Abstract
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 interior knee: Control subjects received no intervention. Main Outcome Measures: The average vastus medialis normalized Hoffmann reflex (H(max):M(max) 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 (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 x Time interaction or group differences in H(max):M(max) were found. Conclusions: Menthol did not affect quadriceps MNPE in healthy subjects.