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 15^th 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.     

Norepinephrine mobilization of free fatty acids in endurance trained rats

Summary Wistar rats were trained to run, a male group on 6 days a week for 4 months at 28 m·min⁻¹, and a female group on 5 days a week for 5–6 months at 31 m·min⁻¹. Male rats were given continuous infusion of [1-¹⁴C] palmitate-albumin tracer via a jugular catheter at a constant infusion rate of 80 nCi·min⁻¹. The effect of concurrent norepinephrine (NE) infusion on free fatty acid (FFA) mobilization was then studied in this group. NE increased plasma FFA levels similarly in both control and endurance trained male groups. Turnover of FFA, however, increased in response to NE relatively less in the trained group. Furthermore, NE caused the metabolic clearance rate of FFA (MCR) to decrease in control animals but not in runners. Colonic temperature was slightly increased by NE infusion in the control group only. Female rats were given a bolus injection of 5 ΜCi of [1-¹⁴C] palmitate-rat serum through a venous cannula. The disappearance of radioactivity in the circulation was measured. MCR values were higher in the trained group (p=0.01). The effect of NE infusion on FFA levels was also studied in female animals. NE caused levels to increase in both control and trained rats. FFA concentrations were however more elevated in the control than in the trained group, before and during NE infusion. The relative increase tended to be less extensive in the trained group (p=0.06). It is concluded that long term endurance training diminishes calorigenic and fat mobilizing actions of NE in the rat in vivo. Supported in part by grants from the Medical Research Council of Canada and le Ministère de l'Education du Québec Recipient of a pre-doctoral fellowship of the Muscular Dystrophy Association of Canada.     

Fitness standards for male college students

The endurance fitness of 135 American male college students was evaluated by the maximal aerobic power test (bicycle ergometer), and the Harvard step test. Comparison of results with those previously reported indicated that our sample was representative of students in a number of countries. The following endurance fitness standards were therefore constructed: Aerobic power — less than 2.4 l/min or 34 ml/kg-min, poor; 2.4 to 2.9 l/min or 34 to 40 ml/kg-min, low average; 3.0 to 3.5 l/min or 41 to 48 ml/kg-min, average; 3.6 to 4.0 l/min or 49 to 55 ml/kg-min, good; greater than 4.0 l/min or 55 ml/kg-min, excellent: Harvard step test index — less than 54, poor; 64 to 67, low-average; 68 to 82, average; 83 to 96, good; greater than 96, excellent.Supported by Medical Sciences Branch, Research Division, Medical Research Branch, Office of the Surgeon General, U.S. Army, under contract No. DA-49-193-MD 2741.     

Defining cardiac adaptations and safety of endurance training in patients with m.3243A>G-related mitochondrial disease

Background

Cardiac hypertrophic remodelling and systolic dysfunction are common in patients with mitochondrial disease and independent predictors of morbidity and early mortality. Endurance exercise training improves symptoms and skeletal muscle function, yet cardiac adaptations are unknown.

Methods and results

Before and after 16-weeks of training, exercise capacity, cardiac magnetic resonance imaging and phosphorus-31 spectroscopy, disease burden, fatigue, quality of life, heart rate variability (HRV) and blood pressure variability (BPV) were assessed in 10 adult patients with m.3243A>G-related mitochondrial disease, and compared to age- and gender-matched sedentary control subjects. At baseline, patients had increased left ventricular mass index (LVMI, p < 0.05) and LV mass to end-diastolic volume ratio, and decreased longitudinal shortening and myocardial phosphocreatine/adenosine triphosphate ratio (all p < 0.01). Peak arterial–venous oxygen difference (p < 0.05), oxygen uptake (VO₂) and power were decreased in patients (both p < 0.01) with no significant difference in cardiac power output. All patients remained stable and completed ≥ 80% sessions. With training, there were similar proportional increases in peak VO₂, anaerobic threshold and work capacity in patients and controls. LVMI increased in both groups (p < 0.01), with no significant effect on myocardial function or bioenergetics. Pre- and post-exercise training, HRV and BPV demonstrated increased low frequency and decreased high frequency components in patients compared to controls (all p < 0.05).

Conclusion

Patients with mitochondrial disease and controls achieved similar proportional benefits of exercise training, without evidence of disease progression, or deleterious effects on cardiac function. Reduced exercise capacity is largely mediated through skeletal muscle dysfunction at baseline and sympathetic over-activation may be important in pathogenesis.     

Continuous exercise training and curcumin attenuate changes in brain-derived neurotrophic factor and oxidative stress induced by lead acetate in the hippocampus of male rats

Context: For many years it has been known that lead is life-threatening, not only as an air pollutant but also because of it has been associated with several conditions including neurodegenerative disease. Curcumin (the principal curcuminoid found in turmeric) has demonstrated potent antioxidant properties.

