The influence of physical activity on characteristics of the fibrin network structure of active and sedentary males

Abstract

Background - In 1990 cardiovascular disease (CVD) was the main cause of death world wide (Murray & Lopez, 1996). Regular physical activity is associated with a lower risk of CVD. The mechanisms through which regular physical activity reduces the risk of CVD is not fully understood. The independent, probably causal association of increased plasma fibrinogen with CVD is established (Meade et al. , 1986). This association seems to be stronger than that of cholesterol with CVD (Ernst et al., 1992). It is hypothesised that part of this association may be mediated by the quality of fibrin network structures formed when fibrin(ogen) monomers polymerise. The plasma metabolic environment determines the characteristics of the fibrin network structure that is formed. Regular physical activity results in changes in the metabolic environment, which is expected to influence formation of fibrin network structures. Changes in diet also lead to changes in the metabolic environment. When a diet consisting of a high glycaemic index (GI) is ingested, large variations in blood glucose and insulin responses have been found, while the ingestion of a low GI meal results in the slow release of glucose and insulin with less variations (Wolever, 1990). The effect of physical activity and a combination of activity with a low or high GI pre-exercise meal on the formation of the fibrin network structures are not known. Objectives - The purpose of this study was to determine the influence of a maximal exercise bout on fibrin network characteristics. The combinations of a low or high GI pre-exercise meal and physical activity on the network structure characteristics were also investigated. Methods - Fifteen active and 14 sedentary males were recruited to participate voluntarily in the study. The respondents were subjected to a maximal exercise, blood samples taken fasting, during maximal activity, and after 30 minutes of recovery. Maximal activity was achieved by exercising the respondents to exhaustion on a Monark bicycle ergometer. The resistance was increased with 50 watt increments after every four minutes. Maximal

activity was reached when the heart rate reached aged predicted maximum (according to Karvonen's equation), or the respondent could not continue. The heart rate and blood pressure was recorded after 3 minutes in every stage before the resistance was increased. The characteristics of the fibrin network structure determined were the permeability coefficient (Ks), mass-length ratio (MLR) and compaction. These were interpreted against the background of changes in several haemostatic variables in plasma. To determine the influence of the GI of a meal, the same study design was used with a high and low pre-exercise GI meal given in a random order. Blood samples were taken fasting and at 1-hour post meal, maximal exercise, and after 30 minutes of recovery. The Ks, MLR, compaction and selected biochemical variables were determined at all the times. Results - Maximal exercise resulted in an increase in Ks of the fibrin network structure from plasma of active males, while the MLR decreased when compared to that at rest. After 30 minutes of recovery the Ks decreased slightly, but remained higher than the Ks obtained at rest. The MLR increased after 30 minutes of recovery to values significantly higher than at rest. It seems that the active males formed fibrin network structures that were less resistant to lysis (Blom back et al., 1990) after 30 minutes of recovery than at the start of activity. This is possibly due to the fibrin network structure being more permeable with shorter and thicker fibres. In the sedentary males, the Ks decreased while the MLR increased in response to the maximal activity. After 30 minutes of recovery the Ks of the sedentary males decreased even more, to result in less permeable fibrin network structures than before activity. The MLR increased with maximal activity, but after 30 minutes of recovery decreased to values lower than before activity. It seems that the sedentary males formed fibrin network structures after maximal activity that were less permeable and more resistant to lysis, possibly due to longer and thinner fibres. After ingestion of the GI meal, the network structures were characterised 1 hour postmeal, at maximal activity and after 30 min of recovery. The low GI meal resulted in a smaller insulin response together with an increase in compaction in comparison with the high GI meal. In the case of the sedentary group the low GI meal also had a smaller insulin response, with an increase in MLR. This increased MLR suggests that shorter and thicker

fibrin network structures are formed with the ingestion of a low GI meal when compared to a high GI meal. The advantage of the low GI meal compared to the high GI meal was seen in the increased MLR and compaction in response to maximal activity in the active males. A slight increase was also seen in Ks. This suggests that the active males formed more permeable fibrin network structures that are more readily dissolved than those formed with the high GI meal. The low GI meal also increased compaction and less fluctuation in insulin levels were found in the active males. The results found in the sedentary males were not clear. The characteristics of the fibrin networks indicated a trend towards a decrease in Ks while the high GI meal decreased compaction and the low GI meal increased compaction. Recovery from the maximal exercise resulted in a decrease in Ks of the active males with both the high and low GI meals. The low GI meal resulted in values higher than initially measured at fasting. The MLR showed similar changes. MLR values were higher after activity in combination with the low GI meal than with the high GI meal. The same trend was found in the sedentary males, but the MLR and Ks values after recovery in combination with the high GI meal were lower than at fasting, values returned to the fasting values when the low GI meal was eaten. An increase in Ks suggests an increase in permeability of the fibrin network structure, while an increase in MLR, shorter and thicker fibrin fibres. (Blomback et al., 1990). These types of networks are less thrombogenic and less resistant to lysis. A decrease in these characteristics will have the opposite effect with more lysis-resistant fibrin network structures being formed. Conclusion - It is concluded that the effects of physical fitness and acute bouts of intensive exercise on fibrin networks formed from plasma of healthy young males may differ. These fibrin networks formed from plasma of healthy young males are influenced by the glycaemic properties of the pre-exercise meal. Changes in the metabolic environment occurred that possibly affected the characteristics of the fibrin network structures during exercise and after meals. More research is needed for a better understanding of underlying mechanisms, and to relate these differences to health outcomes.