Recovery Kinetics Following Change of Direction Training

This study aims at investigating the recovery kinetics of skeletal muscle damage, neuromuscular fatigue and performance following a single change of direction (COD) training session in competitive soccer players. The impact of COD degrees will be also examined by comparing a 45o vs. 90o COD training session. Ten male soccer players will perform a COD45 \[A single training session including 2x(10x \~27.6m) sprints with two 45o COD in each sprint\], a COD90 \[A single training session including 2x(10x \~21.2m) sprints with two 90o COD in each sprint\] and a Control trial (No intervention included, only daily measurements) in randomized, repeated measures, crossover design. Assessments related to skeletal muscle damage, neuromuscular fatigue and performance will be performed prior to training session and daily for three consecutive days post-training, in each trial.

Ten male soccer players will be included in this study. Participants will be initially informed about the aim of study as well as the associated risks and benefits and subsequently will provide their signed consent form. At baseline, they will undergo assessment of their anthropometrics (i.e. body mass and body height), body composition (by DXA), physical conditioning status \[maximal oxygen consumption (VO2max), Yo-Yo Intermittent Endurance test level 2 and Yo-Yo Intermittent Recovery test level 2\] and daily dietary intake. Thereafter, they will participate in two experimental trials and one control trial in a randomized, crossover, repeated measures design: i) COD45: Participants in this trial will perform a COD training session consisted of 2 sets of 10 x \~27.6m sprints with two 45o COD in each sprint and a resting period of 16 sec and 2:20 min between sprints and sets, respectively, ii) COD90: Participants in this trial will perform a COD training session consisted of 2 sets of 10 x \~21.2m sprints with two 90o COD in each sprint and a resting period of 16 sec and 2:20 min between sprints and sets, respectively, iii) Control: Participants in this trial will only participate in daily assessments to control for day to day variability in the depended variables (they will not receive any intervention). Prior to each trial, participants will provide a resting blood sample (for the determination of blood lactate, white blood cell count and creatine kinase activity) and undergo assessment of their delayed onset of muscle soreness (DOMS), maximal voluntary isometric contraction (MVIC), countermovement jump \[will be assessed using two force platforms at 1000 Hz and electromyography instrumentation (EMG)\], isokinetic peak torque of knee extensors and flexors (will be assessed on an isokinetic dynamometer), agility (will be assessed using the Illinois test), 10m and 30m sprint time (will be assessed by using light cells) and repeated sprint ability (5x30m sprints will be performed with 25 sec rest in-between). In COD45 and COD90 experimental trials, a blood sample will be collected immediately post-training for the determination of blood lactate concentration while assessment of DOMS, MVIC and countermovement jump will be performed at 1, 2 and 3 hours post-training. In all trials assessment of DOMS, MVIC, countermovement jump (CMJ), isokinetic peak torque, agility and sprinting performance as well as determination of creatine kinase activity and white blood cell count will be performed at 24, 48 and 72 hours post-training. A 7-day wash out period will applied between trials.

Eligibility Criteria:
Inclusion Criteria:

* Soccer players participating in at least 5 training sessions per week and 1official match
* Participation at a competitive level for at least 4 years
* Free of musculoskeletal injuries
* No use of ergogenic supplements or medication
* Non-smokers

Exclusion Criteria:

* Musculoskeletal injury
* Use of alcohol, caffeine and any type of ergogenic supplements or medication during the course of the study