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Michael G. Dolan, Brian G. Pietrosimone, J. Ty Hopkins and Christopher D. Ingersoll

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Cody B. Bremner, William R. Holcomb, Christopher D. Brown and Melanie E. Perreault

Clinical Scenario:

Orthopedic knee conditions are regularly treated in sports-medicine clinics. Rehabilitation protocols for these conditions are often designed to address the associated quadriceps strength deficits. Despite these efforts, patients with orthopedic knee conditions often fail to completely regain their quadriceps strength. Disinhibitory modalities have recently been suggested as a clinical tool that can be used to counteract the negative effects of arthrogenic muscle inhibition, which is believed to limit the effectiveness of therapeutic exercise. Neuromuscular electrical stimulation (NMES) is commonly accepted as a strengthening modality, but its ability to simultaneously serve as a disinhibitory treatment is not as well established.

Clinical Question:

Does NMES effectively enhance quadriceps voluntary activation in patients with orthopedic knee conditions?

Summary of Key Findings:

Four randomized controlled trials (RCTs) met the inclusion criteria and were included. Of those, 1 reported statistically significant improvements in quadriceps voluntary activation in the intervention group relative to a comparison group, but the statistical significance was not true for another study consisting of the same sample of participants with a different follow-up period. One study reported a trend in the NMES group, but the between-groups differences were not statistically significant in 3 of the 4 RCTs.

Clinical Bottom Line:

Current evidence does not support the use of NMES for the purpose of enhancing quadriceps voluntary activation in patients with orthopedic knee conditions.

Strength of Recommendation:

There is level B evidence that the use of NMES alone or in conjunction with therapeutic exercise does not enhance quadriceps voluntary activation in patients with orthopedic knee conditions (eg, anterior cruciate ligament injuries, osteoarthritis, total knee arthroplasty).

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Daniel H. Huffman, Brian G. Pietrosimone, Terry L. Grindstaff, Joseph M. Hart, Susan A. Saliba and Christopher D. Ingersoll


Motoneuron-pool facilitation after cryotherapy may be mediated by stimulation of thermoreceptors surrounding a joint. It is unknown whether menthol counterirritants, which also stimulate thermoreceptors, have the same effect on motoneuron-pool excitability (MNPE).


To compare quadriceps MNPE after a menthol-counterirritant application to the anterior knee, a sham counterirritant application, and a control treatment in healthy subjects.


A blinded, randomized controlled laboratory study.




Thirty healthy subjects (16 m, 14 f; 24.1 ± 3.9 y, 170.6 ± 11.4 cm, 72.1 ± 15.6 kg) with no history of lower extremity surgery volunteered for this study.


Two milliliters of menthol or sham counterirritant was applied to the anterior knee; control subjects received no intervention.

Main Outcome Measures:

The average vastus medialis normalized Hoffmann reflex (Hmax:Mmax ratio) was used to measure MNPE. Measurements were recorded at 5, 15, 25, and 35 minutes postintervention and compared with baseline measures.


Hmax:Mmax ratios for all groups significantly decreased over time (F 4,108 = 10.52, P < .001; menthol: baseline = .32 ± .20, 5 min = .29 ± .18, 15 min = .27 ± .18, 25 min = .28 ± .19, 35 min = .27 ± .18; sham: baseline = .46 ± .26, 5 min = .36 ± .20, 15 min = .35 ± .19, 25 min = .35 ± .20, 35 min = .34 ± .18; control: baseline = .48 ± .32, 5 min = .37 ± .27, 15 min = .37 ± .27, 25 min = .37 ± .29, 35 min = .35 ± .28). No significant Group × Time interaction or group differences in Hmax:Mmax were found.


Menthol did not affect quadriceps MNPE in healthy subjects.

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Conrad M. Gabler, Adam S. Lepley, Tim L. Uhl and Carl G. Mattacola

Clinical Scenario:

Proper neuromuscular activation of the quadriceps muscle is essential for maintaining quadriceps (quad) strength and lower-extremity function. Quad activation (QA) failure is a common characteristic observed in patients with knee pathologies, defined as an inability to voluntarily activate the entire alpha-motor-neuron pool innervating the quad. One of the more popular techniques used to assess QA is the superimposed burst (SIB) technique, a force-based technique that uses a supramaximal, percutaneous electrical stimulation to activate all of the motor units in the quad during a maximal, voluntary isometric contraction. Central activation ratio (CAR) is the formula used to calculate QA level (CAR = voluntary force/SIB force) with the SIB technique. People who can voluntarily activate 95% or more (CAR = 0.95–1.0) of their motor units are defined as being fully activated. Therapeutic exercises aimed at improving quad 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 QA 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 2 of the most successful treatments for increasing QA levels in patients with QA failure. Both modalities are hypothesized to positively affect voluntary QA by disinhibiting the motor-neuron pool of the quad. 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. However, it remains unknown whether 1 is more effective than the other for restoring QA 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.

Focused Clinical Question:

Is TENS or cryotherapy the more effective disinhibitory modality for treating QA failure (quantified via CAR) in patients with knee pathologies?