Effects of Menthol-Based Counterirritant on Quadriceps Motoneuron-Pool Excitability

in Journal of Sport Rehabilitation
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Context:

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).

Objective:

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

Design:

A blinded, randomized controlled laboratory study.

Setting:

Laboratory.

Participants:

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.

Intervention:

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.

Results:

Hmax:Mmax ratios for all groups significantly decreased over time (F4,108 = 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.

Conclusions:

Menthol did not affect quadriceps MNPE in healthy subjects.

Huffman is with the Dept of Kinesiology, Texas A&M University, Corpus Christi, TX. Pietrosimone is with the Dept of Kinesiology, University of Toledo, Toledo, OH. Grindstaff, Hart, and Saliba are with the Dept of Human Services, University of Virginia, Charlottesville, VA. Ingersoll is with the Herbert H. and Grace A. Dow College of Health Professions, Central Michigan University, Mt Pleasant, MI.