Effectiveness of Blood Flow Restriction During Aerobic Cycling
Condition: Exercise Intervention
Study type: Interventional

Summary: 
      Blood flow restriction (BFR) training has become a popular alternate rehabilitation modality,
      intending to improve muscle strength, hypertrophy, metabolic response, and functional
      outcomes in diverse populations. However, there is a paucity of research evidence on the
      effectiveness of using BFR during aerobic exercise. Most BFR interventions have used BFR
      cuffs in two to four limbs, however, it is unknown if using BFR cuffs in a single limb
      instead of multiple limbs can produce the desired outcomes in muscle physiology and muscular
      adaptations. Therefore, we have divided the purpose of this study into the following three
      aims:

      Compare physical performance measures of balance, isokinetic muscle strength, knee stability,
      and aerobic capacity between cycling exercise with and without BFR.

      Compare physical performance measures between performing cycling exercise at 60% versus 80%
      blood flow occlusion.

      Compare physical performance measures between bilateral BFR versus single-leg BFR during a
      cycling protocol.

      These aims will be accomplished by randomizing 55 participants into five groups of eleven
      participants each: 1) control; 2) bilateral BFR cuffs with 60% occlusion; 3) bilateral BFR
      cuffs with 80% occlusion; 4) single-limb BFR with 60% occlusion; and 5) single-limb BFR with
      80% occlusion. All participants will undergo balance, isokinetic knee strength, knee
      stability, and aerobic testing at baseline, 3-week, and 6-week follow-ups. The intervention
      for all groups will consist of 15 minutes cycling on a stationary ergometer at 70
      revolutions/minute. A within- and between-group (5) by time (3) repeated measures analysis of
      variance (ANOVA) will be used to explore differences between group and time in addition to
      the interaction between these two.
    

Detailed description: 
      Experimental Design & Sample Size: This study is a randomized controlled trial with five
      groups of 11 participants each (N=55). Sample size was estimated with GPower using a 5-group
      within- and between-groups repeated measures design with three follow-up visits (0, 3, 6
      weeks) yielding a power greater than 80% including 10% in attrition or missing data.
      Population: Healthy adults between the ages of 21-35 will be recruited. Recruitment will be
      as close to an equal amount of women and men as possible for all groups as the participation
      of women in intervention studies assessing the effectiveness of BFR training has been
      documented to be no more than 17%. Other criteria for participation in the study will be
      committing to the training and testing sessions, being in good health, and familiarization
      with physical activity and exercise, including riding a stationary bicycle. Participants will
      be excluded if they have any of the following: 1) suffered a musculoskeletal injury in the
      lower extremities or lower back in the past three months, 2) any contraindication to aerobic
      exercise testing as determined by The American College of Sports Medicine [12], 3) any
      contraindication to blood flow restriction training, 4) meeting or exceeding the recommended
      ACSM exercise guidelines of aerobic exercise 5-times/week for >20 minutes and strengthening
      exercise > 2-days/week [12], and 5) pregnancy for female participants (self-reported). Each
      participant will be required to read and sign an informed consent document approved by the
      Institutional Review Board before enrolling in the study and any testing being performed. The
      55 participants in the five groups of 11 participants will be randomized by using a random
      number generator. The five groups will be randomized as follows: 1) control (Con), 2) 60%
      bilateral occlusion BFR (60BILAT), 3) 80% bilateral occlusion BFR (80BILAT), 60% unilateral
      BFR occlusion (60UNIT), and 80% unilateral BFR occlusion (80UNIT).

      Instrumentation & Outcomes: Single leg balance will be measured using a Balance System SD
      (Biodex Medical Systems, Inc, Shirley, NY). This device measures static and dynamic
      multidirectional balance by the use of the validated Balance Error Scoring System (BESS) by
      measuring sway with eyes closed in the following conditions: 1) double-leg firm surface, 2)
      single-leg firm surface, 3) tandem stance firm surface, and 4) repeating the previous tests
      on a foam (unstable) surface. Balance and postural stability are fundamental components of
      athletic performance and activities of daily living making its assessment imperative to
      measure changes during different conditions such as injury, fatigue, concussions, etc.
      Furthermore, recent evidence suggests that BFR training improves balance in functional
      activities, but the only evidence is in the population of older adults. Knee stability will
      be measured during a 5-repetition single-leg step down from a 30-cm step platform with a
      10-camera (120Hz sampling rate) motion analysis capture system (Qualisys AB, Göteborg,
      Sweden) time-synchronized to a wireless electromyography (EMG) system (Trigno, Delsys, Inc.,
      Natick, MA). EMG data will be collected through three pre-amplified (Ag) electrodes (Trigno,
      Delsys Inc., Natick, MA; Bandwidth: 450 ± 50 Hz > 80 dB/dec; overall channel noise: <0.75uV)
      bilaterally from the vastus medialis, rectus femoris, and vastus lateralis at 2kHz and
      filtered through a 2nd order Butterworth filter. Knee stability is an essential outcome in
      rehabilitation as it is the foundation for proper alignment to prevent injuries [14], while
      muscle activation is one of the main constraints to knee instability, helping to prevent
      injuries. Given there is evidence showing BFR training increases muscle recruitment and
      muscular activation by the use of EMG it is imperative to determine if such improvements
      translate into better motor control and knee stability during functional activities. Muscle
      strength of the quadriceps and hamstrings will be measured with an isokinetic dynamometer
      (System 4 Pro, Biodex Medical Systems, Inc, Shirley, NY) at the speeds of 60˚ and 180˚
      degrees per second. The dynamometer will be calibrated according to the manufacturer's
      recommendations. Several investigations have found improvements in isokinetic strength after
      BFR training. Therefore, assessment of muscle strength via isokinetic dynamometer will allow
      to make comparisons between the study and the current literature. Aerobic Capacity will be
      measured during a cycle ergometer protocol in a stationary ergometer (Velotron, Quarq
      Technology, Spearfish, SD) while connected to a gas analyzer (TruOne 2400, Parvomedics, Salt
      Lake City, UT) for the assessment of oxygen consumption [VO2 (ml/min)]. This is an
      exploratory outcome as aerobic exercise in a cycle exercise for 15 minutes is not expected to
      improve cardiovascular metabolic performance. However, Abe et al 2010 reported improvements
      in VO2max with a similar protocol to this study of 15 minutes of cycling with BFR cuffs.
      Thus, by evaluating VO2, the study will be able to determine if there is any benefit of BFR
      training during aerobic exercise and compare our results to the small cycling evidence with
      BFR cuffs.

