This document discusses the strength duration curve (SDC), which demonstrates the inverse relationship between the strength (amplitude) and duration of electrical current required to excite tissue. Shorter durations excite larger sensory fibers, while longer durations are needed for smaller fibers. SDC plotting can determine if muscle is innervated, denervated, or partially denervated. Additional metrics discussed include rheobase (minimum current to elicit contraction), chronaxie (duration of double rheobase current), temps utile (minimum time for contraction at rheobase current), accommodation threshold (current for "infinite" triangular pulse contraction), and accommodation quotient (ratio measuring nerve tissue adaptation ability).

1. STRENGTH
DURATION
CURVE
Aditya Johan .R, M.Fis

2. STRENGTH DURATION
CURVE
 The strength (amplitude) and time (duration) of
current determine tissue excitability
 This is the law of excitation The strength-
duration curve (SDC) demonstrates the inverse
relationship between these two variables
 As phase duration increases, less peak
amplitude is required to achieve the desired
physiological response

3. – Shorter durations excite the large sensory afferents, whereas the longer durations are necessary
to excite the smaller A-delta and C fibers

4.  The purpose of S-D curve plotting is to know whether the stimulated muscle is innervated,
denervated or partially denervated
 S-D curve should be plotted after 20th day of injury/lesion
 After 21st/22nd day, regeneration of nerve will start, generally it take about 270 days to
regenerate

5.  SD Curve is graphical representation of a quantitieves non linier relationship between intensity
and duration
 It is graphical representation of excitability of muscles and nerve tissue under test

6. RHEOBASE
 The Rheobase is a measure of tissue
excitability represented by the minimum
amplitude of the rectangular current
impulse, of 1000 ms duration, eliciting the
minimal contraction (threshold) of an
excitable tissue
 The chronaxie is another measure of the tissue
excitability. It is the Duration of an impulse
heaving the amplitude of doubled rheobase

7. CHRONAXIE
 A simple methode of
discriminating between
innervated and denervated
muscle
 Normal innervated values vary
somewhat from one muscle to
another
 Below 1 ms for constant current
& below 0.1 ms for constant
voltage

8. Chronaxie

9. TEMPS UTILE
 This is the minimum time needed for a rectangular pulse to produce a
just perceptible contraction at a current amplitude equal to the
rheobase
 For healthy muscle tissue, the temps utile is around 10 μs

10. ACCOMODATION TRESHOLD
– This is the current amplitude that a triangular pulse of ‘infinite’ duration
must have in order to produce a just perceptible contraction

11. OPTIMUM PHASE
 The phase time required for a triangular pulse at a minimum
current amplitude to produce a just perceptible contraction
 For healthy tissue the optimum phase time is around 20 ms

12. ACCOMODATION QUOTIENT
 Healthy nerve tissue has the ability to adapt to gradually increasing
pulses
 This causes a gradual increase in the triangular pulse curve with respect
respect to the rectangular pulse curve
 Accommodation quotient is determined by dividing the
accommodation threshold by the rheobase
 For healthy nerve tissue, the value lies between 2 and 6. A lower value
indicates degeneration of the nerve, while higher values may be a sign
of neurogenic dystonia

13. Accomodation Quotient

19. Strength Duration Curve

23. THANKS