Defining the Temporal Changes in the Acute Phase Response During Graded Exercise: A Prospective Study

Injury, ranging from a paper cut that barely splits the skin to a high-speed motor vehicle
accident that rips through muscle and bone, causes a disruption of tissue compartments. This
breach of compartments disposes tissue to four principle problems: 1) bleeding, 2)
susceptibility to infection, 3) hypoxia, and 4) tissue dysfunction. The acute phase response
(APR) is the physiologic system that resolves these four problems of injury. It is divided
into two temporally distinct phases: survival and repair. The survival phase utilizes
coagulation and inflammation to temporarily seal off breached compartments in order to stop
bleeding and prevent the spread of infection. Once the life-threatening problems of
hemorrhage and susceptibility to infection have been resolved, the body enters the repair
phase, where it works to restore the disrupted blood supply and regenerate damaged tissue.
These processes, coupled together, replace the temporary sealant and restore the injured
tissue to its original form and function.

Plasmin is the key fibrinolytic protease that transitions the APR from survival to repair.
Plasmin is traditionally known for its ability to degrade fibrin clots. Previous work has
demonstrated that plasmin also activates many targets outside of fibrin degradation that are
essential for musculoskeletal tissue healing. Plasmin initiates the repair of injured tissue
by removing the temporary fibrin sealant required for hemostasis, which allows access for
repair machinery to enter the site of injury. Subsequently, plasmin activates proteases that
promote angiogenesis and cell differentiation to stimulate tissue regeneration. Without
adequate plasmin activity, the body fails to transition from survival to repair and is unable
to reconstitute the compartments damaged by injury.

All tissue injury activates the acute phase response. Exercise is a form of contained tissue
injury that harnesses the beneficial effects of the acute phase response to build muscle and
promote overall health. Given that the controlled injury of exercise minimizes compartment
disruption, there is a limited need to mount a response to hemorrhage or containment of
infection (survival). Exercise increases the metabolic requirement of muscle to the point
that it outstrips the supply of oxygenated blood and results in sustained hypoxia. In
response to hypoxia, plasmin stimulates angiogenesis and activates cells involved in tissue
regeneration (repair). In exercise physiology, if major injury is avoided, the body thereby
bypasses the survival phase and transitions into an early and prolonged repair phase.

Despite studies demonstrating alterations in the APR with exercise, the relationship between
the intensity of exercise and the extent of APR activation is not yet well defined [8-10].
Our aim is to gain a better understanding of the precise changes in the APR in order to
maximize the reparative potential of exercise. We hypothesize that moderate intensity
exercise selectively enhances plasmin-mediated fibrinolysis (repair) without inducing the
procoagulant arm of the APR (survival). Additionally, we propose that the systemic activation
of fibrinolysis achieved in exercise promotes global tissue health at spatially distinct
locations in addition to the site of initial tissue injury (hypoxic muscle). To evaluate
this, we will define the precise temporal changes in the APR in healthy individuals
participating in graded intensities of exercise (rest, light, and moderate). Through
elucidation of the precise temporal activation of the APR as it relates to the intensity of
exercise, it may allow future studies to develop an exercise regimen that harnesses the
reparative potential of fibrinolysis while avoiding the potentially harmful activation of the
procoagulant survival phase of the APR.

The purpose of this study is to detail the precise temporal changes in the APR that occur in
response to exercise in order to determine the types of exercise that confer maximal
reparative fibrinolysis. Published research and preliminary studies conducted in our lab
suggest that different types of exercise will preferentially activate fibrinolysis without
changes in coagulation, thereby promoting improved global tissue health. As such, measuring
markers of the APR in healthy individuals 1) at rest, 2) walking (light intensity exercise),
and 3) running (moderate intensity exercise) will allow us to establish a baseline for the
temporal changes in the APR that avoid activation of the procoagulant survival phase while
maximizing the repair phase.

Specific aims

1. To measure the acute phase response fibrinolysis, plasminogen consumption, and
inflammatory profiles of healthy individuals before and after graded exercise (at rest,
light intensity, and medium intensity), as defined by changes in fibrinolysis,
plasminogen consumption, and inflammatory response.

2. To track the APR through modulated exercise in order to determine the type of exercise
that enhances physiologic benefit and limits harm.

Inclusion Criteria:

- Healthy individuals (male or female) aged 18-29

- Regular participation (at least 2 times per week) in moderate intensity exercise

- BMI between 18.5 and 30.0

Exclusion Criteria:

- Pre-existing health conditions or injuries that may limit the ability to safely
participate in exercise

- Acute disease process such as an infection, broken bone, or asthma attack

- Chronic or recent use (within the last 10 days) of any anticoagulant medication or
NSAID

- Pregnant women

- Recent inpatient admission within the last six months

- History of smoking or illicit drug use