This study aims to determine how flywheel-based inertial training (FIT) implemented according to principles of velocity-based training (VBT) and High-Intensity Interval Training (HIIT) affects disuse-induced physical de-conditioning including loss of voluntary muscle strength, aerobic capacity, and balance regulation.
The primary objectives of this project are: 1. To assess how 30d of unilateral lower limb suspension (ULLS) with and without FIT exercise affects voluntary and electrically-evoked twitch force, motor unit recruitment, and anisotropic measures. 2. To determine how muscle anisotropy (assessed through diffusion tensor imaging) and motor unit action potential train (MUAPT) characteristics relate to contractile function in loaded and unloaded limbs Secondary objectives include: 1. To assess impact of ULLS with and without FIT on aerobic capacity 2. To assess impact of ULLS with and without FIT on balance regulation during single-leg stance This study aims to recruit 10 healthy, physically active participants (both male and female). Participants will undergo 30d of ULLS to unload the left limb during daily living activities. Subjects will wear a specially modified shoe with a 5cm rocker-style stack on the right leg and ambulate using crutches. Participants will be randomly assigned to either a control or exercise group. Those in the exercise group will perform Flywheel-based Inertial Training (FIT) leg press three times per week. Moment of inertia of the flywheel will be adjusted to elicit movement speeds of 0.4 m/s for resistance training (four sets of 10 repetitions). For High Intensity Interval Training, flywheel moment of inertia will be adjusted to elicit movement speed of 1.0m/s during upright squats (four sets of 3 min). Before and after the intervention, subjects will complete a series of tests including: 1. Body Composition - height, weight, waist circumference, and tetrapolar bioelectrical impedance analysis will be conducted. 2. Balance assessment - center of pressure will be assessed using portable force decks during single leg stance with eyes open and closed. This test will be repeated in the shod and unshod conditions. MUAPT data (high density surface electromyography) will be collected for the soleus and tibialis anterior during this test. 3. Aerobic capacity test - VO2max will be determined during a graded exercise test on a cycle ergometer (3 min per stage). Gas exchange and heart rate data will be collected continuously throughout the test. Pedal force will also be assessed. Additional outcomes such as ventilatory threshold and substrate utilization will be assessed. 4. Muscle Imaging - Diffusion tensor imaging (DTI), a magnetic resonance technique will be used to assess anisotropic measures, muscle volume, fascicle length, and fascicle orientation of the mid-thigh. 5. Muscle strength testing - Maximal voluntary isometric and isokinetic strength of the knee extensors, flexors, and ankle plantar- and dorsi-flexors will be assessed. Interpolated twitch (electrical stimulation of the femoral nerve) will be used to assess twitch characteristics and voluntary activation of the quadriceps
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
NONE
Enrollment
16
Participants will ambulate unilaterally using a shoe modified with a 5cm rocker-style stack and forearm crutches for the duration of the study. All participants will complete two testing sessions prior to ULLS, one testing session at day 13, and two testing sessions at the end of the study. Those assigned to the exercise group will perform a both high-intensity resistance and aerobic exercise three times per week
Participants will ambulate unilaterally using a shoe modified with a 5cm rocker-style stack and forearm crutches for the duration of the study. All participants will complete two testing sessions prior to ULLS, one testing session at day 13, and two testing sessions at the end of the study.
University of Kentucky
Lexington, Kentucky, United States
RECRUITINGVoluntary activation
Voluntary activation of the quadriceps will be assessed with electrical stimulation of the femoral nerve before, during, and after a maximal voluntary isometric contraction (MVIC) using the interpolated twitch technique.
Time frame: Baseline, day 13, and day 30
Twitch Properties-Electromechanical Delay
Electromechanical delay will be calculated as the time difference between the onset of electrical impulse and onset of torque development during femoral nerve stimulation. This will be measured before and after a maximal voluntary isometric contraction.
Time frame: Baseline, day 13, and day 30
Twitch Properties-Rate of Torque Development
Rate of Torque Development will be calculated as the change in torque divided by the change in time in the linear phase between 20 and 80% of peak twitch torque during femoral nerve stimulation. This will be measured before and after a maximal voluntary isometric contraction.
Time frame: Baseline, day 13, and day 30
Twitch Properties-Time to peak Tension
Time to peak tension will be calculated as the time difference between the onset of electrical impulse and peak twitch torque during femoral nerve stimulation. This will be measured before and after a maximal voluntary isometric contraction.
