Introduction
Endurance training is typically associated with high training volumes, often with insufficient rest, leading to chronic systemic stress [1]. This may alter factors that promote blood coagulation, such as enhanced sympathetic activity and inflammation [2]. Moreover, although regular exercise typically protects against cardiovascular disease, a single bout of maximal exercise can paradoxically trigger a cardiac event or stroke [3]. This may be attributed to exercise-induced hypercoagulability and the formation of denser blood clots [4]. Interestingly, little is known regarding the impact of training status on resting and post-exercise hemostasis.
Recently, a novel and sensitive rheology method for assessing hypercoagulability has been developed. The method provides a measure of incipient clot microstructure through the determination of fractal dimension (df), where a higher df is indicative of a more dense and stronger clot, and a lower df reflects a less dense and weaker clot [5].
Aims/Objectives
The purpose of this study was to assess clot microstructure in recreationally active (REC) and endurance trained (ET) females at rest and following a battery of intensive exercise. We hypothesized that ET females would have a higher df at rest and after maximal exercise compared to REC females.
Methods
The study protocol was approved by the Ethical Committee of Copenhagen Region H (H-21032399). Seven REC (V̇O2max: 45.3 ± 0.9 mL∙kg-1∙min-1; training 2.1 ± 0.4 hours per week) and 6 ET females (V̇O2max: 52.3 ± 1.7 mL∙kg-1∙min-1; training 8.4 ± 0.6 hours per week) were recruited. Participants rested for 15 minutes before a baseline blood sample was drawn and immediately analyzed for df. Participants then completed a cycling battery including: a 12-minute graded warm-up, a V̇O2max test to exhaustion, time to exhaustion at 100% watt max (Wmax), and a 10 minute isokinetic time trial. Immediately after the exercise battery, a blood sample was drawn for determination of df. Statistics were performed using Graphpad Prism 9.3.1 (California, USA). An unpaired t-test was used for comparing Wmax, a two-way ANOVA (group x time) was utilized for df analysis, and a Pearson correlation was used for correlational analysis. Data are reported as mean ± SEM.
Results
Wmax during the V̇O2max test was higher in the ET (313 ± 14 W) compared to the REC females (271 ± 10 W) (p = 0.03). However, Wmax relative to body mass was not different (6.0 ± 0.4 W∙kg-1 vs. 6.0 ± 0.3 W∙kg-1) (p = 0.97). At rest, df was significantly higher in the ET (1.67 ± 0.02) compared to the REC females (1.59 ± 0.01) (p = 0.002). Resting df correlated significantly with relative V̇O2max (R2 = 0.61) (p = 0.002). After the maximal exercise battery, df increased significantly in REC females (p = 0.004), whereas no change was observed in ET females.
Conclusions
This study provides novel insight into the impact of intensive high-volume training on clot microstructure. These findings indicate that higher training volumes and/or fitness may be associated with hypercoagulability at rest and abolition of exercise-induced changes in clot microstructure. Further studies investigating the underlying mechanisms are ongoing.