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

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 (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.

Conclusions:

Menthol did not affect quadriceps MNPE in healthy subjects.

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Blaine C. Long and J. Ty Hopkins

Context:

It is reported that thermotherapy decreases motoneuron-pool recruitment. Any decrease in recruitment might have a significant impact on an athlete’s ability to return to competition.

Objective:

To determine whether moist heat application influences involuntary motoneuron-pool recruitment or voluntary plantar-flexion peak torque of the soleus muscle immediately or 30 min after application.

Design:

A 3 × 3 crossover design.

Setting:

Biomechanics laboratory.

Participants:

Eighteen healthy subjects with no history of lower extremity surgery or injury 12 months before the study volunteered.

Intervention:

A series of short-duration, high-intensity stimuli was delivered to the tibial nerve to find the Hmax and Mmax measures. Immediately after the Hmax and Mmax measures, subjects were positioned on an isokinetic dynamometer where they performed 5 submaximal warm-up repetitions. Immediately after the warm-up, 5 maximum-intensity peak plantar-flexion torque repetitions were performed. After the dynamometer measures, subjects returned to the table, where a moist heat pack, no heat pack, or a dry nonheated heat pack was applied.

Main Outcome Measures:

Hmax, Mmax, peak plantar-flexion torque, surface temperature (°C), and ambient temperature (°C).

Results:

Moist heat did not influence the H:Mmax ratio or peak plantar-flexion torque. Temperature increased with moist heat pack. Ambient temperature remained constant.

Conclusions:

Moist heat did not influence involuntary motoneuron-pool recruitment or voluntary peak plantar-flexion torque of the soleus muscle immediately or 30 min after application.

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Harriet G. Williams and Jeanmarie R. Burke

A conditioned patellar tendon reflex paradigm was used to study the contributions of crossed spinal and supraspinal inputs to the output of the alpha motoneuron pool in children with and without developmental coordination disorders. The basic patellar tendon reflex response was exaggerated in children with developmental coordination disorders. Crossed spinal and supraspinal influences on the excitability of the alpha motoneuron pool were similar in both groups of children. However, there was evidence of exaggerated crossed spinal and supraspinal inputs onto the alpha motoneuron pool in individual children with developmental coordination disorder.

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B. Andrew Krause., J. Ty Hopkins, Christopher D. Ingersoll, Mitchell L. Cordova and Jeffrey E. Edwards

Objective:

Correlate skin temperature and motoneuron-pool recruitment during cooling and rewarming.

Design:

Within-subjects, correlational analysis. H reflex was correlated to ankle-skin temperature over time using a Pearson product-moment correlation coefficient and a coefficient of determination (R2).

Subjects:

Ten healthy, physically active college students.

Measurements:

Soleus H reflex and ankle-skin interface temperature were measured during ice application and rewarming. Electrical stimulation was delivered to produce 75% of each subject's maximum H reflex.

Results:

Ankle cooling (r = −.95, P < .05) exhibited a strong inverse relationship with soleus H reflex. A positive correlation was observed between rewarming (r = .74, P < .05) and soleus H reflex.

Conclusions:

Temperature accounts for nearly 90% (R2 = .90) of the variability in the soleus H reflex during cooling and 55% (R2 = .55) during rewarming, suggesting that more motoneurons are recruited as temperature decreases. These interactions appear to involve both local and central nervous system functions.

