Proper neuromuscular activation of the quadriceps muscle is essential for maintaining quadriceps strength and lower extremity function. Quadriceps activation failure is a common characteristic observed in patients with knee pathologies, and it is defined as an inability to voluntarily activate the entire alpha motor neuron pool innervating the quadriceps. One of the more popular techniques used to assess quadriceps activation is the superimposed burst (SIB) technique. The SIB technique is a force-based technique which uses a supramaximal, percutaneous electrical stimulation to activate all of the motor units in the quadriceps during a maximal, voluntary isometric contraction of the quadriceps. Central activation ratio (CAR) is the formula used to calculate quadriceps activation level (CAR = voluntary force/SIB force) with the SIB technique. People who can voluntary active 95% or more (CAR = 0.95 - 1.0) of their motor units are defined as being fully activated. Therapeutic exercises aimed at improving quadriceps strength in patients with knee pathologies are limited in their effectiveness due to a failure to fully activate the muscle. Within the past decade, several disinhibitory interventions have been introduced to treat quadriceps activation failure in patients with knee pathologies. Transcutaneous electrical nerve stimulation (TENS) and cryotherapy are sensory-targeted modalities traditionally used to treat pain, but they have been shown to be two of the most successful treatments for increasing quadriceps activation levels in patients with quadriceps activation failure. Both modalities are hypothesized to positively affect voluntary quadriceps activation by disinhibiting the motor neuron pool of the quadriceps. In essence, these modalities provide excitatory afferent stimuli to the spinal cord, which thereby overrides the inhibitory afferent signaling that arises from the involved joint.6 However, it remains unknown as to whether one is more effective than the other for restoring quadriceps activation levels in patients with knee pathologies. By knowing the capabilities of each disinhibitory modality, clinicians can tailor treatments based on the rehabilitation goals of their patients.

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To be published in Journal of Sport Rehabilitation.

© 2015 Human Kinetics, Inc. as accepted for publication. http://dx.doi.org/10.1123/jsr.2014-0292

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