Clinically Important Parameters and Dose Ranges

Aussie current is a form of neuromuscular electrical stimulation (NMES) the main purpose being to increase the force generating capacity of a muscle.  This form of electrical stimulation is most commonly used by physiotherapists to help “retrain” the muscles by stimulating nerves of the affected area after injuries such as stroke. However, the use of medium frequency kHz BMAC, such as Aussie and Russian currents, it can be used to increase muscle strength. The experiments conducted by Ward and colleagues examined different ranges of carrier frequencies, burst frequencies and duty cycles which resulted in the creation of Aussie Current.

As discussed in our previous post the specific parameters of Aussie Current include;

• 1-kHz alternating current (AC).
• 50-Hz bursts of 4ms duration.
• 20% duty cycle. 

(Ward, Oliver & Buccella, 2006)

In 2004 Ward, Robertson and Iannou examined the effect of different ranges of frequency and duty cycle on muscle torque production and patient discomfort.  With a range of frequencies from 0.5 kHz to 20 kHz it was determined that the greatest torque was produced at a frequency of 1 kHz.  They also found that with increasing duty cycle torque decreased.  The least discomfort was reported with a 20 – 25% duty cycle.  A duty cycle of 20% also produced the lowest voltage / torque ratio and hence the best stimulation efficacy (Ward, Robertson & Iannou, 2004).  An important discovery from Ward’s research is the effectiveness of using a lower duty cycle.  This increases the safety of using medium frequency AC as only a fifth of electrical stimulation compared to continuous interferential AC is being used, greatly decreasing the likelihood of tissue damage when using these higher frequencies.

As Aussie current is defined by the above parameters any deviation from this prescription will mean that Aussie Current is no longer being used.  As such, no adjustments to amplitude or pulse duration to compensate for change of frequency are made for the accommodation of patient comfort.  However, patient comfort was discovered to improve with a lower duty cycle which has been included in the dosage parameters as 20 % duty cycle (Ward, Oliver & Buccella, 2006). Amplitude was not specified in the literature, which may be due to the highly individulised tolerance and muscle activation levels of the participants.

    This clip outlines the use of EPA for muscle strengthening

 and endurance.  The parameters are not Aussie Current

      however there are similarities as burst modualtion is used. 

    Notice the Russian Current setting under Electrotherapy.

Our research did not identify any information on specific dosage for strength program using Aussie Current.  However during the Ward, Oliver and Buccella 2006 study 15 minute test sessions were used.  As this type of stimulation is used for muscle strengthening an individual’s fatigue would likely be a limiting factor to session duration.  This would also be highly variable between patients, dependent on initial strength and extent of injury if being used as a rehabilitation tool.  Variations of fatigue rate using kHz frequency AC has also been investigated by Ward with Robertson in 2000.  This study identified the increased recruitment of fatigue-resistant fibers contributing to torque with frequencies between 1-10 kHz, compared with the low frequency (1-150 Hz), short duration pulsed current used with functional electrical stimulation (FES) often used in rehabilitation (Ward & Robertson, 2000).  This provides evidence to implement Aussie Current as a clinical application in rehabilitation and not solely as a mode to create muscle hypertrophy.  Delaying a patient’s fatigue will increase the level of treatment session length.  As neuroplasticity is greatly improved by high repetition the use of Aussie Current over FES may increase muscle response and decrease rehabilitation time.

References

Ward, A., Oliver, W. & Buccella, D. (2006). Wrist Extensor Torque Production and Discomfort Associated With Low-Frequency and Burst-Modulated Kilohertz-Frequency Currents. Physical Therapy, 86. 1360-1367 Doi:10.2522/ptj.20050300
http://physther.org/content/86/10/1360.full.pdf

Ward, A. & Robertson, V. (2000). The variation in fatigue rate with frequency using kHz frequency alternating current. Medical Engineering and Physics, 22: 637-646.
http://www.sciencedirect.com.libraryproxy.griffith.edu.au/science/article/pii/S1350453300000850

Ward, A., Robertson, V. & Iannou, H. (2004). The effect of duty cycle and frequency on muscle torque production using kilohertz frequency range alternating current. Medical Engineering & Physics, 26. 569 – 579. Doi: 10.1016/j.medengphy.2004.04.007.
http://www.sciencedirect.com.libraryproxy.griffith.edu.au/science/article/pii/S1350453304000700