The Effect of Neuromuscular Electrical Stimulation (NMES)
Condition: Muscle Fiber Atrophy, Type II
MeSH terms: Atrophy
Study type: Interventional
Phase: Phase 2

Summary: 
      The purpose of this project is to test the effectiveness of neuromuscular electrical
      stimulation (NMES) that produces 40 % of maximum voluntary contraction (MVC) in increasing
      muscle size and improvement in muscle force output within the thigh muscle of elderly people.
    

Detailed description: 
      Declines in whole skeletal muscle strength and size are features commonly associated with
      aging. Aging reduces the number of fibers in the whole muscle, which explains the loss of
      muscle mass. Frontera et al studied muscle strength, cross sectional area, and contractile
      properties of skinned parts of single fibers of the quadriceps muscle. He found that the
      strength and the whole muscle cross sectional area of knee extensors were significantly
      higher in young men compared to old subjects, but there were no differences between old and
      young subjects when the whole muscle strength was adjusted to the whole muscle cross
      sectional area (specific tension). He also found that muscle fibers from young men were
      stronger than muscle fibers from old men expressing the same myosin heavy chain isoform even
      after adjusting for size. Therefore they concluded that abnormality in the quantity and/or
      function of the contractile or regulatory proteins could explain the reduction in the ability
      of muscle fibers to generate force.

      Along with the loss of muscle fibers, atrophy of the fibers also has been attributed to the
      aging process. This atrophy has been found to be selective to type II muscle fibers. Lexel et
      al found in a study done on the cross sections of the whole vastus lateralis muscle from 20
      men (19-84 years of age) that the mean Cross Sectional Area (CSA) of type II fibers from
      muscles of older individuals was on average 35 % smaller while the mean CSA of type I was
      approximately 6 % smaller than that of young individuals.

      Aging and muscles Maintaining muscle strength and size with aging has become a significant
      issue for elderly trying to keep up independent living and good quality of life. Several
      studies on old men and women have proven the effectiveness of the resistance exercises in
      reversing sarcopenia related problems . However in order to increase the size of type II
      muscle fibers we need to apply high intensity exercises (80 % of 1 RM), or by applying low
      resistance exercise that is very intense and is done with a large number of repetitions.

      The use of electrical stimulation is well documented to improve quadriceps femoris muscle
      torque output. Numerous experiments have been done to characterize the pattern of activation
      of muscle fibers during electrically stimulated muscle contraction, and the results show that
      the recruitment of motor units during electrically induced muscle contraction is non
      selective. In other words, both type I and II fibers may have equal chance of being recruited
      during electrically induced muscle contraction. It has been found that NMES is more likely to
      activate type II muscle fibers at relatively low force levels compared to voluntary exercise.
      If this is found to be true, then we may have an alternative intervention to improve muscle
      strength and muscle hypertrophy for elderly individuals who could not perform high intensity
      exercises to achieve these same benefits. This alternative approach might result in improved
      overall physical function for these individuals.

      The quadriceps muscle has been proposed to be treated because there is significant
      relationship between quadriceps muscle strength and dynamic stability during chair rise and
      gait at preferred speed in functionally limited elderly individuals

      Methods This study is a two group, repeated measures, randomized clinical trial. Baseline
      measurements of quadriceps muscle cross-sectional area, type II muscle fiber cross-sectional
      area, quadriceps power output, the timed up and go test, the SPPB, stair climbing test and
      ramp up power test will be obtained from subjects prior to the interventions. Following the
      baseline assessments subjects will be randomly assigned to either the NMES group or the
      comparable isometric strengthening exercise group. A set of sequentially numbered envelopes
      will be created and a document indicating the intervention assignment will be placed in the
      sequentially numbered envelopes. Upon completion of the baseline assessment, the study
      coordinator will take the next envelope in the sequence and open the envelope. The study
      coordinator will assign the subject to a group based on the randomized group assignment
      information obtained from the sealed envelop. During the intervention period of the study
      subjects will receive either NMES or isometric strengthening exercise 3 times a week for 12
      weeks. Each session will last from 15-30 minutes. Post training outcome measures will be
      taken at the end of the 12 week intervention period.
    

Intervention name(s): Neuromuscular electrical stimulation; voluntary strengthening exercise
Intervention type(s): Other; Other
Intervention description(s): neuromuscular electrical stimulation that produce 40% of the maximum voluntary contraction; contracting the quadriceps muscle voluntarily to produce 40% of maximum voluntary contraction
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: muscle fibers; aging