Time frame: Baseline, day 13, and day 30
Twitch Properties-Peak Twitch Torque
Peak twitch torque during femoral nerve stimulation will be calculated as the highest torque output immediately (approximately 200ms) following femoral nerve stimulation. This will be measured before and after a maximal voluntary isometric contraction.
Time frame: Baseline, day 13, and day 30
Twitch Properties-Relaxation Rate
Relaxation rate will be calculated as the change in torque divided by the change in time during the relaxation phase of twitch following femoral nerve stimulation. This will be measured before and after a maximal voluntary isometric contraction.
This platform is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional.
Time frame: Baseline, day 13, and day 30
Post activation Potentiation
Post-activation will be calculated as the percentage difference in peak twitch torque in femoral nerve stimulation before and after a maximal voluntary isometric contraction.
Time frame: Baseline, day 13, and day 30
Motor unit action potential train (MUAPT) firing rate
Firing rate of individual motor units of the vastus lateralis (VL) will be assessed with high density surface electromyography (EMG) using four-pin high density surface electromyography electrodes. Firing rate at 30, 60, and 90% MVIC will be reported. Motor unit firing rate will also be reported during static stance. Participants will use a screen displaying real-time torque output. Participants will voluntarily increase torque (5 seconds), hold at a pre-determined torque level (10 seconds), and gradually reduce force back to resting (5 seconds) with the knee held in a fixed position. This test will be completed with a 10s isometric hold at 30, 60, and 90% of maximal voluntary isometric force.
Time frame: Baseline, day 13, and day 30
Motor unit action potential train (MUAPT) recruitment threshold.
Recruitment threshold of individual motor units of the VL will be assessed with high density surface electromyography using four-pin high density surface electromyography electrodes. Recruitment threshold will be measured during isometric ramp contractions of the quadriceps Participants will use a screen displaying real-time torque output. Participants will voluntarily increase torque (5 seconds), hold at a pre-determined torque level (10 seconds), and gradually reduce force back to resting (5 seconds) with the knee held in a fixed position. This test will be completed with a 10s isometric hold at 30, 60, and 90% of maximal voluntary isometric force.
Time frame: Baseline, day 13, and day 30
Motor unit action potential train (MUAPT) de-recruitment threshold.
De-recruitment threshold of individual motor units f the VL will be assessed with high density surface electromyography using four-pin high density surface electromyography electrodes. Recruitment threshold will be measured during isometric ramp contractions of the quadriceps Participants will use a screen displaying real-time torque output. Participants will voluntarily increase torque (5 seconds), hold at a pre-determined torque level (10 seconds), and gradually reduce force back to resting (5 seconds) with the knee held in a fixed position. This test will be completed with a 10s isometric hold at 30, 60, and 90% of maximal voluntary isometric force.
Time frame: Baseline, day 13, and day 30
Muscle size
Muscle size will be measured by MRI. Anatomical MRI scans will allow for assessment of anatomical cross sectional area.
Time frame: Baseline and day 30
Muscle Physiological cross-sectional area
Diffusion tensor imaging (DTI) will be used to assess muscle volume and fascicle length. Physiological cross-sectional area will be calculated as Muscle volume divided by fascicle length.
Time frame: Baseline and day 30
Muscle Fractional Anisotropy
Diffusion tensor imaging (DTI) will be used to assess anisotropic measures. A ratio of the diffusivity in the principal planes will be used to calculate fractional anisotropy.
Time frame: Baseline and day 30
Muscle Diffusion properties
Diffusion tensor imaging (DTI) will be used to assess rate of water diffusion in three principal planes. We will report rates of water diffusion in three ways: 1) mean diffusivity (average rate in all three plane), 2) axial diffusivity (rate of diffusion along primary axis), and 3) radial diffusivity (rate of diffusion perpendicular to the primary axis).