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Takashi Kato, Yusaku Takeda, Toshio Tsuji and Tatsuya Kasai

The present study investigated the relative contribution of the cortical and spinal mechanisms for post-exercise excitability changes in human motoneurons. Seven healthy right-handed adults with no known neuromuscular disabilities performed an isometric voluntary wrist flexion at submaximum continuous exertion. After the subjects continued muscle contraction until volitional fatigue, the H-reflexes induced by an electric stimulation and motor evoked potentials (MEPs) induced by a transcranial magnetic stimulation (TMS) from a flexor carpi radialis (FCR) muscle were recorded 7 times every 20 s. The H-reflex was used to assess excitability changes at the spinal level, and the MEP was used to study excitability changes at the cortical level. H-reflexes showed a depression (30% of control value) soon after the cessation of wrist flexion and recovered with time thereafter. On the other hand, an early (short latency) MEP showed facilitation immediately after the cessation of wrist flexion (50% of control value) and thereafter decreased. A possible mechanism for the contradictory results of the 2 tests, in spite of focusing on the same motoneuron pool, might be the different test potential sizes between them. In addition, a late (long latency) MEP response appeared with increasing exercise. With regard to the occurrence of late MEP response, a central mechanism may be proposed to explain the origin—that is, neural pathways with a high threshold that do not participate under normal circumstances might respond to an emergency level of muscle exercise, probably reflecting central effects of fatigue.

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Christopher Kuenze, Jay Hertel and Joseph M. Hart

Purpose:

Persistent quadriceps weakness due to arthrogenic muscle inhibition (AMI) has been reported after anterior cruciate ligament (ACL) reconstruction. Fatiguing exercise has been shown to alter lower extremity muscle function and gait mechanics, which may be related to injury risk. The effects of exercise on lower extremity function in the presence of AMI are not currently understood. The purpose of this study was to compare the effect of 30 min of exercise on quadriceps muscle function and soleus motoneuron-pool excitability in ACL-reconstructed participants and healthy controls.

Methods:

Twenty-six (13 women, 13 men) healthy and 26 (13 women, 13 men) ACL-reconstructed recreationally active volunteers were recruited for a case-control laboratory study. All participants completed 30 min of continuous exercise including alternating cycles of inclined-treadmill walking and bouts of squats and step-ups. Knee-extension torque, quadriceps central activation ratio (CAR), soleus H:M ratio, and soleus V:M ratio were measured before and after 30 min of exercise.

Results:

There was a significant group × time interaction for knee-extension torque (P = .002), quadriceps CAR (P = .03), and soleus V:M ratio (P = .03). The effect of exercise was smaller for the ACL-R group than for matched controls for knee-extension torque (ACL-R: %Δ = −4.2 [−8.7, 0.3]; healthy: %Δ = −14.2 [−18.2, −10.2]), quadriceps CAR (ACL-R: %Δ = −5.1 [−8.0, −2.1]; healthy: %Δ = −10.0 [−13.3, −6.7]), and soleus V:M ratio (ACL-R: %Δ = 37.6 [2.1, 73.0]; healthy: %Δ = −24.9 [−38.6, −11.3]).

Conclusion:

Declines in quadriceps and soleus volitional muscle function were of lower magnitude in ACL-R subjects than in healthy matched controls. This response suggests an adaptation experienced by patients with quadriceps AMI that may act to maintain lower extremity function during prolonged exercise.

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Bradley T. Hayes, Rod A. Harter, Jeffrey J. Widrick, Daniel P. Williams, Mark A. Hoffman and Charlie A. Hicks-Little

Context:

Static stretching is commonly used during the treatment and rehabilitation of orthopedic injuries to increase joint range of motion (ROM) and muscle flexibility. Understanding the physiological adaptations that occur in the neuromuscular system as a result of long-term stretching may provide insight into the mechanisms responsible for changes in flexibility.

Objective:

To examine possible neurological origins and adaptations in the Ia-reflex pathway that allow for increases in flexibility in ankle ROM, by evaluating the reduction in the synaptic transmission of Ia afferents to the motoneuron pool.

Design:

Repeated-measures, case-controlled study.

Setting:

Sports medicine research laboratory.

Participants:

40 healthy volunteers with no history of cognitive impairment, neurological impairment, or lower extremity surgery or injury within the previous 12 mo.

Intervention:

Presynaptic and postsynaptic mechanisms were evaluated with a chronic stretching protocol. Twenty subjects stretched 5 times a wk for 6 wk. All subjects were measured at baseline, 3 wk, and 6 wk.

