E-Stim for Treating Muscle Flashcards
Neuromuscular electrical stimulation (NMES)
E-stim for muscle depolarization
- AP of muscle developed by electrically stimulated motor nerve is similar to that produced physiologically
- but there is a difference in order of recruitment of motor units
E-stim for muscle depolarization
voluntary muscle contraction
- progressive recruitment of small, slow motor units to large, fast motor units
E-stim process is reversed
- large diameter axons (lower resistance to current) innervate larger, fast twitch muscle fibers, fast fatiguing
-increased fatigue with E-stim vs voluntary contraction
- longer rest times needed between contractions
Factors that influence the force-frequency relation
- muscle length
- muscle temp
- fatigue state
- degree of potentiation of the muscle
Muscle contraction innervated muscle
- to excite a tissue, stimulation must be long enough, strong enough, and rise quickly enough ( shultz law)
- low frequency 1-2 stimuli per second= twitch contraction
- higher frequencies 15 pps APs will begin to summate= unfused tetanus
- at progressively higher frequencies (>30pps) a sustained contraction will occur this is caused by a succession of stimuli= tetanus
Spatial motor unit recruitment
- electrically evoked: large to small
- voluntary: small to large
temporal motor unit recruitment
- electrically evoked: synchronous
- voluntary: asynchronous
Muscle loading
- electrically evoked: against resistance
- voluntary: against resistance
Strengthening
- electrically evoked: increased motor unit recruitment, increased muscle hypertrophy
- voluntary: increased motor unit recruitment, increased muscle hypertrophy
E-stim to increase strength in healthy muscle
- stimulated contraction needs to be at least 50% of max voluntary isometric contraction (MVIC)
E-stim to increase strength in injured muscle
- stimulated contraction needs to be only 10% of MVIC
- stronger contractions will produce greater gains
Strength training via E-stim: overload theory
- the larger the load placed on a muscle the greater force of contraction the muscle will produce, thus strength will be greater than if smaller loads are applied
- applies to E-stim and voluntary muscle contractions when the same force is applied
Strength training via E-stim: Specificity theory
- E-stim stimulates large fast twitch type II muscle fibers (motor units) before small slow twitch type I muscle fibers
- should produce greater strength gains than exercise alone with the same force contractions
patient comfort dependent on
- Pt coping style
- did stimulus cause muscle contraction
- pt judging unpleasantness of stimulation
Smoothness of onset of contraction
- E-stim: rapid and more jerky onset of contraction, all motor units of a given size contract simultaneously
- physiological stimulation of muscle is smooth due to asynchronous recruitment of motor units in size as needed
E-stim to support or assist with joint positioning (study)
-E-stim reduced shoulder subluxations in pts with hemiplegia better than controls even when arm was supported
E-Stim to increase blood flow (study)
- high frequency electrical stim promoted blood flow in extremities in both healthy subjects and patients
E-stim to treat urinary incontinence secondary to pelvic flood dysfunction (study)
-Reduced stress incontinence due to transcutaneous electrical stim
Muscle contraction: denervated muscle
- does not recieve input from motor nerve
- cannot be stimulated by E-stim used for NMES
- if electrical current has a pulse duration greater than 10 ms, then muscle will contract
- continuous DC stimulation is usually used for this purpose
- contraction due to stim of muscle cell membrane and not muscle motor nerve
- muscle cell membrane does not accommodate- slow rising stimulus can be used
Muscle contraction denervated muscle study
- studied rat denervated muscle
- E-stim may retard motor nerve sprouting and regeneration
E-stim for denervated muscle today
- Bell’s palsy
- may be no better than placebo
Muscle strengthening parameters
- Pulse frequency: 35-80 pps
- Pulse duration: 150-200 us for small muscles; 200-350pps for large muscles
- amp: to >10% of MVIC in injured; >50% healthy
- on/off times ratio: 6-10 sec on, 50-120 sec off; ratio of 1:5 to start
- ramp time: @ least 2 sec
- tx time: 10-20 mins
- times/day: every 2-3 hours when awake