      Procedures: After consenting to participation, demographic and anthropometric information
      will be recorded. After measurements, participants will be equipped with retroreflective
      markers per Qualisys CAST model, using appropriate hypoallergenic double-side retroreflective
      markers for individual markers and elastic bandages with Velcro for retroreflective casts.
      EMG electrode placement will follow a standardized setup previously published by Ortiz et al.
      To minimize the effects of fatigue in task performance, the order of testing will remain
      constant in the following order: 1) BESS, 2) single-leg step down, 3) isokinetic testing, and
      4) aerobic capacity. For the BESS, the order of the testing will be according to the protocol
      displayed on the platform's computer screen. Participants will perform all tests with eyes
      closed for 20 seconds with 10-seconds rest between conditions. Each participant will first
      perform the three stable conditions (double-leg, single-leg, tandem) followed by the same
      conditions after placing a 6cm thick foam pad over the balance platform. A special note for
      those participants in the single-leg BFR group will be written, denoting which leg was used
      for the BFR cuffs. The single-leg step-down will be performed from a 30-cm step for three
      5-steps repetitions per leg, alternating legs. Each participant will stand initially on the
      step with both feet on the step. Upon the command "go," they will lift the corresponding leg
      and step down touching the floor (force plate) with the non-weight-bearing leg and will
      return to the original stance position. This process will be performed continuously five
      consecutive times. Valgus motion will be tracked with the 3-dimensional motion system and EMG
      through the entirety of the five single-leg stance time epochs. Valgus will be measured at
      the point where the participant touches the force plate. The highest valgus and EMG amplitude
      (RMS) of the three middle trials will be considered for analysis. A special note for those
      participants in the single-leg BFR group will be written, denoting which leg was used for the
      BFR cuffs. For the fatigue analyses, the average of the five trials for motion analysis and
      the entire frequency of the EMG signal will be considered for analysis. Muscle strength
      assessment of the quadriceps and hamstrings will follow the step-down assessment. Each
      participant will be seated in the dynamometer based on standardized positions. The right leg
      will be tested first, followed by the left one. For those participants in the single-leg BFR
      group, a special note will be written denoting which leg was used for the BFR cuffs. The
      standardized protocol set by the dynamometer computer will be followed with 60˚ and 180˚ per
      second. A familiarization warm-up of three to five repetitions at each speed will be
      performed previous to the testing at each speed, followed by a minute of rest. A total of
      five contractions will be performed at 60˚/second and 10 repetitions at 180˚/second. Aerobic
      capacity will be assessed through a standardized maximal cycle ergometer protocol. VO2 max,
      VO2 peak, and heart rate will be measured directly from the metabolic analyzer during this
      protocol. After a 10-minute rest to obtain resting heart rate, participants will start
      pedaling at 70 rev/min with a load of 25 Watts. Heart rate (HR) will be monitored
      continuously in real-time and the heart rate at the end of the first three minutes will be
      used to determine further load increases. The test will continue until the participant
      reaches one or more of the following criteria: reaches 80% of their predicted heart rate by
      using the heart rate reserve formula; (([220-age] -resting heart rate) x 80%) + resting heart
      rate, reaches an RER >1.0, or there is a leveling of the oxygen curve. Intervention: Control
      group: the control group will perform 15 minutes of cycling in a stationary cycle ergometer
      at 70 rev/min three times a week for six weeks. Subjects will wear a polar heart rate monitor
      through the training to record their heart rate response during the 15 minutes of training.
      BFR groups: all four BFR groups will perform the same training as the control group while
      using the BFR cuffs. This training program follows the recommendations for stationary cycling
      while wearing BFR cuffs of 45-60 minutes per week. Each participant in the BFR group will
      undergo the protocol defined by Delfi (Delfi Medical Innovations, Inc., Vancouver BC,
      Canada), consisting of placing the BFR cuff in the upper part of the thigh while the
      participant is lying supine on a table against gravity to determine full occlusion then to
      derived the percentage of desired occlusion (60% or 80%).

      Data Analysis: Data will be screened for normality, homoscedasticity, and outliers.
      Independent t-tests will be performed to compared demographic (age, weight, height, BMI)
      variables between groups. A within- and between-group (5) by time (3) repeated measure ANOVA
      with interactions will be used to compare groups for all outcomes of interest. Post-hoc
      analyses will be used to follow up significant differences between groups, time, and the
      group by time interaction.
    

Intervention name(s): Exercise
Intervention type(s): Other
Intervention description(s): Cycling 3 times a week for 15 minutes at 70 rpm using blood flow restriction cuffs at different occlusions.
Other intervention name(s): Blood flow restriction training
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: exercise; cycle ergometer; strength