Repeated Bout Effect and Indirect Biomarkers After Eccentric Exercise 
Induced Muscle Damage 
 
11 February 2026 
 

 
2 
Information for Participants and Consent to Participate in Research 
The purpose of this study is to investigate changes in markers of exercise-induced muscle 
damage following an acute and a subsequent eccentric exercise of the knee joint extensors 
performed on an isokinetic dynamometer. During the study, the following 
measurements/assessments will be carried out: 
 
Eccentric exercise (knee extensors) 
Eccentric exercise of the knee joint extensors will be performed on an isokinetic 
dynamometer. The exercise will consist of 5 sets of 10 repetitions (knee extensions), while 
the angular velocity will be set at 60°/s. 
 
Assessment of peak torque 
An assessment of isokinetic peak torque will be performed on an isokinetic dynamometer. 
The assessment will consist of one set of 8 repetitions for familiarization and one set of 5 
maximal-effort repetitions. 
 
Possible discomforts 
Muscle fatigue and cardiovascular strain. In rare cases, there is a possibility of fainting; in 
such a case, the appropriate equipment (examination bed) is available, while the tests will be 
conducted at times when a doctor or nurse will be present at the faculty facilities. To reduce 
discomfort, a warm-up will be performed (low-intensity exercise on a cycle ergometer for 7 
minutes and stretching exercises of the main muscle groups) and a cool-down (stretching). 
Approximately 2 days after the eccentric exercise, the sensation of muscle pain during 
movement (delayed onset muscle soreness) in the exercised muscle groups will peak. The 
sensation of pain will gradually subside over the following days. 
 
Blood sampling 
On the days of the assessments, a blood sample of 10 ml will be taken from the vein on the 
inner side of the elbow joint (basilic vein). A total of four (4) blood draws will be performed 
during the study. 
 
Possible discomforts 
Mild local pain and the possibility of bruising (hematoma) in the area. In rare cases, there is a 
possibility of fainting; in such a case, the appropriate equipment (examination bed) is 
available. Blood sampling will be performed by a doctor at the facilities of the School of 
Physical Education and Sport Science. 
 
Muscle oxygenation 
On the days of the assessments, a NIRS device will be placed on the knee extensors for 
monitoring muscle oxygenation and will be there for the whole period of the data collection.   
 
Possible discomforts 
None. 
 
It is important that you do not withhold any information you know that relates both to your 
current health status and to any issue that may arise during the measurements. The results of 
the measurements are confidential and will be used only by the research team, while any 
publication of results will be anonymous. A necessary condition for your participation in the 
study is examination and written approval by an internal medicine physician stating that you 
can participate in maximal-intensity exercise without risk to your health. 
 
Consent Statement 
I declare that I have understood the procedure of the above assessments and the risks involved 
and I wish to participate in the research program. I also understand my right to withdraw from 

 
3 
the above tests at any time I wish, without any obligation to provide any explanation to the 
researchers. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Participant’s name: 
Signature: 
 
 Researcher’s name: 
Signature: 
 
Witness’s name:  
Signature: 
Date ……/……/ 2025 

 
4 
Study design 
Experimental groups performed 2 eccentric exercise sessions unilateral 
sessions using the knee extensors on an isokinetic dynamometer (Biodex, 4 
pro, Shirley, NY, USA). The second eccentric exercise session was performed 
3, 6, 9 or 12 weeks after the initial exercise bout. A number of physiological 
and biochemical markers related to muscle damage were assessed. 
Specifically, physiological markers of muscle function and damage [pain-free 
range of motion (ROM), delayed onset muscle soreness (DOMS), and 
isokinetic peak torque] and biochemical markers of muscle damage (creatine 
kinase; CK) and inflammation (C-reactive protein; CRP) were measured prior 
to as well as 48 and 72 h post each exercise session.  
 
Statistical analysis 
The distribution of all dependent variables will be examined by the 
Kolmogorov–Smirnov test. The anthropometric characteristics of the 4 groups 
at baseline will be examined using an unpaired Student’s t test. A two-way 
repeated-measures ANOVA test [group (3, 6, 9 and 12 weeks) × time (pre-
exercise 
and 48- and 72-hours post-exercise)] will be performed to compare muscle 
function and damage biomarkers between the groups and to compare the 
effect of each exercise mode on muscle damage biomarkers in each week of 
intervention. When a significant interaction will be obtained, pairwise 
comparisons will be performed through the Sidak test that counteract the 
problem of multiple comparisons. When sphericity will be violated, the 
Greenhouse–Geisser correction will be applied. Data will be presented as 
mean ± standard deviation (SD) and the level of significance will be set at a = 
0.05. 
The SPSS version 26.0 will be used for all analyses (SPSS Inc., Chicago, IL).