The Effects of Caffeine on Human Spinal Motoneurons

Study Overview
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Brief Summary
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This study evaluates the effects of orally ingested, commercially available, coffee (3 mg/kg of caffeine) on the excitability of human spinal motoneurons of the lower leg.

Detailed Description
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Recently, it has been shown that human spinal motoneurons do not simply act as a binary control system. Instead, they are regulated by intrinsic properties that can elicit lingering effects on the descending motoneuron. Caffeine, one of the world's most popular over-the-counter supplements, can potentially augment these characteristics of motoneurons. Using decomposition software and non-invasive, high-density surface electromyography, it is possible to extract the characteristics of these motoneurons. This project will utilize a double-blind, inactive-placebo controlled, crossover design study to examine and quantify the effects of caffeine on motoneuron excitability.

Official Title
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The Effects of Caffeine on Human Spinal Motoneurons

Conditions
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Healthy

Intervention / Treatment
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* Dietary Supplement: Coffee
* Dietary Supplement: Decaffeinated coffee


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: ● Between 18 and 70 years of age Exclusion Criteria: Significant neurological or orthopedic injuries, which may limit volitional torque generation in the tested muscles. Significant change in the subjects' health or treatment in the past month. Known history of cardiovascular pathology (to include: uncontrolled hypertension, cardiac arrhythmias) or medical restrictions to caffeine ingestion. Allergies or dislike of coffee. Women who are pregnant will be excluded due to potential forces at trunk from pelvic safety harness and due to potential adverse effects of caffeine on the developing child. Women who are breastfeeding will be excluded due potential adverse effects on the breastfeeding infant from caffeine administration. Adults unable to consent, minors, pregnant women, and prisoners will not be included.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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All

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: Crossover Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Caffeine<br>Single-dose, orally ingested, instant coffee. | Dietary Supplement: Coffee<br>* Starbucks brand Via instant coffee. (Caffeine Content: 3 mg / kg)<br>|
| Placebo Comparator: Inactive Placebo<br>Single-dose, orally ingested, instant decaffeinated coffee (equal weight to intervention dose). | Dietary Supplement: Decaffeinated coffee<br>* Starbucks brand Via instant decaffeinated coffee. (Caffeine Content: 15 - 25 mg)<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Motoneuron excitability (Delta-f) | Changes in motorneuron excitability, as quantified by Delta-F values. A paired motor unit technique will be utilized (Gorassini et al., 2002). (Typically, these values range from -5 to +10). | Measured repeatedly at set intervals; Pre-Intervention & 30, 60, 90 minutes post-Intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Motor Unit Discharge Rate | Changes in motor unit discharge rate. This is a single value that ranges from, approximately, 0 to 30. | Measured repeatedly at set intervals; Pre-Intervention & 30, 60, 90 minutes post-Intervention | 
| Coherence | Changes in coherence values. Coherence provides a normalized value of the strength of correlation in the frequency domain. The magnitude of the correlation of the Fourier transforms of two spike trains is squared producing a value between 0 and 1, with 1 corresponding to a perfect linear prediction at a particular frequency (Rosenberg et al., 1989). This will be calculated using the composite spike train (Negro & Farina, 2012) and, finally, z-transformed to allow for between-trial comparisons. | Measured repeatedly at set intervals; Pre-Intervention & 30, 60, 90 minutes post-Intervention | 
| Motor Unit Recruitment Threshold | Changes in motor unit recruitment threshold. As assessed by determining the amount of force (percentage of maximum volitional force output) needed to recruit an individual motor unit. | Measured repeatedly at set intervals; Pre-Intervention & 30, 60, 90 minutes post-Intervention | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Motor Neuron, Excitability, Caffeine