The Effects of Spinal Manipulation on Central Nervous System Activity Measured by Reflexive Calf Muscle Recruitment

Study Overview
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Brief Summary
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This study investigated the effects of spinal manipulation on central nervous system activity. The presence of postactivation potentiation, an increase in muscular force production following prior muscular contractions, was measured with electromyography and the muscular force production during electrically-induced calf muscle reflexes. It was hypothesized that significantly greater potentiation would be stimulated by a calf muscle contraction with spinal manipulation delivered immediately beforehand than the potentiation arising from the contraction only.

Detailed Description
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A randomized, controlled, single-blind crossover study design was utilized, and the three independent variables were spinal manipulative therapy (SMT), a 10 second plantar flexion maximal voluntary isometric contraction (MVIC) or SMT immediately preceding the MVIC (SMT + MVIC). The treatment order was randomized for each of the three sessions before the tibial nerve Hmax/Mmax stimulation protocol. Each of the four dependent variables were evoked during the tibial nerve H-reflex stimulation protocol at the conclusion of each session, and included the Hmax/Mmax ratio (%) of the gastrocnemius and soleus muscles and the isometric twitch torque occurring at Hmax and at Mmax. Hmax, the highest H-reflex amplitude, is an indication of the greatest possible reflex activation; as such, it is an estimate of the number of motor neurons a subject is capable of activating in a given state. Further increases in the stimulation intensity cause the subsequent M-wave to reach its highest amplitude, Mmax. Mmax is a compound muscle action potential (CMAP) which represents full muscle activation. Specific to the current investigation, Mmax indicated activation of the total volume of the gastrocnemius/soleus motor neuron (MN) pool. Given that Hmax is an inference of the number of MNs being recruited, and Mmax constitutes the entire motor neuron pool, the proportion of the entire MN pool capable of being recruited can be estimated with the Hmax/Mmax ratio. The Hmax/Mmax ratio was determined by division of the EMG peak-to-peak amplitudes (mV) evoked at Hmax by the preceding Mmax EMG peak-to-peak amplitudes. Differences in each of the four dependent variables (Hmax/Mmax ratios of the gastrocnemius and soleus and the peak twitch torques evoked at Hmax and Mmax) following each treatment form of SMT, MVIC or SMT+MVIC delivered during the three data collection sessions on three separate days were determined with a two-way (treatment × time point) repeated measures ANOVA. Percent changes from baseline were also calculated for each of the dependent variables, and the same type of ANOVA was used to determine differences in the within-subjects effects of each treatment.

Official Title
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The Effects of Spinal Manipulative Therapy on Postactivation Potentiation

Conditions
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Subluxation of Joint of Lumbar Spine

Intervention / Treatment
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* Procedure: Spinal Manipulation
* Procedure: Max Voluntary Isometric Contraction
* Procedure: SM+MVIC


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: At least one year of resistance training experience and current completion of at least three training sessions per week Males needed to be able to back squat a minimum load of 1.5 x body weight Females needed to be able to back squat 1 x body weight Exclusion Criteria: Any pain in the lower back, abdomen or legs and/or surgeries performed in these regions

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Factorial Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Spinal Manipulation SM<br>In a repeated measures, crossover design, all subjects received one of three randomized treatments during three separate sessions: SM; a 10 second plantar flexion maximal voluntary isometric contraction (MVIC) or the manipulation immediately preceding the contraction (SM+MVIC). | Procedure: Spinal Manipulation<br>* Manual, side-posture, high-velocity low-amplitude spinal manipulation targeting the lower lumbar spine and sacroiliac joints<br>|
| Active Comparator: Max Voluntary Isometric Contraction MVIC<br>In a repeated measures, crossover design, all subjects received one of three randomized treatments during three separate sessions: SM; a 10 second plantar flexion maximal voluntary isometric contraction (MVIC) or the manipulation immediately preceding the contraction (SM+MVIC). | Procedure: Max Voluntary Isometric Contraction<br>* A 10 second plantar flexion maximal voluntary isometric contraction<br>|
| Active Comparator: SM+MVIC<br>In a repeated measures, crossover design, all subjects received one of three randomized treatments during three separate sessions: SM; a 10 second plantar flexion maximal voluntary isometric contraction (MVIC) or the manipulation immediately preceding the contraction (SM+MVIC). | Procedure: SM+MVIC<br>* The spinal manipulation immediately preceding the maximal voluntary isometric contraction<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in H-reflex amplitudes of the gastrocnemius and soleus muscles compared to baseline | Peak-to-peak EMG amplitudes (mV) at Hmax of the gastrocnemius and soleus were recorded before and immediately following the three separate treatments | Data were collected at 17 time points during a 20-minute tibial nerve electrical stimulation protocol post-treatment: 20 seconds, 40 seconds, 1:00, 2:00, 3:00, 4:00, 5:00, 6:00, 7:00, 8:00, 9:00, 10:00, 12:00, 14:00, 16:00, 18:00 and 20:00 minutes | 
| Changes in isometric twitch torques of the gastrocnemius and soleus muscles compared to baseline | Twitch torques (Nm) of the gastrocnemius and soleus at Mmax were recorded before and immediately following the three separate treatments | Data were collected at 17 time points during a 20-minute tibial nerve electrical stimulation protocol post-treatment: 10 seconds, 30 seconds, 50 seconds, 1:30, 2:30, 3:30, 4:30, 5:30, 6:30, 7:30, 8:30, 9:30, 11:00, 13:00, 15:00, 17:00 and 19:00 minutes | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Manipulation, Spinal, H-Reflex, Muscle Contraction, Muscle Strength Dynamometer