Brain and Gut Plasticity in Mild TBI or Post-acute COVID Syndrome Following Growth Hormone Therapy

mTBI Inclusion criteria 1. Male or female with a diagnosis of mild TBI. 2. At least 6-month post-injury. 3. Ages 18 to 70 years. 4. Participant is willing and able to give informed consent for participation in the study. mTBI Exclusion criteria 1. Unable to walk unassisted. 2. Significant heart, liver, kidney, blood or respiratory disease. 3. History of chest pain or coronary heart disease. 4. Uncontrolled Diabetes mellitus. 5. Any history of a recently (12 months) diagnosed cancer other than a skin cancer (excluding melanoma). 6. Recent (within 6 months) treatment with anabolic steroids or corticosteroids. 7. Current alcohol or drug abuse. 8. Premorbid history of psychiatric disorder. 9. Premorbid history of head trauma. 10. Pregnancy or become pregnant during the trial. 11. Coumadin because of the risk of bleeding with daily injections of rhGH. 12. Subjects who are deficient in cortisol or thyroid at screening will be excluded until hormone abnormalities have been corrected. 13. Subjects with chronic pain who are being managed with narcotics will be excluded as the effects of central nervous system depressants may interfere with study test results. 14. Subjects with a history of inflammatory bowel disease, Celiac disease or active diverticular disease. 15. Other medical condition or medication administration deemed exclusionary by the study investigators. Control Inclusion criteria 1. Ages 18 to 70 years. 2. Participant is willing and able to give informed consent for participation in the study. Control Exclusion criteria 1. Significant heart, liver, kidney, blood or respiratory disease. 2. Uncontrolled Diabetes mellitus. 3. Any history of a recently (12 months) diagnosed cancer other than a skin cancer (excluding melanoma). 4. Recent (within 6 months) treatment with anabolic steroids or corticosteroids. 5. Current alcohol or drug abuse. 6. Premorbid history of psychiatric disorder. 7. Premorbid history of head trauma. 8. Pregnancy or become pregnant during the trial. 9. Subjects who are deficient in thyroid at screening will be excluded until thyroid hormone is replaced. 10. Subjects with a history of inflammatory bowel disease, Celiac disease or active diverticular disease. 11. Other medical condition or medication administration deemed exclusionary by the study investigators. PASC Inclusion criteria 1. Male or female with a history of COVID with diagnosis confirmed by PCR test. 2. Minimum of 6 months since diagnosis of COVID by PCR test. 3. Ages 18 to 70 years. 4. Score of 3 or higher on any question 1-3 of the Brief Fatigue Inventory (BFI) questionnaire. 5. Participant is willing and able to give informed consent for participation in the study. PASC Exclusion criteria 1. Current COVID infection. 2. Unable to walk unassisted. 3. Significant heart, liver, kidney, blood or respiratory disease as determined by Principal Investigator. 4. Uncontrolled diabetes mellitus. 5. Any history of a recently (12 months) diagnosed cancer other than a skin cancer (excluding melanoma). 6. Current alcohol or drug abuse. 7. History of psychosis. 8. Pregnancy or become pregnant during the trial. 9. Subjects who are being managed with narcotics will be excluded as the effects of central nervous system depressants may interfere with study test results. 10. Other medical condition or medication administration deemed exclusionary by the study investigators.