Main Outcome Measures:

Ankle-dorsiflexion ROM, Hmax:Mmax, presynaptic inhibition, and disynaptic reciprocal inhibition.

Results:

Only ROM had a significant interaction between group and time, whereas the other dependent variables did not show significant differences. The experimental group had significantly improved ROM from baseline to 3 wk (mean 6.2 ± 0.9, P < .001), 3 wk to 6 wk (mean 5.0 ± 0.8, P < .001), and baseline to 6 wk (mean 11.2 ±0.9, P < .001).

Conclusions:

Ankle dorsiflexion increased by 42.25% after 6 wk of static stretching, but no significant neurological changes resulted at any point of the study, contrasting current literature. Significant neuromuscular origins of adaptation do not exist in the Ia-reflex-pathway components after a long-term stretching program as currently understood. Thus, any increases in flexibility are the result of other factors, potentially mechanical changes or stretch tolerance.

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Dana M. Otzel, Chris J. Hass, Erik A. Wikstrom, Mark D. Bishop, Paul A. Borsa and Mark D. Tillman

Context: Following a lateral ankle sprain, ∼40% of individuals develop chronic ankle instability (CAI), characterized by recurrent injury and sensations of giving way. Deafferentation due to mechanoreceptor damage postinjury is suggested to contribute to arthrogenic muscle inhibition (AMI). Whole-body vibration (WBV) has the potential to address the neurophysiologic deficits accompanied by CAI and, therefore, possibly prevent reinjury. Objective: To determine if an acute bout of WBV can improve AMI and proprioception in individuals with CAI. Design and Participants: The authors examined if an acute bout of WBV can improve AMI and proprioception in individuals with CAI with a repeated-measures design. A total of 10 young adults with CAI and 10 age-matched healthy controls underwent a control, sham, and WBV condition in randomized order. Setting: Biomechanics laboratory. Intervention: WBV. Main Outcome Measures: Motoneuron pool recruitment was assessed via Hoffmann reflex (H-reflex) in the soleus. Proprioception was evaluated using ankle joint position sense at 15° and 20° of inversion. Both were assessed prior to, immediately following, and 30 minutes after the intervention (pretest, posttest, and 30mPost, respectively). Results: Soleus maximum H-reflex:M-response (H:M) ratios were 25% lower in the CAI group compared with the control group (P = .03). Joint position sense mean constant error did not differ between groups (P = .45). Error at 15° in the CAI (pretest 0.8 [1.6], posttest 2.0 [2.8], 30mPost 2.0 [1.9]) and control group (pretest 0.8 [2.0], posttest 0.6 [2.9], 30mPost 0.5 [2.1]) did not improve post-WBV. Error at 20° did not change post-WBV in the CAI (pretest 1.3 [1.7], posttest 1.0 [2.4], 30mPost 1.5 [2.2]) or control group (pretest −0.3 [3.0], posttest 0.8 [2.1], 30mPost 0.6 [1.8]). Conclusion: AMI is present in the involved limb of individuals with CAI. The acute response following a single bout of WBV did not ameliorate the presence of AMI nor improve proprioception in those with CAI.

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Igor E.J. Magalhães, Rinaldo A. Mezzarane and Rodrigo L. Carregaro

motoneurons. However, the authors considered this explanation speculative, as the FAC occurred only in the healthy subjects. It was concluded that there are numerous descending inputs to the motoneuron pool that could generate these effects. However, these inputs could not be specified using the methods

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Roel De Ridder, Tine Willems, Jos Vanrenterghem, Ruth Verrelst, Cedric De Blaiser and Philip Roosen

joint. The exact working mechanism of taping remains as of yet unclear and has been attributed to mechanical restriction, 9 to improved sensorimotor control by potentially affecting proprioception, 10 motoneuron pool excitability, 11 and lower-leg muscle activity, 12 as well as to psychological