Recovery Following Acute Endurance Training
Condition: High Intensity Interval Training; Continuous Running; Control Condition
Study type: Interventional

Summary: 
      Aerobic capacity is critical for many athletes, especially for endurance athletes. Althgough
      several training methods are implemented by coaches to improve endurance performance,
      recovery following acute endurance training is not adequately studied. However, such
      information is crucial for coaches to effectively design the most favorable training program,
      to avoid muscle injuries and overtraining, and ultimately to improve performance of their
      athletes. This study aims to examine the acute effect of different continuous and HIIT
      training protocols on indices of metabolism, EIMD, neuromuscular fatigue and performance in
      middle- and long-distance runners.
    

Detailed description: 
      Aerobic capacity is critical for many athletes, especially for endurance athletes. Endurance
      training leads to cardiopulmonary and musculoskeletal adaptations, which in turn lead to
      improvement of endurance performance. Several training methods have been established for the
      improvement of aerobic capacity and performance, including long distance and low speed
      training, and high intensity interval training (HIIT). Training methods are used depending on
      the kind of endurance that aim to improve, and the specific characteristics and energy
      demands of the event. Especially regarding middle- and long-distance runners, the energy
      comes mainly from the oxidative system, however, the contribution of the glycolytic pathway
      is equally important. Thus, improvement mainly of the low-intensity endurance, but also
      high-intensity endurance is important for these athletes. Additionally, both continuous
      endurance and HIIT are effective training methods for improving cardiorespiratory and
      metabolic function, and athletic performance, while evidence also exists in favor of HIIT
      being more effective. Thus both training methods are used by coaches to improve aerobic
      capacity and performance of their athletes.

      Coaches should be careful regarding the frequency of HIIT training during a microcycle, to
      provide adequate recovery between training sessions to avoid muscle injuries and
      overtraining. Existing evidence suggests that endurance exercise (continuous or HIIT) may
      result in exercise-induced muscle damage (EIMD), inflammatory responses, oxidative stress,
      and performance deterioration, yet, the timeframe of recovery of physiological and
      biochemical indices following different endurance training protocols has not been adequately
      studied. However, such information is crucial for coaches to effectively design the most
      favorable training program for their athletes.

      This study aims to examine the acute effect of different continuous and HIIT training
      protocols on indices of metabolism, EIMD, neuromuscular fatigue and performance in middle-
      and long-distance runners.

      According to a preliminary power analysis (a probability error of 0.05, and a statistical
      power of 80%), a sample size of 8 subjects per group was considered appropriate in order to
      detect statistically meaningful changes between groups. Thus, 10 men and female middle- and
      long-distance runners, will participate in the study.

      The study will be performed in a randomized, cross over, repeated measures design. During
      their first 1st and 2nd visit, all participants will sign an informed consent form after they
      will be informed about all the benefits and risks of the study and they will fill in and sign
      a medical history questionnaire. Fasting blood samples will be collected in order to estimate
      muscle damage concentration markers. Participants will be instructed by a dietitian how to
      record a 7-days diet recalls to ensure that they do not consume to greater extent nutrients
      that may affect EIMD and fatigue (e.g. antioxidants, amino acids, etc.) and to ensure that
      the energy intake during the trials will be the same. Assessment of body mass and body
      height, body composition, and aerobic capacity (VO2max), will be performed. Using a
      photocells system, countermovement jump will be performed to assess jump height, and 30 sec
      Bosco test to assess mean jump height, peak power, mean power, and fatigue index. The peak
      concentric, eccentric and isometric isokinetic torque of the knee flexors and extensors, in
      both limbs will be evaluated on an isokinetic dynamometer at 60°/sec. Maximal voluntary
      isometric contraction (MVIC) of the knee extensors at 65o in both limbs, as well as the
      fatigue rate during MVIC through the percent drop of peak torque between the first and the
      last three seconds of a 10-sec MVIC, will also be evaluated. Afterwards, participants will be
      randomly assigned into, and perform one of the three different conditions of the study
      design: a) Continuous running (CT) for 40 min at lactic threshold, b) High intensity interval
      training (HIIT): 10x2min running at vVO2max with active recovery at 40% της VO2max
      (interval:recovery 1:1) with a load of 10% of body weight (BW), and c) control condition, no
      training (measurements only). The training protocols will be matched for mean power and total
      duration (Tschakert and Hofmann 2013). Prior and immediately after each experimental trial,
      delayed onset of muscle soreness (DOMS) in the knee flexors (KF) and extensors (KE) of both
      limbs, as well as blood lactate will be assessed. Additionally, DOMS of KF and KE, peak
      concentric, eccentric and isometric isokinetic torque, CMJ height, as well as mean jump
      height, peak power, mean power, and fatigue index during a 30 sec Bosco test, will be
      assessed 24h, 48h and 72h after the end of the trial. MVIC of the knee extensors of both
      limbs, as well as the fatigue rate during MVIC will also be assessed at 1h, 2h and 3h, as
      well as 24h, 48h, and 72h after the end of the trial. Creatine kinase will be assessed at
      24h, 48h, and 72h after the end of the trial. The exact above procedures will be repeated by
      the participants during the remaining two experimental trials. A 2-weeks wash-out period will
      be implemented between trials.
    

Intervention name(s): High Intensity Interval Training; Coninuous Running; Control Trial
Intervention type(s): Other; Other; Other
Intervention description(s): 10 x 2 min running at vVO2max, interspersed by 2 min recovery at 40% VO2max; 40 min continuous running at lactate threshold; The participants will perform only the baseline and post acute-training evaluations, without performing exercise
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: The same participants will participate in three different conditions
Masking: None (Open Label)
Primary purpose: Screening