Objective: We investigated neuroprotective effects of endurance exercise and/or curcumin on lead acetate-induced neurotoxicity in the rat hippocampus.

Materials and methods: Forty male Wistar rats were randomly divided into five groups: 1) lead acetate, 2) curcumin, 3) training, 4) training + curcumin, and 5) control. The rats in the training groups performed treadmill running five times a week for 8 weeks (15–22 m/min, 25–64?min). All groups except control received lead acetate (20?mg/kg), whereas the control group received curcumin solution (ethyl oleate). In addition, the curcumin and training + curcumin groups received curcumin solution (30?mg/kg) intraperioneally.

Results: Lead acetate resulted in a significantly increase in the malondialdehyde (MDA) in plasma (72%), but not significant in hippocampus (59%). In addition, it led to significantly decreased brain-derived neurotrophic factor in hippocampus (17%) and total antioxidant capacity (27%), as compared to control group. Treadmill running, curcumin supplementation or both resulted in a significant decrease in hippocampus MDA (17, 20, 31%, respectively) and plasma MDA (60, 22, 71%) and also, significantly increased brain-derived neurotrophic factor (76, 45, 94%) and total antioxidant capacity (47.13, 47.11, 61%) levels, as compared to lead acetate group.

Discussion and Conclusion: These results provide a rationale for an inhibitory role of curcumin and regular exercise in the attenuation of lead-induced neurotoxicity.     

Scientific-Therapeutic-Exercise-Progressions

Abstract

The purpose of this article is to provide basic information about the S.T.E.P. approach to exercise. The S.T.E.P. approach is based on current research in neurophysiology, histology and exercise physiology. The S.T.E.P. method is an individually adapted approach that aims to reduce symptoms and improve functional tissue tolerance. Specific examples are given on how to dose an exercise program and how to optimally facilitate muscle fiber recruitment. S.T.E.P. represents an active alternative to traditional, passive schools of thought in modern manual therapy.     

835名军机飞行员颈肌强度与耐力分析

目的通过分析军机飞行员颈肌强度与耐力,探讨飞行员颈肌训练的必要性和可行性,为制定飞行员颈肌肌力的军用标准提供参考。方法采用CME-1型飞行员颈肌训练器对835名军机飞行员进行颈部各肌群等长模式肌力测试。每一个方位测试10次,10次中最大肌力均值作为该侧肌群的强度,各方位10次测试中每次最大冲量（肌肉力量与时间乘积）均值作为该肌群的耐力。按机种、年龄分别对颈部各肌群平均最大肌力、平均总冲量值进行统计分析。结果高性能机组飞行员颈肌前、后、左、右各肌群的平均最大肌力、平均总冲量值最高,差异有统计学意义（P〈0.05）。而运输机组飞行员颈肌前、后、左、右各肌群的平均最大肌力、平均总冲量值最低,差异有统计学意义（P〈0.05）。按年龄分组,〈30岁组飞行员前、后、左、右侧肌群平均最大肌力及平均最大总冲量均较其余两组高,差异有统计学意义（P〈0.05或者P〈0.01）。结论军机飞行员应加强地面针对性颈肌强度及耐力训练,提高应对高载荷的能力,不断提高作战能力。     

Elevated hair cortisol concentrations in endurance athletes

Engaging in intensive aerobic exercise, specifically endurance sports, is associated with HPA axis activation indicated by elevated cortisol levels. Whether the repeated short-term elevations in cortisol levels result in higher long-term cortisol exposure of endurance athletes has been difficult to examine since traditional methods of cortisol assessments (saliva, blood, urine) reflect only relatively short time periods. Hair segment analysis provides a new method to assess cumulative cortisol secretion over prolonged time periods in a retrospective fashion. The aim of this study was to investigate cumulative cortisol secretion over several months reflecting intensive training and competitive races by examining hair cortisol levels of endurance athletes. Hair samples were obtained from 304 amateur endurance athletes (long-distance runners, triathletes, cyclists) and 70 controls. Cortisol concentrations were determined in the first to third 3-cm hair segments most proximal to the scalp. In addition, self-report measures of training volume were obtained. Endurance athletes exhibited higher cortisol levels in all three hair segments compared to controls (p<.001). Positive correlations between the cortisol concentration in the first hair segment and each indicator of training volume were found (all p<.01). These data suggest that repeated physical stress of intensive training and competitive races among endurance athletes is associated with elevated cortisol exposure over prolonged periods of time. These findings may have important implications with regard to somatic and mental health of athletes which should be investigated in future research.