Acute Metabolic and Neuroendocrine Responses to Maximal Treadmill Exercise in Patients Recovering from Traumatic Brain Injury (TBI)
Public awareness of the incidence of traumatic brain injury (TBI) increased significantly throughout the past decade. The increased awareness is primarily the result of a heightened understanding of the impact of blast-related TBI in the wars in Iraq and Afghanistan and a renewed interest in sport-related concussion. A TBI can have devastating effects on an individual, yet many of the symptoms are subtle and may not be visibly evident. Impairments caused by TBI can lead to increased morbidity, decreased functional independence, and an increased reliance on the public health-care system. TBI can cause cognitive and behavioral impairments, reduced peak physical and metabolic work capacity, and endocrine irregularities. Chronic fatigue is one of the most common complaints in patients recovering from TBI and affects many facets of life, including the ability to return and contribute to the workforce. It has been documented that patients with a TBI have reduced peak aerobic capacities compared to sedentary controls and that growth hormone (GH) deficiency is associated with lower peak aerobic capacity. Moreover, research suggests that GH deficiency may be related to perceived fatigue. The hormonal response to exercise is predictable and well documented in apparently healthy controls (CON), but to date few if any studies have quantified the endocrine response to exercise in TBI. The series of studies in this dissertation demonstrate that (1) peak metabolic, ventilatory, and cardiovascular responses are lower than predicted in patients with a TBI, irrespective of gender; (2) peak metabolic and ventilatory anaerobic threshold (VAT) responses to exercise are lower in patients with a TBI compared to healthy, sedentary CON; (3) the GH/insulin-like growth factor-1 response to exercise is similar in patients with a TBI and sedentary CON, but there are marked differences in the responses of prolactin (PRO) and cortisol (COR); and finally (4) perceived fatigue is associated with lower resting insulin-like growth factor-I (IGF-1) levels and VAT responses, but not the exercising response of hormones. Together, the results strongly support the use of intense physical exercise in rehabilitation of patients recovering from a TBI.