Hello, welcome back to Training Course One.
This is Lesson Two: Reduced Aerobic Fitness in Adults and Older Adults with Moderate to Severe Traumatic Brain Injury.
The learning objectives are to understand current levels of aerobic fitness in adults after moderate to severe traumatic brain injury, the mechanisms that contribute to reduced aerobic fitness, why aerobic fitness training is important for this population, and the known and probable benefits of improving aerobic fitness.
Around 11 studies have used gas analysis to measure aerobic fitness using VO₂ peak or VO₂ max, which reflects peak oxygen capacity. These studies have mainly involved men aged 30 to 39 years. When compared with normative values from the American College of Sports Medicine, the average fitness levels observed in these studies fall below what is considered poor for that age group. This highlights that individuals with moderate to severe traumatic brain injury commonly have very low fitness levels.
There are several reasons for this reduced fitness. Research exploring these mechanisms shows both central and peripheral factors are involved. Reduced maximum oxygen capacity is influenced by prolonged bed rest and inactivity, as well as factors directly related to the brain injury.
Central changes include effects on the cardiac system, largely due to inactivity and bed rest, which are common in many conditions involving immobility. There are also changes in the pulmonary system. These may be more pronounced following traumatic brain injury due to associated injuries such as rib fractures or pneumothorax, as well as impairments in respiratory muscle strength and coordination.
Peripheral changes are also significant. These include muscle loss and deconditioning due to inactivity, but are often more severe in this population due to physical impairments and hormonal changes caused by the brain injury. These hormonal changes can lead to hypermetabolism and hypercatabolism, resulting in rapid weight loss, particularly loss of muscle mass. As a result, individuals often enter rehabilitation with substantial muscle wasting.
In addition, there are brain-specific factors. Cognitive and behavioural changes may limit a person’s ability to reach maximal effort during testing, which is why VO₂ peak is often used instead of VO₂ max. Exercise efficiency may also be reduced due to physical impairments or associated injuries, limiting the ability to perform higher intensity activities.
All of these factors contribute to reduced fitness after injury. Ongoing physical inactivity after discharge can further compound this issue, as individuals may struggle to return to normal daily activities.
Improving aerobic fitness is important because it supports a return to everyday activities and helps reduce physical fatigue. Physical activity can be understood across different domains such as household, work, leisure, and transport, and across different intensity levels measured in METs. Light activity is less than 3 METs, moderate is between 3 and 6, and vigorous is above 6.
MET values represent the oxygen requirement of an activity. For example, mowing the lawn has a MET value of 5.5, meaning it requires five and a half times the oxygen of resting.
When comparing this to someone with reduced fitness after brain injury, their overall capacity may be just enough to perform moderate activities like mowing the lawn, but with limited reserve. This means the activity can feel highly fatiguing. As fatigue increases, individuals may reduce their activity levels, which in turn leads to further reductions in fitness. This creates a cycle of declining activity and increasing fatigue.
Conversely, improving aerobic fitness increases aerobic reserve. This allows individuals to perform activities more easily, with less fatigue, and supports greater participation in daily life.
Beyond functional improvements, increasing aerobic fitness can also reduce the risk of mortality and chronic disease. Long-term research in the general population shows that low fitness is a major risk factor for mortality, even more significant than many commonly discussed factors such as obesity, smoking, or cholesterol.
There is also emerging evidence in people with traumatic brain injury that improving fitness can enhance mood, particularly following structured exercise after hospital discharge. Additional potential benefits include improved physical function, reduced risk of falls, better cognitive function, enhanced social participation, improved quality of life, and reductions in body mass index.
In summary, aerobic fitness is a critical component of recovery and long-term health in this population.
That concludes Lesson Two. Please complete the quiz before moving on to Lesson Three.
Blair SN. Physical inactivity: the biggest public health problem of the 21st century. Br J Sports Med. 2009;43(1):1-2. https://bjsm.bmj.com/content/43/1/1.long.
Hassett L, Moseley A, Harmer A. The aetiology of reduced cardiorespiratory fitness among adults with severe traumatic brain injury and the relationship with physical activity: a narrative review. Brain Impair. 2016;17(1):43-54. https://doi.org/10.1017/BrImp.2015.28.
Ozemek C, Bonikowske A, Christle J, Gallo P. ACSM’s Guidelines for Exercise Testing and Prescription (12th Edition). Baltimore: Walters Kluwer, 2025. ISBN: 978-1-9752-1920-8.