Dopamine and Muscle Function in the Heat

Study Overview
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Brief Summary
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our goal is to study the effects of dopamine activity, using Ritalin ingestion, on neuromuscular function over the course of a progressive heating and cooling protocol developed in our lab. We hypothesize that Ritalin will minimize the previously reported progressive impairment in neuromuscular function with hyperthermia compared to placebo, suggesting that dopamine activity preserves neuromuscular capacity with hyperthermia.

Detailed Description
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Increased core temperature (hyperthermia) has been associated with impaired neuromuscular performance, with the majority of research suggesting that the observed fatigue is related to the central nervous system. Small doses of Ritalin has been used to study how changes in dopamine activity affects exercise capacity in the heat. This study found that 20 mg of Ritalin had no effect on exercise capacity in a thermoneutral environment of 18°C. However, when in a hot (30°C) environment, the Ritalin resulted in a 16% improvement in finishing time compared to the placebo trial. Interestingly, the higher output during the Ritalin-hot condition also resulted in higher rates of heat production and a higher ( 0.6°C) core temperature, suggesting that dopamine enabled greater voluntary tolerance of hyperthermia. This matches recent work from our own work showing that motivational skills training increased both exercise tolerance and final core temperature, and it is possible that dopamine activity played a role in this improvement. Ultimately, fatigue is shown in an inability to sustain muscular force. However, the role of dopamine activity on neuromuscular function (e.g., central activation and recruitment of muscle) during hyperthermia is unknown. One study reported that 20 mg of Ritalin did not alter neuromuscular function, but this study was done without thermal stress. Therefore, our goal is to study the effects of dopamine activity, using Ritalin ingestion, on neuromuscular function over the course of a progressive heating and cooling protocol developed in our lab. We hypothesize that Ritalin will minimize the previously reported progressive impairment in neuromuscular function with hyperthermia (5, 7) compared to placebo, suggesting that dopamine activity preserves neuromuscular capacity with hyperthermia.

Official Title
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The Influence of Dopamine Activity on Neuromuscular Function During Passive Heat Stress

Conditions
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Muscle Force, Hyperthermia

Intervention / Treatment
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* Drug: Ritalin 20 mg Tablet
* Drug: Placebo Oral Tablet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: High aerobic fitness (>55 mL/kg/min maximal aerobic capacity) Exclusion Criteria: diagnosed cardiovascular, respiratory and/or neuromuscular disease, prescription of Ritalin or any drugs for hyperactivity within the past 1 year, any current prescription medication (except for asthma/allergy inhalers), any contraindications to Ritalin.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 30 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: Healthy males 18-30 years of age
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Ritalin<br>20 mg Ritalin, 90 min before testing | Drug: Ritalin 20 mg Tablet<br>* Single dose for all participants<br>|
| Placebo Comparator: Control<br>Identical size/taste placebo pill, 90 min before testing | Drug: Placebo Oral Tablet<br>* Placebo with same appearance/taste<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Wrist flexion torque | Maximal voluntary contraction of wrist flexion | 2-4 hours after ingestion |