Time frame: Baseline and day 30
Muscle cross-sectional area (Ultrasound)
cross-sectional area of the vastus lateralis and rectus femoris will be measured by ultrasonography
Time frame: Baseline, day 13, and day 30
Fascicle length
Panoramic views of the mid-portion of the VL will be measured by ultrasonography
Time frame: Baseline, day 13, and day 30
Pennation angle
Pennation angle of the mid-portion of the vastus lateralis will be assessed by ultrasonography
Time frame: Baseline, day 13, and day 30
Voluntary Isokinetic Muscle Strength
Maximal voluntary isokinetic concentric strength of the knee extensors/flexors and ankle dorsi-/plantar-flexors will be assessed at 60 deg/s
Time frame: Baseline, day 13, and day 30
Voluntary Isometric Muscle Strength
Maximal voluntary isometric strength of the knee extensors/flexors and ankle dorsi-/plantar-flexors will be assessed during a (10 seconds) maximal effort contraction.
Time frame: Baseline, day 13, and day 30
Aerobic Capacity
Subjects will complete a VO2max exercise test on a stationary bicycle. Gas exchange and heart rate data will be collected continuously. Initial workload will be set at approximately 2 METS. Every three minutes, we will add more resistance to the pedals (\~1.5 METS). Subjects will continue to pedal until they can either not maintain pedal speed (50RPM) or until a plateau in VO2 occurs. Pedal force for each limb will be assessed.
Time frame: Baseline and day 30
Ventilatory Threshold
Gas exchange data from the aerobic capacity test (VO2, ventilation; VE, and VCO2) will be used to calculate ventilatory threshold during exercise
Time frame: Baseline and day 30
Substrate utilization
Gas exchange data from the aerobic capacity test (VO2, respiratory exchange ratio; RER, and VCO2) will be used to calculate substrate utilization (energy expenditure, carbohydrate use, and fatty acid oxidation) at varying exercise intensities
Time frame: Baseline and day 30
Body Composition
Bioelectrical Impedance Analysis (BIA) will be used to assess body composition. Subjects will lie supine and have small adhesive electrodes placed on the right hand, wrist, ankle, and foot. A small (imperceptible) electrical current will be delivered to one electrode and the amount of resistance to the electrical current will be used to measure body composition. Percent body fat will be measured. Muscle mass will be calculated using previously established formulae.
Time frame: Baseline and day 30
Postural sway area
Subjects will complete a series of balance assessments while standing on one leg using a dual force plate system. Subjects will stand still on one leg for 15 seconds with hands on hips. This will be repeated on both legs with eyes open and with eyes closed in the shod and unshod conditions in random order. Postural sway area will be calculated as an index of postural control.
Time frame: Baseline, day 13, and day 30
Postural Sway Velocity
Subjects will complete a series of balance assessments while standing on one leg using a dual force plate system. Subjects will stand still on one leg for 15 seconds with hands on hips. This will be repeated on both legs with eyes open and with eyes closed in the shod and unshod conditions in random order. Mean Postural sway velocity will be calculated as an index of postural control.
Time frame: Baseline, day 13, and day 30
Motor unit firing rate - single leg stance
Subjects will complete a series of balance assessments while standing on one leg using a dual force plate system. Subjects will stand still on one leg for 15 seconds with hands on hips. This will be repeated on both legs with eyes open and with eyes closed in the shod and unshod conditions in random order. High density surface EMG sensors will be adhered to the skin over the tibialis anterior and soleus muscles with double-sided tape. Exponential functions will be fit to describe the relationship between motor unit firing rate and action potential amplitude on an individual manner to determine how firing rates of various motor unit pools relate to postural control.
Time frame: Baseline, day 13, and day 30
Change in heart rate at rest
heart rate measured
Time frame: Baseline and day 30
Change in blood pressure at rest
blood pressure measured at the arm
Time frame: Baseline and day 30
Change in heart rate variability
for 20 minutes electrodes will be placed on the skin of the chest and a respiratory belt will be wrapped around the chest and blood pressure will be taken at the arm. During the final 10 minutes, 5 minutes of regular breathing (minutes 11-15), and 5 minutes of controlled breathing at a rate of 12 breaths per minute will be done. Resting heart rate (throughout), respiratory rate (throughout) and blood pressure (min 15 and 20) will be collected.
Time frame: Baseline and day 30
Change in heart rate recovery after exercise
a maximal-effort exercise test on a stationary bicycle will be done. Immediately upon finishing the cycling, participants will rest on the bike for 5 minutes while remaining as still as possible. Heart rate will be collected throughout the this time to give a measure of heart rate recovery
Time frame: Baseline and day 30