The Effects of Spinal Manipulation on Central Nervous System Activity Measured by Reflexive Calf Muscle Recruitment
Condition: Subluxation of Joint of Lumbar Spine
Study type: Interventional

Summary: 
      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: 
      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.
    

Intervention name(s): Spinal Manipulation; Max Voluntary Isometric Contraction; SM+MVIC
Intervention type(s): Procedure; Procedure; Procedure
Intervention description(s): Manual, side-posture, high-velocity low-amplitude spinal manipulation targeting the lower lumbar spine and sacroiliac joints; A 10 second plantar flexion maximal voluntary isometric contraction; The spinal manipulation immediately preceding the maximal voluntary isometric contraction
Allocation: Randomized
Intervention model: Factorial Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Manipulation, Spinal; H-Reflex; Muscle Contraction; Muscle Strength Dynamometer