Cross-Education Of Contralateral Antagonists
Condition: Muscle Strength Quantitative Trait Locus 1
Study type: Interventional

Summary: 
      Previous studies well documented the impact of unilateral training of limb muscle on the
      untrained contralateral homologous muscle. The aim of this study is to evaluate whether the
      electrical muscle stimulation on the dominant wrist flexors for 6 weeks cause an increase in
      the muscle strength of the contralateral wrist extensors in healthy adult men.

      Ethical approval was obtained from Institutional Review Board. All participants were
      volunteers and provided written informed consent. Among young adult males working in our
      hospital, 30 subjects who voluntarily accepted to participate in this study were assessed for
      eligibility. Twenty three young-adult healthy males were included in this double-blind
      prospective study. These volunteers were randomized into two groups. In Electrical Muscle
      Stimulation (EMS) group, electrical muscle stimulation of the right wrist flexor muscles was
      applied; in Controls, transcutaneous electrical nerve stimulation was applied. Electrodes
      were placed over the flexor aspect of the right forearm in both groups. Electrical
      stimulation was applied for thirty sessions (one session a day, five days a week for six
      weeks) in both groups by the same researcher. Compex2 (Medicompex SA, Switzerland) was used
      for electrical stimulation. Isokinetic torque was measured in the right and left wrist
      flexors and extensors before and after trial. Isokinetic torque was measured in the right
      (trained) and left (untrained) forearm with the Cybex (Humac 2004/Norm) extremity-testing
      system.
    

Detailed description: 
      It has been reported that strength training of unilateral limb causes an increase in
      voluntary strength not only in the trained limb, but also in the contralateral untrained
      limb. This phenomenon is known as "cross-education, cross-training or contralateral strength
      training effect" . Cross-education of muscle strength can occur in both upper and lower limb
      muscles.It is not gender and age specific and can occur with training accomplished by
      voluntary effort, electrical stimulation of muscles or mental practice of unilateral
      contractions. Electrostimulation is one of the most efficient methods to induce
      cross-education.

      Although it is clear that unilateral training has a contralateral effect, the mechanisms
      behind this effect remain unclear. Because of the specific nature of cross education,
      modification in neural function is the more likely mechanism underlying this effect. The
      potential neural mechanisms can be broadly categorized as either ''central" or ''peripheral
      (spinal)" adaptations. Central neural mechanisms involved in the excitation of the relevant
      part of the cortex during voluntary contraction of the trained limb are thought to produce
      contralateral facilitation. The cross-extension reflex is the primary spinal neural mechanism
      for cross-education.

      In the studies performed up today, the contralateral effects of unilateral training were
      evaluated in the contralateral homologous muscles. However it's not reported whether a change
      in the muscle strength have been observed in the antagonists of the contralateral homologous
      muscles. In a study, after one session of unilateral surface electrical stimulation of the
      rectus femoris, an increase in the isometric force and EMG activity of the contralateral
      rectus femoris, but a decrease in the EMG activity of the contralateral biceps femoris was
      reported in adult men. It's proposed that, the EMG activity decrease in the biceps femoris
      may be explained by cross-extension reflex. The effect of long-time exercise or electrical
      muscle stimulation on the antagonists of the contralateral homologous muscles is not clear.

      The aim of this study is to evaluate whether the electrical muscle stimulation on the
      dominant wrist flexors for 6 weeks cause an increase in the muscle strength of the
      contralateral wrist extensors in healthy adult men.
    

Intervention name(s): Experimental group; Control group
Intervention type(s): Procedure; Procedure
Intervention description(s): Electrical muscle stimulation (EMS) of the right wrist flexor muscles was applied. EMS was applied for 20 minutes. Maximum current intensity tolerated was used so as to stimulate the highest possible number of motor unit. The stimulation intensity increased every five minutes during a session. Electrical stimulation was applied for thirty sessions (one session a day, five days a week for six weeks.); Conventional mode of transcutaneous electrical nerve stimulation (TENS) was applied for the control subjects. TENS was applied for 20 minutes. The stimulus intensity was adjusted as the lowest current at which the subject felt only a slight tickling of the impulses. A visible, and palpable muscle contraction was not provided during TENS stimulation. The stimulus intensity was not changed during the first session. Subsequently, TENS was applied at same intensity in all sessions. TENS was applied for thirty sessions (one session a day, five days a week for six weeks).
Other intervention name(s): Electrical Muscle Stimulation; Transcutaneous electrical muscle stimulation
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Cross education; Muscle training