Date of Award

Spring 5-1-2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Life Sciences

First Advisor

Chris Ingersoll

Second Advisor

Jeffrey Edwards

Third Advisor

Peter Duong

Abstract

Objective: Cryotherapy is a widely used rehabilitative modality in sports medicine. Cooling joint tissues has been observed to facilitate active exercise following injury. Mechanisms effecting motoneuron recruitment during and following cryotherapy are presumed to be both local and central in nature. Focal cooling facilitates motoncuron pool recruitment and may alter the excitability of motoncurons. The purpose of this investigation was to determine if changes in focal temperature alter the characteristics of the maximum peak-to-peak Hoffmann reflex (Hmax) and muscle response (Mmax). Design and setting: A 4x5 factorial design with repeated measures on time was used in this study. Hmax and Mmax measures were collected from each volunteer prior to and following therapeutic cold and warm immersion. Subjects: Forty-eight healthy students (age=21.7±2.lyr; ht=172.6±9.4cm; mass=71.2±15.lkg) volunteered. Measurements: Percutaneous electrical stimuli were administered to establish baseline Hmax and Mmax recruitment curves for each subject. Each subject received a 40-minute treatment segmented into two phases. Subjects were randomly assigned to one of four treatment orders using a balanced Latin Square. The treatment orders included: 1. Control-Control, 2. Control-45°C, 3. 1-3°C-Control and 4. 1-3°C-45°C. Hmax, Mmax, the stimulating intensity that produced Hmax (Hstim), the stimulating intensity that produced Mmax (Mstim), Hmax latency, Mmax latency, and temperatures were recorded every 10 minutes for 40 minutes. Results: A 4X5 factorial MANOV A yielded a time by treatment interaction (F96,1408=2.40; P5:: 0.0001). Differences were detected in Hmax between control-control groups and control-cooling groups at l O minutes (F3,44 =3.394; p,s,_ 0.026) and 20 minutes of rewarming (F 3,44 =4.455; Ps0.008). Mmax for the control-control group was different at 10 minutes (F3,44 .379; Ps 0.026) and 20 minutes of rewarming (F3,44 =5.192; Ps 0.004) compared to control-cooling and cooling-warming treatment group. No differences were observed in the stimulus intensities needed to elicit Hmax (F4,176=1.48; P=0.21) and Mmax across time (F4,176=0.76; P=0.55). Conclusion: Focal temperature change facilitates the Hmax and Mmax. This suggests a centrally mediated state change in the motoneuron pool of the soleus. A state change may effectively lower the threshold for alpha motoneuron firing. These data provide evidence regarding the mechanisms that drives motoneuron pool recruitment during focal cooling and warming.

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