Longitudinal change in cardiorespiratory fitness and the association with cardiovascular disease and all-cause mortality in young Asian men: a cohort study.

Introduction: Cardiorespiratory fitness (CRF) in young adulthood is a determinant of chronic disease risk. To better understand whether CRF might also behave as a modifiable risk factor, we examined the associations between longitudinal changes in 2.4 km run times and health outcomes in a cohort of healthy young men. Methods: Our dataset comprised individual run times and health outcomes captured in four national registries. Cox proportional hazards models were used to examine the association between baseline run times and relative hazards of first major adverse cardiovascular events (MACE) and all-cause mortality (ACM). Relative hazards associated with longitudinal change in run times were estimated using models that were adjusted for run-time at baseline. Results: The study sample comprised 148 825 healthy men ages 18-34 years who had undergone at least two routine fitness tests that were 5-9 years apart. During 1 294 778 person-years of follow-up, we observed 1275 first MACE and 764 ACM events occurring at mean ages of 43.2 (SD 6.0) years and 39.2 (SD 6.6) years, respectively. A 1% increase in run-time per annum was associated with a 1.13 (95% CI 1.10 to 1.16) times greater hazard of first MACE and a 1.06 (95% CI 1.02 to 1.10) times greater hazard of ACM. The association between longitudinal change in run times and first MACE was preserved in sensitivity analyses using models adjusted for body mass index at baseline. Conclusion: Among men under the age of 35 years, longitudinal change in run times was associated with the risk of cardiovascular disease two decades onwards.

Thermal strain and fluid balance during a 72-km military route march in a field setting.

Introduction: A physiological profiling study was conducted to evaluate thermal strain as well as fluid and electrolyte balances on heat-acclimatised men performing a 72-km route march in a field setting. Methods: 38 male soldiers (age range 18-23 years) participated in the study, as part of a cohort that marched for 72 km, with loads for about 26 hours. Core temperature and heart rate sensors were used for the duration of the march. Fluid and food intake and output were monitored for the duration of the march. Blood samples were taken one day before the march (pre-march), immediately after the march (Post 1) and on the 15th day after the march to ascertain recovery (Post 2) to assess fluid and electrolyte profiles. Results: Mean core temperature was within safe limits, ranging from 37.1 to 38.1°C throughout the march. There was an overall decrease in serum sodium levels, a decline in serum sodium concentration in 28 participants and three instances of hyponatraemia (serum sodium concentration <135 mmol/L). Conclusion: Our study found low thermal strain heat-acclimatised individuals during a 72-km route march. However, there was an overall decrease in serum sodium levels, even when the participants were allowed to drink ad libitum. Challenges of exercise-associated hyponatraemia during prolonged activities remain to be addressed.