High-Intensity Exercise Does Not Activate Coagulation

Background: Current guidelines for cardiac rehabilitation advocate moderate-intensity continuous exercise training (MICT) at ≈60% peak oxygen uptake (VO2peak). High-intensity interval training (HIIT), with repeated bouts of exercise at >80% VO2peak appears to be an effective alternative, resulting in greater improvements in VO2peak (1), but concern remains about its link with thromboembolic events (2). Exercise activates coagulation in an intensity-dependent way, potentially leading to thrombophilia (3). We therefore conducted the first study to examine in-vivo coagulation in maximal exercise, HIIT and MICT using Fourier transformation rheology. Methods: Sixteen active men (age: 21±3 years, stature: 1.80m ± 11.6cm and mass: 85.8kg ± 3.9kg) were recruited and after random assignment into either a HIIT or MICT group, undertook a cycling challenge to volitional exhaustion on a mechanically braked ergometer (Monark, Varberg, Sweden). VO2 was sampled using an online metabolic cart (Medgraphics UK, Gloucester, UK) and power output corresponding to 40% and 80% VO2peak (HIIT) or 60% (MICT) was noted. Participants returned 3 days later and performed an acute, isovolumic bout of HIIT or MICT. Pre/post exercise, blood was sampled from an intravenous cannula. 10 mL of blood was drawn and discarded, then exactly 7mL of fresh whole blood was injected into a double walled concentric rheometer (Discovery Hybrid 2, TA Instruments, DE, USA), for analysis of blood fractal dimension (Df ) using previously described methods (4). Data were analysed using a 2-way repeated measures ANOVA and Bonferonni corrected paired sample t-tests and independent sample t-tests. Significance was established at P<0.05 and data were expressed as mean ± SD Results: There were no differences in Df prior to exercise between groups (1.81±0.01, HIIT vs. 1.74±0.11, MICT). Df increased in both groups after maximal exercise (1.95±0.08, HIIT vs. 1.87±0.10, MICT, P<0.05). Acute HIIT did not alter Df (1.82±0.07) but acute MICT increased Df vs. pre-exercise (1.83±0.16, P<0.05). Conclusion: An acute bout of MICT at the current recommended training intensity for cardiac rehabilitation increased Df (figure 1, B). The reference range for Df is 1.74±0.07 (5), which suggests MICT activated coagulation and increased the density and cross-linkage of the insipient clot outside the reference range. Conversely, an acute bout of HIIT did not increase Df. Our data conflict with the present literature that used less sensitive in-vitro markers of coagulation (6,7) and suggest that HIIT is a safe, viable exercise regimen and deserving of further examination in patients.A 70 year-old female who underwent an oesophagectomy for oesophageal cancer developed ischaemia of the gastric conduit and was left with a pharyngostomy, and a feeding jejunostomy. Further surgery for restoration of the upper gastrointestinal tract with a colonic interposition which involved another major thoraco-abdominal operation was offered, however the patient’s fitness for surgery was stratified as high-risk. The medical history also included a myocardial infarction and coronary artery bypass graft. Following CPET to symptom limited exhaustion to determine baseline fitness, a ten-week supervised HIIT intervention was conducted. Three exercise sessions of 40 minutes duration separated by 48 hours recovery were completed each week using cycle ergometry. Each session comprised six, two-minute bouts of heavy exercise (50% of the difference between power output at peak exercise and anaerobic threshold (AT)) interspersed by three minutes of moderate exercise (80% of the power at AT) in accordance with previous research (West et al. 2015). Heart rate was monitored by 12-lead ECG alongside blood pressure, and rate of perceived exertion recorded. Cardiorespiratory fitness was reassessed by CPET every two weeks and HIIT intensities adjusted accordingly. The HIIT intervention was well tolerated with no adverse events occurring and 29 of 30 sessions completed. After 10 weeks, pulmonary oxygen uptake at peak exercise and anaerobic threshold increased by 36 and 27% respectively (18.6 versus 13.7 and 10.5 versus 8.3 ml.kg-1.min-1) and traversed a fitness stratification threshold of 15 ml O2.kg-1.min-1 for peak oxygen uptake. The patient was subsequently referred for surgery. Despite the high intensity of exercise, HIIT proved feasible, safe, and well tolerated. Impressive cardiopulmonary adaptation occurred in excess of variation typically observed during repeated measures (Rose et al., 2018). Improved CRF over a short period of time enabled the fitness for surgery classification to move from “unfit” to “fit”, and thus supports investigating HIIT in future trials as an adjunct prior to major surgery. References Levett et al. (2018). Br J Anaesth 120, 484-500. Moran et al. (2016). Br J Anaesth 116, 177-191. Rose et al. (2018). Br J Anaesth 120, 1187-1194. West et al. (2015). Br J Anaesth 114, 244-251.